The season-long drought and extreme heat have created conditions prime for Aspergillus ear rot to develop in corn, so growers should scout their fields and inspect their grain, a Purdue Extension plant pathologist said.
The fungus, which infects corn ears through the silks or wounds, produces aflatoxin, a toxic carcinogen that also can cause health problems for livestock that consume contaminated corn.
“Aspergillus ear rot is out there, but it varies greatly from field to field, mostly depending on planting time and environmental conditions at pollination,” Kiersten Wise said. “There is no field without some potential for the disease.”
Fields most at risk are those in which corn was planted in late March to early April, due to the high temperatures and drought stress that occurred when that corn was pollinating. Even if corn was planted later in April, it is still at risk if it was under extreme drought stress during pollination, planted in sandy soils or experienced insect and hail damage.
“Producers should scout fields prior to harvest and determine the level of incidence of the disease in the field,” Wise said.
The disease can be identified by its olive green, moldy growth on corn ears. Ohio State University Extension specialists recommend walking fields and examining ears from multiple plants at multiple locations. The fact that weather conditions this year have been favorable for Aspergillus ear rot does not automatically mean that you have an ear rot problem. The risk is indeed high, but the level of infection and grain contamination usually varies from field to field, depending of soil type, hybrid susceptibility, and cropping practice. Check for Aspergillus ear rot by stripping back the husks and examining the ears of 80 to 100 plants from across the entire field for the yellow-green or gray-green mold.
Samples for aflatoxin testing could be collected directly from the field, truck, grain stream, or grain bin. However, regardless of where the sample is being collected, it is important to make sure that it is representative of the entire grain lot.
Toxin contamination is never uniform throughout a grain lot, it is often found in hot spots. Therefore it is extremely important to pull multiple samples from every part of the lot. When sampling from the grain stream, collect samples at regular intervals. Pool and mix the individual samples into one composite sample from which about five to 10 pounds of grain is sent for testing.
From there, adequate handling of samples is an important part of the aflatoxin testing process. Samples should be dried to 12% to 14% moisture and shipped in cloth or paper package to minimize aflatoxin buildup during shipment and storage.
The U.S. Department of Agriculture regulates how much aflatoxin can be in finished livestock feed and corn for human consumption. Regulations vary by species but are especially tight for consumption by humans and dairy cattle, at 20 parts per billion. Regulations for other species are:
• 100 parts per billion in corn grain for breeding cattle, swine and mature poultry.
• 200 parts per billion in corn grain intended for finishing swine of 100 pounds or greater.
• 300 parts per billion in corn grain intended for finishing beef cattle.
Grain elevators are likely to reject loads of corn that exceed government regulations, or they could penalize producers by docking the price.
“At this point in the season, there are no management strategies for reducing ear rots in fields that will remain for grain production,” Wise said.
But she and several of her Purdue Extension colleagues teamed up to offer some strategies to help keep the aflatoxin issue from worsening:
• Harvest corn as early as possible. Late-season rains can increase mold growth and aflatoxin levels.
• Dry grain to less than 15% moisture. Make sure to dry grain promptly to keep aflatoxin problems from getting worse.
• Remove fine material. Fines often contain higher toxin levels than the grain and can interfere with drying and aeration.
• Clean equipment inside and out before and after use. Moldy or insect-infested kernels can contaminate next year’s crop.