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Cotton Update
Author: Tom Barber, Extension Weed Scientist

According to the latest crop update released by the USDA, approximately 31% of the Arkansas cotton crop contains an open boll, well ahead of our average 5 year maturity of only 13% at this time.  Several thousand acres of cotton will be defoliated by the end of this week.  The Arkansas cotton crop was rated this week to be approximately 60% good or excellent, 25% fair and 15% poor, overall I believe we will have an above average yield for the 2012 cotton crop.  The crop as a whole continues to mature about two weeks ahead of schedule and the bulk of the Arkansas crop will most likely have the first application of defoliant by the middle of September.  This is the time of year when cotton begins to look ugly.  There is a lot of variability in this cotton crop and it has become more apparent as we move near maturity.  Potassium deficiencies, differences in plant height and maturity can be seen easily from the road.  The extreme drought and high temperatures during peak boll fill periods has made it difficult to manage this crop under irrigated conditions, especially in Northeast Arkansas.  We call it supplemental irrigation in Arkansas for a reason.  It is hard to make above average yields with cotton in years where no rain is received to replenish soil moisture and provide cooler temperatures for maximum efficiency.  Many fields under furrow irrigation are showing signs of variability due to poor water infiltration.  Infiltration can be increased by watering down every middle vs. every other in most cases if well capacity is strong enough.   Tight compaction layers have been observed in many situations, and roots are not able to penetrate to search for moisture or nutrients.  In many fields where pottasium deficiency has been observed, the soil tests for K have been in the high range.  The problem in most cases is either the health of the root system, or the lack of moisture (water penetration) to move the potassium into the root zone.  It will be important to monitor these fields where the variability or symptoms are showing up for nutrient and nematode sampling following harvest.  Nematode populations can also be to blame in many fields for variability in plant heights and nutrient issues.  Deep tillage following harvest, may eliminate many of these problems for next spring and should be focused particularly on these problem fields first.  Fields where bacterial blight is identified should be cultivated following harvest prior to the deep tillage to bury residue containing the bacteria.

Most of the cotton has reached a point where we no longer want to spend money on insect protection or irrigation.  For the few acres that have still not reached cutout (NAWF =5), the last possible day to mature a bloom based on the last five year average temperatures is August 15th for Northeast, August 20th for Central and August 23 for Southeast Arkansas.  The majority of the cotton has cutout well before these dates.  Termination timings for insects and irrigation past either the physiological cutout or the calander cutout date are:
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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