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Cotton Cutout and Termination Timings
Author: Tom Barber, Extension Weed Scientist

Cotton Status:
The 2011 Arkansas cotton crop has turned around and looks good in most counties, especially where irrigation was initiated on time and held to a fairly strict schedule. The Arkansas Agricultural Statistics Service ranks 47% of the Arkansas cotton crop in the good to excellent category, 35% fair and 18% poor or very poor.

Last Effective Bloom Date:
The last effective bloom date is the last date (based on historical weather data) that a white flower position will accumulate enough heat units to mature into a full size boll. If you look at the 30 year average temperatures for Arkansas, our last effective bloom date, which is the date based on the probability of accumulating 850 heat units through the remainder of the season, for Northeast Arkansas is August 10th using a 50% chance probability. Last effective bloom dates for the remainder of the state are August 15th for central and August 18th for Southeastern Arkansas. If we look at average temperatures over the past 5 years, these last effective bloom dates could be extended 3 to 5 days at each location, resulting in August 15th for Northern, August 20th for Central and August 23rd for Southern Arkansas. If temperatures this fall stay as high as last season, the effective bloom dates could be extended another five days at each location. Unfortunately, my crystal ball is broken, and I have no idea what September will bring.

Establishing the dates of cutout is important in identifying the last group of bolls that will contribute significantly to yield and profit. It is this group of bolls and their development on which we base our end-of-season decisions. If you have fields that will not reach physiological cutout (NAWF 5) until after the last effective bloom dates, then in most cases calendar dates should be used to determine cutout. High temperatures and steady heat unit accumulation has helped much of this cotton crop catch up with blooms coming out of the top or close to the top at a rapid pace. Early planted fields have been cutout (NAWF=5) for a week or more, and many of the later planted fields should reach cutout on or before the last effective bloom dates. Fields across the state are experiencing a heavy shed and are catching another growth spurt. These fields have been hovering around NAWF= 4 or 5 for a couple of weeks and scattered rains may have caused some fields to grow again. Monitor these fields closely for cutout to get a starting point for termination decisions based on heat unit accumulation. Manage end of season irrigation appropriately. After peak boll fill, the water requirement for cotton decreases and excess water can and will promote rank growth, especially after a heavy shed. In these cases, extending days between irrigations may be beneficial to manage end of season rank growth.

Once you know your cutout dates you can go to the University of Arkansas Division of Agriculture website and select the county where the field is located and the cutout date. The program will calculate heat the heat units received, as well as potential dates for future terminations based on 30 year average temperatures.

Termination suggestions based on heat unit accumulations past NAWF=5:

Plantbugs = 250 heat units passed cutout

Bollworm/Budworm = 350 heat units passed cutout

Stinkbugs = 450 heat units passed cutout

Irrigation = 450 heat units passed cutout

Defoliation = 850 heat units passed cutout

Please note that the above termination timings are suggestions and each field should be monitored closely before any decisions to terminate insecticide applications, irrigation or initiate defoliation applications are made.

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