Cotton defoliation is a sensitive process. For a successful harvest, defoliation must be carefully timed and carried out. Poor defoliation can lower fiber quality, while defoliating too early lowers yield and micronaire. Late defoliation increases the likelihood of boll rot and lint damage or loss due to weathering. Late defoliating also increases the possibility that defoliant activity will be inhibited by lower temperatures
Three ways to determine crop maturity and defoliation timing:
- 60% to 75% open bolls (only 60 for uniform crop).
- Sharp knife – cotton strings when boll is cut, seed are fully developed (brown coat and cotyledons).
- NACB – 4 or less (around 3 days per node). There is often a relationship between percent open bolls in the canopy and the number of nodes between the uppermost first position cracked boll and uppermost first position harvestable boll (NACB).
Most harvest aid materials do not translocate or move very far within the plant. Therefore, application coverage is important. To ensure adequate foliar coverage use the proper spray pressure, ground speed and nozzle size in order to apply the desired spray volume in accordance of label instructions.
WATER VOLUME CAN SIGNIFICANTLY IMPACT OVERALL PERFORMANCE, THE MORE WATER THE BETTER (SHOOT FOR 15 GPA).
The wind damage from tropical system last week may make defoliation with ground sprayers a challenge for area cotton growers.
Rainfall occurring after applications can affect defoliant activity. Be sure to consider weather forecasts when making applications and pay attention to rain-free periods of particular products. Thidiazuron is of particular concern, since it requires a 24 hour rain-free period. Below is a chart of rainfast periods of cotton defoliants.
Three Way Defoliation Mixtures:
I have been getting numerous questions about defoliation rates especially for the “Three Way.” Below is a chart that will answer some of these questions..
In cases where weeds are present at harvest, some cotton defoliants are products that have herbicidal activity on particular pests. See the table below from the UGA Pest Management Handbook for specific recommendations.