Evaluation of Optical Sensors as a Variable Rate Defoliation Aid

ABSTRACT A two year study was conducted at the Oklahoma State University’s Southwest Research and Extension Center in Altus, OK to determine a prescription application rate for cotton harvest aids using the GreenSeeker® optical sensor system. A self-propelled sprayer system was modified to accommodate a six row sensor system used for measuring plant Normalized Difference Vegetation Index (NDVI). During the 2010 growing season study plots were four rows wide by 160 foot long. Predetermined prescription rates were determined and applied at two different crop maturity levels which were 50% open boll and 80% open boll, to ensure visual difference in maturity and collected data. The rates were applied beginning at 100% of a normal recommended application rate and ending at approximately 12% of the recommended rate using a log sprayer. The rates changed on approximate 30 foot intervals. Node above cracked boll (NACB) and percent open boll data were collected at five locations within the plots along with NDVI to monitor the chemical effectiveness and crop maturity. Promising results were observed from the first year of study even though the experiment was terminated due to an early frost. Similar results are expected during the 2010 growing season. A good correlation was found between the percent of defoliation and NDVI numbers. The correlation can be used to accurately predict a prescription rate of harvest aid needed based on specific crop maturity levels. The prescription equation will help to account for most of the field and crop maturity variability.