By Keith Edmisten and Guy Collins, North Carolina State University
It is impossible to predict the effects of tropical storm Matthew on the cotton crop in North Carolina, but it may be helpful to think about observations from past storms.
Many fields 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 had 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.
Cotton leaves defoliate through hormonal responses to stress (wind, defoliants etc.). This is related primarily to the ratio of ethylene and auxin. A stress caused by frost, wind or herbicidal type defoliants increases the production of ethylene which leads to the formation of abscission zones.
Some of you may have some cotton with more lint blown out on the ground. Some fields did have a lot of attached bolls close to or on the ground where they will be more likely to rot. Quick defoliation and boll opening will help those plants straighten up some and help reduce boll rot.
Listed below are some additional observations from prior storms:
- Cotton loses some leaves, but usually there is not sufficient natural defoliation to allow harvest without the application of harvest aids. The winds can act almost like a “preconditioner” for defoliation.
- It was easy to defoliate with Def and other herbicidal defoliants. This was true where the wind damage had turned leaves red.
- Wind-damaged cotton had limited regrowth. Injury seemed to shut the plant down. This includes further boll development. However, if the cotton had existing regrowth when the storm hit, growers will need to deal with regrowth as the lower canopy is opened up to receive more sunlight. With cooler temperatures likely following the storm, growers may want switch from mixtures containing thidiazuron to products that contain both thidiazuron and diuron, such as Ginstar or similar generics.
- Defoliated cotton lost a great deal more lint than less mature cotton that was not defoliated.
- Small bolls were aborted.
As far as harvesting wind-damaged cotton, I think 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. 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 loss estimates now.
Immediate loss. This would be cotton blown out on the ground due to the wind. You could collect cotton from several known areas in the field, dry and weigh it. Otherwise, you have to collect locks and determine how many bolls per foot of row are lost. It takes about 12 bolls per foot to make a bale. This is not very precise. Another example of immediate loss would be hard lock caused by the storm and previous weather. Grab the terminal of plants and shake the plant to estimate the amount of harvest losses you will expect due to hard lock.
Residual damage. This would include cotton knocked off by hi-boys and cotton that rots or sprouts due to 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.
Significant damage. Growers should contact insurance adjusters to estimate losses in fields with significant damage prior to harvest or crop destruction.