Materials and Methods
In the autumn of 2002 field trials were established (Table 1) in a crop of winter wheat at two different ADAS sites, Boxworth (Cambridgeshire) and Rosemaund (Herefordshire) and at SAC in Edinburgh. In 2003 two trials were established at ADAS Boxworth only (Table 1). Fields were selected with a low natural weed population and the desired weed species were hand sown.
Table 1. The location and weed species chosen for each field trial site.
Species/trial year Sites
ADAS Boxworth SAC ADAS Rosemaund Black-grass 2002/03 aa
Black-grass 2003/04 a*
Chickweed 2002/03 a a
Cleavers 2002/03 a aa
Cleavers 2003/04 a
aarepresents two drilling dates for that particular experiment.
*individual plots were selected from a large black-grass trial, with a natural population of black- grass, therefore no specific trial was sown for this project in 2003/04.
Where two drilling dates were required the target drilling dates were late September and late November. No herbicide treatments were applied other than the trial treatments, but all other farm inputs were to standard commercial practice for that particular farm.
Trial design
For the trials with multiple drilling date a split plot design was used, with 3 main blocks for the 3 replicates, sub-divided into 2 blocks in each main blocks for the drilling dates and sub-plots for the combinations of herbicide programme and weed density. Trials with a single drilling date were a randomised block design. The minimum plot size was 3m x 12m.
Weed density
The densities for each species (Table 2) were selected to cover a range where the models predict that the rate of change of crop yield with weed density is at its highest. Weed seed was hand sown into each plot on the day of drilling ahead of a commercial crop of winter wheat being sown. Weed seeds were purchased from Herbiseed, UK and were known to be from non-resistant populations.
Table 2 The weed species target densities for the field validation trials Density (plants per m2)
Weed species Low Medium High
Black-grass 6 36 216
Chickweed 6 36 216
Cleavers 4 16 64
Herbicide treatments
Application timings of the herbicide treatments were determined by the growth stage of the weed species. The early herbicide treatment was applied at 2-leaf growth stage of the crop, and the late treatment at the 8-leaf stage and after canopy closure. The choice of herbicide products and doses were weed dependent and are presented in Table 3. Herbicides were applied using a knapsack sprayer and 3m boom, with Lurmark 02 F110 nozzles, at a rate of 200L water/ha and a pressure of 3.0 bar.
Table 3 The herbicide treatments, application timings and dose rates.
Weed species Treatment Timing Application Timing Herbicide Rate Chickweed Early Post-em (autumn) Treflan 2.0 l/ha Late GS30 (after 1st Feb) Ally (+ Starane)* 7.5g/ha (0.5
l/ha)*
Full control Autumn
(Ally-Spring, after 1st Feb) Panther (fb. Ally if needed) 2.0 l/ha (30g/ha) Black-grass Early Autumn
(up to 2-3 tillers)
Lexus 50DF 20 g/ha
Late Feb/March Topik 0.16 l/ha
Full control Autumn post-em
Autumn 2-3 lvs. Crystal Hawk + Lexus 50DF 4.0 l/ha 2.5 l/ha + 20g/ha
Cleavers Early Autumn
Feb/March IPU Eagle 3.0 l/ha 20 g/ha Late Autumn
Crop GS 31-32 IPU Starane
(+Ally if needed)
3.0 l/ha 0.5 l/ha
Full control Autumn
Spring Panther Starane 2.0 l/ha 1.0 l/ha Assessments
Within each plot one 0.5 m2 permanent quadrat was marked out for seedling emergence (of crop and
weeds) counts. Up to 4 other 0.5 m2 quadrats per plot were destructively sampled as detailed below:-
i)Seedling Emergence Counts
On one of the weed density plots in each replicate, the number of weed and wheat seedlings was counted every 3 or 4 days, depending on the change in numbers observed, until emergence was complete. When emergence is complete, the numbers of seedlings in a sample quadrat in each plot should be recorded to determine the density of weeds.
ii) Biomass assessments and GAI assessments
On the no herbicide application treatments only, a visual assessment of the ground cover was recorded in one 0.5 m2 permanent quadrat and all plants were hand harvested and separated into the
different species. Individual weeds and crops were counted and a growth stage measurement of weed and crop was assessed and recorded by selecting 6 representative plants from each species. For each species (all weeds including natural populations and crop), the leaves and stems were separated and the green area measured. This process was repeated at each of the following timings on the appropriate plots:-
• Three weeks after Early Herbicide Application (when symptoms of treatment were visible)
•
At Canopy Closure (defined as when the GAI of all weeds plus crop reaches 0.75).• Three weeks after Late Herbicide Application (when symptoms of herbicide treatments were visible)
• June (before combining the plot) – all plots.
iii) Final Crop Yield Harvest from combine yield area
The fertile tillers were counted in each plot using each side of a 0.5m rod placed between the crop rows at 5 points per plot. Plots were harvested using a Sampo plot combine and plots length measurements were recorded. Sample of grain were collected and processed for grain moisture content and a thousand grain weight. Plot yields were calculated.
54
establishment and daily meteorological records, a model of green area expansion was run in Matlab to predict the GAI at canopy closure in the no herbicide control treatments. The model used parameter values from the literature. These simulations were used to predict the weed GAI before herbicide application. The difference between this value and that observed after applications was compared with the expected efficacy of the herbicide. The ratio of weed species GAI to winter wheat GAI at canopy closure was used as inputs to the equations used to relate these ratios to winter wheat yield loss.
Statistical Analysis of Observed Data
The times of weed and crop seedling establishment were estimated by fitting logistic curve to the seedling numbers observed in the permanent quadrats. The yield of the winter wheat at harvest, the biomass of each weed species prior to harvest and the GAI of each sown species at emergence, canopy closure was subjected to an ANOVA in Gentstat. Regressions between visual assessments of cover and GAI were conducted. The differences between observed and predicted winter wheat yield loss and between observed and predicted GAI at emergence and canopy closure, were also subjected to an ANOVA. Additionally, the simulation models were fitted separately to each replicate and the fitted values subjected to an ANOVA.
Results
The results from the field trials were evaluated by the experts and tested against the model outputs. Comparison of the predicted and observed crop growth stages from the first season (2002-03)
showed good
agreement. The model was compared with data from the black-grass trial at ADAS Boxworth on crop and weed green area index (GAI) and the effect of weeds and herbicide treatments on crop yield. Autumn 2002 was very dry, leading to exceptionally low germination of the weeds. The model predicted slightly higher germination rates and consequently higher weed GAI than were observed. The weed densities were so low that the differences between treatments (weed sowing density and herbicide programme) were not significant. The predicted yields were lower than the mean observed yields, but these differences also were not significant. Inspection of the data showed similarly low GAIs for the other weed species, so the testing was not repeated, as it was unlikely to show additional information.
The second season (2003-04) included fewer weed species, but the weather conditions gave rise to high weed populations resulting in significant yield losses. The model was assessed on the basis of yield loss in sprayed and unsprayed plots (using several spray programmes), thus testing the combined effects of all the steps in the model.
Examples of the results are summarised below from the 2003/04 cleaver and black-grass trials. Cleaver trial 2003/04 ADAS Boxworth
Crop Wheat
Sown 14 Nov 2003
Previous harvest 31 Aug 2003 (assumed) Cultivation Direct drill (assumed)
Density sown 200-300 based on emergence data Potential yield 10.6 t/ha (see yield table below)
Weed Cleavers Sown 14 Nov 2004
Plant Emergence (mean over treatments) Date Crop density Weed density low Weed density medium Weed density high 15/12/03 213 2 9 35 22/12/03 269 4 16 71 5/01/04 278 15 50 182 12/01/04 294 21 73 238 19/01/04 299 26 81 265 2/02/04 301 29 87 273 13/02/04 289 30 83 263
Spray programmes (table from protocol; dates from diary)
Treatment Timing Application Timing Herbicide Rate
Early 08/12/03 04/03/05 IPU (6159) Eagle (6131) 3.0 l/ha 20g /ha Late 08/12/03 02/05/04 IPU (6159) Starane (7370) 3.0 l/ha 0.5 l/ha Untreated Pre-emergence spray only
Full control 08/12/03 13/04/04 Panther (6128) Starane (7370) 2.0 l/ha 1.0 l/ha All include 05/12/03 – Pre-emergence spray to kill black-grass – Topik and Avadex. System data:
Topik ID = 8 (with adjuvant), Dose = 1.0; Avadex ID = 7419, Dose = no data – omit Eagle doses are 0.03 and 0.04 – use 0.03 on the assumption units are kg.
Starane 2 doses are 0.75, 1.0, 2.0 – use 0.75 in place of 0.5 Cleavers trial results – yield t/ha
Weed density sown
Sprays None Low Medium High
Untreated 9.75-10.73 (10.17) 8.67-9.70 (9.10) 7.17-9.60 (8.51) Early 10.42-10.84 (10.63) 9.19-11.25 (10.29) 10.01-10.63 (10.37) Late 9.86-10.84 (10.29) 9.86-10.58 (10.32) 9.96-10.84 (10.37) Full 10.17-11.15 (10.61)
Model runs
Used Bedford weather (closest available DESSAC site), with gaps filled by Wittering weather site. Cleavers model results (parameter set 1.02) – yield t/ha
Weed density sown
Sprays None Low Medium High
Untreated 10.54-10.60 8.23-9.00 5.01-6.09 2.04-2.79 Early 10.60 10.34-10.43 9.66-9.99 7.80-8.58
56 Comments
• The yield losses in the model from uncontrolled cleavers were far higher than observed.
