Studies of Crop Loss following Insect Attack on Cotton in East Africa

Abstract

The loss of crop following insect attack on cotton was studied in 1950–54 at the Cotton Research Station, Namulonge, which is situated in the elephant-grass zone of Uganda, in which the principal pest of cotton was originally considered to be Lygus vosseleri Popp. In 1953, the main invasion of cotton by Lygus occurred during September and October, originating from cultivated crops of black gram (Phaseolus mungo) and sorghum and from the wild perennial legume, Pseudarthria sp., which earlier workers had considered important. Trials in this zone have demonstrated, over a number of years, that early June is the optimum date for sowing cotton, although such sowings receive the heaviest attack by L. vosseleri. Experiments to determine the maximum loss of yield due to Lygus should therefore be made with cotton sown at this time. Bollworms are also important pests, notably Heliothis armigera (Hb.) and Earias spp., their attacks following those of Lygus and being heaviest in October–November.

Further studies of crop loss following insect attack on cotton in Uganda

“…That pest damage in the elephant-grass zone is negligible is supported by McKinlay & Geering (1957) and Coaker (1957), and by the results with dicrotophos where final yields were unaffected although bollworm was not controlled. Clearly the plants compensate for insect damage incurred in this zone, and the inability of the plant to mature more fruiting bodies under a given set of conditions is the true limiting factor.…”

“…3) have the same form as those of McKinlay & Geering (1957) and Coaker (1957). Analysis of the yields of total and clean seed cotton showed that there were no significant differences between treatments at any of the seven picking dates or between the final yields of total seed cotton or clean seed cotton (Table IV) cotton (angular transformation) showed a significant difference (P < 0-05) between treatments, with dicrotophos having significantly (P < 0-01) more stained cotton than any other treatment.…”

“…On the other hand, at the Cotton Research Station, Namulonge, 16 miles north of Kampala, Buganda, in the elephant-grass zone, McKinlay & Geering (1957) and Coaker (1957Coaker ( , 1958Coaker ( , 1960 showed that protection from insect attack with DDT gave little or no increase in yield of early-sown cotton and only slightly more on late-sown cotton. Of eight other insecticides tested in the elephant-grass zone, only endrin and isobenzan gave significant increases in yields (Coaker, 1960;Ingram & Davies, 1964;.…”

“…Cumulative picking curves (McKinlay & Geering, 1957;Coaker, 1957) had shown that the crop on sprayed cotton was formed earlier than that on unsprayed cotton. It should therefore be possible, with appropriate insecticide applications, to obtain a crop from both the early and late flowering on early-sown cotton.…”

“…Accordingly, a further series of trials to investigate this point was laid down at the Cotton Research Station, during the 1965-66 and 1966-67 seasons. In previous experiments, differentiation of the effects of the damage by the various pest species was assumed to be possible by altering the period during which DDT was applied (McKinlay & Geering, 1957), but in 1965-67 differentiation was to be achieved by the use of selective insecticides.…”