- The aphid infestation in a field is typically patchy.
- The adults and nymphs suck sap from different parts of the plant namely underside of leaves, terminal shoots, stem and branches, flower stalks and pods.
- The Cow pea aphid inject a powerful toxin in to the plant while feeding. Feeding damage is expressed as yellowish hue on the infested leaves.
- Adult prefer to feed on the dorsal surface of the leaves by scraping linear streaks.They also feed on the ventral leaf surfaces rarely.
- The growth of the plant is greatly retarded resulting in stunting of the plant.
- The pods become malformed.The aphids produce considerable amount of honeydew upon which sooty mould fungus grows affecting the photosynthetic ability of the plant.
- More honey dew excretion make the surface sticky. The aphid transmit cowpea mosaic virus.
Select five plants at random and assess the total number of Aphds in 5 cm length of the affected portion. Take the average. Less than 5 mild 5-10 moderate,more than 10 severe.