Begin Monitoring On-Farm Stored Grains for Insect and other Possible Problems

Published: November 15, 2011

Warmer than normal fall temperatures may contribute to the development of stored grain insect populations in on-farm grain storage structures. If grain bins and handling equipment were not sanitized prior to grain fill and the grain was moved to storage without receiving a preventative insecticide application, insect infestations can develop in as little as 3 to 6 weeks following initiation of grain storage. In normal years, cool fall temperatures usually allow the stored grain to be cooled to 50 - 55 degrees Fahrenheit, which causes any insects infesting the grain to become inactive.

The high value of grain crops held in on-farm storage can best be protected by implementation of a monitoring program for detection of insect infestations and other problems within storage structures. Producers should monitor stored grains regularly to assess grain moisture, temperature, and determine whether insect pests are present. Grain should be monitored a minimum of once each month during the winter months of November through April and at least twice per month during the summer months of May through October. Areas of the grain mass most frequently infested include the grain surface and central core. Special attention should be given to these areas when sampling, but other areas of the grain mass should not be ignored.

Scouting methods differ by location in the bin and the specific type of insect present. To determine if insects are present, producers should visually inspect the top of the grain mass by looking through the roof access door. A sour smell, grain clumped together, condensation present on the inside surface of the bin roof, webbing on the grain surface, or the presence of insect larvae, adult beetles or moths all indicate the presence of an insect infestation. If an insect infestation is found on the surface of the grain mass and webbing is present, this usually indicates the presence of Indian meal moth. As this insect only damages the upper 12-14 inches of the grain mass, removal of the webbing and damaged grain along with an application of an appropriately labeled insecticide are recommended (See section 2B of summary for labeled insecticides). Pest strips (dichlorvos or DDVP) hung above the grain mass inside the storage structure may help prevent Indian meal moth infestations by controlling the moths of this common pest as they enter the storage structure. If no insects, webbing or foul grain odors are found during the inspection, then it is unlikely that Indian meal moths are present in high numbers. If the grain was properly leveled and the grain surface treated (capped) with an insecticide after filling of the storage structure the previous fall, it is best not to break or disturb the protective cap of insecticide previously applied at that time.

An inspection of grain from the interior of the grain mass is also needed. Monitoring of the grain mass is best achieved through the side access panel by using plastic tube traps, probe traps, and sticky pheromone traps. These traps are inserted into the grain mass for a certain period of time and then retrieved. These types of traps will attract insects and help determine the kind and number of insects present. If traps are unavailable, a quick, but less accurate method of sampling the grain mass for insects, can be accomplished by direct observation of grain removed from the side door using a grain probe. Deep probes should be collected from several locations in the bin with the collected grain placed in a quart glass jar, plastic bag, or some other container through which insects can be seen if they are present in the grain. These containers of grain should be placed in a warm area to allow the grain to warm to at least 60 degrees F or higher in order to stimulate insect activity. Although there are no reliable thresholds for most insects found in stored grains, it is usually considered that if insects are found in the 1 quart samples of grain collected, the grain content of the bin should be either quickly used or treated (fumigated) to kill insects present in the grain and prevent excess loss of grain quality when stored at summer temperatures.

If infestations of various flour beetles, grain weevils, or other stored grain beetles are found infesting the cold grain mass, then the immediate use of grain for livestock feed or some other use where the insects do not cause a problem in the end product is recommended. The grain should be fed to livestock prior to the arrival of summer temperatures when insect activity increases. If the grain is to be retained into the summer, then fumigation of the entire grain mass is a second, but less attractive management option. Producers can legally fumigate grain bins in Missouri providing they possess a valid private pesticide applicator license when purchasing and using the fumigants. However, due to the extreme hazard associated with the very poisonous gases emitted by the fumigation pesticides and the extreme danger if used improperly, it is strongly recommended that a professional fumigator be contracted to fumigate grain bins and other grain storage structures. A third option would be to move the grain out of the storage facility immediately after the grain has been warmed in the spring. The grain would be moved to another storage structure with the grain being treated with a recommended insecticide as the grain is moved (see section 2A of the summary for labeled insecticides). This method of insecticide application should provide satisfactory insect control on a short term basis. Of these three options, immediate use of the grain as livestock feed is generally the best option. Once the grain in removed from the bin, sanitation procedures should be implemented and the empty bins treated with an approved insecticide both inside and out.

All insecticides for stored grain insects have very specific labeled uses so special attention must be given when selecting an appropriate insecticide. Some insecticides are labeled for use in empty grain bins, but are not labeled for use on grain. Some insecticides are labeled for wheat only or corn only, whereas others may be labeled for both. Be sure to read and follow all insecticide label instructions, restrictions, and precautions when using insecticides for management of stored grain insect pests.

