18/05/2011

Dow AgroSciences Pestwatch service for Wheat Blossom midge has started and, although the soil samples have yet to show signs of pupation, adult Wheat Blossom midges have been image expired

Dow AgroSciences invest in the Pestwatch service to help provide the best advice to farmers, says Sarah Hurry of Dow AgroSciences.  “Pestwatch starts by sampling soils for larvae.  The average population of Orange Wheat Blossom midge (OWBM) taken from 18 sites in this year’s qualitative baseline sampling is 2.5 larvae per kg soil.  The highest population (17.6 larvae/kg of soil) was recorded in a sample from Boxworth in Cambridgeshire.  No pupae were recorded in this round of sampling, but samples were taken before the recent rains.  We have already received reports on our Hotline of adult midge activity in the Southern region and expect other regions to follow.

Sarah reports that Yellow Wheat Blossom midges (YWBM) appear to be more common this year than in previous years.  “Yellow Wheat Blossom midge pupation is underway at all but two of the sites at which the pest was recorded.  Adults emerge at the same time as OWBM, but tend to pupate in drier soils.  They also lay eggs earlier as boots begin to split, rather than on the emerged ear.  They are less persistent than OWBM, lasting about 3 years in the soil as opposed to 10 years.”

She points out that the pest risk relies on the vulnerable growth stages of the crop coinciding with egg-laying activity.  “Orange Wheat Blossom midge larvae overwinter in cocoons and require certain conditions (70 days at <10°C) to break diapause, after which larvae move towards the soil surface.  They require sufficient rainfall to wet the soil to a depth of 10mm and a rise in soil temperatures to above 13°C to stimulate pupation.  The average temperature at the start of May was 12.9ºC and, although a very dry spring, sporadic showers would be sufficient to trigger pupation.”

Rising temperatures following rainfall stimulate hatch of adults from pupae.  Air temperatures above 15°C are particularly favourable for flight.  Adult midges mate at the pupation site and the females, which live for just 7 days, look for a suitable host crop to lay their eggs.  In good conditions, each female can lay around 80 eggs on emerged ears, before flowering between GS53 and GS39.  Eggs hatch in 4-10 days, depending on temperature.  The emerged larvae move to the developing grain and feed for 2-3 weeks.

Growers are invited to use the Dow AgroSciences Risk Assessment Charts to help identify fields at high risk.  “Susceptible sites are those wheat fields where the pest was noted last year, especially if no treatment was carried out.  The economic risk is highest in crops intended for seed or milling, with a threshold for treatment being one midge per 6 ears.  The threshold for feed wheat is one midge per 3 ears.”image expired

Sarah Hurry advises that if treatment is justified when thresholds are met or exceeded, growers should use Dursban WG at 0.6 kg/ha in 200 to 1000 litres of water.  “Dursban WG will control all the life stages of the pest, giving the grower the widest window of opportunity and flexibility to control this damaging pest.  In association with FWAG, Dow AgroSciences recommend a voluntary 12 metre buffer from the edge of the field as part of integrated pest management best practice.”

She also reminds growers that Dursban WG gives effective knockdown of adult midges, persistence of 7 to 10 days to control further flights of adults plus persistence and vapour action to control larvae emerging from eggs laid by the first flight of adults.

Orange Wheat Blossom midge can cause substantial loss of yield and quality.  Typically one 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.

For further information, please contact Sarah Hurry, Dow AgroSciences on the Dow Technical Hotline on 0800 689 8899.