Even though the latest HGCA Wheat Bulb fly survey indicated that only 3% of sites samples were above the threshold of 250 eggs/m², many late drilled crops could still be at risk if they have only one or two tillers at the time Wheat Bulb fly egg-hatch has started.
Egg-hatch for Wheat Bulb fly has already started in Suffolk, Cambridgeshire and Hertfordshire.
The low egg counts in the autumn indicated that Wheat Bulb fly would pose a limited threat to crops sown before November. However the wet autumn delayed drilling and plant development.
Consequently many autumn crops were sown late and for these a lower threshold of 100 Wheat Bulb fly eggs/m² will apply.
In the East of England 47% of monitored sites were above this level and in the North 27%. Later sown crops with just one or two tillers at egg hatch time may benefit from an insecticide treatment, even if egg numbers are in the moderate infestation category (100-250 eggs/m²).
This is particularly so as most later drilled crops will not have had a seed treatment as late drilling was not anticipated.
Slow developing early drilled crops will also need to be monitored and an egg-hatch spray may be worthwhile if these crops have low tiller numbers and Wheat Bulb fly egg numbers are in the moderate infestation category.
Sarah Hurry of Dow AgroSciences urges growers to assess the risk on their own farms and to identify vulnerable fields that may need treatment with Dursban WG (chlorpyrifos).
"Risk is based on locality, previous cropping, drilling date, plant population, tillering and soil type. Late drilled, struggling, backward or thin crops, of which there are many this year, may well benefit from Dursban WG at the first available opportunity in order to promote tiller survival."
"Dursban is an effective soil insecticide and should be applied at egg-hatch at 1 kg/ha in 200-1000 litres of water. It remains active in the soil for at least six weeks, meaning that most larvae will be controlled as they hatch over a longer period of time. If necessary Dursban WG can be applied to frosty ground but should not be tank mixed," says Sarah.
Growers are being advised to take all precautions to prevent drift by using low drift nozzles and an extended buffer zone when applying Dursban WG.
A new "risk assessment" for chlorpyrifos, under its routine EU/UK review, means that the existing label no-spray buffer zones adjacent to watercourses are no longer considered sufficient protection for aquatic organisms by the CRD.
An industry Stewardship initiative – Say NO to drift!- is in place. The aim of this campaign is to protect future availability and use of insecticides containing chlorpyrifos.
"When spraying Dursban WG for Wheat Bulb fly growers must use a LERAP rated 3 star nozzle and adopt a 20 metre buffer zone near to watercourses or a 1 metre near to dry ditches," says Dilwyn Harris from Dow AgroSciences.
Dursban WG (75% w/w chlorpyrifos formulated as a Water Dispersible Granule) is recommended for the control of Wheat Bulb fly as well as Leatherjackets, Frit fly and Wheat Blossom Midge. Two applications at dose rates of 1 kg/ha maybe applied up until flag leaf sheath extending (GS 39). It is packed in a 1 kg pack.