The following summary includes a list of labeled insecticides, use rates and labeled uses. This information was revised November/2011.

Farm Stored Grain Management Summary
1. WHAT TO DO BEFORE HARVEST
A. SANITATION. Thoroughly clean all grain residues from bins. Remove all residues from areas around the bins and any nearby feed bunks or feed storage areas. Remove all grain residues from combines, trucks, and augers. These residues will be the main sources of insect infestations for farm stored grain. This is an important part of a good grain management program and can prevent many stored grain insect problems.

B. RESIDUAL SURFACE SPRAYS TO EMPTY BIN. After all debris and grain residues have been removed, an application of a residual insecticide should be made to the complete inside of the bin. This insecticide should also be applied around the exterior and to all areas where residues were removed. Spray all surfaces until wet; usually one gallon will cover 1,000 square feet prior to storing or handling grain. Use a course spray at a pressure of at least 30 psi. Insecticides are most effective if temperatures are 60F or higher. The labeled effective compounds are:

a. Beta-Cyfluthrin (Tempo SC Ultra - 0.27 to 0.54 fl oz per 1 gallon of Water) for application to empty bin surfaces only, not to grain.
b. Chlorpyrifos-methyl and deltamethrin (Storcide II – 1.8 fl oz per 1 gallon of water) Warning-This insecticide should only be applied from outside the bin using automated spray equipment. Do not enter the bin until all sprays have dried.
c. Malathion (Malathion 5E - several products by various formulators, check specific application rates.) Although labeled, the efficacy of this product is questionable. Some stored grain insect populations, such as Indian meal moth, have developed resistance to this insecticide. Note: Malathion 5 E not labeled for rice.

2. AT HARVEST GRAIN PROTECTANTS

A. PROTECTANTS FOR APPLICATION TO GRAIN. If grain is to be held in storage into the summer months of the year following harvest or longer, then a grain protectant applied at harvest is recommended. Formulated sprays, drips or dusts are typically applied to moving grain stream as it goes into storage vessel.

a. Chlorpyrifos-methyl + deltamethrin (Storcide II) – dilute labeled rate of Storcide II in 5 gallons of water and apply formulated spray into grain stream. Five gallons of formulated spray applied to 1,000 bushel of grain.
Storcide II rates per 1,000 bushel of grain crop are as follows:
Barley 9.9 fl oz per 1,000 bushels;
Oats 6.6 fl oz per 1,000 bushels;
Rice 9.3 fl oz per 1,000 bushels
Sorghum 11.6 fl oz per 1,000 bushels
Wheat 12.4 fl oz per 1,000 bushel

b. Pirimiphos-methyl (Actellic 5E – 9.2 to 12.3 fl oz per 5 gallons of water per 30 tons of grain (approximately 1071 bu.). Note: labeled for corn and sorghum only.)
c. Malathion (Malathion 6% Dust – 10 lbs/1,000 bushels of grain.) Insecticide dust best applied through dust applicator into grain stream. Labeled for barley, corn, oats, rye, and wheat. Malathion not labeled for use on rice.

B. SURFACE TREATMENTS OR TOPDRESSING AFTER BIN FILL IS COMPLETE. Fill bins only to height of side walls and level grain prior to applying surface or top-dress insecticide treatments.

a. Bacillus thuringiensis (Biobit HP and Dipel DF – 1 lb/ 10-20 gal/1,000 square feet). Most often used for Indian meal moth larval control. See label for specific instructions and target pests.
b. Diatomaceous earth (Insecto at 4 lbs/1,000 square feet and Protect-It at 40 lbs/1,000 square feet if grain not previously treated with this protectant). See label for specific instructions and target pests.
c. Pirimiphos-methyl (Actellic 5E – 3.0 fl oz per 2 gallons of water per 1,000 square feet of grain surface. Note: Labeled for corn and sorghum only.)

C. GRAIN FUMICANTS. Recommend use of commercial pest control specialist when using grain fumigants for stored grain insect control.

a. Aluminum Phosphide (phosphine gas - restricted use) (Phostoxin, Fumitoxin, Phoskill, Phosteck, Phosfume Weevil-cide – see specific labels for rates of pellet or tablet use).

3. MONITORING FOR INSECT PESTS IN STORED GRAIN MASS (See previous text)
Color images of common stored grain insects can be found on the Commercial AG Electronic Bulletin Board at http://agebb.missouri.edu/storage/pests/insect.htm.