Large numbers of pet deaths in 2005 and again in 2007 prompted recalls of dog food that contained high levels of corn mycotoxins — potent poisons produced by molds. Mycotoxins are a major health hazard to livestock, pets and people.
What’s a farmer to do, when, under certain weather conditions, some mycotoxins will be produced, even in field corn that is still growing in the field? This is particularly a problem in the southeastern U.S., but also in the Midwest and elsewhere.
Actually, farmers can do quite a bit to keep mycotoxin levels low in their corn, North Carolina State University researchers have found. Dr. Ron Heiniger and his team of graduate assistants presented their very useful findings at a field day at the Fountain Farm of North Carolina’s Upper Coastal Plain Research Station in Rocky Mount.
Practical steps farmers can take was the research focus of graduate student Megan Meyers. “The first step,” said Meyers, “is to plant Bt hybrids well-suited to your area, and plant as early as possible.” Using Bt to control the caterpillars that munch on the ear and cob also helps control fungal infection.
“Insect damage provides an entry for fungi during the growing period,” Meyers continued, “and is particularly important with Fusarium, which produces the deadly mycotoxin, fumonisin.
“We tested three Syngenta Bt hybrids commonly planted in this part of North Carolina, and the clear winner was Viptera hybrid (N78S-3111), which contains two types of Bt proteins lethal to caterpillars. Viptera had the lowest levels of aflatoxin, and also very low levels of fumonisin, the two mycotoxins we are studying.” There was no yield trade-off in planting Viptera.
“Second, planting early and planting shorter-season hybrids resulted in lower mycotoxin levels, both because the growing plants were not exposed for as long a time to the stressful intense heat of summer, and also because the shorter season hybrids aren’t in the field as long to be exposed to fungal pathogens.”
Third, avoid drought stress, particularly during pollination. If a farmer has the ability to irrigate during drought, it’s a wise step to take. Pollination time is when many fungal infections occur. During drought, silking can be delayed, and the pollen tubes grow longer and longer, giving more opportunity for fungal spores to land on and grow up into the tubes and reach the developing ear.
Also, drought stress can result in poorer husk coverage of the ear, which can allow water to penetrate the husk, causing problems.
Fourth, use the fungicides that are most effective against Aspergillus and Fusarium, which produce some of the most serious mycotoxins.
“Farmers in North Carolina routinely spray fungicides on field corn to control foliar diseases,” Meyers continued. If you use the most effective fungicides, “they seem to reduce the ability of the fungus to infect the corn plant by improving plant resistance,” added Dr. Heiniger, who is North Carolina Extension Corn Specialist.
“We sprayed the fungicides on our test plots at between the V5 and VT stage,” explained Meyers.
A fifth action farmers can take to control mycotoxins in corn is to use biocontrols — spreading inoculant in their fields of beneficial Aspergillus strains that do not produce toxins, to outcompete the toxin-producing strains for corn plant tissue.
As with fungicides, the biocontrols used alone also appeared last year to increase total yields per acre, when applied at 7.5 to 10 pounds per acre in a rather wide window of time from V5 to VT. The more bio control in the field, the less aflatoxin was present, the study found.
Sixth, drying the corn quickly after harvest is also important in minimizing mycotoxins. “Farmers around here harvest at 23 or 24 percent moisture then quickly dry it down,” explained Meyers, “to avoid hurricane season, and to make mycotoxin contamination less likely.” Below 13 percent moisture, there is no further problem, although any mycotoxins present will not be destroyed. Below 55 degrees, growth of mycotoxin-producing fungi is also unlikely.
Also, scout your fields for mold problems. “If you find a problem, harvest early,” advised Dr. Heiniger. Mold doesn’t automatically mean mycotoxin problems. The only way to know if mycotoxins are present at unacceptably high levels is to test.
The currently available biocontrols must be reapplied each year, and do not affect Fusarium, which produces the dangerous mycotoxin, fumonisin. NCSU Ph.D. student Megan Sexton is working to change that. A microbiologist, she is screening large numbers of native fungus strains from four states involved in the study.
“I’m hoping to find and genotype native strains of Aspergillus and Fusarium that do not produce toxins; that will survive in the soil and so do not have to be reapplied every year; and that effectively compete with toxin-producing strains,” she explained.
It’s a tall order, but a potentially very important project. Sexton expects to be screening native fungi for three years, then begin field trials with the most promising native fungi.