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ISSUE 15   September 18, 2008


You may have triumphed over insect pest problems on small grains during the growing season, but take some time now to prepare your storage bins and prevent potential stored insect problems through good bin management. Several species of insects infest stored grains - confused flour beetle, Indian meal moth, rice weevil, lesser grain borer, red flour beetle. Damage caused by these insects includes reduced grain weight and nutritional value, contamination, odor, mold, and heat damage, all of which lowers the grain quality. Good grain bin management practices include:

1) Before treating with protectant, make sure that the bins are free of insect-infested grain. Leftover grain should be removed from the bin, and the walls should be swept and vacuumed. All grain handling equipment, including augers, combines, trucks and wagons, should be thoroughly cleaned and grain residues removed before harvest.

2) A residual bin spray, such as malathion, Tempo, or Storcide II, should be applied to all interior bin surface areas 2 to 3 weeks before new grain is placed in the bin. The treatment will kill insects merging from their hiding places (cracks, crevices, under floors and in aeration systems). Also, insects crawling or flying in from the outside will be killed. Apply the spray to as many surfaces as possible, especially joints, seams, cracks, ledges and corners. Spray the ceiling, walls and floors to the point of runoff. Use a coarse spray at a pressure of more than 30 psi and aim for the cracks and crevices. Spray beneath the bin, its supports, and a 15 ft border above the base of the outside foundation. Treat the outside surface, especially cracks and ledges near doors and fans.

The increased use of metal bins with perforated floors for grain drying and aeration has helped produce a serious insect problem in farm-stored grain. Grain dockage (broken kernels, grain dust, and chaff) sifts through the floor perforations and collects in the subfloor plenum creating a favorable environment for insect development. Unfortunately, the floors are usually difficult to remove, making inspection, cleaning and insecticide spraying in the plenum difficult, if not impossible. The infested plenum may be disinfected with an approved fumigant. Note: Fumigants are extremely hazardous for the user and only certified applicators may purchase and apply fumigants. Please remember to read and follow the label.

3) Remove any vegetation / weeds that may attract and harbor insect pests within 10 ft of a bin and preferably the whole storage area. Follow by spraying the cleaned area around the bin with a residual herbicide to remove all undesirable weedy plants.

4) Repair and seal all damaged area to grain storage structures. This helps prevent insect infestation and reduces water leakage which leads to mold growth.

5) Whenever fans are not operated, they should be covered and sealed to reduce the opportunity for insects and rodents to enter the bin through the aeration system.

6) If newly harvested grain and/or insect-free grain must be added to grain already in storage, the latter should be fumigated to prevent insect infestation.

7) It is recommended that grain be treated with approved insecticides as it is augered into the bin if it will be in storage for one or more years. Grain protectants kill insects as they crawl about or feed on treated grain and/or grain fragments. Do not apply grain protectants prior to high temperature drying because extreme heat will result in rapid volatization and reduced residual qualities of the pesticides. Grain protectants applied to 13% moisture grain will have a greater residual life than grain at 15% or great moisture.

Please consult the 2008 Field Crop Insect Management Guide for a complete list of stored grain insecticides.


After binning, some grain protectants may be applied as a surface treatment "top dress" to control surface feeding insects such as the Indianmeal moth larvae. Insecticide product should be applied into the top few inches to improve efficacy. No-pest strips (dichlovorous impregnated strips, DDVP) can also be hung in the open space of grain bins to help control flying insects. It is recommended to suspend one strip per 1,000 cubic feet of air space. No-pest strips may need to be replaced during summer.

When temperatures are above 50 F, bins should be inspected for insect activity every two weeks. Stored grain insect pests are generally inactive at temperatures below 50 F (see diagram).

stored grain chart

Use a grain probe to determine the extent of infestation within the grain mass. It’s important to know what species of insect pests are infesting your stored grain. The Federal Grain Inspection Service differentiates between grain that is infested and grain that is "weevily." Grain is only graded weevily if it contains an internal feeding insect, such as weevil or lesser grain borer. The only option with weevily infested grain is to feed it, sell it at a discounted rate, or fumigate it. Remember, stored grain insects can be thought of as very expensive, unwanted livestock!



There have been several reports of soybean aphid moving out of soybean fields and back to buckthorn. The soybean aphid can survive winter only in the egg stage, as is true of other aphids in temperate zones. Buckthorn (Rhamnus spp.) is the only known overwintering host. Leaves of common buckthorn (Rhamnus cathartica) are dark green and glossy with three to four pairs of upturned veins (see photograph).

Buckthorn tree
Buckthorn tree

Green leaves often remain on trees well into the fall. Small, yellow-green flowers are clustered at the base of leaves in spring. Recent research from NDSU in the Red River Valley determined the supercooling point of winter-acclimated eggs was found to be -38 degrees F in Fargo, ND. In other words, aphid eggs are very winter hardy and can survive extended periods of very cold temperatures. Soybean aphids hatch in the spring and are expected to have two to four generations on buckthorn, with winged females developing during each generation and leaving the overwintering host in search of soybean. Numerous generations of wingless females will develop on soybeans before a winged generation of females and males migrate back to buckthorn in late-summer/early fall to mate and lay eggs.



There have been some questions about Hessian fly and control this fall. Hessian fly causes stunting in seedling plants and lodging as wheat matures. It overwinters in the shiny brown ‘flaxseed’ stage that is generally found at the base of the plants or below broken stems under leaf sheathes in the stem.

Hessian fly pupae
Hessian fly pupae

Hessian fly adults are killed by freezing temperatures and cannot lay eggs. Therefore, delayed planting until after the first freeze is one of the traditional control methods for preventing Hessian fly infestations in winter wheat. In North Dakota, suggested winter wheat planting dates for the northern area are from September 1 to September 15, and for the southern area are from September 15 to 30. However, recent research from Kansas has indicated that the established fly-free dates are too early in regards to Hessian fly activity (source: J. Whitworth and P. Sloderbeck, KSU). Potential contributing factors as to why fly-free dates are too early for reducing Hessian fly populations include: increased reliance on reduced tillage and slight increase in average temperatures in fall. One of the other benefits to planting later is breaking the ‘green bridge" that supports the survival other pests, such as wheat curl mites which vectors Wheat Streak Mosaic Virus.

Janet Knodel
Extension Entomologist

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