As we roll into October, it is time to start thinking about defoliating and harvesting our cotton crop. There are a few things I have been talking about as I venture around the state talking about defoliation, and some of the high points are below:
- Make sure the defoliation “trigger” is pulled at the right time. There are many ways to determine the appropriate time to defoliate your cotton crop – 60 to 75% open boll, 4 nodes above cracked boll (NACB), and the “sharp knife” method. It’s always good to use two methods to determine the correct timing as a way to double check yourself. To determine % open boll, count the number of open bolls, the number of unopened (harvestable) bolls, divide the number of open bolls by the total bolls and multiply by 100. For NACB, count the number of nodes from the uppermost first position cracked boll to the uppermost first position harvestable boll. When that number is 4, on average you are good to pull the trigger. And lastly, for the sharp knife method cut into the uppermost boll you intend to harvest and look for a black seed coat with developed cotyledons inside, and you want the lint to string out.
- Make sure you are using the correct products and rates to accomplish your intended goals. There are 3 main goals in defoliation – leaf removal (juvenile and mature leaves), regrowth prevention, and boll opening. Determining which goals you are trying to accomplish, as well as the environmental conditions surrounding defoliation, will assist in the decision on products and rates. For regrowth control and juvenile leaf removal, thidiazuron containing products will be needed in the tank mix. Thidiazuron alone is available under many trade names (Dropp, Freefall, Klean-pik, etc.), and there is also a premix of thidiazuron + diuron (Ginstar, Cutout, Adios, etc.). Mature leaf removal can be accomplished with a number of products. The main one utilized in Georgia is Folex (tribufos), but there are a number of PPO inhibiting herbicides that can be utilized as well (Aim, ET, Sharpen, Reviton, Display, Blizzard, Resource). Lastly, your boll opening products contain ethephon. Whether it is ethephon alone (Boll Buster, SuperBoll, Setup, etc.), ethephon + urea sulfate (Cotton Quik, First Pick), or ethephon + cyclanalide (Finish), these will all open bolls.
The most common tank-mixture utilized by Georgia growers includes thidiazuron (Dropp), tribufos (Folex), and ethephon (Prep). Below is a table to assist in rate selection for each product from early to late season.
For ethephon and tribufos, as the season progresses and it gets cooler, rates should increase to get the desired effects. Whereas once we get to the end of the season, thidiazuron is removed from the tank-mix because as it gets cooler outside there is a lower risk of regrowth. Keep in mind that you can substitute tribufos for any of the aforementioned PPO inhibiting herbicides, and I would follow the same trends with rate selection (lower rates when it’s warmer outside, increase as it gets cooler). Recommended rates on each product discussed here throughout the season can be found beginning on page 143 of the 2023 UGA Cotton Production Guide, which is at the following link: http://www.ugacotton.com/production-guide/. Also, I will be in constant contact with our UGA County Extension agents throughout defoliation and harvest season, so if you have questions about products or rates feel free to reach out to your local UGA County Extension Agent.
- Mo’ water is mo’ better. A higher sprayer output (gallons per acre) works better than a lower sprayer output with respect to defoliation (even if you decide to use dicamba nozzles). Let’s shoot for 15 GPA if you’re defoliating with a ground rig to get defoliant down in the canopy.
- KEEP DEFOLIANTS ON TARGET!!!! I have talked about this a lot in the last few years. It is imperative that we apply all pesticides responsibly, let’s not forget that at the finish line. Keep the lessons from Using Pesticides Wisely trainings at the forefront of your mind as we apply all pesticides, including defoliants. Keep in mind what is around your fields, the wind speed and direction at the time of and after application, keep the spray booms 24” above the crop canopy, and use nozzles that produce larger droplets with a higher spray output. It is important from the aspect of reducing pesticide drift in general, but also from the standpoint of protecting the chemistries we use.
- Timely defoliation and harvest are key to producing a high quality crop. Only defoliate what you can come back and harvest in about 10 to 14 days. This helps preserve crop quality and can reduce the likelihood of an extraneous matter call. And speaking of extraneous matter, handle your modules carefully and be sure to get grocery bags/balloons out of your field prior to harvest to reduce the likelihood of plastic contamination. It’s a 2X deduction from the classing office and our friends at the gin don’t like plastic. Let’s do our part to reduce plastic contamination.
I hope that everyone has a safe and prosperous defoliation and harvest season. As always, if you ever have questions or need anything please don’t hesitate to reach out to your local UGA County Extension Agent. They, along with us specialists, are here to help!