Thomas Isakeit, Professor and Extension Plant Pathologist, t-isakeit@tamu.edu:  

As a requirement of one of the federal grants that supports my research and educational programs for mycotoxin reduction in corn, I must obtain feedback from growers about their mycotoxin problems and control approaches. This past winter, with the help of county agents, I received an excellent response from growers surveyed at four AgriLife Extension meetings where I made presentations. These meetings were: Bell County Crops Conference, Upper Gulf Coast Feed Grain Production Conference, Wilson County Winter Ag Conference, and Blackland Income Growth Conference. The total number of respondents was 139 and mostly represent growers in the Blacklands and Upper Gulf Coast. Based on how the survey was conducted and the number of respondents, the results should be considered a “snapshot”, rather than a comprehensive assessment (remember the adage, “There are lies, damned lies and statistics”). Here, I will point out highlights of the survey, with my interpretations. Ranges of percentages refer to the four meetings.

Aflatoxin continues to be a chronic contaminant in corn in the Upper Gulf Coast and in the Blacklands, where 24% and 41% of the growers reported it as an annual problem, respectively. In both areas, 50-63% of the growers reported it as a problem “every few years”. This frequency of occurrence would coincide with conducive drought conditions that vary from year to year. It is noteworthy that most growers (90-95%) are still concerned about aflatoxin, even though, based on analysis of corn samples from throughout the state done by the Office of the Texas State Chemist (OTSC), it would seem that there has been a dramatic shift from mostly contaminated corn (approximately 90% exceeding 20 ppb) prior to 2012, to approximately 20% contaminated from 2012 through 2014. Growers from the Blacklands reported frequent economic losses, while Upper Gulf Coast growers reported less frequent losses.

The OTSC analyses indicate that the High Plains is a perennial hotspot for fumonisin contamination, so it was interesting that more than half of the growers in the Blacklands and Upper Gulf Coast reported fumonisin as a problem every few years, with 5-14% reporting it as problem every year. In contrast to aflatoxin contamination, fumonisin contamination is not associated with drought stress, but is favored by wet conditions, particularly after grain maturation, prior to harvest. It’s possible to have corn that is contaminated with both aflatoxin and fumonisin.

I recommend multiple approaches to manage aflatoxin. See link at
http://agrilife.org/plantpathology/files/2011/11/Best-Mgmt-Mycotoxin_CORN.pdf. The use of an atoxigenic strain, either Afla-Guard or AF 36, is an important component of management. Although these strains have been commercially available for less than 10 years, their rate of adoption has been high: 63-79% of the growers reported using them, with most growers treating 76-100% of their acreage. Overwhelmingly, growers felt that the atoxigenic strains reduced contamination (86-100%). It would be nice to attribute the overall decline in aflatoxin in Texas since 2012 to the use of atoxigenic strains, but weather less conducive to aflatoxin (e.g. timely rain during flowering and grain fill) may have played a significant role as well. The contribution of each is not known. In on-farm trials with non-treated controls, we have measured reductions in aflatoxin with atoxigenic treatments that correlate with the presence of the atoxigenic strains in the kernels we sampled, so these materials truly work. I have also seen farms where atoxigenic strains are not used and there are limited problems with aflatoxin, so not all growers may need to use atoxigenic strains. However, growers that have had problems with aflatoxin in the past should include an atoxigenic strain as part of their management strategy.

A minority of growers (4-13%) reported that they did not see a reduction in aflatoxin with atoxigenics. An interview with these growers would be useful to clarify what happened and determine whether something should have been done differently. For details of some factors that may negatively impact the effectiveness of atoxigenic strains, see http://agrilife.org/plantpathology/files/2011/11/atoxigenic-strains-to-manage-aflatoxin.pdf. Some limitations on the effectiveness of these materials could be addressed with further research. For example, effectiveness may be increased with an earlier application, such as at V5.

With respect to other technology for mycotoxin management, 94-100% of the growers indicated a willingness to use corn hybrids with GMO-associated resistance. Although there is research in this area, there is nothing that will be available any time soon. However, there are several corn breeders in the southern US using conventional breeding approaches, including those with the Texas A&M corn breeding program, which recently released three germplasm lines with reduced aflatoxin accumulation.

Thomas Isakeit, Ph.D.
Professor and Extension Plant Pathologist
College Station, TX
t-isakeit@tamu.edu