Two pathogens commonly found in Arkansas cotton fields diminish the root structure of cotton plants, potentially causing loss of yield and quality.

Craig Rothrock, professor of plant pathology for the University of Arkansas Division of Agriculture, described research conducted with division plant pathologists Jianbing Ma and Terry Kirkpatrick to quantify the changes in cotton plant roots caused by root-knot nematodes and the black root rot fungal pathogen Thielaviopsis basicola during a recent research field day at JuddHill Plantation near Trumann.

The University of Arkansas Division of Agriculture and Arkansas State University, which conduct cooperative research on plots provided by the Judd Hill Foundation, hosted the field day. More than 250 visitors attended the event at the Judd Hill Plantation, located about five miles south of Trumann.

Rothrock said root-knot nematodes and Thielaviopsis basicola both decreased numerous root structure parameters. In his test plots, interaction between the two pathogens reduced root volume more than either pathogen alone.

Understanding the impact of the pathogens on cotton plant roots is important because the damage they do to roots may suppress cotton growth and result in decreased yields. Continuing research should examine their season-long effects on crop growth and development.

In another of the studies featured during the field day, Derrick Oosterhuis, Distinguished Professor of crop, soil and environmental sciences, said very high mid-summer temperatures are one of the main stressors of cotton plants.

"People think that because cotton comes from a hot climate that it likes high temperatures," Oosterhuis said. "Well, it doesn't."

The ideal average temperature range for growing cotton is 86 degrees in the day to 68 degrees at night. That range was exceeded for extended periods in both 2011 and 2012. At day temperatures above 95 degrees, there is a significant decrease in leaf growth and carbohydrate production because of decreased photosynthesis and increased respiration. This results in poor fertilization, fewer seeds, smaller bolls, and reduced yield.

When night temperatures are higher than about 75 degreesrespiration increases significantly. Respiration in plants is the intakeof oxygen and the breakdown ofsucrose to provide energy. During daylight, oxygen is exhaled as a waste product of photosynthesis. At night, photosynthesis does not occur, no oxygen is produced and carbon dioxide is exhaled.

"Therefore, high night temperatures increase respiration, which causes additional loss of carbohydrates." Oosterhuis said.The result is the plant has insufficient sucrose to satisfy its growth needs. The result is loss of cotton bolls and less fiber production. There may also be fewer and smaller seeds per boll.

Oosterhuis is studying the effectiveness of stress-mitigating chemicals that may counter the damaging effects of high temperatures.

Other topics covered during the field day included cotton sustainability through tillage, nitrogen fertilization, irrigation and COTMAN by Tina Teague, a Division of Agriculture entomologist and faculty member of the ASU College of Agriculture; soil moisture monitoring in cotton by Michele Reba, USDA/ARS research hydrologist from the National Sedimentation Laboratory in Jonesboro; and improving irrigation efficiency with surge valves, by Ray Benson, Mississippi County Extension agent.