As we wrap up grain harvest, it is now time to prepare our cotton crop for harvest. To be successful in preparing our cotton for harvest we need to consider when to schedule defoliation, have good removal of foliage while at the same time facilitate boll opening and then schedule harvest operations. Along with all of that, we need dry, sunny weather.
Growers have several methods 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 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, 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 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. Locally, in a few cotton fields I have been monitoring this year, planted the last week of March and reached cutout from June 23 - 27, 850 heat units past cutout will be reached by the end of this week and the beginning of next week.
Finally, cotton growers should 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 adversely. Depending on temperature, cotton bolls need 40 to 60 days to mature.
When planning to schedule defoliations, the farm’s harvest capacity also should 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, regrowth will need to be controlled, adding to harvest costs.
Every year is different in regard 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.
With all of the rain recently, one could classify our cotton as “rank,” meaning we have an ample supply of good foliage on the cotton plants with a dense leaf canopy. Coverage with the defoliant product is challenging. A common mistake is to increase rates in an effort to achieve better defoliation. However, increased rates are likely to cause leaf desiccation at the top of the plant because most spray solution is intercepted there. In rank situations, the best approach is to apply normal rates, keeping in mind that a second application is likely to be necessary. Rank cotton is generally more expensive to defoliate than normal cotton. However, if a good job is done on the first application, the second application may not require the high rates or complex tank mixes. Additionally, a boll opener can be more effective if added to the second application.
I am planning to establish a Harvest Aid Trial again this year in some early cotton to evaluate how different treatments will work with this year’s cotton crop. Plans are to establish the trial on the Claude Otahal Farm, just southeast of Robstown at the intersection of FM 892 and FM 2826 in the southwest corner. Defoliation results from this test will be posted on our web site at http://nueces-tx.tamu.edu/pubcat.cfm?COUNTY=Nueces&CatID=2757