The growing season is winding down and growers are faced with the decision on when they can stop spraying for insect pests without experiencing yield loss. Extensive research has been conducted in the past on terminating insecticide applications in cotton based on crop termination. Cutout is reached in cotton when the number of nodes above the uppermost white bloom on the first position is equal to five (NAWF=5). When a field reaches this point, we can begin keeping track of the number of heat units that are accumulated based on a DD60 model (DD60s are calculated by subtracting 60 from the average daily temperature).
Crop termination recommendations are based on long-standing and ongoing COTMAN research conducted by University of Arkansas Systems Division of Agriculture scientists. Date of Cutout is the flowering date of the last economically significant boll population. If a field reaches physiological cutout [average number of nodes above white flower = 5 (NAWF = 5)] in late July or early August in Arkansas, then heat units are accumulated from the NAWF = 5 date. Otherwise, heat units are accumulated from a seasonal cutout date based on historical weather for that production region. Typically, a boll needs 850 DD60s to mature with acceptable size and quality.
The weather-restricted, seasonal cutout date is the calendar date on which there is a 50% probability that the crop will have the benefit of late season temperatures sufficient to develop a mature boll. Seasonal cutout dates range across the state from Aug. 8 in northernmost parts of Arkansas (Clay County) to Aug. 21 in the most southern portions of the state (Ashley County).
Termination rules vary depending on the insect pest and are shown below:
|Tarnished Plant Bug||Cutout + 250 DD60s|
|Bollworm & Tobacco Budworm||Cutout + 350 DD60s|
|Stink Bug||Cutout + 450 DD60s|
|Fall Armyworm||Cutout + 500 DD60s|
“This work is supported by the Crop Protection and Pest Management Program [grant no. 2017-70006-27279/project accession no. 1013890] from the USDA National Institute of Food and Agriculture.”