Vegetable and Forage Brassicas Update – Mid August 2020

Pests

We have seen an increase in cabbage root fly egg laying and egg hatch over the last week at our monitored crops. Cyantraniliprole can still be applied as a drench treatment to crops in the field such as brussels sprout, cabbage, cauliflower, broccoli, turnip and swede but time for effective control is running out. Note that no more than two applications of a cyantraniliprole product should be applied to a crop in any season and avoid spraying within 5 m of the field boundary to reduce effects on non-target insects. Spinosad can be applied as a foliar drench spray but check the label for approved crops. Some forage brassicas such as kale can receive a spinosad treatment as an Extension of Authorisation for Minor Use (EAMU – 20150102).

Diamondback moth captures in our pheromone traps have jumped in the last two weeks indicating the second generation of moths is now active and laying eggs. Look for caterpillars or eggs on crops and consider an insecticide treatment where found. Note that diamondback moth are capable of laying eggs through some types of mesh or if mesh is damaged or stretched (as can cabbage root fly). Diamondback moth caterpillars may well be resistant to pyrethroid insecticides, so growers may need to use spinosad, indoxacarb, cyantraniliprole or Bacillus thuringiensis as an alternative. Check product labels for specific crop approvals and also check for crop specific EAMU’s for these and other insecticides such as chlorantraniliprole.

We have also seen more large cabbage white butterflies this season. They lay eggs in groups on the undersides of leaves and the caterpillars can cause significant damage.