Integrated pest management of brassicas

This practice combines natural and chemical means to control pests. In SA, brassica farmers tend to stick to a set chemical pest control programme.
Issue date:23 March 2007

This practice combines natural and chemical means to control pests. In SA, brassica farmers tend to stick to a set chemical pest control programme.

Fewer than 1% of SA cabbage farmers use integrated pest management (IPM), while 19 out of 20 New Zealand cabbage producers do.
Farmers are unable to purchase the necessary “bugs” that make IPM more of a proposition. In nature, the pest, which usually hosts a parasitic wasp (parasitoid), will build up in numbers and then the parasitoids start breeding up on the crop until their sheer numbers wipe out the host. This leaves the parasitoid with no means to increase and it dies out, allowing the pest to start up again. n some countries, this see-saw effect is eliminated by the timely purchase of wasps from insectaries.

South African farmers aren’t familiar with these practices and therefore don’t have the necessary wasps for vegetable production. For insectaries to stock relatively unknown parasitoids without there being a demand is costly in advertising and education. M any parasitoids are naturally present and just need to be identified. There are various wasps of about 5mm to 7mm long that are extremely effective against diamond back moth (DBM) larvae. They can wipe out a DBM population, finding larvae on plant parts that are inaccessible to spraying.

With dry and windy weather, as well as sprinkler irrigation with a fair mineral content, minerals accumulate on the leaf surface and render the pesticides ineffective in a short period. This usually takes place during late spring rains. such cases the wasps will still do a good job. have discovered the benefit of these creatures after abandoning a trial after evaluation. stopped spraying and offered my son the leftovers for his pet rabbits.

Noticing it was infested with larvae, told him to clean it up. When returned to remove the remainder, found the larvae had disappeared as they were being parasitised by little wasps. I stopped spraying the next trial, leaving the pest control to the wasps. I didn’t have to spray again for two years. A client who has noticed these wasps on his cabbages is using safe pesticides like B thuringiensis and Bio Cure to reduce populations without harming the wasps.

These wasps make pure white cocoons on leaves and are easily visible. requires observation and scouting to recognise the beneficials and their balance with the pest. When other pests, such as thrips need spraying, choose a pesticide that will have minimum impact on the parasitoids. These bugs are perfect for organic farmers. – Bill Kerr Contact Bill Kerr on (016) 366 0616. |fw