priciples of insecticide use in rice ipm

Resurgence of BPH under Field conditions
Insecticides in Rice IPM (DRR)
The amount of toxicant that comes in contact with N. lugens and its predators is influenced by several
factors. The density of the crop canopy increases with age of the crop, limiting the spray material reaching
the base of the plant, where BPH feeds. Rainfall, which washes the insecticide from the plant, and degree
of resistance to insecticides are additional factors influencing BPH resurgence under field conditions
(Heinrichs et al., 1982b). The situation is further complicated because the insecticide application rates,
application methods, time of application and degree of varietal resistance could also influence the level
of BPH resurgence (Heinrichs and Mochida, 1983).
Effect of Rates of Insecticide Application on BPH and its Predators
When foliar sprays of methyl parathion, deltamethrin, diazinon and carbosulfan (FMC 35001) were applied
at different dosages, higher concentrations of carbosulfan in general led to greater populations of BPH
(Heinrichs et al., 1982 b). Among the three predators of BPH (spiders, Microvelia atrolineata Bergoth
and Cyrtorhinus lividipennis Reuter), deltamethrin was the most toxic to spiders even at low rates;
deltamethrin and carbosulfan were toxic to M. atrolineata, while diazinon was less toxic to both spiders
and M. atrolineata. High rates of all the insecticides resulted in lowest populations of C. lividipennis
(Heinrichs and Mochida, 1983). Krishnaiah and Kalode (1987) observed that insecticides such as
monocrotophos, phosalone and phosphamidon at recommended concentrations (0.05%) checked BPH
build-up while monocrotophos and phosphamidon at suboptimal concentrations (0.02%) resulted in
resurgence. Among the other insecticides deltamethrin at recommended concentration (0.01% and
0.005%) recorded highest BPH population whereas methylparathion and fenvalerate exhibited a tendency
towards BPH resurgence. Deltamethrin also showed high degree of adverse affect on natural enemies
such as mirid bug, C. lividipennis and spiders. Since, resurgence is a dose dependant phenomenon,
emphasis should be placed on the application of correct dosage of effective and recommended insecticides
in addition to selecting the right insecticide (Krishnaiah and Kalode, 1987).
Number, time and Method of insecticide Application and Pest Resurgence
In the tropics, the most popular method of insecticide application is by foliar spraying. According to
Heinrichs et al., (1982a} application of insecticides through foliar spraying induces high degree of BPH
resurgence when compared to application as root zone placement, and as broadcasting. Under field
conditions, dust formulations control BPH, but foliar spraying with insecticides results in resurgence
(Raman, 1981). Application of granular gamma HCH, diazinon, Sevidol (Chelliah and Heinrichs, 1979),
mephospholan, and quinalphos (Varadarajan et al., 1977) was observed to cause BPH resurgence.
Resurgence was also influenced by the time of application. Sprays of methyl parthion and deltamethrin
applied at 50 and 65 days after transplanting induced resurgence, while earlier applications had little
effect. Further, plots receiving only one application had low BPH population as compared to those
sprayed 2, 3 or 4 times (Heinrichs and Mochida, 1983).
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