Effects of intercropping Cabbage with Alliums and Tomato, on the incidence of the Diamondback moth, plutella xylostella (L.)

Thumbnail Image
Luchen, Sina W.S
Journal Title
Journal ISSN
Volume Title
In assessing the efficacy and economic value of intercropping cabbage as a way of managing Diamondback moth (DBM), Plutella xylostella L., six cropping cultures were evaluated. The trial was conducted at the National Irrigation Research Station, in Mazabuka, Zambia, in 1995/96. The cropping cultures consisted of cabbage monocrop and five other crop combinations. These were cabbage + garlic, cabbage + leek, cabbage + onion, cabbage + shallots and cabbage + tomato. Cabbage monocrop had a significantly (P>0.05) higher incidence of DBM immatures in the early growth stage (3"* and 4* weeks after transplanting), than garlic, leek and tomato. There were, however, no significant differences (P>0.05) in the incidence of the pest in subsequent weeks of sampling and in its overall incidence for the whole sampling period. Cabbage monocrop recorded significantly (P<0.05) higher overall leaf damage index (%) for the whole sampling period than leek, shallots and tomato, though weekly observations were not significant (P>0.05). Observed treatment differences for the cabbage mean total yields (t/ha) and cabbage mean marketable yields (t/ha) were insignificant (P>0.05). Cabbage monocrop, however, had significantly (P<0.05) higher percentage yield loss associated with pest leaf damage than other treatments, except for cabbage intercropped with onion. Cotesia plutellae Kurdjumov, a parasitoid, of DBM larva was found to occur in all the six cropping cultures. There were no significant differences (P>0.05) in the incidence of the parasitoid between the six cropping cultures. Actual parasitism levels of DBM larvae by the parasitoid were also insignificant (P>0.05). Overall, the simple linear Correlation Coefficient (r = + 0.87) between mean parasitoid cacoons and DBM larvae was significant (P<0.05). There was thus a positive linear relationship between the overall mean number of parasitoid cacoons and the overall mean number of DBM larvae. The simple linear Correlation Coefficient (r = + 0.96), between overall DBM larvae incidence and overall leaf damage was significant (P<0.05). A positive linear relationship between the parasitoid and the pest was thus confirmed. In terms of profitability, the cabbage + leek combination had the highest positive net returns of + K 11 757 600 00, while the cabbage + tomato combination had the lowest negative net returns (- K 3 059 576 00).
Intercropping , Cabbage