Seed coating and a better knockdown for dry sown crops!
C Reynolds, P Blackwell, R Grima and P Newman, DAFWA
KEY MESSAGES
•
A significant delay in germination (up to 2 days) was achieved through coating seed with an acrylic pavement
sealer. This was translated into delayed crop emergence in pot and field trials.
•
Total crop germination percentage is reduced by coating but may still prove valuable in terms of weed control by
delaying crop emergence compared to weed emergence.
•
Hair cutting method shouldn’t take place any later than the half leaf stage of the crop to ensure minimal risk to
yield potential.
BACKGROUND
Dry autumns and increased cropping percentage has resulted in increased importance on dry sowing (Robertson et al,
2011). This has led to a greater risk with weed control and little opportunity to apply knockdowns before seeding. Extra
tools are needed to complement selective herbicides, with many growers reverting to alternative weed seed control
methods such as mechanical seed collection, burning and crop competition. Whilst these tools all reduce the potential
impact of weeds on crop yield, growers will still be forced to dry sow into potentially weedy paddocks in many years
without a knockdown herbicide because of reduced autumn rainfall incidents. Crop seed coating to delay crop
germination has been used in other parts of the world (Stendahl, 2005) and has been tried in canola by DAFWA
previously, and may provide an alternative weed control option for growers in this situation. “Hair cut” experiments
have been conducted in WA (Newman and Adam, 2002) but results have been less than encouraging. The main issue
is grass seedlings are generally at similar growth stage to the crop. Hence all plants suffer a similar fate.
It is hypothesised that by applying an acrylic pavement sealer to the wheat seed coat, emergence will be delayed by
greater than 48 hours. This will allow weed seed germination to occur before the crop and facilitate a “haircut” using
desiccant knockdown herbicides. It should be noted that use of the seed coat products is not registered, and use of
the spray products onto germinated crops is not a registered activity and contravenes the label use of those products.
Significant industry feedback was sought during this trial to formulate future related work and the development of new
and innovative techniques to combat the threat of weeds in the desired farming system.
METHODS
Wyalkatchem wheat seed was obtained from the Geraldton Research Station and graded over a 2.5 mm sieve to be
used throughout the experiment to minimise seed vigour problems. Seeds were natural (uncoated) or coated with an
acrylic paving sealer, Megatreat Satin Sealer (MSS), obtained off the shelf from the local hardware store. The solution
applied was a mixture of MSS, blue food colouring to enable us to see the extent of the coverage on the wheat seed,
and wetting agent (BS1000) to assist in covering the seed. The seed was coated with different rates of this sealant
solution in three kilograms batches, through the use of a conventional cement mixer and compressed air to ensure the
seed maintained a smooth, flowing motion enabling good coverage. This solution was applied directly to the tumbling
wheat seed in the mixer through a syringe.
Over fifteen different treatments were tested initially in germination cabinets. These included a number of products, all
at different rates, with and without the addition of wetting agent. From this a subset of treatments were tested in pot
trials in controlled growth rooms. From this set of trials the most promising treatments were retained and used for field
experimentation.
Germination tests: Germination tests were carried out by placing moistened napkins in plastic sandwich bags with 50
seeds of the individual treatment, with three replicates each time, and placed in germination cabinets at 20 degrees.
These were observed every 24 hours and recorded for up to two weeks or until full germination had been reached.
Germination speed and percentage were observed.
Pot trial: The selected seed treatments showing most promise were observed in a pot trial. Small plant pots were filled
with the same amount of Debco Seed Raising Potting Mix to approximately 2 cm below the top of the pot. Ten seeds
of each treatment were placed in each pot and filled to the top with the potting mix. This was replicated 15 times for
each treatment. The pots were then placed in a tub of deionised water to absorb water until it began to form on top of
the soil. The pots were then taken out and allowed to drain for a short period of time. This ensured the soil in each pot
was at full water holding capacity. The pots were then randomly placed on a shelf in a controlled
environment room for 14 days. They were observed every 24 hours for emergence and average plant
2013 WA Crop Updates
height. The number of second leaf plants in each pot was also recorded once that stage had been reached.
