THE 4th TROPICAL WEED SCIENCE CONFERENCE 2013

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 99

Materials and Methods

Two experiments were conducted in clay soil lowland fields with good water supply in the Spring-
Summer with dry seeded rice and Summer- Autumn with wet seeded rice of 2006 at the Experimental
farm of CLRRI. Rice variety OM5749-5 is indica rice with IMI tolerance trait. The cultivar was bred
by CLRRI plant breeders by crossing between a promising Vietnamese indica rice and IMI-tolerance
japonica rice from Louisiana State University, USA. In dry seeded rice, 200 kg of cultivated rice seeds
were mixed with 100 kg of weedy rice seeds and broadcasted randomly before incorporation into the
soil surface. In wet seeded rice, 100 kgs of pre-germinated seeds were sown in line by drum seeder.
Pre-germinated seeds of weedy rice at the rate of 100 kg /ha were broadcast randomly one day later.
Field trials with plot size of 20m2 were established using randomized complete block design with four
replications and seven treatments. Three active ingredients of imazapic, imazapyr and imazethapyr
were used as solo and ready-mix formulations at various dose rate from 100 to 120 g a.i./ha . Herbicides
were sprayed at 12 days after emergence (DAE) in dry seeded rice and 10 days after sowing (DAS) in
wet seeded rice. Crop oil was added at 0.5% water volume as non-ionic surfactant.

Results and Discussion

Herbicidal activity
The population of weedy rice, Echinochloa crus-galli, Leptochloa chinensis, Cyperus iria

affected by treatments of imidazolinone herbicides have been presented in Table 1.
All herbicide treatments brought down weedy rice densities significantly as compared to that

in untreated check (182.7 plants / m2). All treatments were very effective in controlling Echinochloa
crus-galli except treatment T6 [Imazethapyr+imazapyr]@120. There was no difference between the
treatments with weedy check. The density of Leptochloa chinensis remained at level of 22 plants / m2
in untreated check whereas in all herbicide treatments, this weed was killed completely. The same trend
was observed in the case of Cyperus iria.

Table 1. Weed and weedy rice density (No. plants /m2) at 70 days after emergence (DAE) as affected
by treatments (CLRRI, 2006 Spring-Summer)

Treatments Weedy rice (*) ECHCG LEPCH CYPIR
T1 Untreated check 182.7 12.0 22.0 17.3
T2 [Imazapic+imazapyr]@100 0.0 0.0 0.0 0.0
T3 [Imazapic+imazapyr]@110 0.0 0.0 0.0 0.0
T4 [Imazapic+imazapyr]@120 0.0 0.0 0.0 0.0
T5 Imazapyr@120 12.7 0.0 0.0 0.0
T6 [Imazethapyr+imazapyr]@120 0.0 14.0 0.0 3.3
T7 Imazapic@120 0.0 0.0 0.0 0.0

LSD(0.05) 81.4 6.1 12.8 14.1

(*) Weedy rice (Oryza sativa); ECHCG:Echinochloa crus-galli; LEPCH:Leptochloa chinensis; CYPIR:Cyperus
iria.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 100

Table 2. Weed and weedy rice dry weight (g/m2) at 70 DAE as affected by treatments (CLRRI, 2006
Summer-Autumn)

Treatments Weedy rice (*) ECHCG LEPCH CYPIR

T1 Untreated check 269.7 35.9 7.7 26.6
T2 [Imazapic+imazapyr]@100 0.0 0.0 0.0 0.0
T3 [Imazapic+imazapyr]@110 0.0 0.0 0.0 0.0
T4 [Imazapic+imazapyr]@120 0.0 0.0 0.0 0.0
T5 Imazapyr@120 21.7 0.0 0.0 0.0
T6 [Imazethapyr+imazapyr]@120 0.0 8.0 0.0 12.0
T7 Imazapic@120 0.0 0.0 0.0 0.0

LSD(0.05) 78.2 25.6 3.5 3.1

The density of Cyperus iria was lower statistically under all treatments except T6
[Imazethapyr+imazapyr]@120. In this treatment the weed remained at the level of 3.3 plants /m2.Dry
matter accumulation of weedy rice and some common weeds observed in the experimental fields at 70
DAE have been presented in the Table 2.

All imidazolinone – herbicide treatments caused the reduction of weedy rice and weed dry weights
statistically as compared to untreated check (269 g/m2). However, the treatment of T5 [Imazapyr]@120
could not control weedy rice completely resulting in the remaining weedy rice dry weight of 21.7 g. /
m2. The Echinochloa crus-galli also was controlled successfully by all tested herbicides. However,
some plants of this weed remained in the treatment of T6 [Imazethapyr+imazapyr]@120 resulting in the
dry accumulation of 8.0 g/m2. Leptochloa chinensis was controlled completely by all treatments. Dry
weights of Cyperus iria were brought down significantly under all treatments as compared to untreated
check (26.6 g./m2) but the weed dry weight remained 12 g/m2 under treatment of T6 [Imazethapyr +
imazapyr]@120.

Yield components and grain yield
The imidazolinone herbicides successfully controlled weedy rice and common weeds in rice

fields and therefore the competition of weeds on rice plants was minimized and rice plants can grow
better as compared with that under untreated plots. The data on yield components and grain yields as
affected by treatments have been presented in Table 3.

Table 3. Yield components and yield of dry seeded rice as affected by treatments (CLRRI, 2006
Spring-Summer)

Treatment No. of No.filled grains / 1000-grain Yield (t/ha )
panicle/m2 panicle weight (g.)
0.9
T1 Untreated check 286 51.1 26.6 1.7
T2 [Imazapic+imazapyr]@100 311 63.5 26.4 1.9
T3 [Imazapic+imazapyr]@110 323 62.1 26.7 1.8
T4 [Imazapic+imazapyr]@120 325 63.2 26.7 1.8
T5 Imazapyr@120 341 63.3 26.3 1.8
T6 [Imazethapyr+imazapyr]@120 345 62.6 26.4 2.1
T7 Imazapic@120 350 67.2 26.5 0.5

LSD(0.05) 48 4.2 0.9

Three treatments of [Imazapic+ imazapyr]@100; 110 and 120 g a.i./h tended to cause the
increment of the number of panicles/m2 but had not reach the level of significance. The rest of the
three treatments of T5 [Imazapyr]@120; T6 [Imazethapyr+imazapyr]@120 and T7 [Imazapic]@120
were superior to untreated check in terms of the increment of the number of panicles / m2 statistically.
All herbicide treatments caused the increment of the number of filled grain per panicle significantly

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 101

as compared to that of untreated check (51.1 grains / panicle). The average of the increment was
24.7%. There was no significant difference of 1,000-grain weights amongst treatments. Rice yields
under treated plots were significantly higher as compared to that of untreated check (0.9t/ha). However,
each herbicidal treatment was equal with the other in terms of yield. On the average of all herbicide
treatments, rice yield increased 106% as compared to untreated check.

In wet seeded rice
One wet seeded experiment with the same design and treatments was conducted during Summer-

Autumn season of 2006.The population of weedy rice affected by herbicide treatments observed at 28,
56 and 84DAS have been presented in Table 4.

Table 4. Density (No.plants /m2) of weedy rice at 28; 56 and 84 days after sowing (DAS) as affected
by treatments (CLRRI, 2006 Summer-Autumn)

Treatments Weedy rice density (No.plants /m2)

T1 Untreated check 28 DAS 56 DAS 84 DAS
T2 [Imazapic+imazapyr]@100
T3 [Imazapic+imazapyr]@110 0.3 0 0
T4 [Imazapic+imazapyr]@120 5.0 0 0
T5 Imazapyr@120 0.4 0 0
T6 [Imazethapyr+imazapyr]@120 10.3 0 0
T7 Imazapic@120 1.8 0 0
0.0 0 0
LSD(0.05)
11.4 28 28

At 28 DAS, the density of weedy rice was 69.3 plants /m2 in untreated check. All herbicide
treatments brought down the population of weedy rice at 28 DAS significantly as compared with that
of check. However, some plants of weedy rice were countable at this stage because the remaining
weedy rice showed the symptoms of injury but have not been killed completely yet. At 56 and 84 DAS,
all weedy rice plants were susceptible and completely killed. In the case of no spraying imidazolinoe
herbicides, weedy rice grew normally and reached the density of 245-246 plants /m2 at 56 DAS and 84
DAS, respectively. The yield components and grain yields of wet seeded rice as affected by treatments
have been presented in Table 5.

