EFFECTS OF TIMING AND INTENSITY OF SPIDER-MITE INFESTATION ON THE OILYIELD OF COTTON CROPS

We assessed the effects of timing and intensity of spider mite (Tetran ychus urticae) infestation on the oil yield of cotton (Gossypium hirsu tum L.) crops. Artificially infested crops of cv. Deltapine 90 (normal leaf) and Siokra 1-4 (okra leaf) were compared in 2 field experiments . Actual timing of infestation ranged from 59 to 127 days after sowing and intensity of infestations ranged from 64 mites per leaf in the mo st severe treatment to almost nil in controls. Mites significantly red uced oil yield in both experiments; yield reductions were greater in t he normal-leaf than in the okra-leaf type. Oil yield losses declined w ith the delay in the onset of infestation. Under low and moderate leve ls of infestation, oil yield losses were associated with reductions in seed production. Under more severe infestations lower seed oil conten t also contributed to the reduction in oil yield.