Whole crop IPM strategy for pest insects in brassica crops

Read about IPM strategy for protecting brassica crops, including the benefits of maintaining natural enemies of pest insects.

The use of net covers can help to control levels of several pest species as long as they are applied at the right time and with a suitable mesh size.

All pest species have natural enemies that help to regulate their numbers. Studies at Wellesbourne have shown that predators such as ladybirds and parasitoid wasps, together with entomopathogenic fungi, can effectively reduce aphid infestations in some years. Field sampling in 2016 indicated that a high proportion of diamondback moth pupae were parasitised by a small wasp (as shown in research project FV 440).

At Wellesbourne, the inappropriate application of pyrethroid insecticides has led to increased problems with cabbage root fly and peach-potato aphid compared with insecticide-free plots.

Where feasible, selective pesticides and/or methods of application should be used to protect beneficial species.

There is clear evidence that pyrethroids should be used sparingly because resistance to this group of insecticides has been identified in several brassica pests. This (along with the fact that they often kill natural enemies) means that pyrethroids have the potential to increase pest damage rather than reduce it.

Repeated use of one insecticide group can select for insecticide resistance in the local population. It is, therefore, good practice to use different modes of action in rotation. Resistance to pyrethroid insecticides in Myzus persicae is well established.  For more information about resistance management, visit ahdb.org.uk/irag 

Diamondback moth

There is no evidence of insecticide resistance in any species of pest caterpillar, apart from the diamondback moth, which has a considerable propensity to evolve resistance to insecticides and the Bt toxin. The resistance status of diamondback moth populations will vary around the world, so when a new population of moths arrives, it’s important to determine its resistance status. Scientists at Rothamsted Research showed that the moths that arrived in the UK in 2016 were resistant to pyrethroid insecticides. Find more information about insecticide resistance in the diamondback moth here: irac-online.org

Aphids

There is no evidence of insecticide resistance in the cabbage aphid or potato aphid. However, populations of peach-potato aphid can be resistant to pyrethroids. Resistance to some neonicotinoids is now apparent in Southern Europe.

Cabbage whitefly

Some cabbage whitefly populations are resistant to pyrethroid insecticides.