There is economic incentive to harvest the crop as soon as possible without sacrificing yield or quality. Under some conditions, it may even be advisable to sacrifice a little yield potential to get started with harvest and avoid potential grade losses due to later inclement weather. Development of quantitative procedures to schedule the application of harvest aid chemicals can provide growers the necessary information to optimize their harvest schedule. The age relationship among bolls on the plant can be established through plant map techniques now practiced in many areas of the U.S. With support from The Cotton Foundation, University cotton scientists in four states initiated collaborative studies in 1990 to develop plant based guidelines for application of harvest aid chemicals. The impact of defoliation on boll size and fiber quality for nodes 1 to 8 above a first position cracked boll was determined.

Averaged over states, boll size decreased an average of 6.68 percent for each node above cracked boll (NACB) above the value of 2.81. The impact of premature defoliation had a similar effect on micronaire. Micronaire decreased an average of 5.90 percent for bolls at NACB positions greater than 2.69. Data from the different states was more variable for micronaire than for the defoliation effect on boll size. The average potential yield loss from early defoliation was calculated using the state average for boll size reduction and assuming yield came from 12 fruiting branches with yield distribution as published by California. Potential percentage loss in yield by defoliating at various NACB was determined.