Defoliating Drought Stressed Cotton
I would rather poke my self in the eye with a tobacco stick than talk about defoliating drought stressed cotton. In drought stressed situations, growers are looking at a difficult defoliation situation with a limited budget. There generally no good answers to offer for defoliation in this situation. Sometimes we forget that probably the best condition for easy defoliation is to have a good boll load.
High micronaire: We often see high micronaire in dry years as the less mature fruit are shed during stress. The less mature fruit have lower micronaire, and when we lose them we are left with the older fruit that tend to have higher micronaire. There are only two things I can think of to do to manage micronaire. One is to defoliate on time and not allow the least mature bolls to become overly mature (black seed coats). The problem is that a lot of the cotton will be ready at one time and if we defoliate it all to stop the upward drift of micronaire values we will be faced with tremendous regrowth. Therefore, I think this is only of value to the portion of the crop that will be harvested first.
The other option is to let the crop try to make a top crop. I donít think I would try this on my entire crop. A conservative recommendation would be to not do this at all. Because defoliating everything at once is not a good option I might keep an eye on some fields to see how viable this option might be. First I would defoliate the better cotton and keep an eye on my worst cotton. Notice if it has started to set any new fruit. For squares developed now, we need to have 2 months of good weather to mature and open the bolls. That is of course a big gamble, but one I might consider on the sorrier cotton if it does, or has already started to set new fruit.
Regrowth: We expect to see significant regrowth in a dry year because the plant will find residual Nitrogen and have little boll load to invest in if moisture returns. I had someone ask me why they hadnít seen any regrowth yet with some of the recent rains? Cotton root development stops during bloom as the plant turns it attention to boll fill. In a drought the root systems actually die back some. Once the rains return it often takes a little time but they will start to grow again and will find unused Nitrogen.
It is easier to prevent regrowth than to take it off. I would lean heavily on Dropp or other products that contain thidiazuron. In general, I would depend more on Dropp (thidiazuron) than on herbicidal defoliants in order to get enough thidiazuron in the plant to help deal with regrowth. This means the standard high rate of 0.2 pounds of Dropp 50 WP that many of us are familiar with, as the higher rate will maximize regrowth activity. This is equal to 0.1 pounds of active ingredient per acre or 3.2 ounces of product of the 4 SC formulations of either Dropp, Freefall, or thidiazuron. If you use a product with a thidiazuron plus diuron mixture, such as Ginstar, you need to be aware that if you apply a high enough rate to get the 0.1 pounds active ingredient of thidiazuron you will very likely stick leaves. The best choice for this product is probably to apply the rate of Ginstar appropriate for the temperatures at the time of defoliation and to spike that with addition thidiazuron to bring the total thidiazuron in the mixture up to 0.1 pounds active ingredient of thidiazuron.
New Defoliants: Most of us have had some experience with Aim and ET by now. Both of these products are PPO-inhibitors that have herbical type activity. Blizzard and Resource are two new defoliants that are also PPO inhibitors and are similar to Aim and ET. Blizzard rates range form 0.5 to 0.6 ounces per acre while Resource rates range from 4 to 6 ounces. With Resource, add a NIS at 1 qt per 100 gal of spray solution. Under dry or cool weather, a methylated seed oil (MSO) or organosilcone adjuvant may be used. The Blizzard label states that a crop oil concentrate or surfactant should be added to mixtures containing Blizzard. Both products can be used in mixtures ethephon based products. Like any herbicidal defoliant, they will tend to release regrowth and should be used with thidiazuron where regrowth is expected to be a problem.