Field Trial: Two field trials were carried out, at Walkaway and Dalwallinu. Both trials had 4 seed coat treatments, 4
spray (knockdown) timing treatments, and 4 replicates making a total of 64 treatments in a completely randomised
block design. Plot width was 1.54 m and 20 m length. The Walkaway trial was seeded at a rate of 100 kg/ha and the
Dalwallinu site at a rate of 80 kg/ha. Both sites were sown with 80 kg/ha Agstar Xtra banded under the seed and 50
kg/ha urea top dressed. Sites were also sprayed with 1 L/ha Spray.Seed before sowing was carried out. Typical broad
leaf spray applications were carried out at the late tillering stage for both trials.
The Walkaway site was seeded on the 10th May. Opening rains fell on the 6th and 7th of June with approximately 35
mm. Plant counts and spraying was carried out on the 12th, 15th and 18th of June.
The Dalwallinu site was seeded on the 22nd of May. Opening rains fell on 6th and 7th of June with 15 mm. Spraying
dates were 15th, 19th and 25th of June. Plant counts carried out on 13th, 15th, 19th, 22nd and 27th of June. Field
yield data represented in this paper is from the Walkaway site.
The 4 seed coating treatments applied to 3 kg Wyalkatchem were nil, 200 mL, 2 x 200 mL (400 mL total, and air dried
between applications), and 400 mL of MSS with 5% BS1000. Once the solution was applied the seed was spread out
on large trays and placed in an oven at 40 degrees over night to dry out. The dry seed was then placed back in the
cement mixer and talc was added at 0.5% w/w in order to stop seed sticking together and allow it to feed through the
trial cone seeder.
The spray treatment was 1 L/ha Spray.Seed herbicide sprayed with AIXR 11002 (yellow) nozzles at 300 kPa and 80
L/ha was applied at the 4 different crop stages nil, 0.5 , 1.0 and 1.5 leaf stages.
RESULTS & DISCUSSION
100
% Germination
In the
germination
90
trial,
significant
80
delays in
germination
70
speed were
achieved with
60
several
treatments
50
(Figure 1). A
reduction in
40
overall
CONTROL
200ml (5%)
400ml (2%)
germination
30
percentage
was also
20
evident was
400ml (5%)
200ml x 2 (5%)
600ml (5%)
in these
10
same
treatments.
0
Six of the
0
1
2
3
4
5
6
7
8
9
10
fifteen
DAS
original
Figure 1: Percentage and speed of germination achieved in germination cabinets for a subset of total number
treatments
of treatments (LSD 95% at 3 days is 15.3%)
tested in the
germination cabinets are displayed in Figure 1. Full germination was achieved for the untreated control treatment
(UTC) within 2 days. Germination speed was only slightly reduced for treatments with solution containing only 2%
wetting agent. When the wetting agent was increased to 5%, germination speed was reduced. This is likely to be from
assisting enhanced seed coverage of the MSS solution at that rate, compared to the 2% rate. Several treatments have
little or no germination observed when the control treatment had reached 100% germination. Germination delays of
approximately 24 hrs are observed for treatments with 400 mLs (or greater) and 5% wetting agent, but overall
germination % was significantly reduced for these treatments.
The treatments demonstrated in Figure 1 from the germination cabinet trial were then trialled and observed in a pot
trial. Similar germination percentage and speed were observed for all treatments tested (data not shown). From these
successful trials a selection of four treatments were tested in two field trials to see treatment effects in a normal
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growing environment and to look at the effect of spray treatments on the different grain treatments. All of the selected
treatments utilised the same 5% wetting agent.
