Scouting for Insect Pests

When scouting for insects in a crop, the aim is to identify any pests present, to assess the potential of one or more species becoming a problem and to estimate the density of the pest population. Because different pests occur from seeding to harvest, weekly inspections are recommended.

Some pests, like grasshoppers, can be seen and their populations estimated by simply walking slowly through the field and making careful observations. Others, like seed maggots, root maggots, and cutworms, may require getting down on your knees and using small tools (ex, trowel, pen knife, soil sieve, hand lens). Still others, like lygus bugs, may require the use of a sweep net or other collection device.

Estimating Percent Defoliation

Many economic thresholds for insects are based on percent defoliation of the plans they are feeding on. Figure 1 may assist in determining the percent defoliation. Although the photo below is of sunflower leaves, this figure can be used to estimate percent defoliation for many crops.

Percent defoliation of sunflower leaves

Figure 1. Percent defoliation of sunflower leaves