Check crops for wheat blossom midge now

UK - June 02, 2008

As wheat ears emerge, growers must look out for wheat blossom midge, warns Dow AgroSciences. 

Wheat blossom midge adversely affects crop yield and grain quality. The damaged grain is more susceptible to fungal attack, potentially increasing mycotoxin levels. HGCA estimates that the 2004 epidemic cost UK growers £60m and that was when feed wheat was worth £60/tonne.  

Dow AgroSciences’ Pestwatch, in conjunction with ADAS, monitors high risk sites to predict the likely emergence dates of adult midges. Warm, wet soils favour pupation and adult emergence, which is now underway as far north as Yorkshire. Critical weather conditions, that encourage adult emergence and egg laying, are warm air and light winds after rainfall. If such weather coincides with ear emergence (GS53-59) damage can occur. 

“Current soil moisture and temperatures favour further midge development so vigilance is needed everywhere,” warns David Roberts, Dow AgroSciences technical specialist. “Use the Dow AgroSciences risk assessment charts to identify high risk fields, and place pheromone or sticky yellow traps in these fields and check them regularly.” 

Pheromone trap thresholds over 2-3 days are 20 adult midges for milling wheat or 30 adult midges for feed wheat. Sticky yellow trap thresholds are 10 adult midges caught in the period just before full ear emergence. Alternatively, spraying is justified if one or more midges are found in three ears of feed wheat crops or in six ears of a milling or seed crop. 

“If midge numbers reach threshold levels that justify treatment, Dursban WG (chlorpyrifos) should be applied at 0.6kg/ha in 200L/ha of water. Timing is critical and should not be delayed,” says Mr Roberts. “A Dursban WG spray provides up to eight days control of adult midges, eggs and exposed larvae on the ear. Chlorpyrifos is the only approved active ingredient that controls larvae before they enter the floret.”

Where spraying is justified to protect wheat yield and quality, Dow AgroSciences have developed a recommendation with FWAG to leave a 12m buffer around the field margin to allow natural predators to re-colonise the field rapidly.