3.2. Losses due to weeds

3.3 Drought and yield losses

3.4 Losses due to nutrient deficiencies

3.5 Losses due to peg drying

3.6 Losses in post-production system

3.7 Storage losses

3. Overall Losses

3.1 Pre-harvest losses due to diseases and pests

The major diseases of economic importance affecting groundnut crop in the field in India are early and late leaf spots (Cercospora arachidicola [Mycosphaerella arachidis], Phaeoisariopsis personata (M. berkeleyi), rust (Puccinia arachidis), collar rot (Aspergillus spp.), root rot (Macrophomina phaseolina) and stem rot (Sclerotium [Corticium] rolfsii). These ailments cause 13 to 59 percent yield losses during both the rainy and summer seasons. Thrips and jessed are the major pest of groundnut, incidence of these pests is reported significantly higher in the fields not sprayed by the insecticide monocrotophos and pod yield loss due to the pest attack are about 39 percent, which exceeded the economic loss of 12 percent.

Crop losses caused by Sclerotinia sclerotiorum, S. minor and Sclerotium rolfsii [Corticium rolfsii] were evaluated in the southern region of the groundnut-producing area in the province of Cordoba, Argentina. Production losses were calculated using the equation: PL=(AY/1.0-LP)-AY where PL represents losses, AY the actual yield and LP the proportion of losses. The actual yield is that obtained by the producer while proportional losses are equivalent to the percentage of dead plants (incidence). Furthermore, the incidence of blight and wilting was often higher in groundnut crops where the preceding crop had been groundnut, soyabean or sunflower (Helianthus annuus) than in groundnut crops preceded by sorghum (Sorghum bicolour), maize, alfalfa (Medicago sativa, lucerne), lovegrass (Eragrostis curvula) or grassland. The fact that these diseases are becoming increasingly widespread, together with the losses caused by them throughout the groundnut-growing region are of major importance (Marinelli, et al., 1998).

Among the major arthropods in soil and plant samples taken from groundnut farms in Mali, Burkina-Faso, Niger and Nigeria, termites of the genus Microtermes (Isoptera: Termitidae) were the most abundant and widely distributed species of economic importance. Most of the whitegrub (Coleoptera: Scarabaeidae) and millipede (Myriapoda: Odontopygidae) species identified belonged to the genera of Schyzonycha and Peridontopyge, respectively. Percentages of plants attacked by termites, white grubs and millipedes were 39, 11 and 9 percent, respectively. Yield loss due to termites, which predominantly damaged harvested kernels, was estimated at 10 to 30 percent and was significantly correlated with percentage of plants damaged by termites (Umeh et al., 1999).

Termites and julids are very serious pests of groundnut in Burkina Faso causing scarring and perforation of pods just before the groundnut harvest. Other more qualitative damages, such as increases in aflatoxin content in the damaged pods are also directly linked to pest attacks. Farmers of Burkina Faso are unable to use chemical control against these pests due to their poor purchasing power. Varietal resistance, which is less expensive and definitely more environment-friendly, offers a better alternative. The relationship between resistance level of varieties and their pod yields is low. For example, NCAC 2243, RMP 40 and NCAC 2240 showed a high level of resistance to combined attacks of termites and julids, they had lower pod yields compared to the other susceptible varieties. Losses due to insect pests in India are sown in Table 19.

Attempts to manage insect pests often emphasize an understanding of the relationships between insect densities and crop yield loss, because of many variables involved. For instance, the stage of the crop, the weather pattern and the season are all important. Groundnut seedlings are susceptible to relatively low population densities of defoliators, whereas established plants can withstand a considerable degree of leaf loss, more in the rainy season.

Table 19. Losses due to insect and mite pests as reported from various groundnut-growing areas in India.