Use of Optical Sensors to Evaluate Dicamba Injury to Cotton

A technique was evaluated to assess dicamba herbicide damage to cotton using normalized difference vegetation index on plots treated with a continuously diluting logarithmic sprayer application of dicamba. Five applications were made from early squaring to late bloom, and geo-referenced NDVI readings were taken. Plots were replicated three times in 2008 and four times in 2009. Plots were harvested with a commercial picker equipped with a yield monitor. Dicamba injury to the cotton resulted in reduced yield in all treatments, the magnitude of the loss depended on growth stage at the time of application and concentration of dicamba. In 2008, yield reduction at the full rate of dicamba ranged from 22 to 98 percent. Correlation between yield and NDVI measured with sensors varied.  In general, the correlation was greater for plots with early dicamba application when sensing was completed within 45 days of application.