
It only takes one. Just one live weevil per sample in some cases for a grain inspector to deem a load of corn originated from an infested grain bin – and then for the elevator to dock the price or reject the grain entirely.
As calls about what to do to prevent and treat insects in grain storage increase, Mississippi State University row crop entomologist Don Cook said it’s important to establish first what constitutes an infested bin before pursuing a treatment or prevention plan in following seasons.
What qualifies as an infestation?
For corn, in a 4,000-gram sample pulled by inspectors, there are three possible qualifications that can constitute an infestation.
• One live weevil and five other insects
• Two live weevils
• Ten other insects
If the sample meets any one of those qualifications, the grain from that bin is considered infested.
Maize weevil and rice weevil are the most common and considered the most destructive to stored grain. Other insects commonly found in grain samples include confused flour beetle, saw-toothed grain beetle and red flour beetle. Some of these insects can live up to two years in bins with little moisture or food. Many grain bin pests thrive on old grain dust alone, which makes cleanliness an important aspect of grain prep.
Is it preventable?
“When folks ask me, ‘What can I do?’ the best thing I tell them is to make sure you don’t have any old grain around,” Cook said. “That’s basically a source for infestation, just waiting for you to bring grain in.”
Cleaning out grain bins is standard practice before refilling, but for bins with a history of infestations or bins used in long-term storage, a higher level of clean could be required. In these cases, removing all grain and dust not just from the bin itself, but also from often overlooked areas like sub-floors and augers, can help set storage up for success.
“Basically, starting clean helps avoid these problems,” Cook said.
In northern states where large grain storage facilities are more common, temperature helps play the role of limiting insect issues. But in the South, it can take time for bins to fall to the right temperature to limit insect movement, and a hard freeze to limit insect over-wintering might never come.
“Fifty degrees is where insect activity begins to slow down,” Cook said. “Sometimes that is not practical. When you cut in August and it’s 105 degrees when you put it in the bin, it’s going to be awhile before it reaches 50 degrees.”
Is it treatable?
If a storage facility or area has a history of insect issues, temperature isn’t conducive to good grain storage, or grain will be stored for an extended time, treating bins and grain at the time of storage can help avoid infestation.
If treating a clean bin with an insecticide prior to storing grain, Cook said adding piperonyl butoxide to the tank mix could help achieve greater control.
“If you run a pyrethroid, which is deltamethrin, put PBO with it,” Cook said. “PBO is a synergist. It makes all the difference in the world.”
Typically, treating the walls of any empty bin with insecticide prior to filling can help control grain-feeding pests – but only for so long, Cook said. Grain set for longer storage may also need to be treated with an insecticide before it enters the bin for an extended period of time.
If a bin becomes infested, there are few remaining options for insect control.
“If you have an infestation in a bin, fumigation is your only other option and lot of folks don't like to do that,” Cook said. “If you hire somebody, it's expensive, but it is your only option, other than take the grain out, move it to another bin and treat it with one of the grain protectants.”
Cook said fumigation is a last resort and should be considered carefully before using that approach.
For stored grain insecticide uses and application recommendations in the Delta, check out University of Arkansas’ insecticide fact sheet here: https://mp144.uada.edu/.
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