Density and damage of maize pests under conventional and conservation cultivation

The effects of conventional and conservation tillage on the incidence and damage of the fall armyworm Spodoptera frugiperda (J.E. Smith), armyworm Pseudaletia unipuncta (Haworth) and the small weevil Nicentrus testaceipes (Champion) on corn were studied during the spring-summer period, of 1998, in Chapingo, Mexico. Fifty plants per experimental unit were visually examined at each sampling date. In the particular case of the armyworm, the numbers of larvae in the soil were estimated by samplings, besides of the percentage of corn leaves injured by the insect. The information on incidence of the corn weevil was supplemented by the number of injuries on the three parts of the eighth leaf. The highest percentages of plants damaged by the fall armyworm were 20 in conventional tillage and 4 in the conservation. The armyworm larvae were present only in the conservation tillage, associated to Brachiaria plantaginea plants in which they initiated the damage and on which they consumed 94.5% of the foliage. Out of all lower leaves of the corn plants, 52.7% showed lesions caused by the armyworm. The percentage of plants affected by the weevil was 95% in conservation tillage and 84% in the conventional one. Likewise, the total number of lesions was 44.4 and 10.8, respectively.