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Deciding when to make harvest aid applications can be difficult. Without implementing practices to protect quality and yield losses from poor weather conditions, the value of the crop can be quickly reduced. Timely harvest aid applications can promote an earlier harvest and help preserve fiber quality. Any delays in harvest, even with timely harvest aid applications, can have an adverse effect on both the yield and quality of lint.1
There are two types of defoliants available to use as harvest aids. The first type has herbicidal activity, which works by causing injury to the plants, resulting in the production of ethylene. Ethylene production triggers leaves to drop. If the herbicidal defoliant is applied at rates too high, the leaves may die too quickly, bypassing ethylene production and causing the leaves to remain on the plant (leaf stick).The second type of defoliant has hormonal activity, which promotes ethylene production in the plant, leading to leaf drop. Hormonal defoliants can be less susceptible to leaf stick than herbicidal defoliants.2
Drought-stressed cotton may have thick leaf cuticles which can reduce the efficacy of harvest aids, and the addition of a surfactant may be necessary. Cotton that has rank growth can require two defoliant applications due to the thick canopy preventing complete coverage. Increasing the application rate is not effective because a higher rate is just as unable to penetrate the canopy as a normal rate.2 Selecting flat-fan or hollow-cone nozzles coupled with a carrier volume of 15 gallons per acre can help maximize canopy coverage.3
Harvest aids work best when average temperatures remain above 60° F. Lower temperatures can slow leaf drop and boll opening. Fall harvest aid applications made in the cooler temperatures of late fall can reduce the defoliant efficacy and increase the potential for quality losses due to cool, wet, late-season weather. Delays in defoliation can push back harvest dates and result in significant yield and quality reductions from delayed harvest timing. Fiber length, strength, and color can be affected, resulting in lower lint loan values and net returns per acre. Timely harvest also allows more time for cotton plant residue/stalk destruction. Plant decomposition is an essential part of insect and disease management.
After harvest, the seed cotton must be protected from the elements until it is ginned. To help protect cotton during storage, cover rectangular modules with a high-quality tarp. Tarps should be checked for any tears or pin holes before use. Round bales should be wrapped with plastic that covers the cotton that is most exposed to the weather (Figure 2). A later harvest may result in excess moisture content that can cause condensation; therefore, modules and bales should be monitored.When elevated moisture content levels occur, temperatures can increase within the module potentially reducing lint grade and seed germination. Extreme cases may result in spontaneous combustion. Ideally, cotton harvested at correct moisture content levels should only increase 10 to 15° F in the first 5 to 7 days of module storage, then level off or decrease in temperature. A 15 to 20° F temperature increase during the first 5 to 7 days indicates a high moisture content problem and the module should be ginned as soon as possible.3 After the initial daily temperature check, modules should continue to be checked every 3 to 4 days. If at any time during storage a module reaches a temperature of 120° F, the cotton should be ginned immediately.
Cotton pickers are very large, complex, and expensive pieces of equipment. Heat from the unit combined with dry debris and lint can easily cause a fire within the unit and in the field. These simple tips can prevent or help in the event of a fire:4