Table 5. Yield components and grain yield as affected by treatments (CLRRI, 2006 Summer-Autumn)

Treatment No. of No.filled grains / 1000-grain Yield
panicle/m2 panicle weight (g.) (t/ha )
T1 Untreated check
T2 [Imazapic+imazapyr]@100 142 57.4 26.5 0.88
T3 [Imazapic+imazapyr]@110 301 62.6 26.5 2.22
T4 [Imazapic+imazapyr]@120 339 76.7 27.2 2.25
T5 Imazapyr@120 317 66.6 25.7 2.15
T6 [Imazethapyr+imazapyr]@120 292 71.7 26.0 2.05
T7 Imazapic@120 316 66.5 27.1 2.13
294 70.2 26.5 2.08
LSD(0.05)
46 16.7 2.1 0.48

All the imidazolinone herbicide treatments caused the increments of the number of panicles
/ m2 significantly as compared with untreated check (142 panicles /m2). The number of panicles / m2
in treatment T3 [Imazapic+imazapyr]@110 was the highest (339 panicles /m2) and higher than T5
[Imazapyr]@120 statistically (292 panicles/m2). However, treatment T3 [Imazapic+imazapyr]@110
was not higher than the rest of the other herbicide treatments. The average data of six treatments was

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 102

310 panicles /m2 and increased 118% as compared to untreated check. The 1,000-grain weights were
unchanged amongst all treatments including check. Rice grain yields under all herbicide treatments
were superior to that of untreated check (0.88 t/ha) significantly. There was no significant difference
amongst herbicide treatments. The average yield of 6 treated plots was 2.15 t/ha which increased 144 %
as compared to untreated check (0.88 t/ha).

Acknowledement

Thanks are due to BASF Corporation, USA for granting the research funds and supporting
other activities.

References

Chin, DV, Hien, T.V and Thiet. L.V. (2000). Weedy Rice in Vietnam. In Limited Proceedings No.2.
“Wild and Weedy Rice in Ecosystem in Asia- A Review”,IRRI.

Shanner D.L and Connor, S.L.O. (1991). The Imidazolinone Herbicides. CRC Press. Pp 290 .

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 103

Utilization of weeds in Thailand

Pensee Nantasomsaran Komson Nakornsri Patpitcha Rujirapongchai
Weed Science Group, Plant Protection Research and Development Office, Department of Agriculture,

Chatuchak, Bangkok 10900, Thailand

Abstract

Thailand is in the tropical area with nourish humid climate. Weed is one of the biodiversity
of plant community. The weed is a general pest to limit quantity and quality of yield in agricultural
production. There are many methods to reduce weed problems by using chemical and non chemical
control. However, utilization of weed is one strategy to minimize weed problems. Weed can be grown
by naturally, weed utilization can be compiled in 16 purposes, such as traditional vegetables, medicinal
plants, cosmetics, ornamental plants, artificial flowers, lawn, animal feeding, allelopathic substances,
mulching materials, soil indicator, water pollution absorbent, green fuel and beautiful scenery.



Introduction

Weed is unwanted plant or need to be controlled, on the other hand, weed can be useful. Weed

can be grown by naturally. Utilization of weeds were used for a long time in Thailand and many countries
with various purposes (Vongsaroj et al, 1999). Weeds can be used for native vegetables, medicinal plants,
cosmetics, ornamental plants, artificial flowers, lawn, animal feeding, allelopathic substances, mulching
materials, soil indicator, water pollution absorbent, green fuel and beautiful scenery etc. There are so
many vegetables which come from weeds (Aram and Pichet, 2005). Thailand is in the tropical, with
high moisture content. There are so many plants including weeds to be biodiversity system. The farmers
do not need to grow traditional vegetables such as Ipomoea aquatica Forsk.(morning glory), Marsilea
crenata Presl., Aeschynomene javanica Miq., Momordica charantea L. (Watcharee Prachasuysoradej,
1999). Some weeds become medicinal plants such as Abutilon hirtum (Lam.) Sweet for the eurotic
system, Centella asiatica (L.) Urb. For the protecting Alzimer, the tuber of Cyperus rotundus L. and
the rhizome of Imperata cylindrica (L.) Reauschell to be in the ancient medicine recipes of Thailand
and many countries in Asia and Pacific area (Nantasomsaran et al, 2009).

There are many purposes of weed usefulness. Therefore collection of the weed utilization are

the database for research work and applied usage.



Materials and methods

The collection of data came from many references and from the survey work. After that

classified in the group of weed utilization and compiled them by using references and some research
work that the information will be useful in the future.

Results and Discussions

1.There were 27 species to be traditional vegetables. Watcharee et al, 1999 collected Weeds as
a fresh vegetables and raw material for cooking as shown in Table 1.
2. There were 63 species to be medicinal plants which the Thai name, Scientific name, usage
parts such as leaves, flowers, stem, root or the whole plants and the usage of indication of these plants.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 104

The user can find them in the field or gardener that weeds can be grown by planting or naturally ecology
as shown in Table 2.

3. The weed can be used as homemade industry namely Eichhornia crassipes (Mart.)Solms
for woven materials: bag, basket, mat, plate mat etc. The Aeschynomene aspera L. and Aeschynomene
indica L.were done to be the wreath, artificial flower. The one species of fern used for fine quality lady
bag, and Pennisetum spp. for paper material (Table 3).

4. The weed species showed the indicator of high soil fertility namely Monochoria vaginalis
Presl for nourish nitrogen nutrient. The Xyris indica Linn. showed acidic soil and saline soil in the
some eastern and some southern part of Thailand. The Fimbristylis miliacea Vahl. showed phosphorus
deficiency (Table 4).
5. Weed can be built for the house. In the past, there are many weed species used for the roof
such as Imperata cylindrica Raeuchel and for the wall namely Saccharum spontaneum Linn. (Table 5).
6. Weed can be used for assisting on purify water to absorb heavy metal in the swamp namely
Eichhornia crassipes (Mart.)Solms. The pollution from household and some factory can eliminate by
using Thypha angustifolia Linn. (Table 6).
7. Weed can be used for protection of soil erosion, in the northern area, the farmer used Vetveria
spp. on the slope, mountain and roadsides for assisting land slopes (Table 7).
8.Weeds are used for house and garden decoration, There are so many species which use for
suitable environments. Some have beautiful flowers, pretty shape, Some can be used dry flower to
decorate for a long time namely Echinochloa crus-galli Beauv. and Eragrostis tenella P.Beauv.ex Roem.
et Schult including aquatic weeds can be decorated many types of gardens such as Pistia stratiotes L.
and Salvinia cuculata Roxb. (Table 8).
9. Weed can be used for mulching materials, to keep soil moisture content and control weed
germination namely Imperata cylindrica Raeuchel in vegetable area of the central plain and Rottboellia
cochinchinensis W.D. Clayton on seedling tobacco in the northern part of Thailand, including Azolla
pinnata R.Br. and Lemna minor L. for controlling weed in paddy fields (Table 9).

