After Louisiana’s warm winter, watch out for more insect pests

By Blake Wilson and Sebe Brown

Populations of pest insects are often influenced by factors at play well before crops are planted. Winter mortality is a key regulator of spring insect populations, particularly for pests introduced from tropical regions.

The 2018-2019 winter was mild, especially in the southern half of the state, where temperatures didn’t dip below a light frost. Here we provide a crop-specific breakdown of which pests will benefit from these conditions.

Rice

planthopper nymphs
Rice delphacid nymphs — photo by Weldon Nansen

The rice water weevil and the rice stink bug aren’t heavily influenced by winter temperatures and are consistent threats to rice year in and year out. Populations of stem borers may be above average, particularly in southwest Louisiana.

South American rice miner populations also may be heightened. Warm winters in the past have led to issues with this pest in late-planted rice. Rice scouts should be on the lookout for the rice delphacid, a plant hopper from Central and South America.

Although this pest is not thought to be in Louisiana, it has been damaging ratoon rice fields in Texas in recent years. More information on all rice insects is available at https://www.lsuagcenter.com/topics/crops/rice/insects.

Soybeans

redbanded stink bug
Redbanded stink bug

The primary true bug pests of soybeans are southern green stink bugs, brown stink bugs and redbanded stink bugs. Redbanded stink bugs are an invasive species from South America and do not overwinter well when temperatures are abnormally cold, as they were in the winter of 2018.

However, agriculture professionals should be mindful of potentially large populations of redbandeds moving into soybeans this year due to a mild winter.

Southern green and brown stink bugs, which are native to Louisiana, are consistent threats to soybeans from year to year. Worm pests such as velvetbean caterpillars and soybean loopers do not overwinter in Louisiana, and winter temperatures have little influence on pest populations during the growing season.

Corn

Corn earworms and fall armyworms are the primary ear feeders that affect Louisiana corn. Corn earworms overwinter in Louisiana. Mild winter temperatures typically promote earlier emergence, which can lead to larger populations in the summer.

Fall armyworms do not overwinter in Louisiana, and migration occurs from southern Texas and Florida. Louisiana winter temperatures have little impact on fall armyworm populations during the growing season. Southwestern corn borers and sugarcane borers both overwinter in Louisiana in crop residue. These pests are threats to corn year to year.

Cotton

Tarnished plant bugs are the primary true bug pest of cotton. Tarnished plant bugs are native to Louisiana, and winter temperatures do not significantly influence population numbers during the growing season.

Bollworms are the primary worm pest of cotton, and mild winter temperatures typically promote earlier emergence, which can lead to larger populations in the summer. Spider mites and cotton aphids are secondary pests that overwinter in Louisiana, making them a threat to cotton every year.

Dr. Blake Wilson is a rice and sugarcane entomologist with the Louisiana State University AgCenter. He may be reached at BWilson@agcenter.lsu.edu. Dr. Sebe Brown is an Extension entomologist for cotton, corn, soybeans and grain sorghum with the LSU AgCenter. He may be reached at SBrown@agcenter.lsu.edu.

This article first appeared in the Louisiana Crops newsletter.

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