Match up cereal stages and wheat blossom midge pupation
Despite generally low levels of Wheat Blossom midge this year, some crops will be at the vulnerable stage (GS 53 to 59) when the Wheat Blossom midges are emerging according to Dow AgroSciences latest Pest Watch.
Particularly after last week’s rain, growers should be identifying fields most at risk with regard to their growth stage and consider using pheromone traps at the most susceptible sites, which are those with a problem last year. The best time to inspect crops is on warm, still evenings. Growers and advisors must optimize spray timings to ensure effective pest control and to minimize impact on the environment.
Pestwatch reports that Orange Wheat Blossom midge pupae have been recorded at three of the four sites, with a range of 75% in Norfolk to less than 10% in Yorkshire. This is likely to have been stimulated by the recent increased temperatures. Up until now it has been unclear if pupation would coincide with crops at risk period (GS53-59), but with some forward crops now at ear emergence and pupation beginning, there is a real threat, despite low population numbers. The developmental period between pupation and emergence of adults is temperature dependent, but can be as little as a week. Adult females will live for around 2-3 days, so timing is critical with this pest.
Sarah Hurry of Dow AgroSciences explains that Orange Wheat Blossom midge larvae cause damage by feeding on developing grain. “The economic risk is highest in crops intended for seed or milling, which is reflected in the lower threshold of one Orange Wheat Blossom midge per 6 ears. The threshold for feed wheat is one midge per 3 ears. One Orange Wheat Blossom midge larvae feeding per grain site can cause about 30% yield loss; with two or three larvae per grain site loss can be as much as 75%, or even higher if ear emergence is late. In addition larval feeding can induce premature sprouting in the ear and a reduction in Hagberg Falling Number. Secondary fungal attack can follow under damp conditions.”
She explains that damage occurs when egg laying coincides with the vulnerable growth stages of wheat crops that are susceptible (GS 53-59). “The total winter wheat area planted in the UK this year is estimated to be 20% down and of this 35% of wheat in the ground is an Orange Wheat Blossom midge resistant variety, with Santiago representing a third of this. These varieties don’t need monitoring or treatment. The percentage of OWBM resistant wheat varieties planted is increasing year on year and it is possible that the low pest populations are related to this.”
Sarah advises that if chemical treatment is justified by thresholds being met or exceeded, growers should use Dursban WG at 0.6 kg/ha in 200 to 1000 litres of water between ear emergence and the start of flowering (GS51-59) in order to control developing larvae.. “Dursban WG controls all the life stages of the pest, giving growers the widest window of opportunity and more flexibility to control this damaging pest. Dursban WG gives high knockdown of adult midges, effective activity of 7 to 10 days to control further flights of adults plus effective vapour action to control larvae emerging from eggs laid by the first flight of adults.”
“Precautions must be taken to minimise impact against wildlife by only applying an effective insecticide when necessary. In order to allow an area for beneficial arthropods to survive and colonise the field, growers must comply with the Stewardship ‘Say No to Drift’ guidelines, including adopting a 20 metre no-spray buffer zone beside watercourses, by using LERAP three-star low-drift nozzles and adopting a 12m no-spray buffer zone beside hedges or grass strips" points out Sarah.
Dursban WG (75% w/w chlorpyrifos formulated as a Water Dispersible Granule and packed in a 1 kg pack) is recommended for the control of Wheat Blossom midge, Leatherjackets, Wheat Bulb fly and Frit fly. For Wheat Blossom midge, apply Dursban WG at 0.6 kg/ha between ear emergence and the start of flowering (GS 51-59).