10. Weed can be used for green fuel. Many weed species were done green fuel column and

for charcoal namely Eichhornia crassipes (Mart.)Solms., Mimosa pigra L. and Aeschynomene spp.
(Table 10).
11. Weed can be used for controlling other weeds by allelopathic mechanism such as Imperata
cylindrica Raeuchel can grow only one species in the big area. Some species used for extract solution
namely Ammania baccifera L. and Hyptis sauveolens Poit. to inhibit other weeds(Table 11).
12. Weed can be used for animal feed namely Brachiaria mutica Stapf and Echinochloa colona
Link for cow buffalo sheep goat and hoarse (Table 12).
13. Weed can be used for fish protection from enemy and some species become food for
herbivorous fish namely Eichhornia crassipes (Mart.)Solms., and Ceratophyllum demersum Linn.
(Table 13).
14. Weed can be used for green manure and composed manure since weed can adsorb nutrient
more than crop. Weed can incorporate in the soil for tillage system to increase soil fertility and good
soil structure.
15. Weed can be used for genetic resources, there are many weeds used for father or mother lines to
show the distinguish characteristics: disease resistance, drought tolerance such as Oryza rufipogon Griff.
16. Weed can be used for the name of location or place, province, temple and school such as the
name of Ban nong pangpuay (Thai name of Ludwigia adscendens (L.)hara) in Nakon Pathom province
(Table 14).
The utilization of weed is one of the strategies to reduce weed problems and conserve the
natural resources for human. Weed can be useful without buying from the market. There are various
methods to use weeds especially medicinal weeds. The most importance, the user must understand well
to use the correct plant by learning from the expert. The one weed control method is utilization from
weed instead of eliminate alone. If some species are popular from the consumer. We can promote and
plant them by using Good Agricultural Practice or GAP and recommend to the farmers to grow them
for a good quality material to produce many products.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 105

Table 1 Weeds as the traditional vegetables (Watcharee,1999; Aram and Pichet,2005).

Thai name Scientific names Family Edible parts
Krachab Xanthium indicum Koenig Compositae
Krathin Seedling can be cooked for the soup
Leucaena leucacep0hala de Wit Mimosaceae
Krapanghom Young shoot, young leaves, young pod and seed
Oxystelma esculentum Linn.R.Br. Asclepiadaceae for fresh vegetable, dip with chili paste or fry
Kratokrok with flour, spicy with lemon and chili
Khakhiat Passiflora foetida L. Passifloraceae
Chaploo Monochoria vaginalis Presl Pontederiaceae Young shoot, young leaves, and flower for fresh
Choomhetthai Piper sarmentosum Roxb. Piperaceae vegetable, dip with chili paste, and with minced
Tamlueng Cassia tora Linn. Caesalpiniaceae meat and chili
Talapatluesee Coccinia grandis Voigt Cucurbitaceae
Buabok Limoicharis flava Buch. Limnocharitaceae Young leaves dip in warm water, fried in the hot
Phak kayang Centella asiatica (L.) Urb. Umbelliferae oil
Phak krad Limnophila aromatica Merr. Scrophulariaceae
Spilanthes acmella (L.) Murr. Asteraceae young leaves as a fresh vegetable
Phak cheelom
Phak top chava Oenanthe stolonifera Wall Umbelliferae young leaves as a fresh vegetable and for
Phak phet coconut curry with shrimp fish and snail
Phak bung Eichhornia crassipes (Mart.) Solms Pontederiaceae
Phak tubtao Spilanthes paniculata Wall. Ex DC. Asteraceae young leaves stream and take with some fish and
Phak pang chili paste
Phak wan Ipomoea aquatica Forsk. Convolvulaceae
Phak sean Edible leaves and fruit for soup with minced
Pang puay Mimulus orbicularis Benth. Scrophulariaceae pork

Mara kheenok Basella rubra Linn. Basellaceae Flower and young fruit as fresh vegetable, and
Mawangton Marsilea crenata Presl. Marsileaceae for traditional curry
Yaanang Cleome gynandra L. Capparidaceae
Santawa baipay Leaves, and upper ground level for fresh
Ludwigia octovalis Hara Onagraceae vegetable, and squeeze for juice drink
Sano kindog
Momordica charantea L. Cucurbitaceae Leaves, and stem for frog and fish in the hot
Hoo seua soup
Solanum santiwongsei Craib Solanaceae
Tiliacora triandra Diels Menispermaceae leaves, and stem for fresh vegetable with chili
Ottelia alismoides (L.)Pers. Hydrocharitaceae fish paste, put in the bamboo shoot soup

Sesbania javanica Miq. Papilionaceae Leaves and young shoot
with pork minced (lab) or dip in hot water and
Coleus amboinicus Lour. Labiatae have it with chili paste

Young shoot with chili paste

Leaves and flower for northern curry

Young shoot, leaves as fresh vegetable or put in
the curry

Young shoot, leaves as fresh vegetable and have
with minced meat in lemon and chili

Young shoot, young flower for vegetable, dip
with chili paste, and put in the chili curry

Young shoot as fresh vegetable with chili paste

Whole plant for fermentation to have with chili
paste

Young shoot as fresh vegetable and cook with
chili and lemon juice

Young shoot and fruit in a short time with hot
water for
chili paste, fry with oil, curry

young fruit as fresh vegetable with chili paste

Squeezed leaves for juice put in the chili curry

Young shoot, leaves and young flower as fresh
vegetable with meat chili paste

flower for fermentation, dip in hot water and
have it with chili paste, fry with oil and flower
for dessert

Leaves and young shoot as fresh vegetable with
chili paste

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 106

Table 2 Weeds as medicinal plant (Department of Medical Science,1990 ; Nantasomsaran et al ,
2009).

Thai name Scientific names Part of plant Properties and action

Kratokrok Passiflora foetida Linn. Leaves stem flower Diuretic
root and fruit
kameng Eclipta alba (L.) Hassk. Leaves stem flower Inflammation
Krathin root and whole plant
Krateepyod Leucaena leucocephala Flower for maintenance liver, root for
Krapanghom (Lam.) de Wit Flower, root carminative
Koksay Biophytum sensitivum (L.) Diuretic , maintenance liver,
DC. Whole plant, fresh and antipyretic
Oxystelma esculentum and dry Inflammation of throat and mouth
Linn.R.Br. and laxative
Stem leaves root Antipyretic, antidiarrhoea
Cyperus iria L.
Stolon

Koktumhoo Cyperus kyllingia Endl. Tuber Antipyretic, antidiarrhoea
Koksamleun Scirpus grossus Linn.f. Root
hawkradan Antipyretic, antidiarrhoea
Sida acuta Burm. Whole plant
Khadmon Relieve of cold, protect Inflammation
Abutilon hirtum (Lam.) Sweet Leaves stem flower of liver, bacterial diarrhea and gastro-
Crobjakawan root intestinal infection
Antitussive, Diuretic, protect diabetes
and digestant, blood tonic

Crobphansee Abutilon indicum (L.) Sweet Stem Antidiarrhoea, blood tonic

Cokkrasoon Tribulus terrestis L. Whole plant Diuretic

Chumhetthai Cassia tora Linn. Leaves, seed Laxative, skin cure, Diuretic, protect
Chumhetthes Cassia alata Linn. and whole plant Inflammation of liver
Leaves Laxative for dry leaves and vermifuge
Tamleung Coccinia grandis Voigt for fresh leaves
Tongteng Physalis minima L. Leaves root and fruit Leaves for maintenance eyes,
Namnom Euphorbia hirta L. antipyretic, expectorant, herpies, anti-
ratchasee Whole plant toxin from insect; fruits for diabetes
Buabok Centella asiatica (L.) Urb. Whole plant Diuretic
Fresh and dry
Borapet Protect stomachache
Leaves and over
ground level Diuretic, anti-bacteria, cough,
antipyretic, anti diarrhoea and protect
burn from the heat

Tinospora crispa (L.) Miers ex Stem Antipyretic, drink fresh juice of stem to
Hook.f. & Thomson assist edible tonic

Paka krong Lantana camara L. Leaves Stop blood from the wound, carminative,
allergic and swollen
Phak crad hua Spilanthes acmella (L.) Murr. Whole plant
wan Expectorant, asthma and cold

