Despitegenerally low levels of wheat blossom midge this year, some crops will be atthe vulnerable stage (GS53 to 59) when the wheat blossom midges are emerging,according to Dow AgroSciences latest Pest Watch. Particularly after recentrain, growers should be identifying fields most at risk with regard to theirgrowth 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 onwarm, still evenings. Growers and advisors must optimize spray timings to ensure effective pest control and to minimise impact on theenvironment.
Pestwatchreports that OWBM pupae have been recorded at three of the four sites, with arange of 75% in Norfolk to less than 10% in Yorkshire. This is likely to havebeen stimulated by the recent increased temperatures. Up until now it has beenunclear if pupation would coincide with crops at risk period (GS53-59), butwith some forward crops now at ear emergence and pupation beginning, there is areal threat, despite low population numbers. The developmental period betweenpupation and emergence of adults is temperature dependent, but can be as littleas a week. Adult females will live for around 2-3 days, so timing is criticalwith this pest.
Sarah Hurry of Dow AgroSciencesexplains that OWBM larvae cause damage by feeding on developing grain. Theeconomic risk is highest in crops intended for seed or milling, which is reflectedin the lower threshold of one OWBM per 6 ears. The threshold for feed wheat isone midge per 3 ears. One OWBM larvae feeding per grain site cancause about 30% yield loss; with two or three larvae per grain site loss can beas much as 75%, or even higher if ear emergence is late. In addition larvalfeeding can induce premature sprouting in the ear and a reduction in HagbergFalling Number. Secondary fungal attack can follow under damp conditions.
She explains that damage occurswhen egg laying coincides with the vulnerablegrowth stages of wheat crops that are susceptible (GS 53-59). The total winterwheat area planted in the UK this year is estimated to be 20% down and of this35% of wheat in the ground is an OWBM resistant variety, with Santiagorepresenting a third of this. These varieties dont need monitoring ortreatment. The percentage of OWBM resistant wheat varieties planted isincreasing year on year and it is possible that the low pest populations arerelated to this.
Sarah advises that if chemicaltreatment is justified by thresholds being met or exceeded, growers should use Dursban WGat 0.6kg/ha in 200 to 1000 litres of water between ear emergence and the startof 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 controlthis damaging pest. Dursban WG gives high knockdown of adult midges, effectiveactivity of 7 to 10 days to control further flights of adults plus effectivevapour action to control larvae emerging from eggs laid by the first flight ofadults.
Precautionsmust be taken to minimise impact against wildlife by only applying an effectiveinsecticide when necessary. In order to allow an area for beneficial arthropodsto survive and colonise the field, growers must comply with the StewardshipSay No to Drift guidelines, including adopting a 20 metre no-spray bufferzone beside watercourses, by using LERAP three-star low-drift nozzles andadopting a 12m no-spray buffer zone beside hedges or grass strips. Growers andadvisors can go to www.saynotodrift.co.uk/arable/ for further details, points out Sarah.