Although wheat is the wheat stem sawfly’s preferred host, it will still feed on barley crops. Wheat stem sawflies are a difficult pest to control, because they spend 97 per cent of their life cycle well protected inside the plant’s stem. Once they reach their adult stage and exit the stem, they quit feeding. As a result, they will not consume any chemical sprayed on the plants and are only affected by contact insecticides. Luckily, barley is much more resistant to this pest than wheat.
Sawfly larvae overwinter inside plants stems, pupate in the spring, and emerge as adults in June. The adults lay eggs on plant leaves and stems, where the hatched larvae feed before tunnelling inside the plant. A second generation of adults emerges in mid-summer and lays their eggs on wild grasses or immature volunteer grain. The heads of sawfly-affected plants die and turn white, while the lower stem and leaves stay green. The adult flies are yellowish-white and about five millimetres in length, with three black stripes across their thorax and abdomen.
- Whiteheads caused by wheat stem sawflies are easy to see in green fields, but rarely affect more than one to two per cent of the crop
- Only contact insecticides are effective for controlling wheat stem sawfly, as the adults do not feed on the plants
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