Nuclear polyhedrosis Virus (NPV) of Helicoverpa armigera
Helicoverpa armigera is a serious pest on commercial crop like cotton; pulses like redgram and bengalgram; vegetables like tomato, bhendi and dolichos bean; oilseeds like sunflower, soybean and safflower and cereals like sorghum and maize.
Ha NPV is a highly infective microbial bio pesticide. Ha NPV is used for controlling Helicoverpa armigera attack.
The recommended dosage is 200 ml of NPV/acre or 500 ml/ha containing 100 and 250 larval equivalent (LE) of NPV respectively as active infective material (one LE = 6 x 109 POBs).
100 ml of NPV could be diluted in 200-400 litres of water when high volume sprayer is used and in 50-70 litres of water in case of power sprayers.
It is advised to spray using high volume knap-sack sprayer. Virus should be sprayed during evening hours. Spray should be initiated as soon as some newly hatched larvae are observed or three to five days after a trap catch of 5 moths per pheromone trap. Subsequent sprays should be made at 7-10 days intervals depending upon the pest population.
The viral pathogen seems to be less sensitive to chemical pesticides. When the combination of pathogen and pesticide is used, sometimes synergistic action is noticed. But is recent years mixing of NPV with insecticides is not advisable due to cross resistance problem.
Viruses that cause disease in insects are usually quite specific to their host. They occur often naturally in the field. Farmers will sometimes find dead caterpillars in the crop, which were killed by a virus. These virus-infested caterpillars can be grinded up in water. Spraying this solution over the crop will further spread the disease amongst caterpillars of the same species.