Phak chee lom Oenanthe stolonifera Wall Whole plant Expectorant, asthma and cold

Phak top chawa Eichhornia crassipes (Mart.) Whole plant Inflammation
Solms Fresh flower Tooth ache

Phak phed Spilanthes paniculata Wall.
Ex DC.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 107

Thai name Scientific names Part of plant Properties and action
Young shoot and
Phak boong Ipomoea aquatica Forsk. leaves Tonic, eye maintenance

Phak boong Ipomoea pes-caprae Sweet Root leaves and Root for diuretic, tooth ache; Leaves for
talae whole plant diuretic, skin cure, haemorrhoid, Whole
plant for jellyfish toxin
Phak pang Basella rubra Linn. Leaves stem Diuretic, dysentery, skin allergy,
Phak wan Marsilea crenata Presl. flower root Laxative
Whole plant
Phak sean pee Cleome viscosa L. Expectorant, antianagesic
Whole plant
Pan ngu khao Achyranthes aspera L. Take care wound in lung liver, sprain,
Pan ngu khiaw Whole plant anthelmintic, dysentery and tonic
Stachytarpheta jamaicensis
(L.) Vahl. Whole plant Diuretic, antipyretic

Pang puay Ludwigia octovalis Hara stem flower and Antipyretic, diuretic, anthelmintic
fruit
Pha talay jone Andrographis paniculata Diuretic, swollen, detoxifier, cough, skin
(Burm.f.) Wall ex Nees Root and Whole allergy
plant Root for anthelmintic, anti malaria fever,
Mara kheenok Momordica charantea L. Whole plant for Antipyretic, antiseptic of
Stem flower fruit bactria diarrhea, Expectorant and cough
and seed Anti bile duct infection, antipyretic,
relief body heat, anti virus and cancer
Mawang kreao Solanum trilobum L. Root, fruit Root for antipyretic, expectorant,
diuretic, Fruit for cough, expectorant,
Mawang ton Solanum santiwongsei Craib Fruit and diabetes
Hing men Crotolaria spectabilis Roth. Root, extract fruit Diuretic, decrease sugar blood
Root relief heat in the body,
Maiyarab Mimosa pudica L. Leaves root extract fruit for inhibition tumor
Antipyretic, decrease debility, cure of
Yaanang Tiliacora triandra Diels Leaves root wound
Fresh and dry
amai- Looktai bai Phylanthus niruri L. Whole plant Antipyretic
ai Leaves
Santawa bai Ottelia alismoides (L.) Antipyretic
paai Eriocaulon sexangular L. Stem
Relief heat in the body
Saray huamai- Leaves shoot stem
kheedphai root Antipyretic
Leaves stem
Sabraeng Ageratum conyzoides L. Antipyretic, antianalgesic, sprain
sabkaa Protect cold and cough, stop blood,
anti skin itchy
Sab suea Chromolaena odorata (L.)
R.M. king Stop blood

Sano kindog Sesbania javanica Miq. Leaves stem flower Leaves ground with powder to
root external protection wound: detoxifier,
inflammation, swollen Flower for
Yaa kled hoy Desmodium triflorum Dc. Whole plant intestine protection, Stem roast and put
Yaa kled plaa Phyla nodiflora Greene Whole plant in the water to be alkaline solution for
diuretic Root relief heat body, refrigerant
Antipyretic, relief heat body, refrigerant
Diuretic

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 108

Thai name Scientific names Part of plant Properties and action
Fresh and dry root
Yaa khaa Imperata cylindrica Diuretic
(L.) Reauschell Whole plant
Yaa nguang Fresh and dry tuber Diuretic, swollen, carminative
chang Heliotropium indicum R.Br. Whole plant
Yaa channakad Leaves Diuretic
Yaa sai Panicum repens L. Fresh whole plant Diuretic
Yaa teenka Leersia hexandra Sw. Whole plant Detoxifier
Yaa preak Eleusine indica Gaertn. Carminative, antipyretic, blood vomid
Cynodon dactylon (L.) Pers. Leaves stem Antipyretic, antitussive, anti skin
disease: elephant foot
Yaa laong Vernonia cinerea Lees. Whole plant Diuretic, take care of stone kidney,
Tuber antianagesic, diabetes, hypertension,
Yaa hnuad Orthosiphon aristatus Whole plant decrease uric acid
maew (Blume) Miq.
Leaves Cure of skin
Mhak dib Hedyotis biflora (L.) Lam.
namkang Cyperus rotundus L. Root, leaves Maintenance digestive system
Haew moo Emilia sonchifolia (L.) DC. Antipyretic, tonsil gland, dysentery,
Root, tuber diarrhea, allergy
Hoo pla chon Solution of leaves to protect inside ear,
nasal congestion, carminative
Hoo seoa Coleus amboinicus Lour. Root for blood toxic, antipyretic,
expectorant, vomid and allergic
Ngon kai pa Celosia argentea L. Root for haemorrhoid, tuber for oil to
Uttapit cure wound
Typhonium trilobatum (L.)
Schott

Table 3 Weeds as industrial plants (Department of Industry extension,1989).

Weed species location item
Toy, tray, basket, hand bag, Slippers,
Eichhornia crassipes (Mart.) Solms River canal lake swamp cass soucer box, hat, earring, neglect
Mat, bag and toy
Scirpus grossus Linn.f. canal swamp Mat, bag and toy
Cyperus corymbosus Linn. canal swamp Artificial flower
Aeschynomene aspera L. paddy field Artificial flower
Aeschynomene indica L paddy field Bag ,bracelet ,neglect
Lygodium flexuosum(L.)Sw. Forest and rubber garden paper
Pennisetum spp. Non crop area

Table 4 Weeds as soil indicator (Vongsaroj et al, 1999).

Weed species location Soil indicator

Eleocharis dulcis (Burm.f.) Henschel Paddy field Acidic soil and saline soil

Xyris indica L. Paddy field Acidic soil and saline soil

Fuirena ciliaris (L.)Roxb. Paddy field Acidic soil and saline soil
Eriocaulon cinereum R.Br. Paddy field Acidic soil and saline soil
Scleria poaeformis Retz. Paddy field Acidic soil and saline soil
Scirpus juncoides Roxb. Paddy field Acidic soil and saline soil
Monochoria vaginalis (Burm.f.) Presl Paddy field rich nitrogen
Aeschynomene spp. Paddy field Lack nitrogen
Fimbristylis miliacea (L.)Vahl Paddy field Lack nitrogen

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 109

Table 5 Weeds as human house (Department of Industry extension,1989).

Weed species Weed in the crop usage
Imperata cylindrica (L.) Reauschell Fruit crop , non crop area Roof
Saccharum spontaneum Linn. Wall
non crop area

Table 6 Weeds as water purification (Department of Industry extension,1989).

Weed species Weed in the crop location
Eichhornia crassipes (Mart.) Solms Canal Makkason swamp,Bangkok
Canal
Cyperus corymbosus Linn. Swamp Lam Phakbia, Petchburi province
Scirpus grossus Linn.f. Swamp Lam Phakbia, Petchburi province
Typha angustifolia L. Lam Phakbia, Petchburi province

Table 7 Weeds as soil erosion protection.

Weed species Weed in the crop location
Mountain slopes
Vetveria spp. non crop area, slope area Roadside edge

Digitaria ciliaris (Retz.)Koel. Fruit crop, field crop, upland rice, Roadside edge
vegetable, non crop area Roadside edge
Roadside edge
Dactyloctenium aegyptium P.Beauv. Fruit crop, field crop, upland rice,
vegetable Roadside edge

Chloris barbata (L.)Sw. Fruit crop, field crop, vegetable Roadside edge
Roadside edge
Pennisetum polystachyon (L.)Schult. Fruit crop, field crop, non crop Roadside edge
area

Pennisetum pedicellatum Trin. Fruit crop, field crop, non crop
area

Pennisetum setosum (Swartz)L.C.Rich. Rubber crop, oil palm crop, non
crop area

Chrysopogon aciculatus Trin. Fruit crop, non crop area

Eleusine indica (L.)Gaertn. Fruit crop, non crop area

Table 8 Weeds as decoration of house and garden.

