EFFECTS OF ARTIFICIAL DEFOLIATION ON SUNFLOWERS

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Abstract
Sunflowers were defoliated artificially to various degrees at three stages of growth to simulate the effects of rust and other foliage diseases. Complete defoliation at the flowering stage was most injurious. It reduced seed yield by 88 to 93 per cent in all five years of the experiment. It also reduced plant height at maturity in one of two years in which heights were recorded, and it reduced weight of 200 seeds, and oil content and protein content of the seed. Removal of 50 per cent of each leaf at flowering reduced seed yield by 22 to 30 per cent, and reduced plant height, but did not cause other statistically significant reductions. Removal of all leaves on the upper half of the stem reduced yield and 200-seed weight significantly.Complete defoliation of seedlings reduced seed yields significantly in two years and reduced plant height in one year. Complete defoliation of maturing plants reduced seed yield significantly in one year. Partial defoliation (50 per cent and 25 per cent) of seedlings and maturing plants produced no significant effects.The results of artificial defoliation should be useful in evaluating damage caused by insects and by hail as well as the effects of foliage diseases.

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