Scientists for the USDA’s Agricultural Research Service (ARS) in College Station, Texas have developed a new technique to discover boll weevil hideouts.

Growers in the Lower Rio Grande Valley typically mow cotton plants after harvest and may spray with herbicide to prevent boll weevils from living in the regrowth.  Mother Nature fights against this management plan, however, with subtropical, heavy autumn rains.  Because this leads to large areas of “regrowth cotton,” detection of the pest is difficult.  Now ARS meteorologist John Westbrook, entomologist Charles Suh and agricultural engineer Chenghai Yang have found a way to use digital images taken during an aerial survey to find boll weevils.

The team started by growing cotton, defoliating it and then mowing or shredding the stalks.  During this time they arranged nine flights to take high-resolution images of the cotton as it grew and for about two months following harvest.

The scientists also conducted ground-based surveys on the same dates as the aerial surveys, measuring the height and width of cotton plants as they grew, and after plants were harvested and shredded. The team recorded the postharvest daily air temperatures and correlated them with the sizes of the regrowth cotton to predict when regrowth plants would reach sufficient sizes to detect in aerial surveys.

The results show that the airborne imagery can be used to estimate regrowth when the leaf canopies of cotton plants are at least 8-12 inches wide. The scientists also were able to use data on air temperature and plant size to develop a model to predict when the regrowth cotton would reach detectable sizes, based on temperature patterns. The approach will give growers better information regarding areas harboring boll weevils so they can spray for them and reduce the threat they pose in the area.

You can find the research results in the April issue of AgResearch.