Integrated control of wheat blossom midge: Variety choice, use of pheromone traps and treatment thresholds

Abstract

The orange wheat blossom midge (wbm) has continued to increase in importance due to our warming climate. Chemical control is often not effective due to difficulties in determining the risk of attack in time to use the very short window for treatment, and may be unpopular due to perceived environmental risk. This project aimed to develop a system of integrated control based on an improved knowledge of the vulnerability and tolerance of commercial varieties to the pest, and a trapping system designed to assess risk at an early stage.

Some varieties have been shown to be resistant to wbm, yielding well even when heavily challenged by the pest and giving a yield advantage of 2 t/ha or more in such situations. Welford and Brompton are now included on the Recommended List as resistant varieties and more will follow.

Other varieties, such as Option, have been shown to be more vulnerable to the pest than most others, with some varieties, like Einstein, less vulnerable to damage. Susceptibility to damage by the pest has been shown to depend on several genes in a separate study conducted by the John Innes Centre (JIC). A mechanism for testing these traits was developed, and now needs to be applied to all varieties in the Recommended List. Until these tests have been done, the main priority for treatment should be group 1 and 2 wheat and seed crops.

Pheromone traps have been developed through to a marketable product. Tests have identified the optimum release rate and mechanism and trap design for UK conditions. The traps give a reliable indication of male wbm activity and an early warning of when crops may be at risk. The numbers of males caught were correlated to the level of egg-laying at an individual site by females. When the male midges are caught, this typically indicates a 2-day window before eggs are laid in the crop by female midges.

However, the risk of migration from adjoining fields and the suitability of the weather for egg laying caused considerable variation between sites, so a system for assessing these risks is needed as part of a decision making process based on the trap catches. A follow-on project was agreed to develop such a system. Varieties were shown to differ in the levels of the volatile chemicals used by female wbm to identify a suitable host and this may be a cause of varying vulnerability. The volatile chemicals were not successful as baits for traps to monitor numbers of egg laying female midges.