Effect of Neem on damage caused by fall armyworm Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) and three agricultural variables on resistant and susceptible maize.

Abstract

Neem oil was evaluated against fall armyworm Spodoptera frugiperda (J. E. Smith) on plants of two maize lines, one resistant and another one susceptible, planted in Poza Rica, Veracruz, México. The objective of this study was to compare biological development of resistant and susceptible maize plants infested by fall armyworm and sprayed with neem oil under field conditions. A concentration of 20,8% neem oil, was applied on the upper leaves and whorl according to the following treatments: before artificial infestation, one and two weeks after infestation; in addition, a chemical insecticide (Permetrin) and one control (water) were included. In an experiment comparing different doses, neem was applied 3 times at concentrations of 20,8, 2,0 and 0,20%; with a Permetrin and water control included for comparison. Damage to foliage, flowering, plant height, and yield were then recorded. In the experiment to determine time of application the susceptible line showed severe damage from 6,7 to 8,1 on a scale from 0-9. while the resistant line exhibited damage ranging from 4,6 to 6,0. For the neem oil dose experiment, plants in both lines during the winter cycle showed damage ranging from 4,4 to 6,2, while during the spring-fall season damage was from 6,2 to 8,5. Flowering was not affected by application dates. However in the experiment with different neem oil concentrations, for the 20,8% treatment flowering was accelerated up to 7,4 days when compared to the control. No differences were found among treatments on in plant height. The treatment with 20,8% neem oil showed low defoliation, but yields were low at this high doses due to phytotoxicity. Weekly application of 2% neem oil gave more than best protection when applied before pest infestations.