Why Stored Grain Gets Weevils. Some information for Agronomists
“It costs a grain grower $120/tonne to get his grain grown and into his bin,” says Rod McLean. “Of course it will vary with the inputs and the yield per hectare, but this is a reasonable estimate. The cost of protecting the grain in the bin will be $0.50 to $3.50/tonne depending on the storage system and treatment used. Either way, protecting grain from stored insect pests, aka “weevils”, is a small component of the total cost of producing that grain”.
According to Envu consultant, Rod McLean, there are two options if you store grain on the farm. “Some people think aeration will do the job but it is tricky. Below 18C, for most insects, reproduction stops but this does not kill them,” says McLean. “You have to make sure there are no insects to start with and to keep them out. It is also difficult to achieve such a low temperature in an Australian summer. The only options are fumigation or the use of a grain protectant”, says McLean. “But they need to be used correctly”, he added.
“If you have gas-tight silos you can fumigate. Phosphine is the most common. It is the lowest cost and kills insects at all life stages. If done properly there are no residues and the grain will be acceptable in all markets. If you are properly set up it is the best option”, according to McLean. “And Envu does not have a phosphine fumigant!” he added.
Market research conducted earlier this year shows almost 90% of cereal growers have on farm storage. Many had a combination of different types of storage but the most common was unsealed.
“Of those called “sealed”, 60% were over 10 years old and it is doubtful if they are gas tight,” McLean said. “Many silos are sold as “sealed” but after a few years fail the Australian Standard (AS 2628 is an industry bench mark for pressure testing gas tight silos.) You need to maintain the level of fumigant above a minimum for several days, so if it is not gas tight this is not possible. We are seeing insect resistance to phosphine which is due to poor practices when fumigating”.
“If your storage is not gas tight or you are storing in a grain shed you will need to use a grain protectant. They give persistent protection; unlike fumigants when the seal is broken. However several protectants are now failing due to insect resistance. What you use must be chosen with this in mind.”
There are several different types of insects that can infest stored grain. “When we have examined infested grains we often find two or more insect types,” according to McLean. “They are found all over Australia so you can’t be sure what type will affect your grain. Different insects have developed resistance to the various grain protectants. If you want to get good protection you need to use a combination of grain protectants with different modes of action. K-Obiol® in combination with either fenitrothion or chlorpyrifos-methyl gives coverage to all types of insects. We also recommend rotating the K-Obiol with a Group 5 pesticide annually. Just like herbicides on weeds, if you continue to use products with the same mode of action you will eventually get resistance.”
Farmers who want to use K-Obiol must complete the training. Click here to view the applicable stewardship training for your region.
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