CONTROL OF INSECTS

IN FARM-STORED GRAIN

Prepared byExtension EntomologistsTexas A&M University

GRAIN PRODUCERS suffer enormous lossesannually from stored-grain insects. Losses are

due primarily to improPerly cleaned storage struc­tures or to high temPeratures and high moisturecontent. ProPer attention to these factors prior toand at storage time helps greatly in preventinglater infestations.

KINDS OF STORED GRAIN INSECTS

Insects that attack stored grain are classifiedas primary (those that attack whole kernels andcomplete their development inside the kernel) andsecondary (those that feed primarily on cracked orbroken kernels).

Primary Pests

Three primary pest sPecies-rice or com weevil,lesser grain borer and Angoumois grain moth-areconsidered the most destructive stored-grain insectsin Texas. The granary weevil, also a primary Pest,rarely occurs in damaging numbers in Texas. Inthe immature stages these insects feed within thekernel unseen and usually unsusPected. Theseimmature stages cannot be removed by ordinarycleaning machinery and in most cases must be con­trolled by fumigation.

The rice or corn weevil is about one-eighth ofan inch long and can fly long distances. Infestationsmay occur in the field when the grain begins toripen. This is especially true with grain sorghum.The rice or com weevil can be distinguished fromthe granary weevil by the four light spots on itswing covers, and by the fact that it can fly. Thegranary weevil is slightly larger than the rice weevilbut it cannot fly; consequently, infestations aremore limited. Both sPecies are destructive in thelarval and adult stages. The lesser grain borer isa small, dark brown or black beetle with a rough­ened surface, about one-eighth of an inch long and

one-thirty-second of an inch wide. Its head turnsdown under the thorax. The adult Angoumoisgrain moth is small and buff-colored, with a wingspread of one-half to two-thirds of an inch. ~"he

hind wings have a heavy fringe of hairs longer thanthe wing width. The adults do not feed on grain.The females deposit eggs on the kernel, and theyoung larvae bore into the seed and destroy it. Thisinsect also may infest grain while it is in the field.

Secondary Pests

Some of the more common species of secondarystored grain insects are the rice moth, Indian mealmoth, Mediterranean flour moth, flat grain beetle,confused flour beetle, cadelle and sawtoothed grainbeetle. These insects feed primarily on crackedgrain or grain that has been damaged by primaryinsects.

Psocids or book lice and grain mites are addi­tional pests of a secondary nature found occasionallyin large numbers in grain and grain products.

PREVENTION AND TREATMENTOF INFESTATIONS

When storing grain in farm facilities, take ade­quate steps to provide the least favorable conditionsfor insect development. Store clean, sound grainwith a moisture content of 12 percent or less. Graincontaining more moisture attracts insects, promotesmold growth and may induce heating. Dirty or

Angoumois grain moth (adult),wingspread of about 2/3 inchlong -

Lesser grain borer (adult),about '/a inch long and 1/32inch wide

Indian meal moth,wingspread ofnearly 3/.. inch

Flat grain bee­tle, about 1/16inch

Saw - toothed grainbeetle, about 1/10inch

cracked grain more readily attracts insects. Avoidfilling grain bins too full. Allow for working spaceto inspect grain and to fumigate if necessary. i\.ddi­tional information on proper grain storage facilitiesis contained in Extension publication B-227, GrainStorage.

Prior to storage, clean and treat bins thoroughlywith an approved residual spray. When grain isbeing put into final storage, an approved protectantinsecticide can be mixed with the grain. Duringstorage, surface moth infestations can be reducedgreatly by employing surface spray treatments withcertain materials. Control of other pests feedingbelow the surface requires thorough fumigation,vith liquid, gaseous or volatile solid fumigants.

Storage Bin Cleanup

Store grain only in bins that have been cleanedthoroughly. Remove old grain, trash, feed sacksand other debris that furnish living quarters forinsects. Sometimes it is necessary to "sweep down"the ceiling and walls and clean the floor to removehidden waste. Cover cracks with builders moldingor other suitable material to prevent grain fromcollecting. Destroy grain and other material beneathand near the bins.

Residual Bin Spray

After the bin has been cleaned thoroughly, sprayinsid~ surfaces with one of the following formula­tions at the rate of about 2 gallons per 1,000 square

feet of surface area. Larger volumes of the spraymixture will be needed for spraying external areas.

Methoxychlor 2Y2 percentMalathion (premium grade) 2~ percent

Methoxychlor is available both as a wettablepowder and an emulsifiable concentrate. To obtaina 2~-percent mixture of this material, add 2 poundsof 50 percent wettable powder to 5 gallons of wateror one-half of a gallon of 25 percent emulsifiableconcentrate to 5 gallons of water. If malathion isused, mix 1.6 pints of 57 percent premium grademalathion emulsifiable concentrate in 5 gallons ofwater or I gallon of the concentrate to 25 gallonsof water to obtain a 2~-percent mixture.

