During the second week of June 2020, I noticed some soybean fields with thrips feeding.Soybeans usually are not heavily impacted by thrips and plants recover. Later that week, the Plant Disease Diagnostic Laboratory at the University of Kentucky’s Research and Education Center in Princeton received seedlings of late-planted corn showing symptoms of thrips feeding (Figure 1). I found similar damage this weekend while scouting for pests in corn (Figure 2).
Winged adult and nymph thrips feed by sucking out cells of leaves using their penetrating mouth parts. This feeding causes longitudinal, whitish scars that, when caused by a great number of thrips, result in entire leaves or even plants appearing desiccated. This type of damage is frequently observed when rains are absent, during extended periods of hot, dry weather conditions, and when plants are stressed.
Description of Thrips
In Kentucky, several species of thrips can affect corn; however, the grass thrips
may be the most common species of thrips found in seedling corn. Adult thrips have two pairs of feather-like wings and are dark in color (Figure 2). The immature instars or nymphs are yellow or orange slender insects about 1/16 inch (1.6 mm) long.
If drought persists for long periods, plants may become grayish in color and wilt. Severe thrips outbreaks in seedling corn can stunt plants, and insecticide treatment may be justified; however, thrips are a sporadic pest in corn and the threshold for this insect is not established. Usually, young corn plants outgrow the injury and insecticides are not necessary.
- Occasional & Non-Economic Corn Pests, Purdue University (link)
- Prevalence of sporadic insect pests of seedling corn and factors affecting risk of infestation (link)
By Raul T. Villanueva, Entomology Extension Specialist