The Ecology and Control of Potato Whitegrubs of India

Abstract

Whitegrubs are the most destructive and troublesome soil insects, impeding potato production especially in hilly states of India. In hills, the potatoes are grown during the summer season as a rain-fed crop under long-day conditions on sloppy lands with light and loose-textured soils. There are nearly 20 species of whitegrubs which attack potato in different parts of India. The most widely distributed and destructive species in India are Brahmina coriacea, Holotrichia longipennis, Anomala dimidiata, Melolontha indica, Lepidiota mansueta and Holotrichia serrata. H. serrata is found throughout Karnataka, Maharashtra, Tamil Nadu, Andhra Pradesh, Bihar and Uttar Pradesh, whereas B. coriacea and H. longipennis are restricted to the northern parts of India. The economic importance of chaffers is primarily due to feeding activity of the third instar grubs. The infected tubers have scooped out holes or half-eaten tubers which are rendered unfit for marketing. The damage to potato tubers has been reported to vary from 8.5 to 75.0% especially in hilly regions of the country. In India, the biology of B. coriacea, H. longipennis, A. dimidiata, Anomala lineatopennis and H. serrata has been studied and all species complete a life cycle in 1 year. Some species like M. indica and L. mansueta are expected to require 2–3 years to complete their development. The whitegrubs are polyphagous, and no single method of control provides permanent solution for the whitegrub problem. Hand collection of adults at the time of emergence has been practised as a measure of control. The beetles can be conveniently killed by spraying the host trees with some potent contact insecticides when consistent beetle emergence is there. Soil application of chlorpyriphos 20EC at 2.5 kg a.i./ha and phorate 10G at 3.0 kg a.i./ha has been reported effective against whitegrubs. Applying the preventive insecticide around the third week in June will have the insecticide in place when eggs begin to hatch. The cultural practices to be followed in the integrated management of whitegrubs include repeated ploughing, hoeing and forking to expose the grubs and fall/spring ploughing to expose the pupae and hibernating adults.