Dandelion germination 04-07 - oldscollege.ca

Dandelion Germination Trial
Colin A. Clarke, Marilyn Mantei and J.B. Ross
Summary
This objective of this trial was to observe and record the timing of dandelion germination
in a creeping red fescue/Kentucky bluegrass turf and also to determine the best method
for counting dandelions. This study was conducted in Olds, AB within the black soil
zone. In year one, two treatments were evaluated to determine the best method for
counting dandelions. In order to facilitate the weekly counting process, four 0.25m2 plots
were sprayed with Roundup® (Glyphosphate). This was compared with unsprayed plots
that had existing dandelions completely removed. Initial counts of mature dandelion
were taken prior to the Roundup application. Following spraying, weekly dandelions
counts were taken between June and October 2005. Moisture and temperature data was
taken from the Olds College weather station reports. Significantly more dandelions
germinated in the untreated plots than the Roundup treated plots and the spraying did not
assist in the counting process. Total dandelion emergence for the whole year was 415
dandelions per m2 for the untreated plots and 158 dandelions per m2 for the Roundup
treated plots. Trial results indicate that 65% of dandelion emergence occurred between
July 7 and August 3 in the non-herbicide plots and 81% in the Roundup applied plots.
Moisture was not limiting during the trial.
In year two, two treatments were again assessed. Initial weed counts were
conducted on May 23 in one treatment but did not begin until spring seed dispersal
was complete in the second treatment. The thought was that there may not be
sufficient seed from spring seed dispersal in those plots that were started early.
Total dandelion emergence was 429 plants for the early initiated treatment and 331
for the later initiated treatment. There was no need to wait for complete seed
dispersal before initiating the study. In the eight week period from May 23 to July
11, 92% of the seed had germinated in the early initiated treatment versus 80%
germination over the six week period for the later initiated treatment.
The majority of dandelion germination occurred in early summer and mid-summer
in year one of the study and in spring and early summer in year two of the study.
Introduction
Dandelions are a common, widespread problem in turfgrass throughout Alberta. This
non-native, perennial weed will propagate through air borne seed dispersal, dormant seed
germination from the seed bank, and regeneration from root stock if cropped above the
crown region. Dandelions can compete with turfgrass, perennial forages, and other plant
species for vital nutrients and space. The objective of this study was to determine timing
of dandelion germination with respect to their temperature and moisture requirements and
to establish a methodology for effective enumeration of dandelions. Understanding
dandelion biology with respect to germination will aid in the effective use of pre-emergent
herbicide applications.
Materials and Methods

This study was conducted at the Prairie Turfgrass Research Centre research plots located
at the N.W. corner of Olds College campus in a black Chernozemic soil. An initial plant
survey identified four main species within the trial site. These were Kentucky bluegrass
(Poa pretensis), creeping red fescue (Festuca rubra), red/white Clover (Trifolium
pretense/repens) and dandelion (Taraxacum officinale). In year one, dandelions were
allowed to go to seed prior to the initiation of the study to ensure high amounts of viable
seed in the plots. Enumeration of existing dandelions and their growth stage were
recorded prior to the herbicide application (Table 1.0). In year two, the trial was initiated
at an earlier date due to temperature and moisture conditions that were more favourable
for germination.

Plots that measured 0.5 by 0.5m were established in a random sub plot design and were
replicated four times. Two treatment methods were conducted in order to establish the
most appropriate methodology for effective enumeration of dandelions. In both years, the
first method was to manually remove mature dandelions and clover from the plots with a
pen knife in order to increase visibility of newly germinated plants. In year one a second
method was used where plots were sprayed with a 6% solution of Roundup®
(Glyphosphate) to ensure over wintering dandelions had been eradicated in order to
facilitate the weekly counting process. In year two, the second treatment was delayed two
weeks to ensure that spring seed dispersal was complete and that the maximum amount of
seed would be available for germination.

Each plot was observed for dandelion emergence on a weekly basis beginning 22 June
2005 and 23 May 2006. Prior to each weekly evaluation, offset pruning shears were used
to trim the grass to a height of 4.5cm to facilitate the counting process. A 0.25m2
quadrant with 25 individual grids was constructed and was used to facilitate the counting
process. Visible dandelion seedlings were enumerated at the first leaf stage and were then
extracted by cutting into the root zone below the crown region with a pen knife at a 45o
angle. This was done to avoid regenerative growth by the dandelion seedlings and to
facilitate future counts. It should be noted that dandelion counts were not made until the
first true leaf began to emerge because clover cotyledons had similar physical
characteristics as dandelion cotyledons making positive identification difficult.

Precipitation and temperature data were obtained from the weather station located on the
Olds College campus.

