Population dynamics of caterpillars on three cover crops before sowing cotton in Mato Grosso (Brazil).

Direct seeding mulch-based cropping systems under a preliminary cover crop such as millet are common in some areas of Brazil. Lepidopteran pests that damage cotton, soybean and maize crops can proliferate on cover crops, so preventive chemical treatments are necessary. Very little data is available on these pests on cover crops. This paper presents the dynamics of Spodoptera frugiperda, S. eridania, Mocis latipes and Diatraea saccharalis caterpillars monitored at Primavera do Leste, Mato Grosso state (Brazil) during the of 2005/2006 and 2006/2007 cropping seasons on four cover crops, i.e. finger millet (Eleusine coracana), pearl millet (Pennisetum glaucum), sorghum (Sorghum bicolor) and ruzigrass (Brachiaria ruziziensis). The pests were visually counted on plants within a 1 m2 transect (wooden frame). Caterpillars were reared to facilitate identification of collected species and parasitoids. Many S. frugiperda caterpillars were observed on millet in 2005, with a maximum of 37 caterpillars/m2. On sorghum, we found 30 caterpillars/m2, or 0.83 caterpillars/plant. The Diatraea borer attacked sorghum later than the other pests. M. latipes was also observed on millet. The millet cover crop had to be dried for at least 1 month before direct drilling the main cotton crop in order to impede S. frugiperda infestations on cotton plantlets, thus avoiding the need for substantial resowing. The comparative methodological aspects are discussed.