We have defoliated some cotton in the county already. UGA Extension Cotton Agronomist Dr. Jared Whitaker discussed some points on defoliation at our field day a few weeks ago. Here is a summary of what we need to think about as we start defoliating.
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 & 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 mixtures:
Below is a chart to help with defoliation rates for the “Three Way” program:
Additional Weed Control
If weeds are present at harvest, some defoliants have herbicidal activity on plants. The table below is from the UGA Pest Management Handbook as a guide to weed control.