الحد الاقتصادي الحرج للإصابة بدودة القطن Spodoptera littoralis (BOLSD.)‎ (Lepidoptera : Noctuidae)‎ في حقول القطن بجمهورية مصر العربية : مستوى الضرر الاقتصادي خلال مراحل النمو المختلفة لنبات القطن

الملخص EN

The effect of defoliation of cotton plant at 25.

50.

75 and 90 9c of leaf-area (as an artificial imitation of cotton leaf-worm, S.

littoralis, damage) on its yield was investigated during 5 different plant growth stages.

Results of 2 field experiments, conducted during the same season at Giza and Fayoum regions, revealed a significant negative correlation between c/c defoliation and % yield loss existed.

Loss of 1 % leaf-area during the vegetative growth, b dding, flowering, initial fruiting and full fruiting stages decreased cotton yield/feddan by 5.54-6.32, 6.57-6.58, 4.76-5.15, 4.84-5.90 and 2.49-2.57 kg., respectively.

Loss of 50 % leaf-area during any of the considered growth stages of cotton plant reflected yield losses of 24-28 % for vegetative growth stage, 28-49 % for budding stage, 35-37 % for flowering stage, 27-40 % for initial fruiting stage and 14-18 % for full fruiting stage.

Cotton plants were most sensitive to defoliation during both budding and flowering stages, i.e.

the period early June to mid-July.

Economic injury levels of 5.

littoralis on cotton plant at Giza region could be approximated at 40, 31, 44, 60 and 142 egg-masses/feddan or 0.38.

0.30, 0.42.

0.58 and 1.35 larvae/plant for vegetative growth, budding, flowering, initial fruiting and full fruiting stages, respectively.

Corresponding respective levels at fayoum region were 15, 19, 40, 42 and 59 egg-masses/feddan or 0.15, 0.18, 0.38, 0.40 and 0.56 larvae/plant.

The occurrence of relatively lower EIL values at Fayoum than Giza was attributed to the fact that plant growth and size were comparatively smaller at the former region.