Weed species Weed in the crop Type of decoration
Pistia stratiotes L. Paddy field, swamp Put on the bowl or beautiful
container
Salvinia cuculata Roxb. Fruit crop, swamp Put on the bowl or beautiful
Paddy field container
Echinochloa crus-galli Beauv. Fruit crop, field crop Dry and decorate in the vast
Eragrostis tenella P.Beauv.ex Roem. Paddy field, non crop area
et Schult Dry and decorate in the vast
Xyris indica L.
Dry and decorate in the vast

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Table 9 Weeds as mulching materials.

Weed species Weed in the crop Part of plant
Imperata cylindrica Fruit crop, rubber crop, oil
(L.) Reauschell palm crop, non crop area Cut at the ground level, cover on the
Rottboellia cochinchinensis Fruit crop , non crop area soil to protect weed germination
W.D.clayton
Paddy field Mulching with whole plant in tobacco
Azolla pinnata R.Br. seedbed ,red onion and garlic
Paddy field
Lemna minor L. Grow on the surface of water at 7 days
after seeding or after transplanting,
completely cover in 3 weeks

Grow on the surface of water at 7 days
after seeding or after transplanting,
completely cover in 3 weeks

Table 10 Weeds as green fuel.

Weed species Weed in the crop method

Eichhornia crassipes (Mart.) Solms Swamp, canal, river Whole plant condense in a column
Aeschynomene spp. Paddy field Whole plant condense in a column
Mimosa pigra L. Non crop area Whole plant condense in a column

Table 11 Weeds as allelopathic substances.

Weed species Weed in the crop
Ammnania baccifera L.
Hyptis sauveolens Poit. Paddy field
Slope, non crop
Table 12 Weeds as animal feeds.

Weed species Weed in the crop Type of animals

Echinochloa colona (L.)Link Paddy field, field crop, Cow buffalo hoarse
fruit crop
Eichhornia crassipes (Mart.) Solms Swamp, canal, river Pig
Brachiaria mutca (Forsk.)Stapf Fruit crop, non crop Cow buffalo hoarse
Cow buffalo hoarse rabbit
Brachiaria distachya (L.) Stapf Fruit crop, non crop
Herbivorous fish
Lemna minor L. Paddy field, swamp Duck
Hydrilla verticillata (L.f. )RoyLe Paddy field, canal Pig
Dactyloctenium aegyptium P.Beauv. Fruit crop, field crop
Ischaemum rugosum Salisb. Paddy field Cow buffalo hoarse
Paspalum scrobiculatum L. Paddy field Cow buffalo hoarse
Hymenachne pseudointerrupta C.Muell Paddy field Cow buffalo hoarse
Ipomoea aquatica Forsk Paddy field Cow buffalo hoarse
Alternanthera philoxeroides (Mart.)Griseb.) Swamp
Pig
Pig

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 111

Table 13 Weeds as for fish and aquatic animals house.

Weed species location

Eichhornia crassipes (Mart.) Solms Swamp, canal, river
Alternanthera philoxeroides (Mart.)Griseb.) Swamp, canal, river
Ottelia alismoides (L.)Pers. Fish aquarium
Hydrilla verticillata (L.f.) Royle Fish aquarium
Limnophila heterophylla Benth Fish aquarium
Najas graminea Del. Fish aquarium
Ceratophyllum demersum Linn. Fish aquarium
Ipomoea aquatica Forsk. Swamp, canal, river

Table 14 Weeds as the name of the places.

Thai name and weed species Crop Location name

kham Non crop Nongkham, Bangkok
(Saccharum arundinaceun Retz.) Paddy field,
swamp Nongjok, Bangkok
Jok Paddy field
(Pistia stratiotes L.) Phue Amphur, Udonthani province
Paddy field
Phue Nongyasai Amphur,Suphanburi province
(Scleria poaeformis Retz.) Yaplong Amphur,Petburi province: Yaplong
school, NongYaplong temple Ratchaburi
Yasai province:
(Leersia hexandra Sw.) Nongphakwan home, Nakonratchasima
province
Yaplong Paddy field Phaktop home, Khon kaen province
(Hymenachne pseudointerrupta C.Muell)
Pangpuay canal, Ratchaburi province
Phakwaan Paddy field
(Marsilea crenata Presl.) Paddy field
Paddy field
Phaktop
(Monochoria hastate Solms

Pangpuay
(Ludwigia octovalis Hara)

Conclusions and Recommendations

1.There are many methods to utilize weed. The weed can be compiled for 16 purposed usage.
There will be more than these ways for weed utilization. There are various methods to use the weeds,
There are 27 weed species become traditional vegetables. The information can be done more than
those references.
2. There were 63 species to be medicinal plants, They should have more than those references
like the traditional vegetables.
3.The others purpose of weeds could be have a potential use, such as energy compensation,
water purification, mulching material, decoration of house and garden. The study should be done from
many references.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 112

References

Department of Medical Science. (1990). Traditional Medicinal Plants: Research and Development of
Medicinal Plants. Ministry of Public Health. 199 p.

Department of Industry extension. (1989). The Products from Water Hyacinth. Homemade Industry.
Ministry of Industry. 102 p.

Kumklang, A. and Wechwitan, P. (2005). Traditional Vegetables and Medicinal Plants vol.1. Siam
Chareanpanich (Bangkok). 96 p.

Nantasomsaran, P., Nakornsri, K. and Ditchaiwong, C. (2009). Some Medicinal Weeds in Thailand. The
ninth National Plant Protection of Thailand. Sunee Grand Hotel, Ubon Ratchathanee province.
pp. 77-81.

Prachasuysoradej, W. 1999. Native Vegetables: North, Northeast, South area. Botany group, Botany and
Weed Science Division. Department of Agriculture. 81 p.

Vongsaroj P., Nantasomsaran, P. and Nakornsri, K. (1999). Weed Utilization in Thailand. The 17 th
Asian-Pacific Weed Science Society Conference, Bangkok, Thailand, p. 54.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 113

A General View of Weeds in Lowland Rice and Up-Land Crops
in The South of Vietnam

Ho Van Chien
Southern Regional Plant Protection Center – PPD

Introduction

In recent decades, developmental physiology, genetics and molecular biology have helped
biologists and researchers in particular have developed intensive contact with comparative morphology,
taxonomy, systematics and phylogeny – have captured the human mind since earliest time. Since the
beginning, farmers have been concerned with a special world of plants, the so-called “weeds”. When
10,000 years ago in the Middle East, man started to collect and grow wild plants, competition began
between the cultivated “domestic” species and their wild companions. These weed populations escape
absolute definition. Perhaps one can describe them as “plants growing in where and when they are not
wanted”. This description implies that a plant species is only considered to be a weed under certain
conditions, according to a subjective judgement. Although, according to our definition, any plant can
be a weed, there are typical weeds characterized by special peculiarities promoting or maintaining their
spread. They are very resistant and adaptable species which can grow in habitats created or modified by
man. Their most important feature is their effective spread and survival under sometimes unfavorable
conditions. Fortunately, weeds have kept their species diversity, despite intensive mechanical and
chemical control. From the point of view of ecological interaction and genetic potential, it would be
unfortunate to lose this treasure. Apart from their biological importance, their aesthetic richness is also
fascinating.

Three books of publications of authors Toni J. Häfliger, Basel, editor Werner Püntener, Basel of
CIBA-GEIGY – weeds are divided into three groups: Dicot weeds (copyright 1988) with 127 species
from 13 families; Grass weeds (copyright 1981) with 137 species; Monocot weeds (copyright 1982)
with two families: The Sedge family (Cyperaceae) and the Rush family (Juncaceae).

