by Tom Isakeit, Professor and Extension Specialist, Texas AgriLife Extension Service, College Station.
As a consequence of the sustained, heavy rain from Hurricane Harvey, mature cotton in the field, or exposed cotton in modules or bales that stayed wet, may be at risk for aflatoxin contamination. The only way to know for sure is to analyze samples.
Aflatoxin contamination is not just a problem in corn and peanuts, but it can also occur in cottonseed. In Texas, contamination can occur primarily in cotton production areas of south Texas along the Gulf Coast, but it has been reported in the Blacklands (central Texas) as well. Cottonseed is an important and valuable feed for dairy cattle and because aflatoxin consumed in feed ends up in milk, the level of aflatoxin contamination of dairy feed must not exceed 20 parts per billion (ppb). Cottonseed contamination has been a problem for decades, not just in south Texas, but also in Arizona and the Imperial Valley of California. The incidence and severity of contamination can vary by year. Contamination can occur in the field as a result of insect injury to the developing boll and it can also occur after maturation of the boll, as a result of rain or high humidity.
In a 1996 study, cotton from modules in the Coastal Bend were sampled for aflatoxin. The cotton was either harvested before or after a three-week period of frequent rain in mid-August that delayed harvest. In this study, the impact of rain as a factor for contamination was far more important than insect damage to the bolls. The incidence of contamination of non-damaged cotton prior to the rain was 3%, but the incidence in non-damaged cotton after the rain was more than 80%. The level of contamination of many samples exceeded 200 ppb.
In the 1990s, there were also studies that examined the role of modules in aflatoxin contamination. Aflatoxin should not increase during module storage if dry cotton is used to build modules. The fungus that produces aflatoxin, Aspergillus flavus, can infect cottonseed during the growing season and aflatoxin can accumulate in cottonseed in the field. Post-maturation moisture, either in the field or in storage, can result in increased levels of aflatoxin.
Cottonseed exceeding 300 ppb aflatoxin must not enter commerce. Cottonseed with 300 ppb aflatoxin or less, but more than 20 ppb, can be fed to animals other than dairy cattle, depending upon the levels. For detailed guidance on handling contaminated cottonseed, refer to the Commercial Feed Rules (otsc.tamu.edu), which addresses feeding and also the use of aflatoxin binding agents, blending and neutralization with ammonia.
Non-toxin producing strains of A. flavus have been available to growers for a decade. They are used primarily on corn, but AF 36 Prevail is also labeled for cottonseed. These materials are only effective when applied preventatively, during the growing season. They will not affect aflatoxin in cottonseed or corn that is already present.
Thomas Isakeit, Ph.D.
Professor and Extension Plant Pathologist
College Station, TX
t-isakeit@exchange.tamu.edu