Whitney Crow has a bone to pick with two of cotton's most prevalent pests. While tobacco thrips impact many cotton farmers across the state, reniform nematodes are site specific. Both pests, however, can have a significant impact on yield. In 2016, the average loss from thrips damage in an affected cotton field was about 10 percent while reniform nematode damage was around five percent. Both attack seedling cotton, during the early growth and development stages.

The pests are different. Thrips are above-ground insects while parasitic reniform nematodes cling to the roots below ground. Sight unseen, potential damage from reniform nematodes is harder to quantify. Known as a stress pathogen, the damage from reniform nematodes is worse in years when cotton is under greater environmental stress.

Crow, a life sciences doctoral student pursuing an entomology concentration in the Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology, sought to find a correlation between the two pests as part of her dissertation.

Crow explored how seed treatments, cultural practices, and environmental factors can influence how the cotton plant recovers from both pests. She studied compound stresses of tobacco thrips and reniform nematodes on cotton yield.

"My goal was to evaluate the influence of tillage, seed treatment, and nematicide on the control of tobacco thrips and reniform nematodes and determine if there are any interactions between factors," Crow said.

The study, which ran over the course of the 2015 and 2016 growing seasons, occurred in Hamilton, Mississippi across four locations with four replications. Conservational and conventional tillage was observed. One nematicide was observed alongside a control. Six insecticides or combinations of insecticides were observed.

While Crow was able to document damage from both thrips and reniform nematodes, the plants recovered throughout the two optimal growing seasons. Yield was not affected and Crow was unable to tease out a correlation.

"While there was visual evidence early in the season in the form of lower plant biomass and vigor that indicated an interaction between tobacco thrips and reniform nematodes, the yield did not reflect a difference," Crow said. "This shows the resiliency of cotton. There are times when cotton can sustain what would normally be yield limiting stresses but when there is adequate moisture and perfect growing conditions the plants can recover and suffer no yield loss."

The research found that seed treatment, tillage, and nematicides did not negatively affect cotton yield during an optimal growing season. This data also indicates the importance of scouting and utilizing thresholds for management decisions. Continued research includes investigating specific nematicidal efficacy due to limited options for nematode control.

Crow is under the direction of Drs. Angus Catchot, Jeff Gore, Darrin Dodds, Tom Allen, and Don Cook.

Funded, in part, by Cotton Incorporated.