There have been several questions lately about how to defoliate a drought stressed crop, and questions about appropriate tankmixtures and rates to use. Below is some information to help address these questions.

Defoliating a Drought-Stressed Crop:

In general terms, most of the early planted crop is rather mature at this point. Dry weather since mid/late August in many areas has caused several potential upper young bolls to shed, therefore the current uppermost harvestable bolls are fairly mature. Of course, this varies from region to region and from field to field, based on soils and perhaps some rainfall during this time. Even some later planted cotton is rapidly approaching maturity due to dry weather. Although we couldve benefited from a little rain during this time, we have also had really nice weather for boll opening when compared to some Septembers that were cloudy and wet (which leads to severe hardlocking).

Drought stressed cotton can be both primed for defoliation or resistant to it, depending on how you view it. Leaves are fairly depleted and photosynthetic activity is reduced, which can be seen from the color changes from green to reddish/yellow/brown. In this sense, it is primed for defoliation as ethelyne is likely building up in the leaves, however, these leaves also usually have a thicker cuticle which can make it somewhat resistant to defoliation. Several folks have inquired if defoliant rates should be increased or decreased to adequately remove leaves from drought stressed cotton. Typically we advise to stay with recommended tankmixtures (and rates of defoliants) that are suitable for prevailing temperatures and crop conditions. Based on past experience with drought stressed cotton, slightly reducing rates can lead to insufficient defoliation, whereas slightly increasing rates can cause desiccation (leaf sticking). Both of these outcomes can occur even when using rates appropriate for prevailing temperatures, making defoliation of this crop even more tricky and unpredictable. The best advice we can provide is to stay within normal rates for current temperatures, avoid defoliating in hot, humid conditions (88-90 degrees or higher), and try to defoliate when you have sunny conditions for at least a day or two. Avoid using additives unless they are necessary for the tankmixture or conditions (rain expected withing 24 hours when relying on TDZ in your tankmixture, for example). A little rainfall can drastically change the course of drought stressed cotton, so hopefully we’ll get some soon.

Short-term weather outlook:

Several folks have asked about tankmixtures that rely on TDZ for regrowth control. There is very little regrowth currently on plants, but keep in mind that this crop is rather mature. This means that once we do get a little rain, the crop has little to no demands to fill and will therefore cycle around and generate regrowth. So even though there isnt much visible now, a little rain can easily trigger it once we defoliate, so be prepared to address it.

For this week, temperatures are expected to be in the mid to upper 80’s with nighttime lows well into the 60’s. Tankmixtures that utilize TDZ (Dropp, FreeFall, others) can be very effective in these temperatures. A couple of common tankmixtures that come to mind include:

Finish 1 qt/A (can add up to 10 oz ethephon for enhanced boll opening) + Folex 4-6 oz/A + TDZ 3.2 oz/A

– or –

Folex 10-12 oz/A (8 oz/A in high temperatures) + ethephon 1 qt/A + TDZ 3.2 oz/A

Given how mature most early planted cotton is, and how progressed boll opening has been, the Finish tankmixture may not be necessary this week with warmer temperatures, but it will certainly still be effective. In warmer conditions, this tankmixture can accelerate boll opening so that harvest can occur sooner, so be sure to take advantage of those few extra days if you decide to use this tankmixture. For example: At 7-10 days after defoliation, the Finish tankmixture will likely have an advantage for boll opening, however, by 14 days after defoliation, we would expect boll opening of a mature crop to be very similar between these two tankmixtures.

When looking beyond this week, current forecasts are calling for another cool-down, with highs in the 70’s and lows in the 50’s. For the early planted, or otherwise very mature cotton, regular ethephon tankmixtures will likely remain to be effective for boll opening. If there are any fields with somewhat less mature upper bolls (later planted, irrigated, or happened to have rainfall since late August), or if you are anxious to harvest a little sooner, a Finish-based tankmixture is likely to be more appropriate in those temperatures. Likewise, when days are relatively cool and nighttime lows are down into the 50’s consistently (especially below 55 degrees for several days), TDZ may not be sufficient for addressing regrowth. Therefore, switching to a TDZ+diuron mixture (Ginstar, Adios, CutOut, others) may be needed to adequately address both defoliation and regrowth control. TDZ will still have activity in those temperatures but it will be noticeably slower, and if any rains trigger regrowth, it may be insufficient. Tankmixtures that come to mind for this scenario might include the following:

Finish 1 qt/A (can add up to 10 oz ethephon for enhanced boll opening) +  (TDZ+diuron 6.4 oz/A)

– or –

(TDZ+diuron 8 oz/A) + ethephon 32-42 oz/A

In most years, these tankmixtures are also effective in temperatures that are forecasted for this week. However, given the degree of drought stress we are observing, along with a couple of days of near-90 degree temperatures, we should probably avoid using a TDZ+diuron tankmixture this week. Forecasted temperatures for next week are much more appropriate for these tankmixtures, given the current drought stress in several areas. This is all based on current forecasts, which often change. Therefore it is imperative to evaluate fields independently and consider current forecasts when making product selections. There are always exceptions to these cases, and there are other tankmixtures that can be used. Feel free to contact us to discuss this and we’ll be happy to help you.