By Guy Collins
First of all, we pray that everyone is safe from Hurricane Dorian and that damage to homes and property are minimal to none. Our thoughts and prayers go out to everyone impacted by this storm, and please know that the NC State University Cotton Team is willing to help farmers in any way that we can. With that said, we wanted to send out some information that may help growers in the days and weeks to come with regard to evaluating crop damage and management of the cotton crop for the remainder of the season. Preliminary reports indicate cotton crop damage ranging from severe to very little, with the most damage obviously in near-coastal counties and the Blacklands but we will know more as time elapses. Below are some observations from previous experience with hurricanes.
Wind Defoliation: The winds from storm were most significant in the eastern-most areas and have likely defoliated a few older leaves that were already aging. Some remaining leaves may begin to turn reddish because of wind injury to the leaves. Some of these leaves may go ahead and defoliate themselves. Based on the experience with the hurricanes in the past, the “self-defoliation” caused by wind damage is usually not adequate and defoliants will still need to be applied. In a couple days you should be able to evaluate the degree of natural defoliation that will occur by thumping leaves to determine if they have formed an abscission zone. The loss of these leaves may be a good thing in that it could allow for better airflow and sunlight penetration into the canopy, and therefore more rapid drying of both open and closed bolls. In these cases, the wind could serve as a “preconditioner” to defoliation. Fields where leaves were defoliated by wind and remaining leaves are beginning to senesce may be easier to defoliate.
Regrowth: Be ready to address regrowth. Cotton that is blown over exposes many of the axial buds to direct sunlight that were previously shaded. Sunlight, along with high soil moisture, will promote rapid and significant regrowth. In more severe cases if some fields are flooded, some plants may actually drown, therefore regrowth may not be as big of a problem in these fields, therefore evaluating your crop on a field by field basis may be necessary for defoliation decisions. Be prepared to include TDZ of some form in your tankmixes, and don’t cut corners with rates (no less than 3.2 oz/A of 4 lb a.i./gal TDZ…..TDZ+diuron products are used at much different rates).
Lint loss: Opened bolls that experienced heavy winds and rains are naturally prone to falling out onto the ground. In past storms, cotton that was defoliated prior to a storm consistently experienced more lint loss than cotton that had not yet been defoliated (especially those that still had some closed bolls).
As expected, there have already been a number of reports of tangled cotton that has fallen over. As far as harvesting wind-damaged cotton, the main thing we will need to do is slow the picker down. If you are having trouble picking cleanly, slow the picker down and see if it improves picking, or reduces shattering of open bolls. Picking at speeds where rotation of spindles around the drum, matches ground speed can result in cleaner picking. Growers should also read manuals to make sure that lifters are properly adjusted.
Below are some hints about yield/lint loss estimates at this point:
Immediate loss: This would be seedcotton blown out on the ground due to the wind. The best way to estimate losses is to count the number of locks of seedcotton blown onto the ground and determine how many bolls per foot of row are lost. It takes about 12 bolls per foot of row (on 36-in rows) to make a bale, and roughly 4 locks to make a boll. Therefore, 1 lock per foot of row would loosely equate to 10-11 lbs of lint per acre. With this example, 4 locks per foot of row blown onto the ground would roughly equate to approximately 50 lbs/A in lint loss. This is not a very precise estimate, due to differences in boll size, seed weight, etc.
Evaluating the cotton that remains harvestable may be more accurate than estimating how much was lost. Knowing what is left and weighing that figure against your APH in your particular insurance policy may be the best influence over the “harvest or abandon” decisions at this point. Although there is no real way to predict quality losses, it is safe to assume that some quality loss may have occurred if bolls were open prior to the storm. Quality losses will be more severe if remaining lint is muddy or experienced flooding or standing water. This will largely be dictated by weather conditions from this point forward, therefore the degree of quality loss is very unpredictable.
Residual damage: This would include cotton knocked off by sprayers and cotton that rots or sprouts due to its close proximity to the ground. There is no way to predict this damage. If we stay dry and the cotton opens soon, it should straighten up some and minimize this damage. If you have to make an estimate I would not count on any bolls touching the ground at this point to be harvestable in fields that are flooded or have standing water that doesn’t recede quickly.