Recently, the book named “Common weeds in Vietnam” – second edition of authors: Suk Jin
Koo, Yong Woong Kwon, Duong Van Chin and Hoang Anh Cung (2005) weeds are divided into three
groups: Grasses (Poaceae), Sedges (cyperaceae) and Broadleaved weeds (66 families).

In the south of Vietnam, depending on the type of rice production system, farmers often contend
with the same or similar weed species. These species are relatively small, but of great importance and
includes many of the “world’s worst weeds”. Weeds undoubtedly cause great damage in rice cultivations
and other crops. Weeds compete with crop plants for nutrients, water, and light, harbor other pests,
reduce the quality of seed crops, increase production costs. Thus, needs to be developing and testing
on-farm researches of weed control or management but there is no problem of developing resistance,
no environmental pollution.

Rice growing areas and cultural methods of South Vietnam
The largest areas for rice growing is in the Mekong River Delta. Most of rice varieties are

modern varieties with short growth durations. Direct seeding rice is popular in the south Vietnam,
wherein around 85% with hand broadcast, 10% use of drum seeders and 5% transplanting. In the
year 2011, total rice growing areas is around 4,521,685ha wherein Winter-Spring crop: 1,690,985ha;
Summer-Autumn crop: 1,799,600ha; Autumn-Winter and Main crops: 1,031,100ha. There are more than
80 rice varieties with short growth durations are growing in the farmers practice of south Vietnam.

Current weed situations and common weeds
Vietnamese farmers well known about weeds compete with rice crops for sunlight, nutrients

and water, and when not controlled reduce yield. In addition to competitive yield loss, weed seeds can
reduce rice quality and grade. Yield reductions as high as 46% caused by weeds in on-farm studies have
been reported in weed-free plots (Chin and Sadohara, 1994). More than 400 weed species have been

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 114

recorded in rice fields in Vietnam. The two most important families are the Poaceae and Cyperaceae,
which constitute 42% of all weed species (total: 167). Other major families are Asteraceae (26 species),
Scrophulariaceae (18 species), Fabaceae (14) species), Lythraceae (10 species), and Laminaceae (9
species) (Chin, 1995). In a survey of 197 farm sites in 11 provinces in the Mekong River Delta, the
Echinochloa spp. complex was dominant species (higher than 70% of total plant density) at more than
50% of the sites surveyed, and was common (10-70%) at more than 35% of the rest sites. Leptochloa
chinensis and Fimbristylis miliaceae were equally abundant at most sites and were ranked as the next
most important weed species. Both were the most abundant at about 18% of the sites. Cyperus difformis
was the dominant species at about 7% of the sites and was common at 41% of the sites. C. iria was
much less. Weedy/red rice are an emerging pest in direct-seeded rice in Vietnam. In interviews of
4,397 respondents in 128 districts of 18 provinces, 64% of the farmers reported the presence of weedy/
red rice in the rice fields. Compared with cultivated forms, these eco-types typically had a shorter
duration, shuttered more easily. These eco-types have been postulated to have resulted from interspecific
hybridization with O. rufipogon (Buu, 1998). Weed vary in their competitive effects with rice, rice grain
yield reductions have ranged from 5-10 percent with barnyard grass (Echinochloa spp.) 20-30 percent
with weedy/red rice. In direct-seeded rice, weeds are the major threat to crop protection. For major
type of direct-seeding methods in rice practices in the south Vietnam are wet seeding, dry seeding,
zero-tillage seeding, and submergence seeding. Infected weed area of rice growing area is around 5-7%
meaning is about 75,000 – 100,000ha weed infestations per season. Chien et al., (1997) and Mai et al.,
(1998) reported that the quality of farm seed supplies is very poor, the average number of weed seeds
per kilogram of rice seeds was 466, forty-seven-fold higher than the permitted national purity level. The
corresponding number for weedy/red rice seed was 314 seeds per kg rice seed. Regulations on the level
of impurity of weedy/red rice seeds in rice have not yet been established in Vietnam.

Of several weeds affecting rice production, the major weed complexes have been identified
which require an integrated approach for their control. They are the complex formed by various
Echinochloa species but two major species of them are Echinochloa crus-galli and Echinochloa colona.
Leptochloa chinensis is too high populations on upland rice. Particular, the red/weedy rice complex
occurred on both of low and upland rice. For the red/weedy rice: One of the major constraints to the
production of rice in direct-seeded areas is the incidence of red rice, which is widespread all over the
world. Crop losses due to red/weedy rice incidence may be as high as 60 percent where there is heavy
field infestation (FAO, 2001). In the south of Vietnam, weedy rice infestation is highest under dry rice
seeding followed by wet seeding and zero-tillage seeding. The most severe infestation is observed in
Summer-Autumn. The typical characteristics of weedy/red rice, compared with popular modern rice
varieties in south of Vietnam, are short duration, tall plants, weak culm, small seeds, easy shattering
and red pericarp. The average yield loss due to weedy rice ranges from 15 to 17 percent. (Chin, D.V.
and Mortimer, 1999). Barnyard grass: Echinochloa muricata, E. crus-galli is a variable annual species
causing serious competition (Holm et al. 1977), (Abeysekera Anuruddhika, 2001). Asian sprangletop:
Leptochloa chinensis: A strongly tufted annual or perennial grass, “associated with wetlands, swamps,
or streams in open lowland regions. Can grow in heavy or light soils, along streams and watercourses,
in marshy grounds and in lowland rice fields” (Holm et al., 1977).

Surveying of weed populations in five typical rice fields by weed infestations without herbicide
control in Diem Hy village, Chau Thanh district, Tien Giang province we found out that Echinochloa
crus-galli: 26 plants per sq.m. (4.9%), Leptochloa chinensis: 193.5 plants per sq.m. (36.6%), Cypreus
difformis: 37.5 plants per sq.m. (7.1%), Fimbristylis miliacea: 249.3 plants per sq.m. (47.2%), and
Ludwigia octovanlis: 22.3 plants per sq.m. (4.2%) at 45 DAS (SRPPC, 2011).

Besides, some common broad leaf species with their infestations are a concern for many farmers’
rice fields on lowland rice.

Trend of weed invasion by inter-trading, global warming by climate change

- Weed invasion by inter-trading
Since the invasive species frequently cause economic and ecological impact, invasion by exotic
plants is growing issue, contamination of weed seeds in agricultural products are the major causes of

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 115

alien plant invasion, with the naturalization of deliberately introduced plants being the most common
source of invasive plants. Grain trade is a major route of uninternational introduction of those weeds
(Mack et al., 2000, Shimono & Konuma 2008). Some studies reported that various kinds of weed seeds
were contained in imported grain seeds (Fay, 1990; Huelma et al., 1996). In Vietnam, very limited study
has focused on understanding how many species are introduced the invasive plants. The economic
losses associated with invasive plants such as water lettuce Pistia stratiotes, giant mimosa Mimosa
pigra, water hyacinth Eichhomia crassipes, victoria grass Panicum repens and siam weed Chromolaena
odorata in Vietnam were reported, not including damage to ecosystem function or loss of biodiversity,
which also contribute to agricultural production (IUCN, 2006).

- Landscape ecologies and climate change
Climate change, diminished water resources, loss of rice or plant crop cultivations and other
changes in the future could have profound effects on the landscape ecology. Future research will need
to address a number of issues regarding how to best rice in the background of these changes. How
climate change will affect weed species in rice is not clear. Because flooding or drought we do not know
which crop growing and weed species will be richness, whole community studies over multiple years
will be necessary to understand the effects of changing climate in different environments. Shrinking
irrigation water will certainly force farmers in many area to adopt irrigation practices that include
periodic drying of the irrigated rice fields. Very strong increases in weed infestation were observed with
both direct-seeding and poor water management. Therefore, research is needed to examine how changes
in irrigation contribute to weed species richness and what measures might be available to mitigate the
negative effects. When not enough water sources will also force farmers that now practice asynchronous
cropping in many areas to shift to more water efficient synchronous cropping for brown plant hopper
and weed management. Research is needed to determine how this change in planting scheme and how
different intercropping manipulations or cropping rotations in weed management.

