Integrated management strategies for varieties tolerant and susceptive to wheat blossom midge

Abstract

The orange wheat blossom midge (owbm), Sitodiplosis mosellana, is an important pest of wheat, causing severe yield loss in some years. Infestations vary from year to year depending on climatic conditions, so being able to predict the risk of damage is difficult. The major aim of this project was to develop owbm control strategies for farmers using tolerant and susceptible varieties by using pheromone traps to determine the need for, and timing of, insecticide treatments and also to identify genes for pest resistance/tolerance for further breeding.

Owbm flight was significantly reduced when humidity was lowered from 70% to 35%. Pheromone traps were highly selective and sensitive and caught over 95% male midges. Yellow sticky traps provided information on numbers of female midges. Pheromone trap catches were very variable between fields on the same farm, and more variable than catches within fields. Crops following wheat were a major source of the pest. In some years, midge infestations were best explained by pheromone trap catches in fields neighbouring the wheat field which acted as a source of the pest. Phenolic acids are believed to be responsible for the resistance of wheat varieties to owbm. However, levels barely differed between resistant and susceptible varieties, suggesting that resistance is not solely due to these compounds.

Resistance in Welford, Brompton and Carlton is due mainly to the Sm1 gene but other genes are involved. The mechanism of Sm1 resistance is thought to be chemical, but other genes could affect flowering time which means that the crop escapes owbm attack.

A decision flow chart was developed to help farmers predict owbm risk. When trap catches exceed 30 midges/trap/day the crop should be inspected to determine if there are sufficient to justify a spray based on existing thresholds of 1 midge/6 ears for feed varieties and 1 midge/3 ears for milling and seed varieties. If pheromone traps catch more than 120 midges/trap/day, an insecticide spray is advisable to protect wheat crops in the immediate vicinity.