There are several methods that one can use to help determine when to use harvest aids to begin defoliating cotton. Here is a brief review of the more common defoliation-timing techniques. The most widely used defoliation-timing method is based on a determination of the total percentage of bolls in the field that have opened. The most common recommendation for defoliant application occurs when the field has 60 to 70 percent open bolls.
Another method used to help determine when to defoliate cotton is the node above cracked boll (NACB), which focuses on the unopened portion of the crop. The NACB is determined by locating the uppermost first-position boll that is cracked open with visible lint and counting the number of main-stem nodes to the uppermost harvest able boll. Most recommendations suggest defoliation at four NACB. If however, you have a low plant population or skip-row cotton, research has shown that you could probably wait until you have reached three NACB, as with this type of crop more yield will be coming from outer-position bolls and bolls on vegetative branches.
The measure of accumulated heat units after cutout is yet another method one can use to help schedule defoliation. A DD60 is a measure of accumulated heat needed for growth and development using a 60-degree temperature minimum. Research has shown that defoliation could begin when 850 heat units past cutout have been reached.
Finally, cotton growers should also visually inspect unopened bolls for maturity. A boll is considered mature if it is difficult to slice in a cross-section with a knife, and seeds have begun to form a brown or black seed coat. Once the dark seed coat has formed, defoliation will not affect yield of those bolls adversely. Depending on temperature, cotton bolls need 40 to 60 days to mature.
When planning to schedule defoliations, the farm’s harvest capacity should also be considered. In general, defoliating only acreage that can be harvested within a 12-day period following the defoliation treatment will help reduce exposure of lint to weathering loss and possible grade discounts. Should weather interfere during this time frame, the regrowth will need to be controlled adding to harvest costs.
It seems that every year is different in regards to how harvest aids will react to the given cotton crop. No one harvest aid or tank mix combination is the “silver bullet” for every field and all situations. Harvest aid selection is often based on prior experience and price. Thorough canopy coverage is essential for acceptable results with all harvest aids. The carrier volumes should be between 10 and 15 gallons per acre. While higher carrier volumes are not convenient, water remains the cheapest thing that you can put in the spray tank.
I with the help of Gary Schwarzlose of Bayer CropScience established a Harvest Aid Trial this year in some early cotton to evaluate how different treatments will work with this years cotton crop. The trial is on the Claude Otahal Farm, just southeast of Robstown at the intersection of CR 69 and FM 2826 in the northwest corner. Defoliation results from this test will be posted in this blog or available in the County Extension Office.
