Striking the right balance between leaf miners and the parasitic wasp population that feed on them is key to the biological control of leaf miner. T o do this you might have to use products on your growing crop that reduce the leaf miner population without harming the parasitoids that might be in an earlier stage of their life cycle. This is called integrated pest management (IPM). Sometimes the wasps reduce the leaf miner population too drastically and then the wasps die out because they have no further means of propagation. On the other hand, if a population of leaf miners establishes itself they will be able to breed rapidly and might do considerable damage, until the wasps appear. Unfortunately in South Africa, as far as I know, we can’t buy the wasps from insectaries as they do in Kenya. In that country stringent restrictions are placed on exported produce with crop-chemical residue. Using insect control is both more effective and more economical than chemicals, but it will only take off in South Africa when farmers become sufficiently receptive to IPM to justify insectaries.
Many chemical products are sold to farmers who are told they are “soft” and will have little effect on the natural enemies of pests. However, such products might be “soft” on ladybirds but harsh on wasps. The first year leaf miners attacked my crops, some of the plants were destroyed. used Abamectin as a quick knock-down and then had to wait three weeks before the second spray. noticed that by then wasps had started to pupate and so would not be knocked out by the Abamectin. Since then have never had to spray and have had no further damage. spot the odd tunnel on my tomatoes, beans and beet, but they don’t become a problem which means the wasp population is healthy. does not mean the status quo will last forever, and will not hesitate to use insecticides should it become necessary. Pyrethroids, chlorpiriphos and many other products wipe out the parasitoids. Products which kill the larvae and adults of leaf miner will have a similar effect. Getting on top of this pest naturally requires noticing what is happening in the crop. It seems difficult at first but one soon gets the hang of it. – Bill Kerr ([email protected] or call (016) 366 0616). |fw
