Rising caterpillar numbers continue to threaten brassica crop quality. After the slow start in crop growth during dull August conditions, damage now could cause further potential problems with consistent supply this winter.
Although cold, wet weather in August checked numbers of Diamond Back Moth, Silver Y Moth and Cabbage White Butterfly, the recent warm, dry spell has seen adult numbers increasing rapidly and extensive caterpillar activity (above).
Carl Sharp of the Allium & Brassica Centre, who monitors pest numbers for the Syngenta Brassica Alert service that provides growers with important early warning of key pest and disease risks, highlights that a late Indian summer last year saw intense insect pest activity right through into October.
"We expect to see insect numbers continuing to rise over the coming weeks," he reports "It’s essential that growers remain vigilant for signs of adult pest activity, and the resulting risk of caterpillar attack.
"Cooler nights will slow down the life-cycle and emergence of damaging larvae, but we are likely to see another flush of caterpillars from the current adult egg-laying," he warns.
Fortunately the large populations of Cabbage White caterpillars are relatively easy to hit and kill with Hallmark Zeon or Dovetail treatments. However, Mr Sharp points out that Diamond Back Moth and the more widespread Silver Y Moth caterpillars tend to reside on the underside of leaves – which makes targeting with sprays more difficult.
Syngenta application research has shown the use of dropleg sprayers has been especially effective at hitting pests and disease on the underside of leaves in brassica crops. However, with conventional sprayers the best results would be attained using an angled Syngenta Potato Nozzle and a water volume of 300 l/ha to get spray throughout the crop canopy, advises Syngenta application specialist, Tom Robinson.
"Operators must aim to keep the boom height down at around 50cm above the crop to ensure good spray penetration; the higher the boom, the less spray will get into the canopy," he adds.
Carl Sharp highlights that spray techniques are also extremely important for improving control of thrips, where significant infestations are currently occurring in leeks and brassica crops - the latter of which could create serious problems of oedema in storage cabbage. Hallmark Zeon treatments for caterpillars can give incidental control of thrips, and there is the new opportunity to control thrips with a SOLA for Agrimec in leeks this season, he adds.
Brassica growers can register free for Brassica Alert on the Syngenta website - www.syngenta-crop.co.uk – to receive pest and disease warnings covering the brassica growing heartland across Lincolnshire. Brassica Alert enables growers to make more proactive crop management decisions on fungicide and insecticide selection and timing, along with providing treatment justification records.
Application techniques in vegetable crops, including the latest dropleg sprayer technology, will be one of the topics for growers at the Syngenta Vegetable Whole Crop Agronomy Open Day, to be held at the PGRO near Peterborough next week (Tuesday 7 September). See the Syngenta website www.syngenta-crop.co.uk for further information.
