Grain Storage Pests

By Emily Unglesbee
DTN Staff Reporter

ST. LOUIS (DTN) — Grain storage pests like insects and mold could be a problem for corn growers looking to manage a bumper crop this year.

Corn prices are headed toward their harvest lows, so many farmers will likely opt to store their grain in hopes of better prices, Kansas State University entomologist Tom Phillips noted in a grain storage webinar hosted by the North Central Integrated Pest Management Center on Sept. 12.

In order for that economic reasoning to pay off, growers must take steps to ensure they don’t lose profits to grain-loving insects and the ear molds emerging in many Midwest cornfields this year.


"One of the big rules is do NOT store new grain on top of old grain," Phillips told growers in Friday’s webinar. "You need to empty that stuff out. There’re a lot of insects living in the grain fragments."

Not only can old grain fragments hold insects, they can also serve as a food for insects and allow them to survive any pre-harvest bin sprays or grain protectant insecticides you might apply, USDA entomologist Frank Arthur noted.

Sealing major leaks in the bins is another must, especially if fumigation is required later in the season.

Quickly cooling and drying the grain is instrumental in slowing mold and insect infestations. At around 55 degrees, most insects become sluggish and their development slows. They won’t necessarily die, but the risk of a rapid-fire infestation taking off is significantly lowered, Purdue entomologist Linda Mason told growers.

Moisture contents as low as 13% are also critical for halting the growth and spread of stored grain fungi like aspergillus and penicillium, as well as the many ear rot fungi circulating in Midwestern fields, such as Diplodia, Gibberella, and Fusarium, Mason said.

Some penicillium mold species actually do quite well in cold temperatures as low as 32 degrees, so only cold and dry grain will do well for long periods of storage, Mason pointed out.

"Aeration is designed to change temperature," she reminded growers. "It can reduce moisture migration, it can manage your mold and insects, but it is not designed to dry grain. You have to better systems in place to dry your grain."


Chemically squelching an insect infestation in stored corn requires knowing which insects you’re dealing with, Mason said.

Insects that feed inside the kernels of corn can only be treated by fumigation, not pre-harvest bin sprays or grain protectants. "Residual (insecticides) are going to be used to treat either the bin itself or the outside of the kernel," Mason explained. "They’re not going to penetrate or soak into the kernel compared to a fumigant, which isn’t going to coat the kernel, but it is going to penetrate into the kernel and kill the insect from within."

The most common internal feeding insects for corn growers are the maize weevil and the angoumois grain moth. Lesser grain borers are rarer but can be a problem if the corn is stored on top of old wheat fragments.

The maize weevil is especially prolific, Mason noted. "When you find one in a trap, there’s probably hundreds hidden in the kernels as immatures and you can’t sample them," she said.

Phosphine remains the primary fumigant in the U.S., but resistance has surfaced in some insect species such as the lesser grain borer and red flour beetle, Phillips noted. Checking your bin for insects a week or so after a fumigation can help you assess if you have resistant species, Mason added.

External feeding insects are easier to both treat and find, Mason said. These beetles are more easily spotted and are susceptible to insecticides applied to the bin or the grain, as long as no untreated old grain fragments are hanging around to sustain them.

Common offenders in stored corn include the Indianmeal moth, the sawtoothed grain beetle and mealworms, which love the high-moisture grains that growers might harvest this year.

Mold-feeding insects like the hairy fungus beetle and foreign grain beetle could become a problem this year with the prevalence of ear rots, Mason noted. These insects don’t actually hurt the grain, but their presence is a good early indicator of a mold problem.

For images to help identify stored grain pests, see this USDA website:….

For a comprehensive guide on preventing, sampling, and treating stored grain insect infestations, see this Purdue guide:….

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