ECONOMIC INJURY LEVELS OF RAPESEED (BRASSICA-CAMPESTRIS) APHIDS (LIPAPHIS-ERYSIMI) DETERMINED ON NATURAL INFESTATIONS AND AFTER DIFFERENT INSECTICIDE TREATMENTS
S. Chander et Kg. Phadke, ECONOMIC INJURY LEVELS OF RAPESEED (BRASSICA-CAMPESTRIS) APHIDS (LIPAPHIS-ERYSIMI) DETERMINED ON NATURAL INFESTATIONS AND AFTER DIFFERENT INSECTICIDE TREATMENTS, International journal of pest management, 40(1), 1994, pp. 107-110
Economic injury levels (EILs) were determined for the aphid Lipaphis e
rysimi (Kaltenbach) infesting rapeseed variety DYS-3 of yellow sarson
under natural infestation during 1987-88 and 1988-89 and with the use
of insecticide during 1988-89 and 1989-90 to compare the EILs under di
fferent conditions. The natural aphid infestation did not affect yield
adversely until 80 and 100 days of crop age in 1987-88 and 1988-89 re
spectively. Using insecticide application, the significant decline in
yield started from 80 and 90 days during 1988-89 and 1989-90 respectiv
ely. In a yield-infestation study the period of crop growth between 70
and 100 days was most crucial, when the crop required at least two sp
rays of Quinalphos at a 20-day interval. Under natural infestation, th
e EIL with the best fitting relationship was 1.2 aphids per plant in 1
987-88 (loglinear), and 14.2 aphids per plant in 1988-89 (quadratic).
With insecticide use, EILs for the best fitting relationship (quadrati
c) were 14.2 and 68.9 aphids per plant in 1988-89 and 1989-90 respecti
vely, The EILs calculated after insecticidal application were generall
y higher than that for natural infestation levels for the same forms o
f equation. The EILs computed from the natural infestation seem to be
more correct and reliable as there was no external interference.