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ISSUE 14   August 2, 3006


You may have triumphed over insect pest problems on small grains during the growing season. So, take some time now to prepare your storage bins and prevent potential stored insect problems through good bin management. Several species of insect infest stored grains - confused flour beetle, Indianmeal moth, rice weevil, lesser grain borer, red flour beetle, to name a few.

Rice weevil injury
Rice weevil (courtesy University of Georgia Archives, www.insectimages.org)

Lesser grain borer
Lesser grain borer (courtesy Clemson University)

Red flour beetle
Red flour beetle (courtesy Clemson University)

Damage caused by these insects includes reduced grain weight and nutritional value, contamination, odor, mold, and heat damage, 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. Left over 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, Storcide, 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 lb per square inch 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 impractical. 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.

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 help prevent insect infestation and reduce 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 vertebrates 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 portectants before high temperatures 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 great moisture. Grain treated with Storicide II has CODEX MRL tolerances, and can be shipped to international markets. Please consult the 2006 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 open space of grain bin 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). Use a grain probe to determine the extent of infestation within the grain mass. Itís 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 a very expensive, unwanted livestock!

Storage Grain



1) Continue monitoring for sunflower fields for head insects (banded sunflower moth, red sunflower seed weevil and Lygus bug). Field reports indicate high populations of all three insect pests in sporadic areas of North Dakota. Scout your field to determine what your population level is. See last weeks issue no. 13 of Crop & Pest Report for scouting tips and thresholds.



Data from the NDSU IPM Survey indicated increasing populations of soybean aphids in eastern North Dakota (see maps). Winged Ďalateí aphids are easy to find in early planted, moisture-stressed soybean fields as they move to more desirable fields - later planted field in the vegetative growth stages. Last year, aphid populations rebounded in these later planted soybean fields in late August and early September. So, please be vigilant in continuing to scout fields for aphids!

Soybean Aphid average

Soybean aphid infested

White Dwarf Aphids: Some field reports of little "white" aphids have come in. These are live moving aphids and not casted skins of aphids. These white aphids were reported last year in Indiana and are called "white dwarfs" in the literature. Yes, these are soybean aphids and are NOT "baby" aphids or diseased aphids. Aphids of many different species do this in response to change. Entomologists do not understand what is the cause. It may be due to hot temperatures, higher humidity, shorter day length, nutritional quality, or predator populations? White dwarfs appear to feed less than the "normal" green/yellow aphids, primarily due to their smaller size. However, these white dwarf aphids should be included in any threshold counts.

R5/R6 Growth Stage Thresholds:

Many soybean fields are approaching the R5/R6 growth stage and no one likes to run a tractor over a mature soybean field to spray an insecticide. The recommended economic threshold for R5 (seed fill) growth stage is increasing aphid populations and above 250 aphids per plants on 80% of the plants in field. This would require multiple scouting trips to determine a growing aphid populations and not static one. For R6 (full seed) growth stage, research indicates little yield benefit to treating soybean aphid populations. However, please use common sense in determining treatments for soybean aphid in R5/R6 soybean including yield expectations, net returns, moisture stress, increasing or decreasing aphid populations.

Insecticide Efficacy: There is no "super" insecticide out there, and with high temperatures (>90 F) the upper limit of any foliar insecticide is 2 weeks. One week to 10 days is more realistic. If a company representative offers you a free second spray or long 3-4 week residual guarantee, take them up on their offer and hold them to their agreement. Second applications may be justified this year due to the high numbers of soybean aphids.

Aphid Predators: Numerous aphid predators, such as ladybird beetles have been observed in fields. Research has shown that once aphid populations reach 100 aphid per plants, predators were not be able to keep up with the aphidís reproductive potential. However, if soybean aphids are emigrating out of a field, then predators will probably be able to manage the declining aphid population.

Harvest Restriction for Soybean Aphid Insecticides: The following list contains the registered insecticides for soybean aphid control in North Dakota and their harvest restrictions.


Days Before Harvest (PHI)

Asana XL (esfenvalerate)


Lorsban 4E or Yuma 4E (chlorpyrifos)


Decis 1.5EC (deltamehtrin)


Furadan 4F (carbofuran)


Taiga Z or Warrior (lambda cyhalothrin)


Lannate LV (methomyl)


Mustang Max (zeta-cypermehtrin)


Orthene 97 Pellets (acephate)


Penncap-M (methyl parathion)


Pounce 3.2 EC or Arctic 3.2 (permethrin)


Proaxis (gamma-cyhalothrin)




Question: What is this large caterpillar? It has been observed feeding on grapes and Virginia creeper throughout North Dakota this year.

Sphinx moth
(courtesy G. Fauske, NDSU)

Answer: This is a larvae of the Achemon sphinx (Eumorpha achemon). Sphinx moths (Sphingidae) are medium to large moths with robust bodies. Adult sphinx moths are one of fastest fliers in the Lepidoptera, and a favorite among insect collectors. Achemon sphinx occurs from Massachusetts south to Florida and west to North Dakota and south to Texas. Caterpillars are large (3Ĺ inches long) and can be green, orange, pink or brown with pale white to yellow spots around spiracles. There is one generation a year in the north and two or three generations in south. See Moth of North Dakota website:


Janet Knodel
Extension Entomologist



"When the pigs fly"

1) I added 4 oz. of Lorsban to my pyrethroid insecticide. Have I minimized spider mite potential?

2) I scouted and didnít see any spider mites before treating for aphids. Does spraying a pyrethroid insecticide mean I will have a spider mite problem?

3) I already sprayed for spider mites and aphids. Can I ignore them for the rest of the year and not have yield loss?

4) Will I increase the control or residual of my insecticide by adding an adjuvant?

5) Most plants have very few aphids when I sprayed but a few plants along the edge had 1000s of them. Will I have lower yield because I waited?

6) Field in the area are being sprayed for soybean aphid and spider mites. Doesnít that mean all mine need to be treated?

7) Will my pyrethroid insecticide kill aphids for 21 days?

8) Has yield loss already occurred at 250 aphids per plant?

9) Isnít it more important to just get the field treated than worry about application technique?

10) Shouldnít the 250 threshold be lowered because of the moisture stress?

11) Is my neighbor a genius?

The correct answer to all the questions is - probably not! (Reprinted from SW Minnesot IPM Stuff 2006-10, 8/1/06, B. Potter)


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