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Pearl millet, Pennisetum americanum L. occupies a large proportion of the area growing millets in Africa. Consequently the insect pests that attack this species have received attention over other millets. A list of the major species is presented. Actual data on losses due to insect pests on pearl millet are not readily available. Crop loss assessment methods using incidence and damage ratios are discussed. Quantitative losses determined from insecticide trials at research station are also presented.
FAO has in the past given much attention to the development, dissemination and use of methods to assess pre- and postharvest crop losses. The experience gained shows that losses vary with location, crop, pest and differ from year to year. The collection of data on a national or regional basis is expensive, since data have to be collected over a number of years. Therefore, loss assessment is now mainly used as a tool to develop loss reduction strategies and to assesss the cost-effectiveness of introduced methods.
A reservation is made with respect to the quoting of data on losses, without giving information on how these data were collected and interpreted, because data presented in that way can easily be misinterpreted.
Many useful crop preharvest loss assessment methods are presently available for the researcher, but there is, however, an urgent need for simple methods for use by extensionists and farmers in other situations. The developed methods to assess postharvest losses in grains are adequate.
Yield losses from insect pests were determined by the insecticide check method in 60 crops in the Philippines from 1976–1986 in three rice environments with traditional and modern cultivars in 10 sites. Plot size of 100 m2 minimized interplot interference from insecticide protection on untreated plots. Low and high crop losses were recorded across sites in drylands (2–39%, = 25%), rainfed wetlands (13–24%, = 21%), and irrigated wetlands (5–40%, = 18%). Weighted crop loss for the Philippines based on production by environment and cultivar type averaged 18.3% or 0.57 t/ha per crop. Consistently greater yield loss occurred in the vegetative (50%) than reproductive (30%) or ripening (20%) stages across environments and cultivars. No epidemics affected the trials therefore crop losses were those from chronic pests. The major chronic pests in the wetlands were stem borers, leaffolders, whorl maggot, and rice bug; and in the drylands were ants, seedling maggots, white grubs, leaffolders, stem borers and rice bug. Yield loss variability was greater between fields than crops or sites, therefore a control strategy based on corrective actions when pest numbers reach threshold levels is more efficient than prophylactic actions. Yield loss was more in early maturing cultivars stressing the importance of compensation in tolerating insect damage. Insect stresses perhaps can be compensated by total crop management to increase the plant's ability to tolerate insect damage.
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