Date of this Version
Leptinotarsa decemlineata (Say) densities, potato defoliation levels, and grower insecticide use were monitored in commercial potato fields with differing rotational histories on Long Island, New York. Rotation for 1 year to a nonhost grain crop (rye or wheat) significantly reduced the pest status of L. decemlineata in the following year's potato crop. Early season (late May) adult densities were reduced 95.8% in three of four comparisons in 1982 and 69.5% in two of three comparisons in 1983. In one comparison each year, early season L. decemlineata densities were low in both the rotated and nonrotated fields due to past grower practices. Season-long (June-August) paired comparisons of rotated and nonrotated fields were conducted on four farms in 1982 and five farms in 1983. In these comparisons, growers used an average of one (range, 0-2) additional insecticide application for L. decemlineata control during the first generation on the nonrotated fields. Despite this, defoliation levels and L. decemlineata densities were higher in several cases in the nonrotated fields. The effect of crop rotation was greatest early in the season and was not detectable after the end of the first L. decemlineata larval generation on Long Island.