200
180
160
140
plants/m2
120
100
80
60
40
control
200mL 200mL x2
400mL
20
0
4
6
8
10
12
14
16
18
20
22
days after break
200
180
160
140
plants/m2
120
100
80
60
40
control
200mL 200mL x2
400mL
20
0
4
5
6
7
8
9
10
11
12
days after break
Figure 2: Plant
counts per metre measured at Dalwallinu (bottom) and Walkaway (top). (Vertical bars are LSD at 95% confidence)
Field observations of germination percentage and speed were very similar to that displayed from both germination
cabinets and the pot trial (Figure 2). At Walkaway full crop establishment had been achieved by 5 days after break
(DAB). Only the 200 mL treatment achieved similar total germination numbers compared to UTC, with a slight delayed
germination observed at 5 DAB. The 400 mL treatments had significantly lower germination % than UTC at all timings.
The 2 x 200 mL treatment had a significant plant number reduction at 5 DAB, and whilst total plant germination was
lower than UTC this was not significant. At Dalwallinu total emergence was obtained for UTC at 8 DAB. At this timing
all other treatments had significantly lower emergence. Over 100 plants/m2 had emerged for UTC at 6 DAB, whilst this
did not occur until approximately 10 DAB for both 400 mL treatments. This is the very effect required if the hair cut
window can be increased and exploited.
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Table 1: Yield, quality and establishment of wheat, and grass weed establishment at Walkaway site.
Treatment
Yield
Protein
Screenings Weight
(t/ha)
(%)
(%)
(g)
3.21
No spray: No coating(Control)
12.7
3.42
79.94
No spray: 200 mL
3.35
13.3
78.40
4.11
No spray: 200 mL x 2
3.09
12.7
3.51
79.50
No spray: 400 mL
3.34
12.3
3.88
79.97
2.95
1 L/ha Spseed@ ½ leaf: No coating
12.6
3.75
79.9
1 L/ha Spseed@ ½ leaf: 200 mL
2.73
12.7
3.41
79.61
1 L/ha Spseed@ ½ leaf: 200 mL x 2
3.12
12.8
3.86
79.24
1 L/ha Spseed@ ½ leaf: 400 mL
3.34
13.0
3.83
79.09
2.76
1 L/ha Spseed@ 1 leaf: No coating
12.9
3.79
79.85
1 L/ha Spseed@ 1 leaf: 200 mL
2.96
13.1
3.85
79.04
1 L/ha Spseed@ 1 leaf: 200 mL x 2
2.64
12.8
3.54
79.84
1 L/ha Spseed@ 1 leaf: 400 mL
2.96
12.8
3.63
79.59
0.53
1 L/ha Spseed@ 1½ leaf: No coating
13.5
4.59
78.60
1 L/ha Spseed@ 1½ leaf: 200 mL
1.68
13.5
4.33
78.69
1 L/ha Spseed@ 1½ leaf: 200 mL x 2
1.89
13.2
3.67
79.79
1 L/ha Spseed@ 1½ leaf: 400 mL
1.72
13.4
3.86
79.06
LSD 95% probability
0.63
0.82
0.92
1.20
LSD 90% probability
0.53
0.68
0.77
1.00
Diff at 90% probability are italics and compared to no spray, no coat control.
Diff at 95% probability are italics and bold and compared to no spray, no coat control.
Diff at 95% probability compared to no coat for same spray is shaded
Plants
2
/m
189
181
113
88
167
142
67
70
154
101
89
107
129
152
96
78
59.9
49.8
Ryegrass
/m2
88
230
101
341
118
20
62
151
55
33
25
22
285
204
105
147
231
192
The spray timing effects were easily seen in those plots sprayed at the 1.5 to 2 leaf stage. The greatest effect was in
the UTC seed coat plots and decreased in the plots that had a higher rate of treatment solution applied to the seed
before sowing. This can be seen in Figure 3 where 400 mL treatment has more surviving plants/m2 compared to the
UTC despite compromised plant germination. Hence significant plant mortality for the UTC occurred from the spray
treatment at the 1.5 leaf timing.
