Thrip damage observed in seedling corn in 2022

Dr. Raul Villanueva Extension Entomologist
Dr. Armando Falcon-Brindis, Research Analyst

Description of the problem

While scouting for insects affecting corn and soybeans in the early stages of development, large numbers of thrips were observed in corn seedlings (>20 thrips per plant) (Figure 1A-C). Corn plants with thrips were observed in fields near the Cumberland River in Livingston County during the last week of May but as usual, rainfalls reduced thrip populations. However, the absence of rain and high temperatures in the area during mid-June have increased these populations again. Thus, thrip infestations were observed in both corn and soybeans planted in Caldwell and Lyon counties.

Farmers and scouting personal should be aware of the presence of this pest. Although this insect does not require application of insecticides for its control sometimes damages are noticeable. Usually, corn seedlings outgrow the injury, and insecticide applications are not necessary. Adult thrips are small (1/16 inch long), have two pairs of feather-like wings, and are dark in color (Figure 2). The immature instars or nymphs are yellow or orange.

Both nymphs and adult thrips suck out cells of leaves using their mouth parts. This feeding causes longitudinal, whitish scars that, a great number of thrips, result in entire leaves or even plants appearing desiccated. Damages are more severe when rains are absent or during extended periods of hot, dry conditions.

Management

If drought persists for long periods, plants may become grayish in color and wilt. Severe thrips outbreaks in seed-ling corn can stunt plants, an insecticide treatment may be justified. The economic threshold for this insect is not established in Kentucky. Thrips populations can be reduced by heavy rains hence insecticide applications may not be necessary.