Results and Discussion
Existing dandelion counts, which were conducted in year one prior to the initiation of the
study, averaged 80 dandelions per m2 (Table 1). This was considered to be very high and
would ensure sufficient seed in the soil for this trial. Growth stages of the dandelions
showed that 85% of the dandelions were between the 2 and 10 leaf stage. Dandelions
with few leaves may indicate an early stage of development and that germination may
have recently occurred.
Table 1 – Initial dandelion count and stage of development per individual 0.25m2 plot.

Initial Dandelion Count per 0.25m2
Leaf 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20- 30+ Total

Stage 30

Plot # 4* 4* 44
11
101 2 2 9 6 2 3 6 1 2 2
1 1* 33
*102 213 3 2 12
9
201 62313 71 1 1 3 2 1 23
12
*202 31113 21 17

*301 1 2 1 2 2 1

302 1 4 3 4 7 2 1 1

*401 1 2322 1 1

402 1 1 2 1 6 2 3 1

*Single dandelions appeared to have multiple crowns
**Bold text indicates Roundup applied plots

In year one, analysis of the data showed that there was a significant difference for
germination counts between the Roundup treated and the untreated plots (Figure
1). Total germination over the entire rating period was 415 dandelions per m2 for
the untreated area while 158 dandelions per m2 germinated in the Roundup treated
area. This difference may have been due to moisture retention within the untreated
plots due to the vegetative cover which provided better conditions for germination
or recalcitrant compounds left from the Roundup may have been toxic to the
seedlings.

100

Seedlings per m 2 75
50 Untreated

25

Roundup trt

0
Weeks 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

June July August September October

Figure 1.0 – Year one dandelion germination counts June – Oct 2005

Results indicated that a large percentage of germination occurred over a five week
period between July 7 and August 3. In the Roundup treated area 81% of
dandelion emerged in this period while 65% emergence occurred within untreated
plots (Figure 1.0).

Moisture and temperature data showed a significant impact on initial germination. Prior
to the initiation of the study, conditions had been very dry with much below soil moisture
conditions. Heavy rainfall events on June 7 and on June 18 increased soil moisture levels
allowing for a greater seedling moisture absorption rate. Through the peak germination
period, increased temperatures proved to be a factor as well (Figure 2.0). A direct
correlation between germination and rainfall occurred as germination increased after each

rainfall (Figure 1.0 & 2.0). At the end of the growing season germination dramatically
declined as temperatures dropped.

percipitation (mm) Mean Temp (oC)

Temperature (oC), Moisture (mm) 50
40
30
20
10

0

6/1/05
6/8/05
6/15/05
6/22/05
6/29/05
7/6/05
7/13/05
7/20/05
7/27/05
8/3/05
8/10/05
8/17/05
8/24/05
8/31/05
9/7/05
9/14/05
9/21/05
9/28/05
10/5/05
10/12/05
10/19/05
10/26/05

Date

Figure 2.0 – Moisture and temperature data Olds, AB June – October, 2005
In year two (2006), germination occurred earlier than the previous year which was no
doubt related to moisture and temperature. Daily maximum temperatures recorded
between 14 May and 23 May ranged from 19.0 to 30.8oC. Precipitation recorded between
20 May and 30 May was 64.9mm. As significant germination was evident on 23 May,
soil moisture was obviously not limiting prior to this date.
For the initial treatment, 92% of the dandelions germinated between 23 May and 11 July.
For the delayed treatment 80% of the germination occurred between 6 June and 11 July.

Dandelion Germination - Olds, AB.

80Seedlings per m2 2006
70
60 2005
50
40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
30
20
10

0
Weeks

May June July August September October

Figure 3.0 – Dandelion germination counts for two years, 2005 and 2006. Week one
corresponds to 23 May.
Data from Figure 3.0 shows that minimal germination occurs after August 1 and that if
moisture and temperature is not limiting, the majority of germination will occur soon after
spring seed dispersal. From our observations the peak of spring seed dispersal in Olds
typically occurs from mid until the end of May. It would also appear that germination
occurs soon after seed dispersal which would indicate that a dormancy period does not
occur. Our findings show a decline in germination after the initial surge, which could be
the result of seed bank depletion after spring seed dispersal.
Clover and dandelion removal may have influenced the germination process. By reducing
competition through the extraction of mature weeds and seedlings, this may have made
resources more available for growth (sunlight, nutrients, moisture).
Recommendations for future emergence trials are that initial counts should start when
moisture and temperature conditions create ideal conditions for germination, possibly as
early as mid May. In addition, dates of dandelion seed dispersal should be noted. It does
not appear necessary to make an initial application of Roundup to facilitate the counting
process. Close clipping of the turf is all that is necessary.