Controlling aphids on brassicas
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CTA. 2008. Controlling aphids on brassicas. Rural Radio Resource Pack 08/2. Wageningen, The Netherlands: CTA.
Permanent link to this item: http://hdl.handle.net/10568/57445
Helpful tips on cultural and biological control of aphids
Controlling aphids on brassicas Cue: The brassicas are one of the most important families of plants in agriculture, including crops such as cabbage, cauliflower and kale. Brassicas are also vulnerable to pest attack, particularly by aphid insects. There are over 4000 different types of aphid, and more than 200 of them cause trouble to farmers and gardeners, not only by feeding on crops, but also by infecting plants with diseases and viruses. Colonies of aphids can often be found on the underside of plant leaves, or on the growing tips. The young insects grow quickly, and if their food supply begins to dry up they develop wings and fly off to infest other plants. Shepherd Musiyandaka and Isabel Chirere are experts in aphid control. They work for the African Farmer?s Organic Research and Training, a non government organisation based in Bulawayo, Zimbabwe. Sylvia Khumalo visited them at their offices and began by asking Mr Musiyandaka how big a problem these tiny insects are. IN: ?They are quite a serious problem ? OUT: ?ladybirds but they are actually pests.? DUR?N: 4?48? BACK ANNOUNCEMENT: Shepherd Musiyandaka and Isabel Chirere with some advice for vegetable growers on how to manage aphid pests in their cabbages, and other brassicas. The interview comes from a resource pack produced by CTA. Transcript Musiyandaka They are quite a serious problem. I am not going to go into details about the economic damage that they might inflict on any brassica crop but they actually damage the crop by sucking the plant sap and spreading other diseases like viruses and excreting a liquid, a sticky liquid that covers the plant and usually that can also attract other pests to come and attack the crop and usually that results in the plants or the brassicas becoming deformed and stunted and you may actually produce an unmarketable crop. Khumalo Talking about aphids being a problem, pests as they are, we want to talk about the control of aphids now. Chirere I am talking generally about the control of aphids. The first thing that one must do is to plant the crop in a well prepared fertile seed bed to promote vigorous growth. And it is also wise not to apply too much nitrogenous fertiliser as this will make the plant very soft, juicy and attractive to aphids. The third point would be to avoid planting near an aphid infested crop or on land from which an infested crop has been recently removed. Rainfall and overhead irrigation tend to discourage aphids. Growing strong smelling plants such as garlic, onion or parsley near the crop will reduce infestations of aphids and spraying, soaping with a soapy solution helps to wash off aphids and it disturbs their breathing. Khumalo Using biological control, from your experience how best would a farmer go about controlling an aphid using another pest? Musiyandaka Aphids are actually controlled by a number of what we call farmers? friends or natural enemies. These have a tendency to keep the pest at acceptable levels if measures are taken to conserve and encourage them. However it is sometimes difficult for natural enemies to attack aphids since some of the species of ants, which are attracted to the aphids by the sweet sticky juice that the aphids produce, have got a tendency of fighting the farmers? friends that we want to control the aphids. But for the farmers? friends that are usually found in the garden we have ladybird beetles and hover-fly larvae or caterpillars. Khumalo How do you identify these? Musiyandaka Ladybird beetles they usually take the form of tortoises. They have almost like a shell like that one of a tortoise. Khumalo A hard shell? Musiyandaka Almost, it looks like a shell which is dome-shaped and they have many colours. You usually find them being black and red or red and white or completely black. Khumalo How do you attract them to your field to ensure that at any one time you are controlling aphids? Musiyandaka Most of the natural enemies that would control any pests, they prefer or they need what I call a balanced diet. They get their protein from eating the pest which is the aphid but they also require some carbohydrates for energy and the carbohydrates they get them from flowers, the nectar. So these farmers? friends or ladybird beetles prefer yellow or white flowering plants. Plants that easily come to mind are things like fennel. Chirere Mustard. Musiyandaka Mustard yes, mustard you are right. Khumalo So if you grow these crops you are sure that you would have them around? Musiyandaka Yes, what we would encourage would be to intercrop your brassicas with these flowering plants like mustard, fennel or sunnhemp. At times I have seen farmers planting borders of sunnhemp within their plots. Including crops like marigold as well which produce very bright colours. Khumalo So are the beetles, are they not harmful to the plant? Musiyandaka They are completely harmless to our crops. Although farmers have to learn to observe them. There are some species which might look like the ladybirds but they are actually pests. End of track