Some good cotton defoliation advice from Curtis D. Fountain, Duplin County Agricultural Extension Agent – Field Crops
Much of the 2014 Duplin Co. 7,537 acres cotton crop is planted on sandy soils. Due to seasonal rainfall amounts/frequency, most root systems are relatively shallow. Seasonal conditions have promoted mature leaves. Seasonal conditions should also lessen regrowth potential.
The above may not be true for cotton planted on better nutrient/water holding capacity soils. Remember remaining soil nutrients (particularly nitrogen) will promote juvenile growth (new leaves prior to defoliation) and regrowth (new leaves after defoliation) if moisture/warm temperatures exist. Consider and group fields accordingly as you develop your cotton defoliation/harvest strategy.
For large acreage/timely harvest situations, it is best to group/defoliate fields during desirable weather intervals rather than defoliate the entire acreage at one time. Defoliating the entire acreage at one time places greater risk on desirable weather conditions for the selected time period. Soon after defoliation if the weather forecast abruptly changes, more acreage may require retreatment. Also after successful defoliation, a total acreage crop exposed to weathering for an unknown, significant time period is not desirable Remember from a yield/quality standpoint, a cotton boll is the best it will ever be the day it opens. Extended weathering reduces yield and quality.
There are many boll opener/defoliation/regrowth prevention brand products available. In most cases, there is more than 1 product or combination of products that will achieve satisfactory results. Focus on weather forecasts, plant condition, harvest timing, and product(s) costs when selecting product(s). Please refer to NCSU 2014 Cotton Information pages 137-155 for additional information.
Two techniques are suggested to determine defoliation field readiness. Fields with 2-3 plants per row foot can be safely defoliated when the topmost 1st position harvestable boll is 4 nodes or less above the 1st position cracked boll. A cracked boll is defined as a boll with some visible lint but not enough for spindle grab. This nodes above cracked boll (NACB) technique considers the unopen portion of the crop and is based on the fact that a high percentage (85% or more) of late season bolls are set at the 1st position. For fields with a significant percentage of harvestable late bolls (bolls present on vegetative branches or outer positions of fruiting branches), a NACB of 3 may be more appropriate.
Harvestable bolls that are not open can be cut to determine maturity. Mature bolls are not damaged due to defoliation. Mature bolls are defined as 1) hard bolls that are difficult to cut in cross section with a sharp knife, 2) bolls that string fiber when cut, and 3) when observing a boll cross section, the seed cavity is completely filled (there is no gel within the seed cavity).
Weather & Spray Coverage Important
Preferred defoliation weather conditions are sunny, warm, high humidity days. If possible, apply defoliants when the expected average temperature will exceed 65 degrees F for at least 3 days following treatment. Ideally, defoliants should be applied 10-14 days prior to anticipated harvest for optimum lint weight and quality.
Since defoliants are not translocated, good spray coverage is essential. For ground applications, 15-20 gallons/acre of spray solution should be applied at 40 psi (or higher) using flat fan nozzles.
First defoliated cotton that will be picked 10-14 days after treatment should not require regrowth prevention. First defoliated cotton will likely require a boll opener to hasten unopen boll opening and defoliation.
Second defoliated cotton may require regrowth prevention. Warm temperatures, good soil moisture, and remaining soil plant available nutrients will promote regrowth of cotton. Remember cotton is a perennial plant. Since harvest timing is less certain, regrowth prevention is more important.
Final defoliated cotton (defoliated mid-October or later) should not require regrowth prevention. Cotton defoliated in mid-October should be ready to harvest at the end of October. Typically the end of October brings cooler temperatures and frost, unfavorable conditions for regrowth.