Modern chemical harvest aids are applied to induce leaf abscission, hasten mature-boll dehiscence, and inhibit regrowth (Gwathmey and Hayes 1997; Snipes and Cathey 1992). Their use can result in increased machine harvest efficiency and fewer lodged plants while reducing boll rot, the trash in seed cotton, and the time from defoliation to harvest (Benedict 1984). The challenge of using harvest aids is the inconsistent way cotton responds to them, making defoliation one of the most unpredictable management practices (Benedict 1984; Gwathmey and Hayes 1997).