By James Griffin
Cotton Extension PhD. Student
Applying cotton harvest aids has been referred to as an art. In this article, we will examine methods to change the narrative to more of a science. The first decision to make is when to “pull the trigger,” secondly rather to make one or two applications, and finally which products to use. From my experience, the 60% open boll method has been the standard for some time although other methods are most likely more accurate than eye balling percentage open while driving down the turn row. Furthermore, the percentage open boll method does not always accurately represent maturity of cotton plants as boll positioning or fruiting gaps sites can potentially be misleading. Finally, research has shown applying harvest aids prior to 60% open bolls can reduce yield.
Two other popular methods are maturity of uppermost harvestable boll which consists of cutting bolls in half and looking at seed coat coloring (Figure 1). Seed coats with tan to brown coloration are mature and are primed for boll openers. The last method is nodes above cracked boll (NACB). When using the NACB methods, first locate the uppermost first position cracked boll, and then count the main stem nodes above up to the uppermost harvestable boll. Sufficient research has shown that harvest aids applied at four NACB will not result in any lint weight loss. If harvest aids are applied at NACB greater than four, yield loss can be expected.
The second decision is the number of harvest aid applications. This decision is based on the stature of the plant meaning larger, ranker plants generally need an additional shot to removed lower vegetation sometimes referred to as the “skirt.” A two pass program is more desirable than an aggressive rate one pass program that requires a second pass. In a two pass system, as much vegetation should be removed as possible to reduce lint staining and trash, while minimizing desiccation or “sticking” leaves, which is due to defoliants “killing” the leaves before a proper abscission layer can be from at the base of the petiole. A general rule of thumb is to use lower harvest aid rates to injure the leaf, but not desiccate it. The final decision is which harvest aid program to apply. Successful harvest application is affected the most by the condition of the cotton plants, namely the fruit load, available nutrient supply, water stress/excess, among many others. Drought stressed cotton may require higher rates due to thickened leaf cuticle. Harvest aid selection is also determined by how quickly a producer wants to begin harvesting. Along those lines producers should not apply harvest aids without intentions of harvesting within 14 days or lint values can significantly be reduced beyond this timeframe. In other words, do not get ahead of yourself with the sprayer. Potential weather delays and general timeliness between harvest aid application and harvest may factor into the decision to add a regrowth limiting product such as thidiazuron. Table 1 below shows each labeled product. One final note is to ensure adequate spray coverage, as most harvest aids do not translocate throughout the plant. Harvest aids should be applied with a minimum water volume of 15 GPA. Recent research has shown, water volume has a greater significance than nozzle type, with that said, the recommendation is to still use flat fans or hollow cone nozzle tips.
|Harvest Aid1||Active Ingredients||Labeled Broadcast rate oz/ac||Max use/ Season (oz)||Rainfree Period (hours)||Estimated min. temp (F)2||Mature leaves||Juvenile growth||Re-growth prevention||Boll opening|
|Finish 6 Pro||Ethephon +
|FirstPick||Urea sulfate +
Table 1: Harvest Aid options and Anticipated Performance
1Adjuvants may increase harvest aid performance during low night temperatures or when cotton is drought stress, although when temperatures are warmer, adjuvants increase chances of vegetative desiccation or “sticking.”
2Estimated temperatures are estimates only and are not exact. Conditions such as rain free period, crop stress (drought), temperatures, and remaining nutrient levels also affect product performance.
3Glyphosate performance rating only for non-glyphosate traited varieties
4This is a brand name and many products containing the same active ingredient are available
5Sharpen requires 1% v/v MSO plus ammonium-based adjuvant according to label
6Usage of paraquat inhibits development of immature bolls; rates depend on open boll percentage
Source: University of Tennessee Extension, “Cotton Harvest Aids” Drs. Chris Main and Robert M. Hayes
This table listing does not indicate an exclusive endorsement of these products alone. Table 1 is not a complete list of products in the market place, as other products are available and may be comparable. Always read and follow labeled rates for your area.
Cotton Harvest Aid Recommendations, Texas A&M-San Angelo:
Preparing for the 2015 South Texas Cotton Harvest:
Cotton Harvest Aids, University of Tennessee:
2014 Cotton Harvest Aid Guidelines for Louisiana: