STUDIES ON THE ECONOMIC THRESHOLD FOR "SUMMER APHID" (APHID GOSSYPII GIOVER) DAMAGING COTTON
ZHang Geng-qiao;Yuan Quan-chang, (Plant Protection Research Institute of the Shanghai Academy of Agricultural Sciences)
There always is a peak of population of Aphid Gossypii on cotton during july and August in the suburbs of Shanghai, which is called "summer aphid". The aphid cause the great reduction of yield, so the economic threshold is crucial for the management of this pest. The studies were conducted during 1979, 1980 and 1984 years in both field and caged plots. The result shows that the relationship of yield loss and amount of aphids individuals can be expressed by a linear regression equation, Y=1.1850X-0.1344 r=0.98 where Y is probability value of yield decresed. X is Logarithm value of amount of aphid. Compare to the control the significant difference can be detected by t-test when the percentage of yield loss is 21.90%, which is caused by amount of 3500 aphids individuals per plant. The L. S. D. of percentage of yield loss is 19.30% and the coresponding amount of aphids individuals is 3286. The calculated economic threshould is 12% plants, each having 3286 aphids individuas.