Herbicides for paddy field in the coming years
Weeds are at present the major biotic constraint to increased rice production of south Vietnam.

The importance of their control has been emphasized in the past by various authors (De Data and
Baltazar, 1996; Labrada, 1996). Chemical weed control has increased significantly over the past ten
years. This is due to labor shortages, particularly in the Mekong River Delta, leading to an increased
shift from transplanted rice to direct-seeding, with a subsequent increase in herbicide use. As has been
stated in the past, Labrada (1996) shows that, although herbicide use has increased productivity, there
are several weed problems that remain unsolved by the use of the herbicides commonly applied in rice
cultivation.

Following Circular letter No. 10/2012/TT-BNNPTNT of Ministry of Agricultural and Rural
Development, date: February 22, 2012 there were 195 active ingredient and 584 trade names of
herbicides in Vietnam.

Weedy/red rice and other species, such as Echinochloa spp., Leptochloa chinensis and red/
weedy rice, present the major weed problems for rice. The most popular methods of weed control are:
i) field inundation at 4 DAS (giving 14.8-30.3% higher yields than with 12 DAS); ii) fields subjected
to two rounds of rotovation (higher yields than with one round of rotovation, while zero tillage did not
promise better yields for farmers); iii) use of herbicides (>82.2% of Vietnamese farmers), normally
supplemented by hand weeding (85% of farmers); and iv) hand weeding, which takes about 150-200
work days/ha and is normally done at 10-15, 25-30 and 40-45 DAS (Chin, 2001).

Herbicide use in rice production has increased quickly in Vietnam over than last decade because
of the increasing availability and rising cost of labor for hand weeding, lack labor in agriculture.

Herbicide resistance
In the past two decades, evolution of newer herbicides provided wider user choice. Selection of

most promising prudent products intensified in use followed by genetically induced herbicide resistant
crops. This is how the broad-spectrum herbicides created a great deal of impact on the stakeholders.
The loss of herbicide effectiveness due to selection of herbicide-resistant weed populations has negative

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 116

impact on farmers. Herbicide-resistance is the inability of a herbicide to effectively control a weed
species that was previously controlled by the same herbicide. Herbicide-resistance is detected when
a biotype within a weed species possessing a resistant trait increases in abundance while susceptible
biotypes are controlled by use the same herbicide. The resistant trait is inheritable and therefore, is
passed from one generation to the next. Once a herbicide-resistant population has been selected for, the
likelihood of the weed population reverting back to a population dominated by the susceptible biotype
is low. Resistant weed population become a serious constraint because it develops far faster (in 3 to
5 years) than the time and money investment on research, testing and registration for another newer
chemical that meet modern environmental and health regulatory standards. As a result, herbicides with
a new mode of action will not likely serve as a solution for herbicide-resistant weed populations.

For the red/weedy rice: Discussion and analysis regarding transgenic rice cultivars resistant to
herbicides (HRC), particularly in the red/weedy rice in the south of Vietnam.

- There is no simple method for the control of weedy/red rice. Only through the integrated
control approach can weedy/red rice infestation be effectively reduced.

- The main sources of weedy/red rice infestation are: rice seeds contaminated with weed seeds,
and weedy/red rice seed bank in soil. Therefore, any control measure should be aimed at the reduction
of infestation from these sources.

- In some countries the presence of weedy/red rice seeds is tolerated in rice seeds. However,
experience in the control of this weed in countries that use advanced technologies shows that not even
one single weedy/red rice seed should be tolerated in rice seeds.

- The reproduction of basic and foundation seed should be carried out in areas which are totally
free of weedy/red rice infestation. Certified rice seeds should be free of weedy/red rice seeds.

- To date, the most efficient control measures have been those based on the combination of wet
soil preparation (to bring about the emergence of weedy/red rice seeds), followed by the application of
herbicide (e.g. glyphosate) over the weed stand and before rice seeding, and water management before
and after seeding.

- Under upland and irrigation conditions, it is advisable to implement, whenever possible,
minimum tillage or zero tillage combined with the use of non-selective herbicides. This practice is
cheap and sustainable for rice farmers.

- The use of post-emergence herbicides in the process of land preparation needs improvement.
It is necessary to find other chemical alternatives in order to avoid repeated use of the same chemical.
This also applies to post-harvest application in rice areas.

- Within the context of integrated management, it is necessary to conduct regular studies of the
behaviour of available rice cultivars in terms of: their ability to compete with weedy/red rice; life-cycle;
and tolerance to submersion during flooding.

Agrochemical industry has founded an international body, Herbicide Resistance Action
Committee (HRAC) primarily aiming to collect information and prepare a database on resistant biotypes
(biotypes: Bubny, Jihlav, Karlín, Kochia - Kochia biotype belong to the C4, photo-synthesis class).

For types of resistance, herbicides target attack at one or more location in a weed plant. These
locations can either be enzyme proteins, other non-enzyme proteins, cell division path etc. are called
site of action. The generally focus of herbicide-resistance included interference to “ALS”=Acetolactate
synthase (also called AHAS=Acetohydroxy acid synthase), ACCase inhibitors=Acetyl Co
Enzyme-A Carboxylase, Synthetic auxins, “HRA”=Hill reaction activity, “PS (I)”=Photosystem I
(activity), Photosystem II inhibitors, Ureas and Amides, Glycines, Chloroacetamide, Dinitroaniline,
Thiocarbamates, Bipyridiliums, multiple resistance and weed-resistance to herbicide following these
factors: weed biology, intensity of use, rate (incorrect), rain before herbicide is completely absorbed
by the weed, drought or cold, no coverage of weeds below canopy, early morning applications, weed
emerging after herbicide application.

In order to understand which species of weed resistance to what organo-chemical of herbicides
and where the country is, look for in a handbook of “A Practical Field Guide to: Weeds of Rice in Asia”,
IRRI publication, 2010.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 117

Application of GMO in weed management
The risks of genetically modified crops: Some concerns that have been raised by scientists,

community groups and members of the public include:
- Cross-breeding - other risks include the potential for cross-breeding between GM crops and

surrounding vegetation, including weeds. This could result in weeds that are resistant to herbicides and
would thus require a greater use of herbicides, which could lead to soil and water contamination. The
environmental safety aspects of GM crops vary considerably according to local conditions.

- Herbicide tolerant (HR) crops - the introduction of the Glyphosate resistant soybean in
1996 was the start of crops that gave farmers an opportunity to reduce the cost of their herbicide use.
However, the increasing acreage of HR crops (such as soybean and canola) has resulted in an increase
in the types of weeds that are now Glyphosate resistant (GR). These GR weeds may have a major
environmental influence on crop production in years to come.

The extensive use of herbicides and insect resistant crops could result in the emergence of
resistant weeds and insects. This has often occurred as a consequence of conventional herbicide and
insecticide spraying. Several weed species have developed resistance to specific herbicides which are
extensively used in combination with herbicide-resistant genetically modified crops. Insect-resistant
Bt-crops similarly could lead to the emergence of Bt-resistant insects. The extent and possible severity
of impacts of resistant weeds and insects are subject to continuing scientific investigation.

- Pest and weed resistance - Scientists agree that extensive long-term use of Bt crops and
Glyphosate and Gluphosinate, the herbicides associated with herbicide tolerant (HT) crops, can
promote the development of resistant insect pests and weeds. Similar breakdowns have routinely
occurred with conventional crops and pesticides and, although the protection conferred by Bt genes
appears to be particularly robust, there is no reason to assume that resistant pests will not develop.
Worldwide, over 120 species of weeds have developed resistance to the dominant herbicides used with
HT crops, although the resistance is not necessarily associated with transgenic varieties. Because the
development of resistant pests and weeds can be expected if Bt and Glyphosate and Gluphosinate are
overused, scientists advise that a resistance management strategy be used when transgenic crops are
planted. Scientists disagree about how effectively resistance management strategies can be employed,
particularly in developing countries.

