Abstract
Effective methods are needed for timely areawide detection of regrowth cotton plants because boll weevils (a quarantine pest) can feed and reproduce on these plants beyond the cotton production season. Airborne multispectral images of regrowth cotton plots were acquired on several dates after three shredding (i.e., stalk destruction) dates. Linear spectral unmixing (LSU) classification was applied to high-resolution airborne multispectral images of regrowth cotton plots to estimate the minimum detectable size and subsequent growth of plants. We found that regrowth cotton fields can be identified when the mean plant width is ∼0.2 m for an image resolution of 0.1 m. LSU estimates of canopy cover of regrowth cotton plots correlated well (r2=0.81) with the ratio of mean plant width to row spacing, a surrogate measure of plant canopy cover. The height and width of regrowth plants were both well correlated (r2=0.94) with accumulated degree-days after shredding. The results will help boll weevil eradication program managers use airborne multispectral images to detect and monitor the regrowth of cotton plants after stalk destruction, and identify fields that may require further inspection and mitigation of boll weevil infestations.
Highlights
Boll weevil eradication programs have effectively eliminated weevil populations throughout all temperate regions of the United States Cotton Belt
There were no significant differences of mean plant height (F 1⁄4 0.61; df 1⁄4 3;12; p 1⁄4 0.6214), plant width (F 1⁄4 0.53; df 1⁄4 3;12; p 1⁄4 0.6698), red (F 1⁄4 0.07; df 1⁄4 3;12; p 1⁄4 0.9745), green (F 1⁄4 0.04; df 1⁄4 3;12; p 1⁄4 0.9897), blue (F 1⁄4 0.03; df 1⁄4 3;12; p 1⁄4 0.9911), or NIR (F 1⁄4 0.03; df 1⁄4 3;12; p 1⁄4 0.9911) reflectance, Green NDVI (GNDVI) (F 1⁄4 0.34; df 1⁄4 3;12; p 1⁄4 0.7958), or normalized difference vegetation index (NDVI) (F 1⁄4 0.35; df 1⁄4 3;12; p 1⁄4 0.7892) between plots on the pretreatment date of 29 June
Our results show that the mean width of regrowth cotton plants is highly correlated with degree-day (DD15.6°C) accumulations regardless of the shredding date
Summary
Boll weevil eradication programs have effectively eliminated weevil populations throughout all temperate regions of the United States Cotton Belt. The mandatory and timely elimination of cotton plants following harvest and subsequent creation of a host-free period has been deemed critical to the success of eradication programs. Cotton plants may regrow from shredded stalks following harvest, and subsequently provide weevils with a year-round source of food and host for reproduction. Detection of regrowth cotton plants, which can serve as hosts for boll weevils during and beyond the production season, is critical for completing eradication in South Texas. Timely detection of regrowth plants is a challenging process given the expansive cotton production areas. Regrowth plants occurring in the middle of large fields are difficult to detect because such plants are not readily apparent from turn rows or roadsides
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