Growers should contact insurance adjusters to estimate losses in fields with significant damage prior to harvest or crop destruction.
Closed bolls: Dry weather and sunshine are the best thing for closed bolls at this point. These bolls remained protected during the storm, but are also prone to rot or hardlock if they are blown over and are in direct contact with other wet plant material or wet soil. Small bolls will likely abort at this point therefore should not be counted as harvestable. The longer that wet conditions prevail, the more likely closed bolls are to rot. Due to thrashing from the wind, some ethylene buildup is likely already underway in bolls that are fairly close to maturity, and therefore will likely open soon. High moisture conditions that occur when these bolls first pop open may result in increased hardlock. Quick defoliation (using a tankmixure that includes a high rate of a ethephon-containing product) as soon as fields are passable may help minimize rotting, however dry conditions and sunlight at this point will have much more of a favorable impact on closed bolls. Additionally, defoliation can help straighten up lodged plants further reducing contact of closed bolls with the ground or other plant tissue.
The good news is that most places were dry going into this storm. There are a few reports of standing water in places, but there are also several reports of rapid drainage or little standing water. If we encounter sunny, warm, and dry conditions (with very little rainfall) for the next several days or even a couple of weeks, closed bolls should open normally (unless they were flooded or blown down into standing water or mud), and yield/quality losses of open bolls still in the burr should cease. If cotton is ready for defoliation, growers are encouraged to proceed with defoliation, assuming fields are passable. This will enable some cotton to stand up and enable more lint to be harvested.
Defoliation Practices: There’s a number of tankmixes that can be used, with several combinations of various products, therefore please see our previous articles for more information, or contact your NC State University county agents or cotton extension specialists for product selection. Here are a few other tips.
- Use appropriate application volume. 20 GPA is best. 20 is a little better than 15. 15 is a whole lot better than 10.
- Use appropriate tips. Hollow cones are best at fogging the entire canopy and achieving adequate coverage, however, most growers use ground speeds much too high for hollow cones to be effective. Flat fans or twin fans equipped to apply the ideal application volume mentioned above are a good tradeoff for droplet size. Avoid larger droplet nozzles such as AI or TTI tips.
- Defoliate on a warm sunny day, followed by another warm sunny day. For whatever reason, the first couple of days following defoliation can have a big influence on overall defoliation. Defoliating on cloudy cooler days consistently results in poor defoliation, necessitating a second application
- As mentioned earlier, be prepared to use optimal rates of ethephon and TDZ in your tankmixes. Use appropriate rates but don’t cut corners on these. Match rates to prevailing and expected temperatures and crop conditions.
- If cotton is ready, go ahead and defoliate it. This may help preserve yields and quality. However, don’t defoliate more than can be harvested 10-14 days later. Let the picker follow the sprayer at a similar pace throughout the fall. Defoliating your entire crop before you begin harvesting only prolongs lint exposure to weather, results in more regrowth, and potentially risks yields if more weather events occur. If another tropical storm heads our way, DO NOT defoliate any cotton that still has closed bolls (protected bolls) unless you can harvest it before the storm arrives.
- There have been several questions about preconditioning cotton that is blown over. In many cases, a one-shot defoliation program will defoliate the top 1/3rd to ½ of the upper canopy, resulting in one side of the plant that is defoliated and the other side with leaves still in tact. However, the right application volume, nozzles, and weather can negate a lot of this. Due to the inconsistency of performance with preconditioning, it is advised that growers (who want to precondition their cotton) target the fields that are 1.) ready for normal defoliation anyway (don’t compromise young bolls), and 2.) the fields that they know wont likely be harvested in the 10-14 day timeframe, and 3.) are willing to make 2 trips through the field. Preconditioning can be effective occasionally but also inconsistent….in many cases, assuming application volume/nozzles/weather/product selection was done correctly, a one-shot program would suffice. Low rates of Folex (4-6 oz/A) alone, TDZ alone, or Ethephon alone are most consistent for preconditioning, but the results from the practice alone can often be inconsistent.
- Be ready with the picker. When all harvestable bolls are open, and nearly or all leaves have been removed, go ahead and harvest it. Nothing good comes from delayed harvest.