Trend of weed management on these crops in the coming years
Weeds undoubtedly cause great damage in agriculture. However, for definition of “weed” in

some situations such plants can be used by farmers to their advantage. They have learned to manage
populations of weeds and to strike a balance between competition, soil protection and weeding costs.

Integrated weed management (IWM) is the control of weeds through a long-term management
approach, using several weed management techniques such as: Physical control, Cultural control
Chemical control, Biological control.

Physical control is the removal of weeds by physical or mechanical means, such as mowing,
grazing, mulching, tilling, burning or by hand. The method used often depends on the area of weeds to
be managed, what the land is used for, physical characteristics and the value of the land. It is important
that, when using physical control, any item that can move from a weed-infested site to an un-infested
site, such as machinery, vehicles, tools and even footwear, is cleaned free of weed seed before moving,
to stop the spread of weeds to new areas. As with most control methods long-term suppression of weeds
requires follow up weed prevention.

Cultural control is usually associated with farming systems, although some elements are relevant
to landscape and bushcare practices. It largely involves manipulating farming practices to suppress
weed growth and production, while promoting the development of the desired plant. The principles and
techniques used to prevent weed spread are relevant to cultural control methods to limit the spread of
weeds between different land areas.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 118

- Cultural control methods:
Encourage the competitiveness of desired species that are more competitive and fast growing.
This suppresses weed growth by reducing access to available sunlight, nutrients and moisture and can
include:
. Choose plant and crop species or cultivars that are naturally more competitive. This can include
using plant species that suppress other plant species by the release of toxins.
. Use high quality seeds, as they are more likely to produce vigorous and competitive plants.
. Use shallow seeding techniques, where possible, to allow the desired species to grow above
the soil surface more quickly.
. Ensure the desired plant is placed in the optimum growing environment.
. Use fertilizers in the optimal growth period to encourage rapid growth of the desired species.
. If possible grow nectar flowers on the bunds using “Ecological Engineering” for pest
management and on the other hand, to avoid some weed species can grow up on the bunds following
spread to the rice fields.
Make it hard for weeds to adapt to weed management techniques. Using the same land
management routines year after year may result in weeds adapting to these practices. Some practices
that make it hard for weeds to adapt and therefore reduce their spread and vigor include:
. Rotate crops: if a weed has adapted to grain crops continuously being sown, then alternating
with a broadleaf crop will remove the environmental condition to which the weed has adapted.
. Rotate species with different seasonal and growing cycles.
. Rotate herbicides with different modes of action to help delay the development of herbicide
resistance.

- Weed prevention
Prevention is the most effective method of dealing with weeds. Once a weed has entered an area
and become established, eradication is far more expensive and it is likely that greater resources will be
required to control its further spread and reduce its impact.
The first step in weed prevention, and the most cost effective means of managing weeds, is
preventing the entry of new weeds into the country.
Early detection and eradication requires an awareness and understanding of the factors that
favor the establishment and spread of weeds, and applying appropriate management practices that can
prevent or reduce the risks.

- Chemical control
Although the use of chemicals is not always essential, herbicides can be an important and
effective component of any weed control program.
In some situations herbicides offer the only practical, cost-effective and selective method of
managing certain weeds. Because herbicides reduce the need for cultivation, they can prevent soil
erosion and water loss, and are widely used in conservation farming.
In some cases, a weed is only susceptible to one specific herbicide and it is important to use
the correct product and application rate for control of that particular weed. Common mistakes include
incorrect identification of the weed or using inappropriate products.
In most cases, weeds must be actively growing to be vulnerable to herbicide treatments.
Herbicide resistance can also be an issue with some species.

- Biological control
Plants that have become weeds in Australia are rarely invasive and troublesome in their natural
range. This is often because natural populations are regulated by a variety of natural enemies such as
insects and pathogens (disease-causing organisms like fungi and bacteria) that attack the seeds, leaves,
stems and roots of a plant. If plants are introduced to a new region that does not have these natural
enemies, their populations may grow unchecked to the point where they become so prevalent that they
are regarded as weeds. It is critical that the biological control agents introduced into Vietnam do not
become pests themselves. Considerable testing is done prior to the release of biological control agents
to ensure they will not pose a threat to non-target species such as native and agricultural plants.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 119

Although in the long term, biological control can be cost effective and can reduce the need for
less desirable management practices, not all weeds are suitable for biological control.

There have been several other successful biological control programs in Vietnam such as leaf
beetle coconut – importation of parasitoid have been mass-rearing and released. There is also major
research being undertaken on biological control for a number of other weed species.

- Procedure to import and release a biological control agent
To avoid such problems in future, the process for approving biological control agents is much
more rigorous now than it has been in the past.
Before commencing the search for biological control agents, agreement needs to be sought
from the MARD–Vietnam, with initial application through the PPD to target the weed species for bio-
control. The next step is to undertake host specificity testing. This is a requirement under the MARD
and PPD. Once host specificity testing is completed, biological control agents must be assessed and
meet the requirements of the Quarantine and the Environment Protection before approval can be given
for their introduction and release in practice.
To meet the requirements of the Quarantine - Biosecurity assesses the risk regarding proposed
importation and release of biological control agents. PPD - Biosecurity assesses the risk of release of
exotic biological control agents via a risk analysis, based on the results of host specificity testing. Host
specificity testing is required under the process to ensure that the agent will not damage native flora or
agricultural stock or crops.

Advantages and Disadvantages of Weed Management
By using several techniques to control weeds you reduce the chance that weed species will

adapt to the control techniques, which is likely if only one technique is used. For example, if a herbicide
is used over a long period of time, a weed species can build up a resistance to the chemical.

A long-term integrated weed management plan, that considers all available management
control techniques or tools to control weeds, can be developed for a particular area. Any integrated
weed management plan or strategy should focus on the most economical and effective control of the
weeds and include ecological considerations.

The long term approach to integrated weed management should reduce the extent of weeds and
reduce the weed seed stock in the soil. It should consider how to achieve this goal without degrading
the desirable qualities of the land, such as its native ecology or agricultural crops.

The soil seed bank refers to the natural storage of seeds, often dormant, within the soil of most
ecosystems. Many cases have been classified according to the longevity of their seeds in the soil seed
bank. Seeds of transient species remain viable in the soil seed bank only to the next opportunity to
germinate, while seeds of persistent species can survive longer than the next opportunity - often much
longer than one year.

A study of weed seed banks in rice field cultivation of Go Cong district, Tien Giang province,
(SRPPC. 2011). The results show that weed seed banks in surface soil layer (0-10 cm depth) with 65,681
plants per sq.m. and in lower surface soil layer (10-20 cm depth) with 22,272 plants per sq.m., wherein
seven major weed species are: Leptochloa chinensis,Echinochloa crus-galli, Oryza sativa, Fimbristylis
miliacea, Cyperus difformis, Ageratum conyzoides and Hedyotis corymbosa.

Longevity of seeds is very variable and depends on many factors; In typical soils the longevity
of seeds can range from nearly zero (germinating immediately when reaching the soil or even before) to
several years. The mortality of seeds in the soil is one of the key factors for the persistence and density
fluctuations of plant populations, especially for annual plants. There are indications that mutations are
more important for species forming a persistent seed bank compared to those with only transient seeds.
The increase of species richness in a plant community due to a species-rich and abundant soil seed bank
is known as the storage effect.

The 4th Tropical Weed Science Conference, 23-25 January 2013, Chiang Mai, Thailand TWSC 2013 120

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SPONSORSHIP
ACKNOWLEDGEMENT

The organizing committee of TWSC 2013 would like to express our sincere thanks to the
following for their support and sponsorship to the success of the 4th Tropical Weed Science
Conference (TWSC 2013) on “Weed Management and Utilization in the Tropics”

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THE 4th TROPICAL WEED SCIENCE
CONFERENCE 2013
Weed Management and
Utilization in the Tropics