By Rusty Mitchell
Louisville, MS
The objectives of any cotton defoliation program are to remove cotton leaves, assist in boll opening and desiccate weeds that can interfere in harvest efficacy. Timing of a harvest-aid application is determined by the crop maturity. However, crop and weather conditions, as well as harvest schedule, have to be considered.
Boll maturity is the most important factor to consider in timing defoliation applications. Minimal maturation occurs after the removal of leaves. Thus, premature leaf removal can result in reduction of cotton yield and lint quality. Late defoliation can result in increase in boll rot and lint quality loss due to weathering as well as place one in a situation where defoliant activity is inhibited by less than ideal environmental temperatures.
It is generally safe to defoliate when 55 to 60 percent of the bolls are open, and the youngest boll one expects to harvest is mature. To check boll maturity, choose the uppermost boll you intend to harvest and slice it cross-section with a sharp knife. If mature, it should be difficult to slice, fibers should string out when cut, and the seed coat should be light brown in color with the seed cavity completely filled with no jelly center. Mature bolls will also be too hard to dent when squeezed with your hand.
Another method often used to time defoliation applications is counting the nodes above cracked boll (NACB). Research has shown that at least four nodes above the highest first position cracked boll will be mature enough not to be affected by the application of a harvest aid. Thus, when the first position cracked boll is within four nodes of the last boll you intend to harvest, the field can be defoliated.
Proper harvest-aid product selection, tankmix partners and rates vary with environmental and crop conditions. Producers must take into account these conditions at the time of application when making a decision on the product(s) to be used.
To allow for the highest potential cotton yield and quality at harvest, chemical defoliants may be considered. Herbicidal defoliants, such as PPO inhibitors Aim, Display, ET, Folex and Sharpen, injure the plant and enhance leaf drop.
Factors that increase the performance of many harvestaid chemicals:
- Humid, sunny weather.
- Low but sufficient soil moisture to maintain growth of the cotton plant.
- Low soil nitrogen level.
- Minimal secondary growth.
- High percent open bolls.
- Plant that has reached cutout and began some natural shed of mature leaves. Factors that may negatively affect the performance of harvest-aid chemicals:
- Cool (below 60 F), cloudy conditions.
- Prolonged periods of wet weather following application.
- Moisture-stressed plants with tough leaves at time of application.
- Plants in vegetative state of growth due to low fruit set.
- High soil moisture and nitrogen, which contribute to rank, dense foliage and delayed maturity.
- Plants with significant regrowth following cutout.
- Poor application rates and coverage due to improper calibration levels.
Talk to your local retailer to find an effective harvest aid that fits your defoliation program.
Contact Rusty Mitchell in Louisville, Miss., at (662) 803- 9302 or rusty.mitchell@fmc.com.