Allow treated surfaces to dry thoroughly beforeputting grain into the bin.

Grain Protectants

Premium grade malathion may be used as agrain protectant on wheat, oats, rice, corn, rye,barley, grain sorghum, peanuts and field or gardenseeds. This material may be applied as a dust orspray at the time the grain is being placed in finalstorage. The spray application is preferred overthe dust treatment. Use only premium grade mala­thion. One pint of 57 percent premium grademalathion mixed with 2 to 5 gallons of water isrequired to treat 1,000 bushels of grain. A speciallyprepared 1 percent malathion impregnated wheatflour may also be used at the rate of 60 poundsto 1,000 bushels of grain.

Sprays may be applied to the grain stream asthe grain is being unloaded or turned into finalstorage. Any type of standard spray arrangementis suitable for applying malathion. After the sprayequipment has been selected, calibrate the sprayerby spraying a known volume of water to determinethe exact amount of water the sprayer puts out ina given time. Correlate this volume with the rateof grain flow and apply the correct amount ofmalathion per 1,000 bushels.

Small quantities of grain to be used for plantingseed can be protected from insects by treating withmalathion or methoxychlor dust at a dosage to

provide 2 ounces of active ingredient per bushelof seed. Do not use treated seed as food or feed.

Insect-free planting seed also may be protectedfor several months by storing in commercially avail­able insecticide-treated bags.

Surface Treatments

Post-storage surface treatments help prevent orcontrol surface infestations of the rice moth, Medi­terranean flour moth and Indian meal moth. Applypremium grade malathion wheat flour dust ormethoxychlor dust to the grain surface to provide5 ounces of actual malathion or 0.13 ounces ofactual methoxychlor per 1,000 square feet of grainsurface.

Water sprays prepared from premium grademalathion or methoxychlor emulsifiable concen·trate can also be used as surface treatments formoth control. Apply mixed sprays at the rate of1 to 2 gallons per 1,000 square feet of grain surface.Mix concentrates with water in the proper propor­tion to provide application rates of 5 ounces actualmalathion or 0.13 ounces of methoxychlor per 1,000square feet of grain surface. For example, mostmalathion emulsifiable concentrates contain 5pounds (80 ounces) of active ingredient per gallon.Mix one-half pint (8 fl. oz. or 1/16 gallon) ofmalathion concentrate in the amount of water tobe applied per 1,000 square feet to obtain thecorrect rate of malathion (5 ounces) by weight.

To control established infestations of Indianmeal moth on shelled corn or grain sorghum~ userefined mineral oil instead of malathion or meth­oxychlor. Mineral oil used for this purpose mustmeet the following specifications: (1) unsulfonated;(2) technically white; (3) 100 to 200 seconds viscosity(Saybolt, 1000 F); and (4) free of objectionableodors. Apply 2 quarts per 100 square feet (5 gal­lonsfl,OOO square feet). If the treated surface isdisturbed by walking across the grain or probingfor insects, retreat the disturbed area. Major oilcompany bulk stations can usually supply mineraloils meeting the above specifications.

Surface treatments are ineffective for controllingweevils~ beetles and Angoumois grain moths feedingbelow the grain surface.

Fumigants

Effective control of primary insects developinginside grains and others which feed below the grainsurface requires fumigation with one of severalapproved chemicals. Fumigants are available inliquid, gases and "olatile solid formulations.Formulation choice depends upon experience, appli­cation and safety equipment available, amount ofgrain to be treated, construction of storage facilitiesand other factors. Fumigants are highly toxic tohumans and should not be used by inexperiencedperwns or without proper safety equipment.

Liquid Fumigants

Several commercially available liquid fumigantsare effective against stored-grain pests. Formula­tions usually contain a mixture of two or moreliquids, and it is impractical to list the variouscommercial mixtures in this publication. Sincedosages vary according to the ingredients and some­times according to types of grain, follow directionson the label explicitly. Observe strictly all safetyprecautions to avoid application hazards.

Liquids commonly used in fumigant mixturesinclude ethylene dibromide, ethylene dichloride,carbon tetrachloride and carbon disulphide. Donot use carbon disulphide alone because of the firehazard.

Liquid fumigants are usually applied to thegrain surface and the fumes, because they areheavier than air, penetrate the grain mass to a depthof 10 to 12 feet. Control is much less effective atgreater depths.

Gaseous Fumigants

Two gaseous fumigants, methyl bromide andhydrogen cyanide, are commonly used. They areusually released from pressurized containers into thestorage areas. Since these gases are lighter thanair and will not effectively penetrate downwardthrough the grain mass, they are normally employedin facilities having recirculation systems which forcethe fumigants through the entire grain mass.Gaseous fumigants are hazardous and requirespecial equipment and precautions for handling.Application should be done only by experiencedpersons equipped to use these materials.

