Aphids

Key Points

• Cabbage aphid infestations can cause severe losses in many brassica crops
• Populations can increase rapidly if left untreated
• Early treatment is recommended for best results
• Apply Dursban WG in 600 to 1000 litres of water per hectare with a non-ionic wetter/spreader

Introduction

The most significant aphid pest of vegetable crops is the Cabbage aphid — Brevicoryne brassicae. Serious losses can result from Cabbage aphid infestations in crops of broccoli, Brussels sprouts, cabbage and cauliflower. The virus that causes Cauliflower Mosaic disease can also be transmitted by Cabbage aphid.

Small, bleached areas on leaves are the first sign of attack, followed by yellowing and curling of infested leaves. In the most severe attacks leaves can be completely lost and young plants killed. Infestations in broccoli, cabbage and Brussels sprouts can cause the produce to be rejected, even when the aphids present are dead. Aphid numbers are always worst when the second half of summer is warm and dry. Cool, wet weather reduces the speed of aphid multiplication

Biology

Overwintering can occur as small, elongate, black eggs or, where conditions are mild, as adult aphids. If winters are severe, new populations will emerge from eggs laid on the stems and leaves of broccoli, Brussels sprouts, cabbage and kale. Eggs hatch during March and April.

Young aphids are wingless and bluish-grey in colour with a characteristic mealy covering. They feed on shoots and leaves, migrating by the end of May to the flower buds. From the end of May onwards winged aphids are produced. These infest newly planted brassica crops, multiplying rapidly if conditions are favourable during August and September.

Product Choice

Aphid infestations in crops of broccoli, cabbage, calabrese, cauliflower and Chinese cabbage can be controlled successfully with applications of Dursban* WG (active ingredient chlorpyrifos). Treatment should be made when aphid numbers are first detected, normally in early summer. An approved non-ionic wetter/spreader should always be used with Dursban WG to maximise control of Cabbage aphid.

Strains of some aphid species are resistant to many aphicides. Where aphids resistant to products containing chlorpyrifos occur, Dursban WG is unlikely to give satisfactory control. Repeat treatments of the same product are unlikely to improve efficacy.

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