Hot Temperatures & Drought Cause Thrips Population Spikes in Corn

Description of the Problem

While scouting for insects affecting corn and soybeans in their early stages of development, large numbers of thrips were observed in corn seedlings (greater than 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 thrips populations. However, the absence of rains and presence of high temperatures in the area during mid-June have increased these populations again. Thus, thrips infestations have been observed in both corn and soybeans planted in many counties in Kentucky.

Figure 1A. Seedling corn field in Livingston County, B. Leaf showing typical injuries of thrips feeding, and C. Thrips (red arrows) feeding on corn leaf (Photos: Armando Falcon-Brindis).


Pest Description & Damage

Adult thrips are small (1/16 inch long), have two pairs of feather-like wings, and can be seen in the upper or lower surfaces of corn leaves (Figure 2). The immature instars or nymphs are yellow or orange.

Figure 2. Adult thrips found in corn.

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

Management

Farmers and scouting personnel should be aware of the presence of this pest. This insect does not require insecticide applications for its control in Kentucky compared with southern states where thrips pressures is high. Sometimes damage is noticeable, especially when years are hot and dry; however, in Kentucky, corn seedlings outgrow the injury.

If drought persists for long periods, plants may become grayish in color and wilt. Severe thrips outbreaks in seedling corn can stunt plants, and 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.


By Raul T. Villanueva, Entomology Extension Specialist and Armando Falcon-Brindis Research Associate.

Posted in Grains
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