Yield observations at the Walkaway site indicated that only spray treatments at 1.5 leaf stage of UTC provided a
significant yield penalty (Table 1). All other spray timings did not impact yield at all. In this trial therefore spraying up to
the 1 leaf stage of the crop would have been considered safe. This may have been facilitated by sieving the seed to
2.5 mm, possibly resulting in greater seedling energy. Plant densities for 2 x 200 mL and 400 mL treatments for all
spray timings were significantly reduced compared to UTC, but this did not cause a yield reduction. This site was
relatively weed free, allowing the crop to compensate for low plant numbers without competition from weeds. Hence it
could be reasonable to expect from this trial that seed coating in its own right does not reduce yield if weed numbers
are low. The trial would need to be replicated in weedy environments in order to fully understand the implication of
reduced seedling germination. Alternatively new products that do not suffer the total germination issues could be
sought. There were very little significant differences between treatments for protein, grain weight and screenings.
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Figure 3: Photos demonstrating the visual impact on seed establishment from some of the spray treatments on
untreated seed at the Walkaway site.
CONCLUSIONS
This series of trials is deemed “blue sky” experimentation and not applied. Many factors restrict the use of these
products in this manner for genuine farm businesses. Firstly, the haircut technique is not a registered use of any
paraquat based products. Application of this product to growing wheat crops would contravene label use. Secondly,
there is no registration for the seed coat product trialled here. Thirdly, no analysis or experimentation has been
conducted to assess how this seed coating may be applied to large volumes of seed grain, or its probable cost
It appears using an acrylic pavement sealer product on wheat seed can result in delayed germination of at least 24
hours, and in some field observations up to 5 days. We successfully identified that one commercial acrylic sealer not
designed for the purpose of coating wheat can delay wheat germination enough to improve the length of the "haircut"
window, allowing improved weed control in dry sown wheat crops. However, overall crop germination was also
reduced and seeds rates would need increasing to compensate. Robust expansion of this technology will require more
detailed investigations, and should focus on product chemistry as well potential for use in other species, especially
canola. Replicating this work in a weedy environment would provide increased knowledge of its fit. Industry has
indicated their support for continuing this work to overcome the already identified issues. This work also demonstrated
that effects observed in the field are closely mirrored in pot trials. This will facilitate trialling many products quickly at
reduced costs.
When applying desiccant knockdown herbicides post sowing, this trial indicates this should not be conducted after the
1.0 leaf stage. However significant yield penalties can occur after the 0.5 leaf stage (Newman 2002). Great caution is
urged before applying this technique across broad areas of established crop because trial work and anecdotal
evidence suggests yield penalties can occur at earlier crop timings than observed in this experiment.
Creating a larger hair cut window would allow growers to dry sow with more confidence into paddocks where weed
control in previous years has not been achieved to an acceptable standard. However, issues relating to appropriate
timing would need to be considered to ensure label guidelines are adhered to. It is unclear exactly how long the haircut
window needs to be broadened in order to be useful for growers as a weed control tool. It is envisaged that 48 hours
would be the absolute minimum and more if possible. Seed application techniques have also not been developed and
could prove to be a barrier.
KEY WORDS
Seed coating, hair cut, dry sowing, delayed germination, emergence, wheat
REFERENCES
Robertson, M. Weeks, C. O’Conner, M. Abrecht, D. Grima, R. Newman, P. (2011) Pros and cons of dry seeding to
counter variable season breaks. In Crop Update proceedings pp208-212
http://www.agric.wa.gov.au/objtwr/imported_assets/content/amt/agb/crop_updates_proceedings_february2011.pdf?noi
con.
Stendahl, F (2005) Seed coating for delayed germination. Department of Ecology and Crop Production Sciences,
Swedish University of Agricultural Sciences. Uppsala, ISSN 1404-2347
Newman, P. and Adam, G. (2002) “Hair cutting” wheat with Spray.Seed®: Does it work? In Crop Update proceedings
http://www.agric.wa.gov.au/objtwr/imported_assets/content/pw/weed/2002_cuweeds.pdf#page=105
ACKNOWLEDGMENTS
NEAR Project 5 for funding. Trevor Bell, Dave Nicholson, Katherine Ayres, Anne Smith, Jo Walker, Dirranie Kirby,
Gareth Rowe, and Liebe staff
Paper reviewed by: Darshan Sharma, Glen Riethmuller
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