Cabbage Integrated Pest Management : An Ecological Guide.

Ecology of Insect Pests and Natural Enemies4.11 Management and control activities for pest insectsNext to biological control by natural enemies, pest populations may be managed by other methods. Theuse of insecticides is often used alternative but there are other options that may be valuable. Some ofthese options are listed in this section.Specific management and control practices, like many cultural methods, that are important for managingpest insect populations in the field are mentioned in the next chapter, for each pest insect individually.4.11.1 Use of insect nettingCultivation under “net houses” is increasingly receiving interest. A net house, or insect cage, is a frame ofwood a little higher than the cabbage plants, covered with fine mesh netting. The netting prevents insectsentering the crop from outside, particularly lepidopterous pests like moths and butterflies but also aphidsmay be prevented from entering the plants when the netting is fine enough. Net houses do not preventinsects coming from the soil like flea beetles. Often, the net houses are placed over nurseries, to preventdamage from caterpillars to the young plants. Also, in crops like tomato or hot pepper, net houses onnurseries can provide good initial control against aphids or whiteflies, which may carry virus diseases.Net houses may also be higher: about 2 - 3 meter. These can be used for both nurseries and productionfields. For good insect prevention, they need to be closed properly!Net house: plants in, pests out!Good experience with the use of a net house in eggplant was obtained from a field study in Bangladesh.A net house was made out of bamboo poles and nylon nets. Plant left-overs and pupae foundin the top layer of the soil were removed before placing the net house over the eggplants. Less insectinfestation of shoots and fruits was found on the net house plants as compared to the uncoveredplants.Unfortunately, some of the studies were not successful because the nets were stolen from thefield…! (pers. comm. Prabhat Kumar, 1999, Bangladesh).Although initial investment for preparing the net houses is high, savings from reduced sprayings canmake it interesting. When properly prepared and maintained, net houses can be used more than once.Inside a net house, the temperature may be a bit lower due to shading effect of the net and the humiditymay be a bit higher than outside. This may result in a quicker growth of the crop but it may also result insome more disease problems.Related exercises from CABI Bioscience/FAO manual:2-B.9. Roofing and screening of seed beds4.11.2 Use of trapsThere are several types of traps to catch insects. Most traps will catch adult insects. These traps areoften used for monitoring the populations rather than actual control. However, since some traps catchlarge quantities of insects they are often considered as control measures in addition to monitoring.61 Cabbage Ecological Guide - 2000