Adult gout flies are now active in high numbers across southern and eastern England and egg-laying is underway on spring crops in high-risk areas.

The warning comes from ADAS entomologist John Young who is monitoring winter and spring wheat and barley crops as part of the Pestwatch report service provided by Dow AgroSciences.

"Adult emergence is similar to, or slightly earlier, than last spring and with high numbers causing damage in the autumn it is likely that, in areas with a history of damage, we will see a repeat over the coming eight weeks or so," he says.  Gout fly emergence and egg-laying occur simultaneously, explained Young, and although economic thresholds remain very much an unknown quantity, action may be justified where more than 20-25% of plants are affected."

"Spring and less advanced winter cereals are at greatest risk as damage depends very much on plant growth stage," he says.  "Early attacks on spring sown cereals result in stunted, 'gouty' tillers that fail to produce an ear. Crops attacked between GS31 and 37 suffer internal feeding damage to the upper stem.  This can trap and distort ears, often leading to blind grain sites and yield reduction."

Risk to autumn-sown crops at or approaching flag leaf emergence is receding, but late-sown spring crops or backward winter crops should be monitored closely in areas with a history of damage, Young suggested.

His advice was to check susceptible crops for adult fly activity and the presence of eggs on upper leaf surfaces.  Adults are about 3-4 mm long with distinctive yellow/black markings. 

"Adults will be most abundant in winter cereals that were attacked last autumn, with surrounding areas of grassland also acting as a reservoir for the pest.  Once adult flies emerge, they move to unaffected plants or migrate to spring crops where egg-laying will commence. The minute, cigar shaped eggs are about 1 mm long, are laid on the upper leaf surfaces andhatch within about 10 days."

David Roberts, who leads Dow AgroSciences' technical hotline, points out that the newly hatched larvae are immune to control measures once they have moved beneath leaf sheaths to feed within stems, highlighting the importance of spray timing to coincide with the very early stages of egg laying and egg hatch.  Trials work conducted by the company in early-sown cereals last autumn (and previous independent trails) confirmed this observation. The best control of gout fly in these studies came from Dursban WG applied as soon as eggs were visible.

"No products are currently recommended for gout fly control," says Mr Roberts, "but insecticides such as Dursban WG (chlorpyrifos) can be used to control frit fly or leatherjackets and if application falls within 7-10 days of egg laying, gout fly is unlikely to be a problem."

For further information growers and advisers should call the Dow AgroSciences technical hotline on 0800 689 8899.