Alabama: Cotton Boll Rot – Potential Causes, Management Considerations

    Boll Rot in cotton is a frequent issue in Alabama, and when growers notice it in their fields around harvest time questions invariable arise: what caused Boll Rot  in my crop and what can I do to prevent it?

    Like many issues in crop production systems, there seems to be no single “silver bullet” to prevent Boll Rot. However, there are some interesting causal issues such as  1) diseases, 2) weather & micro climates, and 3) insect damage that certain management consideration could address to reduce risk of Boll Rot in cotton.

    Pathogens

    Boll Rot is known to be caused by several fungi and bacteria including Fusarium, Diplodia, and Alternaria species. These diseases infect the bracts and enters the boll at cracking or through injuries to the boll. Lesions appear that eventually spread turning the entire boll brown to black.

    Unfortunately, past and current research investigating fungicide treatments has shown no cost-effective effect on Boll Rot. Anecdotal associations have been made between symptoms of Bacterial Blight or Leaf Spot diseases and Boll Rot.

    Although extreme infection has been known to cause Boll Rot in other parts of the world such as India, those diseases are not associated with Boll Rot in the U.S.

    Weather & Micro Climates

    With most diseases, environmental conditions are the biggest factors in infection rates.

    Persistent rain, moisture and/or cloudy weather with cooler temperatures are huge contributors to Boll Rot incidence – especially when occurring when bolls are cracking. Additionally, rank cotton with heavy vegetative growth and a dense closed canopy can create persistent moist, humid conditions in the bottom of the crop.

    These are prime conditions for pathogen introduction and infection.

    Insect Damage

    Boll feeding insects have the potential to pierce bolls and create an opening that allows infection of Boll Rot pathogens if present. Traditional Boll Rot and resulting hard lock occurs at boll crack when bolls are fully mature and being more prevalent in the bottom crop.

    Herbicide Resistance Info


    However, the less seen cases of boll rot in the upper canopy are often result of one culprit: Stink Bugs. Damage from Stink Bugs happens when bolls are about 10 days old, or half matured, and nearly always occurs from the middle to top of the crop.

    One caveat to this is the Brown Marmorated Stink Bug which feeds on fully mature bolls. Stink Bug injury begins by delaying maturation of the bolls. Feeding points can be identified by lesions or “warts” on the inside of the maturing boll. Injury symptoms progress into malformation of the bracts at boll opening and eventually rotting of immature lint.

    Management promoting a healthy plant and good fruiting through fertility and water management, maintaining appropriate plant populations and preventing rank growth can all help to reduce risk of pathogen incidence and infection. If Stink Bugs are detected during scouting, Bidren is recommended to be sprayed during the 3rd-4th week of bloom, and again 2-3 weeks later.

    If fields are highly infested, are near known over-wintering sites such as pine tree stands, or if there has been a mild winter which increases potential for Stink Bugs, 3 sprays should be considered.

    Again there is no single solution, and it will continue to plague producers in Alabama. But there are some management options to consider to potentially reduce risk Boll Rot.




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