An attack of orange wheat blossom midge is possible this year if rain follows the current high temperatures, as soil samples indicate high numbers of larvae present.
"Unusually high temperatures have pushed soil temperature above the 13 C needed to wake hibernating larvae," said Jon Oakley, ADAS. "These larvae moved to the soil surface ready to pupate, but were waiting for wetter conditions before pupating. Sufficient rainfall fell in some places through the bank holiday weekend. Falls of 10 mm or more may have been sufficient to trigger pupation."
So far the rainfall has been fairly patchy and will result in considerable variation in activity. Where sufficient rain fell a hatch is likely by the last week of May, in time to coincide with the vulnerable ear emergence stage of many wheat crops.
"In this situation pheromone traps can be very useful in confirming where midges aren't a problem and crop inspection is a low priority," said Jon Oakley. "Research within the Orange Wheat Blossom Midge LINK project has shown that pheromone traps are most useful when placed in the most important sources of midges on a farm rather than in the wheat crops under threat. These sources will be crops damaged by orange wheat blossom midge within the two previous harvest years."
Traps should be put in place a few days before the earliest wheat crops reach the ear emergence stage and kept in place until the latest crops reach the flowering stage.
Catches of less than 30 midges confirm that there is no risk to nearby crops. 30-100 midges could represent a risk if conditions for flight are good. Catches in excess of 100 midges may suggest a significant threat even if the weather is less favourable for flight. A high count in pheromone traps indicates that there is a threat over the following week to any crops in the vicinity passing through the vulnerable ear emergence growth stages (GS53-59).
"Resistant varieties are now grown in 19% of the crop area," said Graham Jellis, HGCA director of research. "Resistant varieties on the HGCA Recommended Lists are Brompton, Gatsby, Glasgow, Oakley and Robigus. Resistance has also been identified in the spring wheat variety Chablis. More varieties are becoming available. Resistant varieties will not require spraying against orange wheat blossom midge and so a healthy population of natural predators can be maintained in the crop."
Resistant varieties kill all the larvae that try to feed on them and suffer very little yield loss even at high levels of attack. They are still susceptible to other pests and may respond to insecticides if other pests are present.
For further information, HGCA has produced a guide 'Orange wheat blossom midge - assessment and control' which is available on the HGCA website here
Release date: 9 May 2007
For further information contact:
Jon Oakley, ADAS, jon.oakley@adas.co.uk
Graham Jellis, HGCA director of research, 020 7520 3932 graham.jellis@hgca.com | 
