This item is adapted from an AgriLife submission to Texas Grain Sorghum Association’s “Sorghum Insider”

Dalton Ludwick, Ph.D., Assistant Professor & Extension Entomologist, TAMU Dept. of Entomology, Corpus Christi, (361) 698-7400 ext. 1225, dalton.ludwick@ag.tamu.edu, Twitter: @SouthTXBugs

Insecticides

There are several key pests of grain sorghum production in Texas. Along the Coastal Bend, rice stink bug is a major, annual pest that moves between non-crop hosts and crops (e.g., rice, grain sorghum). In 2009, Dr. M.O. Way (retired professor, Texas A&M AgriLife Research, Beaumont) documented poor control with an insecticide whose active ingredient was lambda-cyhalothrin and that other active ingredients were better for managing the pest, though they were not labeled in grain sorghum.

Rice stink bug adult. Image by Pat Porter, Texas A&M AgriLife Extension Service.

In the 2010s, some research from Louisiana State University documented lambda-cyhalothrin resistance issues in rice stink bugs collected from Wharton County, TX. In the decade since, rice stink bug has received little attention and no efforts were made to better understand this product control issue.

Starting in 2021, my program has sought to understand how far this poor control extends in Texas and other states, the severity of the issue, and the alternative insecticides that could be used to manage rice stink bugs. During our surveys from 2021–2023, we discovered lambda-cyhalothrin resistance extended from Jefferson County, TX, southward to the Lower Rio Grande Valley.  This resistance was highest in major grain sorghum production areas like Nueces and San Patricio Counties. This matched well with reports from crop consultants, producers, and Texas A&M AgriLife Extension Service IPM Agents.

Following the identification of the problem, we evaluated insecticides labeled in grain sorghum or other crops to manage stink bugs. We tested products containing lambda-cyhalothrin, dimethoate (not labeled for stink bugs in grain sorghum in 2021), and dinotefuran (not labeled in grain sorghum) alongside an untreated control at the Texas A&M AgriLife Research & Extension Center in Corpus Christi.

Our results were positive and showed that lambda-cyhalothrin was ineffective at controlling rice stink bugs in grain sorghum while dimethoate was better than the control. In addition, we saw strong, persistent effects against rice stink bug nymphs when dinotefuran was applied. Using this information, we first spoke with the Texas Department of Agriculture regarding options to alleviate producer issues and then with dimethoate manufacturers. In 2022, two dimethoate products (Dimethoate 400, Dimethoate 4EC) received Section 2(ee) bulletins to allow use in grain sorghum for management of rice stink bugs, and a third bulletin was approved (Dimethoate 400EC) in 2023.

Thresholds

In the late 1970s, research at Texas A&M was conducted to understand the relationship between rice stink bug density (i.e., number of rice stink bugs per head) and grain sorghum yield. Research at that time was used to develop a threshold for producers to manage rice stink bug populations. In the early 2000s, these data were revisited and analyzed again by Extension Entomologists to ensure accuracy in the recommendations. These revisions were the basis of our thresholds for nearly 20 years and even informed our online rice stink bug threshold calculator.

Since those data were collected, other states have investigated the relationship between rice stink bug and grain sorghum. Research from the University of Arkansas showed a relationship between the heading stage (e.g., flowering, milk, soft dough, and hard dough) and the impact of rice stink bugs. Following fertilization, the developing seeds were incredibly sensitive to feeding and as they matured, the tolerance to feeding substantially increased. Given this new information, Texas A&M AgriLife Extension Service Extension Entomologists revised the grain sorghum management guidelines. Lastly, we are now generating new data for each heading stage in the Coastal Bend to revisit this topic and better define our recommendations for decades to come.