Volatile Solid Fumigant

Pellets or tablets containing 55 percent alumi­num phosphide (Phostoxin®) can be used to fumi­gate stored grain. This material is extremely dan­gerous if improperly used) so it should be appliedonly by experienced persons who are thoroughlyfamiliar with proper use procedures. Tabletsproperly placed in the grain mass are activated bymoi ture to release highly toxic phosphine gas.Depending upon grain temperature, fumigation iscomplete after 3 to 5 days. In certain applications,the tablets can be pulverized and applied with aspecial grinder-blower apparatus.

PROPER USE OF FUMIGANTS

All fumigants are dangerous and can causeserious injury or death if improperly handled orapplied. Before using any fumigant, read the labelthoroughly to avoid misuse which might result inpoor control, application hazards or exce si e resi­dues. Use only on specified stored grains. Fumi­gants properly applied for approved u es will notresult in excessive residues above those permittedunder federal regulations if all applicable restric­tions are conscientiously observed.

When to Fumigate

In many instances, grain is infested in the fieldand should be fumigated as soon as it is stored.

After grain has been stored, make inspectionsat about 2-week intervals. Take probe samples atvarious areas and depths throughout the grain.Sift the samples through a 10 to 12-mesh screenand examine them for insects. Apply fumigantsif one granary weevil, one rice weevil or one lessergrain borer or as many as five insects of otherspecies, such as bran beetles, cadelle or grain mothsare found per quart sample of grain. Before fumi­gation, spray the outside of the bin with a residualspray to kill insects forced out of the building bythe fumigant. Also, destroy all waste grain outsideof the bin to preven t carryover of insect pests.Fumigants are most effective when the grain tem­perature is 70 to 85 degrees F. and the air is calm.

How to Fumigate

Make a special effort to make the grain bin astight as possible before fumigation. The grain

surface should be level to insure even penetration.Apply liquid fumigants to the entire grain surfaceas a coar e spray. A 3 to 5-gallon capacity hand­type compressed air sprayer may be used to obtaina coarse pray; remove the spray nozzle and flattenthe tip of the spray rod with pliers, or remove thedi c from the spray nozzle.

U e some form of power equipment when fumi­gating a large volume of grain. Compressed airtanks or diaphragm or brass gear pumps may beused. These pumps may be operated by a smallmotor or from the power take-off of a tractor. Selector construct a discharge nozzle that disperses theliquid in an even pattern as a coarse spray. Closethe bin immediately after applying the fumigantand do not open it for at least 24 hours-preferably4 or 5 days. Air the bin at least overnight beforeentering. Fumigated grain may be fed to livestockas soon as no fumigant odor is present.

Fumigants, when applied properly, penetrategrain and in most cases kill all stages of insects toa depth of 10 to 12 feet. Grain may be fumigatedeffectively at greater depths when bins are equippedwith proper aeration facilities. Even when fumi­gation is carried out in structures that are air tightthe movement of outside air influences fumigationefficiency. Consequently, best results are obtainedif fumigants are applied when the air is calm.

CAUTIONS

A II fumigants are dangerous if improperly used.Carefully follow the cautions listed on the manu­facturer's label and use only in strict accordancewith label directions.

Wear gas masks with a full facepiece and propercanister approved by the U. S. Bureau of Mineswhen applying fumigants inside bins. Gas masksof this type will not protect the wearer againstheavy concentrations in bins where oxygen has beenreplaced by fumigants. The effective life of a gasmask canister is limited. Keep an accurate accountof the time that a canister is used and replace itafter 30 minutes of continuous or intermittent ex­posure to grain fumigan ts.

Avoid spilling the fumigant on the skin, cloth­ing or shoes. Remove clothing wet with fumigantat once and wash the skin thoroughly with soap

and water. Do not use or feed grain that has beenfumigated to livestock until aeration has eliminatedthe fumigant odor.

lVhen applying fumigants always work withsomeone who can assist you in case of an accidentor excessive exposure.

Recommendations contained herein were cur­rent at publication. Insecticide restrictions, toler­ances and appro ed uses are subject to change, soalways confirm recommended uses by referring tocurrent labels on insecticide and fumigant con­tainers.

ACKNOWLEDGMENTS

Information in this leaflet was revised andadapted from a previous leaflet by the same titleprepared by C. F. Garner and R. L. Ridgway,former Extension entomologists, and assisted byother members of the Texas A&M University De­partment of Entomology.

For further information contact your localcounty agricultural agent or the Extension ent~

mologists, Texas A&M University, College Station77843.

Cooperative Extension Work in Agriculture and Home Eco­nomics, Texas A&M Universtiy and the United States Depart­ment of Agriculture cooperating. Distributed in furtheranceof the Acts of Congress of May 8, 1914, as amended, andJune 30, 1914.20M-6-70, Revised E T