ifoam'96 Book of Abstracts 11th IFOAM Scientific Conference 11-15 August 1996, Copenhagen, Denmark

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Relay intercropping of tomato with cabbage E19

Wakerere University, Faculty of Agriculture and Forestry, Department of Crop Science, Box 7062 Kampala, Uganda

Cabbage, an important crop in Uganda has had its yieds increasingly reduced by pests, especially Diamondback moth (DBM), (Plutella xylostella), forcing produ cers to use higher quantities of pesticides. Apart form these pesticides proving danger to humans and livestock, they also contaminate the soil and have resulted in development of resistence in pests, especially DBM. While various researchers have shown that intercropping, especially of cabbage with tomatoes, have resulted into reduction of DBM populations, no work of this phenomenon has been reported in Uganda. It is therefore not clear which crop combinations are most suitable, neither are appropriate planting densities known. A study was therefore conducted at Makerere University to investigate effect of increasing tomato population density in cabbage crop and varying time of intercropping with cabbage, on incidence and damage of DBM on cabbage. Copenhagen market variety was established as sole crop and as an intercrop in alternate rows, with increasing populations of tomato cultivar MT 150. The cabbage were simultaneoulsy and relay planted with tomatoes after an interval of 14 days. Once a week DBM population density was established by recording eggs, larvae, pupae numbers and larval damage on cabbage leaves. In additon, records of other pests and predator incidence were also taken. DBM eggs and larvae densities in the field experiment, were high at the beginning of the season, and reduced as the cabbage matured. Relay intercrops had less eggs, larvae, pupae density and larval damage than simultaneously planted ones. With the least density recorded in plots with 20% and 40% tomato populations. Increasing tomato populations resulted in a decrease of cabbage yields the highest yields being recorded in the monocrop. Generalist predators of DBM like earwigs, ladybird, syrphids and spiders were more abundant in the monocrop than in the cabbage/tomato mixture and significantly less predators were found in relay intercrops than in the sumultaneously planted plots. Some of the predators showed a marked decrease in the plots planted with 20% and 40% tomato population. Relay intercropping of cabbage/tomato with cabbages planted 14 days after the tomatoes reduces the incidence and damage of Diamonback moth, especially in the plots intercropped with 20% and 40% tomato population. Generalist predators did not seem to have been solely responsible for DBM population reduction in the experiment.