Harvest aids have several main functions, including crop defoliation, boll opening and regrowth suppression. A lot of logistical factors influence the timing of harvest aid application, but there are several crop indicators that give the green light for applications of defoliants, boll openers, etc.
The goal is that properly timed harvest aid applications will not reduce yield and fiber quality and will allow rapid, once-over harvest ASAP. Several methods can be used, and it is a good idea to incorporate more than one in determining the timing of these treatments.
Other methods exist, but these are straightforward and easily performed.
1. Percent Open Boll.
Sixty percent open boll is a long-accepted standard. It’s quick and easy and can be accomplished from the window of a pickup at 60 mph. Or so we think! In rank crops with dense, lingering foliage, sometimes our percent open estimates are impaired. Even so, we should be able to distinguish between 40 and 80 percent open.
More commonly, in the Lower Southeast, I often see delays until 90 percent open. We can safely go earlier than that… and SHOULD to expedite harvest. I will add that though I’ve been doing this a long time, a couple of years ago in a trial at Brewton I estimated and then actually counted open/unopen bolls.
I tended to overestimate percent open, probably because the canopy was dense and there were a significant number of lateral (2nd and 3rd position) and vegetative-branch bolls.
2. Nodes Above Cracked Boll (NACB).
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If a 1st position bolls is cracked – even partially so as to expose any seed cotton – then 1st position bolls 4 (or possibly 5) nodes above that are sufficiently mature to proceed with harvest aid application. The NACB method is simple on a plant by plant basis, and if done in an area that is representative of the entire field, it serves as an excellent decision making tool.
3. The Sharp Knife Method.
Mature, ready-to-harvest bolls are difficult to cut through even with a sharp knife. Some, for ease and safety, substitute PVC pipe cutters or small pruning shears for a good knife. A cross section cut of a mature boll typically strings out the fiber and reveals seed with well-formed cotyledons and seed coats that are yellow, tan or darker (brown to black) in color.
The seed coat color progression has similarities to the “black layer” observed in harvest-ready corn. Immature bolls have seed with jelly-like contents and seed coats that are clear in color. This technique is valuable in determining if borderline bolls are ready and confirming other timing methods.
Two additional points.
Keep in mind that we are often biased by where we walk into a field. What the cotton is like at a natural, common entry point affects how we think about the field as whole. That area may or may not be indicative of the entire field. Try to assess the overall field, and make decisions based on the large majority of the crop.
Secondly, the uppermost bolls – because of limited size or number – are sometimes not worth the wait. They may contribute very little to total yield and are prone to be riddled with late season stink bug damage. Waiting for these upper bolls puts the larger crop at risk to adverse weather and associated losses in yield and quality.