• The control obtained by the late spray programme was far less than observed.
• Therefore, in order for it to have an effect, the second treatment had to be brought forward to March. With this timing, the yield is similar to that from the Early programme. This was thought to be a feature of the model.
The model was tested using the alternative parameter sets that were considered on 8 March: 1.04 – emergence refitted by Jonathan Storkey, rejected because of large changes in many weeds 1.05 – other parameters fitted by Laurence Benjamin using PCA – small changes to most weeds 1.06 – combination of 1.04 and 1.05
Cleavers model results (parameter set 1.04) – yield t/ha Sprays Weed density sown
None Low Medium High
Untreated 10.60 10.36-10.45 9.74-10.03 7.84-8.61 Early 10.60 10.58-10.59 10.52-10.55 10.28-10.39 Late 10.60 10.37-10.45 9.76-10.04 7.88-8.64 Full 10.60 10.60 10.58-10.59 10.52-10.55 Cleavers model results (parameter set 1.06) – yield t/ha
Sprays Weed density sown
None Low Medium High
Untreated 10.60 10.26-10.38 9.36-8.76 6.91-7.84 Early 10.60 10.44-10.50 10.00-10.20 8.54-9.16 Late 10.60 10.27-10.39 9.38-9.78 6.96-7.88 Full 10.60 10.60 10.56-10.57 10.44-10.50 Parameter set 1.05 gave even lower yields than 1.02.
Comments
• The evidence is insufficient to recommend a change of parameter sets, especially as the results for black-grass (see below) are different. Further investigation of GAI, etc was required before a decision was made whether the fault is with weed development, crop development or competition.
Black-grass trial (ADAS Boxworth 2003/04)
Crop Wheat
Sown 16 Oct 2003
Previous harvest 31 Aug 2003 (assumed) Cultivation Direct drill (assumed)
Density sown 150-250 based on emergence data Potential yield 9.2 t/ha (see yield table below)
Weed Black-grass Sown Natural population Density 100-250 based on early emergence Emergence
Date Crop density untreated Crop density sprayed Weed density untreated 4/02/04 162-286 (239) 144-358 (260) 98-240 (144) 27/04/04 168-244 (202) 216-316 (253) 208-506 (388) 6/07/07 128-182 (155) 180-218 (200) 124-212 (168)
Spray programmes (table from protocol; dates from diary)
Treatment Timing Application Timing Herbicide Rate
Early
(T4 from BG slots trial)
02/12/03 Lexus 50DF + Stomp [+Fortune]
(6141) + (7214) 20 g/ha + 3.3 l/ha [+ 1.0 l/ha] Late (T20 from BG slots trial) 23/01/04 Atlantis [+ BioPower] (7185) 0.4Kg/ha [+ 1.0 l/ha] Untreated
(T44 from BG slots) Use untreated plots from black-grass slots trial 2004 21/10/03 Crystal
(6130) 4.0 l/ha
Full control
18/12/03 Hawk + Lexus [+Fortune]
(6134) + (6141) 2.5 l/ha + 20g/ha [+ 1.0 l/ha] From system Lexus 50DF dose 0.02 Stomp 400 EC dose 3.3 Atlantis WG no data Crystal dose 4.0 Hawk no data
Hawk = clodinafop-propargyl + trifluralin 12.383 g/l
clodinafop-propargyl = Topik (250 g/l, ID = 8 (with adj), dose = 1) trifluralin = Alpha Trifluralin (480 g/l, ID = 6148, dose = 2.3) Black-grass trial results
Treatment Timing Yield t/ha
Untreated 2.13-6.47 (4.91)
Early spray 5.38-9.03 (7.12) Late spray 8.2-9.11(8.73) Full control 8.59-9.77 (9.21) Model runs
Used Bedford weather (closest available DESSAC site), with gaps filled by Wittering. Black-grass model results (parameter set 1.02) – yield t/ha
Treatment Timing Sensitive Resistant
Untreated 6.44-8.48 6.44-8.48
Early 8.61-9.14 8.25-9.07
Late * *
Full 9.00-9.18* 8.66-9.14*
*Unable to simulate the late programme due to the absence of data for Atlantis. Full programme used mixture in place of Hawk due to absence of data.
Comments
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If the density is increased to 250-500 (the range for late emergence) the results are Black-grass model results (parameter set 1.02, high density) – yield t/ha
Treatment Timing Resistant
Untreated 4.95-7.36 Early 7.52-8.75 Late *
Full 8.21-8.98 Comments
• These are closer to the trials, but still on the high side for untreated, and required very high densities. The potential yield probably should be increased, given that the maximum with the full treatment is lower than observed, which would then raise all the yields.