The final battle in this year’s war against blackgrass and other grassweeds needs careful planning, says Stuart Jackson of Dow AgroSciences.
To date, the 2014/15 campaign has gone well. There has been a significant shift of tactics with farmers adopting cultural means of control such as increased use of stale seed beds and delayed drilling. In addition, the season has favoured the performance of pre-emergence treatments which have increasingly been applied as combinations or ‘stacks’.
“Moist soils mean these materials have worked well,” says Mr Jackson, Dow AgroSciences cereal herbicide specialist. “However, delayed drilling and a change in the weather meant only a small proportion of the winter wheat crop has received post-emergence treatments. This is good news as any blackgrass this spring is relatively small, making control easier.”
In a nutshell, Mr Jackson’s advice is to assess weed populations and growth, select products that suit the field, the weed challenge and stage of growth and the weather conditions.
The aim is to look to apply a post-emergence contact spray as soon as active growth begins. The larger the weeds become, the harder they are to control.
Product choice for blackgrass up to GS24 is UNITE (pyroxsulam+flupysulfuron) with an approved wetter. This will not only tackle grassweeds, but will also provide control of a range of broad-leaved weeds.
“Up to the end of February, it is worth considering adding a residual,” says Mr Jackson. “Pay attention to products used earlier in the season and if possible select a different mode of action to help reduce the challenge of resistance.”
Once blackgrass exceeds GS24, then consider a specific graminicide recommended for later growth stages and add Spitfire (fluroxypyr + florasulam) to ensure cleavers and other broad-leaved weeds are controlled.
Timing and application method are critical.
“In essence, you need to apply when weather and soil conditions will allow three days of active growth before and after treatment,” says Mr Jackson. “Temperature fluctuations and crop stress will impair performance.”
Attention to detail continues in application. UNITE needs to be applied at the correct dose in 130-150 L/ha of water using appropriate nozzles, boom height and forward speed.
“Given the work pressure there will be this spring, UNITE has the advantage of being compatible with a wide range of T0 fungicides,” says Mr Jackson.
Some growers may find high levels of blackgrass populations when they inspect fields. There is a tough decision to take – whether to leave the crop or burn it off.
“It is becoming accepted that exceeding 100 plants/m2 is a level at which to consider pulling a crop up and sowing a spring crop,” says Mr Jackson. “Keeping crops with such populations, especially if resistance is developing, is a recipe for short-term yield loss together with a longer term legacy of ever increasing population pressure.”
