EFFECT OF A NUCLEAR POLYHEDROSIS VIRUS ON Spodoptera frugiperda (SMITH) (LEPIDOPTERA: NOCTUIDAE) LARVAE, ITS DAMAGE AND YIELD OF MAIZE CROP

Resumo

The efficiency of Baculovirus in a wettable powder formulation to control the fall armyworm Spodoptera frugiperda (Smith) was evaluated using variations of the recommended dose of 50 grams per hectare (2.5x10¹¹ polyhedron inclusion bodies - PIB/ha): 50 or 100g/ha applied once, and variations of two applications at seven-day intervals, of 25+25, 25+50, 50+25 and 50+50g/ha, compared to untreated plots. The treatments were arranged in a randomized complete block design with six replications. Each plant at 6-8 or 8-10-leaf growth stages, was artificially infested with 10 newly hatched larvae. The virus suspension (300L/ha) was applied 24 hours after larvae infestation using a back-pack-manual sprayer at 40PSI (2.8 kg/cm²) and a regular flat fan nozzle. Larval mortality rate obtained from plots with the application of 50g of Baculovirus wettable formulation ha^-1, at once (96.2%), was significantly higher than that obtained with the application of 25+25g/ha (85.3%) or 25+50g/ha (87.8%). However, it was lower than that obtained from the other virus treatments, which had no significant difference among them (mean of 99.2%). The damage caused by S. frugiperda on the leaves of plants of untreated plots (average of 4.5 in an visual scale from 1 to 5) was significantly different from that observed in plots sprayed with virus (1.75 to 2.33), Plants protected with the virus produced significantly higher yield (mean of 7.577Kg/ha) than plants unprotected (6.140Kg/ha), that is, 23.4% higher.