How do insects and fungi manage to invade grain bins year after year?
“It’s easy. I have yet to see a grain bin of any kind with a perfect seal,” said Blaine Timlick, entomologist with the Canadian Grain Commission.
“It’s impossible to keep them out of your bins. You have to deal with them. Even with the welded steel hopper bins, we see insects get in through the vents and the top and bottom ports. Same thing with concrete grain elevators.”
Timlick said producers have to learn to deal with them, because they’re everywhere.
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“We sometimes find live insects inside hermetically sealed packaging from seed plants. They chew through plastic and seals and gaskets. They find holes we can’t detect.”
One way to reduce the number of pests in a bin is to plan which crop will go into which bin, and clean it as quickly as possible. The longer that old crop residue sits in a bin, the more pests there will be.
While there are numerous insecticides for stored cereals, the grain commission recommends no chemical insecticides for bins that will hold canola or flax. These two oilseed crops can absorb insecticide traces.
Fungus alert
Timlick said the presence of fungi is also easy to understand. The fungal spores come in with the grain. The spores themselves aren’t the problem because, without heat, they are benign.
The problem is that grain holds heat too well. That’s why aeration in cold weather is so important. Timlick said it’s a situation the farmer can’t prevent. The only thing to do is deal with it.
“When you’re storing grain, you want it dry and cool. But saying it is easier than doing it.”
The price of not doing it can be a bin full of spoiled grain. He said that if conditions in the bin are right for fungi, they’ve already gone well past the point where they’re right for the typical grain insect.
“When storage fungi develop, they create more heat. The primary insect pests that have been feeding on the grain now have an even better environment, so they really thrive.
“The other thing that happens now is the insect species which feed on fungi are attracted to this bin. They sense the storage fungi. And this is the beginning of serious grain spoilage.”
The circumstances leading to this crisis are well understood. Grain in the bin is warm and can hold heat all winter.
Air outside the bin is cold so the walls of the bin cool down quickly. Cold air moves down the inside walls which forces warm, moist air up the centre of the bin. When this air hits the cool air in the space above the grain, condensation occurs.
Timlick said it doesn’t matter how much the grain dryer has reduced the moisture, condensation will still happen.
“The warmer the grain and the damper the grain, the more condensation you get. And the fungi is off and away to the races.”
The cone that naturally forms at the top as grain pours in can be a major cause of storage fungi and insect invasions, Timlick said.
When aerating, the air has no choice but to follow the path of least resistance. The cone has more grain, and thus more resistance. As a result, the grain cone remains warmer and collects moisture.
“The cone is a perfect home for insects and fungi, so you’ve got to level it out.”
Timlick said that in wheat, the first consideration is to get the moisture down as soon as possible when the crop comes off the field. To be safe, moisture content should be lower than 14.5 percent.
While dryers can easily get the moisture down into the target zone, the temperature might end up at 32 C or higher. That will attract the insects.
“So you’ve got to get it down below 15 C as quickly as possible. You won’t kill any insects at that temperature, but you’ll prevent them from doing an immediate damage.
“Below 15 C, they don’t feed and they don’t reproduce. They’re just moving around a little bit and waiting for things to warm up again in the bin.”
Timlick said if the grain is held for a while, the bin may warm up again in the spring before the grain is moved. That will reactivate the insects and fungi.
If long-term storage is likely, Timlick suggested using the cold winter air to kill the insects and fungi once and for all.
“That means running the aeration a great deal more to force more colder air through the grain. Get it down to at least -5 C and hold it there for a couple of months.
“The colder you go, the more insects and fungi you kill.”
Timlick said the relationship between fungi and insects in stored grain is not well understood. The grain commission had two mycologists in the 1970s and 1980s who initiated research into stored grain fungi and associated insects.
“The mycologists who were here retired and their positions were never filled. So a lot of that basic research they started has never gone anywhere, at least not in this country.”
For more information, contact Blaine Timlick at 204-983-2788 or visit www.grainscanada.gc.ca.
