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ISSUE 11   July 23, 2009


If the weather stays warm this fall, insects may again pose a serious threat to stored grain. Confused flour beetle, Indian meal moth, rice weevil (Fig 1), lesser grain borer and red flour beetle are all potential threats. Damage caused by these insects includes reduced grain weight and nutritional value, contamination, odor, mold and heat damage, which lowers the grain quality.

Figure 1.
Adult rice weevil. (J. Berger, Bugwood.org)

Take some time now to prepare your storage bins and prevent potential stored insect problems. The first step is to make sure that the bins are clean and free of insect-infested grain. Remove leftover grain from the bin and sweep and vacuum the walls. Clean all grain-handling equipment, including augers, combines, trucks and wagons, thoroughly. When cleaning the bins, remember to get under aeration floors and inside aeration tubes as these are great spots for insects to hang out while waiting for you to fill the bin.

Apply a residual bin spray, such as Malathion, Tempo or Storcide II, to all interior bin surface areas two to three weeks before new grain is placed in the bin. The treatment will kill insects emerging from their hiding places (cracks, crevices, under floors and in aeration systems). Also, insects crawling or flying in from the outside will be killed. Check the label for rates.

Remove any vegetation that may attract and harbor insect pests within 10 feet 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.

Repair and seal all damaged areas to the storage structure. This will help prevent insect infestation and reduce water leakage, which leads to mold growth.

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

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. If grain will be in storage for one or more years, grain should be treated with an approved insecticide as it is augured into the bin. Grain protectants kill insects as they crawl about or feed on treated grain or grain fragments.

Do not apply grain protectants before high-temperature drying because extreme heat will result in rapid volatilization 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 more moisture. Moist grain also is more attractive to insect infestations."

Another important step in preventing insect infestations is immediate cooling of the grain after harvest. Grain insects that are flying in the general area will be attracted to harvested grain by smell. They can find and infest grain on the truck or through an open grain bin hatch. If the grain is warm (above 50 F), insects will start feeding and reproducing immediately. Bins should be inspected for insect activity every two weeks. Stored grain insect pests generally are inactive at temperatures below 50 F (Fig. 2).

Figure 2.

A grain probe can used to determine what species of insect pests are infesting the grain and the extent of infestation within the grain mass.

Key Points

  • Warm fall sets stage for insect threat to stored grain
  • Above 50 F, insects will start reproducing
  • Grain destined to be stored for a year or more should be treated
  • A list of insecticides registered for stored grain insect control is available in the NDSU Extension publication "North Dakota Field Crop Insect Management Guide 2009" at:




    Wheat stem sawfly infestations were severe in southwestern North Dakota this year. Sawfly larvae tunnel inside the stem and interfere with water and nutrient flow as the wheat head develops. Losses from wheat stem sawfly injury are of two types:

    1) Larval feeding inside stems reduces yield (5 to 15% decrease in total seed weight) and quality of grain (reduced protein and kernel weight).

    2) Mature larvae cut stems and stems may lodge to the ground with wind and the weight of grain heads, and become unharvestable (Fig 3).

    Producers should sample wheat crops and determine the percent of plants infested by sawflies before harvest. The presence of wheat stem sawfly can be verified by splitting stems and looking for the S-shaped larvae about ½ to ¾ inch long and cream colored with dark head inside the stems (Fig. 4). Another symptom of sawfly feeding is the presence of sawdust-like frass inside the wheat stem. Infested wheat stems often have a darkened area on the stem just below the nodes as a result of the internal feeding from sawfly. This can be used to detect a sawfly infestation without splitting the stems.

    If more than 15% of stems are infested by sawflies, producers should swath the wheat crop. Producers should swath sawfly-infested wheat as soon as kernel moisture drops below 40% to save infested stems before they lodge. If producers decide to swath grain, use a high swathing height to conserve the parasitoids (Fig. 5) that attack wheat stem sawfly.

    Research from Montana State University (source: Dr. David Weaver) has shown that taller residue (at least the lower of the plant)is better for conserving the parasitoids (Fig. 6).

    If 10 to 15% of the crop was cut by sawfly in 2009, solid stem wheat is recommended for 2010 wheat plantings. The 2009 NDSU hard red spring wheat release, ‘Mott,’ has the solid-stem characteristic that has high resistance to wheat stem sawfly.



    With the cool weather, soybean aphid continues to be low and well below the economic threshold level of 250 aphids per plant. In fact, it is hard to find soybean aphids in fields! Only one of the 27 fields scouted by the NDSU IPM Scouts last week had soybean aphids in LaMoure County (Fig. 7). It averaged only 14 aphids per plant and 40% of the plants infested. Stay tuned for more scouting reports.

    Janet Knodel
    Extension Entomologist

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