Cotton Defoliation Update For October

DR. TYSON RAPER

JACKSON, TENNESSEE

We are close to the end but a few still have acres left to defoliate.  Others are considering applying another application to remove small amounts of leaf.  Generally, most all of the harvestable bolls are open.  Yields are off, in many areas considerably more than expected.  At this point, we need to consider what we have in the field and what we might gain from another defoliation application.  Most acres loosely break out to either 1,000+ lb per acre  or far less than 1,000 lb per acre.  The approach on these fields should generally be different. In this blog, I make a few comments and give a couple of examples of the best approach to wrap up 2025.

In both of these scenarios, if all harvestable bolls are open, save the money you were going to spend on ethephon.  It should also be pointed out here that many of the small bolls in the top of the canopy did not have the moisture they needed to fully develop and are probably not going to be harvestable, even if you open them.  Before applying, identify the uppermost harvestable boll and make the assessment on whether the couple of dollars you were going to spend on ethephon is really needed.

1,000 + lb acres

On very good ground which received timely rains OR irrigated ground, a first and second application of defoliant (if needed) will likely provide a return on investment.  From this point forward, expect no activity from thidiazuron or thidiazuron containing products.  Instead, lean heavy on tribufos (Folex) for the first application and on a PPO for a second application.  Again, thidiazuron should not be applied moving forward- you can put it in the tank or keep it on the shelf, the plant response will be the same. Folex does not have great activity on juvenile leaves at low rates, but as we up the rate activity increases.  If we are between 52F and 60F for four consecutive nights after the application, I’m running 8 oz of Folex.  This rate will likely not be hot enough to remove all juvenile leaf, but it should pick up most of it.  If temps creep below 52F for several consecutive nights, my Folex rate is going to 10 oz per acre.

Many may choose to use a thidiazuron plus diuron combo in this window.  Keep in mind all the lifting in that pre-mix is going to be done by the diuron, not the thidiazuron- again, at these temperatures, the activity generated by thidiazuron is extremely low.

After the initial application, the amount of leaf remaining should be assessed.  If there are very few large, mature leaves and not many juvenile leaves, I would seriously consider picking through it.I’ll cover more on this below.  If there is enough leaf remaining to justify the application, rates of PPOs should increase as night temps decrease and adjuvant should shift from 0.25% NIS v/v to 0.5% COC v/v to 1% COC as we move from mild to cold to very cold, respectively.

Less than 1,000 lb cotton 

Many are looking at the lowest yielding cotton they’ve had since 2012, if not since 2007.  On those acres, I would do my best to make a yield estimate before making any other decisions.  A $15 per acre application on cotton that is 480 lb must provide a 3 cent per pound benefit.  Most all of our applications moving forward will cost more than $15 if we include the application cost.

My point- while the first application will most likely provide greater than a 3 cent per pound benefit, it is very possible that the second application may not provide a return on investment on poor groundUnless a considerable (15% plus) amount of leaf remains on the plant, I’m going to skip the second application and pick through the leaf.

I want to add another point here to support this approach.  In a normal year, our gins may leave modules on the yard for over a week.  Since acres are down and yields are also down, the time between harvest and ginning will be much shorter than normal.  Green leaf in a module can support the slow buildup of heat and conditions which severely damage fiber quality.  But if only a small amount of leaf is present and the gin is quick to pull that fiber off the seed, the penalty associated with green leaf will be small.

My one shot mix when we dry back out: 8 oz Folex + 16 oz Ethephon. No adjuvant needed- save that money.

My two shot mix when we dry back out: 

First shot: 8 oz Folex + 16 oz Ethephon- no adjuvant

Second shot: cheapest PPO you can get, adjuvant to match temps, ethephon only if you need it.  Reach out to your local Extension office or myself the morning you apply if you have questions on PPO and adjuvant rates.    ∆

DR. TYSON RAPER

UNIVERSITY OF TENNESSEE

MidAmerica Farm Publications, Inc
Powered by Maximum Impact Development