Many around the state are concerned about the limited availability of thidiazuron and how that will affect cotton defoliation in 2018. Thidiazuron (TDZ) is a key component of many cotton defoliation tank mixes and is excellent at preventing regrowth after defoliation.
Below are our thoughts and 6 suggestions:
#1. Make Plans Now
In general, we can vary rates of TDZ based on weather, potential for regrowth and amount of juvenile tissue present at defoliation.
If one were to use the three-way on their entire crop, they could budget around 2.5 to 3.0 oz of TDZ per acre of cotton and vary rates in particular situations.
A significant portion of the state’s crop was planted after June 1, so a lot of our cotton will be defoliated when conditions are cool enough where regrowth will be less of an issue.
#2. Timing is everything.
Be timely when defoliating and harvesting. Try to defoliate only what you will be able to harvest quickly and try not to leave cotton in the field for extended periods, which allows for regrowth. Without TDZ, regrowth will certainly be much more of an issue in some cases and harvesting quicker after defoliation can limit the impact of regrowth and cotton quality.
#3. Tailor rates for conditions.
Since TDZ does not cause leaf desiccation, producers can use higher rates in some places compared to others and get more out of the TDZ we have. Typically, we would suggest using more early in the defoliation season and where more green tissue is present (3 to 4 oz/A on the high end and 1.5 to 2.5 on the low end). When temperatures drop into the lower 60s at night for several consecutive days, the overall effectiveness of TDZ is limited, so we could drop it out of the three-way mix.
#4. Calibrate, calibrate, calibrate.
If your calibration is incorrect, you may be applying more product than you think. Be sure to use as much water and pressure as possible to get more out of the TDZ that you apply. Defoliants are typically not mobile in the plant. To prevent regrowth, TDZ should actually hit the part of the plant where regrowth occurs.
#5. Be prepared if you have to substitute.
The three-way is our typical standard for cotton defoliation in Georgia. If TDZ becomes unavailable, the next most effective option is usually ethephon and Ginstar (a pre-mix of thidiazuron + diuron). This application can be an extremely comparable option in most situations.
#6. Lower rates where possible.
If all else fails and you cannot get the full rates of needed product, you should evaluate individual fields for their potential for regrowth. Many factors contribute to juvenile regrowth after defoliation but fields that are at the highest risk would be high fertility fields that experienced a premature cutout due to drought stress followed by good soil moisture and warm weather at the time of defoliation and after.
More on Cotton
These crops still have some “horsepower” left and will likely need a full rate. Fields that are at the lowest risk for regrowth are fields that have a heavy boll load, used all of its available nitrogen, and have begun naturally senescing leaves. These are fields that may only require a reduced rate of TDZ.
- Use the TDZ you have wisely, if regrowth potential is low then consider rates between 1.5 to 2.0 oz/A, if regrowth is expected and there is a lot of juvenile tissue is present consider higher rates between 3.0 to 4.0 oz/A
- If no TDZ is available, mixtures of ethephon + Ginstar (TDZ + diuron) can be very effective at removing juvenile tissue and preventing regrowth. An 8 oz/A rate of the Ginstar products has 2.0 oz of TDZ (a 4 lb ai/A TDZ product) and 1.0 oz of diuron (4 lb ai/A diuron product)
- If TDZ isn’t available and Ginstar products are not used, be aware that regrowth can be more troublesome and harvest as timely as possible.
- If no TDZ is available and regrowth potential is lower, then the mixture of ethephon + tribufos (Folex) can be very effective.
- Mixtures of ethephon + PPO herbicides (ET, Aim, Display, etc.) can also be effective. However, these mixtures are sometimes less consistent than mixtures of ethephon + tribufos (Folex) and in general are more consistent later in the defoliation window.