There are several brand names for Aluminum Phosphide, but perhaps the most common is Phostoxin. This product is produced by Degesch America, Inc. You can obtain product labels and Applicators Manuals from their web site. If you have purchased product without a product label or Applicator's Manual, I encourage you to obtain one and review it BEFORE you attempt to use the materal. If there are any differences in information between my publication (ENTFACT-138) and the product label, the information from the product label takes presidence.
This information will soon be available as ENTFACT-138. Clicking here will take you to a site from which the publication can be downloaded.
Fumigation to control an insect infestation in on-farm storage, should be done by a trained, professional fumigator. Since professional fumigators are not always available to provide timely service, this guide is designed to help farmers who decide to do the fumigation themselves. Buy the product from a dealer that has experience in fumigating grain storage facilities. Obtain all the written guides for using the product properly and talk with the dealer about application techniques. Although special training and certification are required before these fumigants can be purchased, this training alone is NOT ADEQUATE to qualify the person to conduct a fumigation. Considerable study and planning will be needed to complete a safe and effective fumigation. Remember, you will not work with any more toxic compound on your farm.
This guide provides general instructions for fumigating stored grain with aluminum phosphide products. It is not intended to replace label instructions or other material provided by the manufacturer. Aluminum phosphide is formulated in tablets, pellets, paper sackets, plates, and blister strips. While other formulations may be effective, the tablets or pellets are most suitable for farmer application and are the only formulations dealt with within this publication.
Because of the specialized equipment required for the application of methyl bromide and the extreme hazards involved in its use, this fumigant is not recommended for farmer fumigation of stored grain. This does not imply that a properly applied application of methyl bromide is not as effective.
Regardless of formulation, all fumigants are EXTREMELY toxic to humans and other warm-blooded animals, as well as to insects and other pests. As a result, they are classified as Restricted Use Pesticides. They may be purchased only by individuals holding a Private or Commercial Applicators Certification.
Fumigants act on all insect life stages. They control pests by diffusing through the space between grain kernels and into the kernels themselves. Thus, fumigants are able to penetrate into places that are inaccessible to insecticide sprays or dusts. Solid aluminum phosphide formulations release hydrogen phosphide gas when exposed to moisture and heat. Warm, humid air accelerates the reaction while cool, dry air slows it down. The reaction starts slowly, gradually accelerates, and then tapers off.
Application and Distribution of Aluminum Phosphide
Aluminum phosphide tablets and pellets may be applied to the grain mass by probing them below the grain surface, adding them as the grain is turned, and applying to the aeration ducts below the grain mass. Treatment during turning of the grain is not generally feasible in on-farm storage and one of the other methods must be used. In shallow bins, tablets may be probed into the grain using a specially designed 5- to 7-foot long hollow tube . These tubes can be purchased or made from electrical conduit or plastic pipe according to the distributor's recommendation.
The following is a step-by-step description of a typical probe application of aluminum phosphide to grain in a circular steel bin.
MAKE SURE THE POWER TO THE BINS IS OFF AND 'LOCKED OUT' BEFORE YOU ENTER A BIN. PLACE A MAN IN BIN SIGN TO WARN OTHERS OR YOUR PRESENCE.
- Man-in-Bin sign placed near the control panel.
- Tape measure to calculate volume to be treated.
- 2-6 ml polyethylene film cut to the size of grain to be covered. A rope should be attached for easy removal after fumigation.
- Cotton gloves for handling phosphine tablets / pellets.
- Proper respiratory protection for two people. Check fumigant label for specific requirements.
- Probes made from conduit or rigid PVC pipe for applying aluminum phosphide tablets.
- Safety rope for anyone climbing into a bin.
- Shovels to level grain mass.
- Grain thermometer to measure grain temperature throughout the grain mass.
- Warning signs for the fumigant being used.
- Lock to keep unauthorized personnel from turning on power to bins and to keep them out of building being fumigated.
- Monitoring equipment to check gas concentration.
- 2 or 3-inch masking tape, spray glue, glue for polyethylene sheets.
- Instruction manual and label.
- Dosage chart.
- Sufficient fumigant.
- Grain sampling probe.
Remove the "cone" and break up any crusted areas that have formed. When grain is peaked, the action of fumigants is similar to rain on a hillside. The heavier-than-air gases simply slide around the peak, resulting in poor penetration of the grain mass and, therefore, greater survival of pests in the peaked portion of the grain.
Moldy or crusted areas near the grain surface are generally caused by moisture condensation when warmer air in the grain rises to the surface and encounters cold air above the grain. These areas are sometimes hidden from view just below the grain surface. Failure to locate and break them up will result in uneven penetration of grain fumigants and may lead to further deterioration of the grain from mold development and invasion of the grain by insects that feed on grain molds.
Sealing the bin is the single most important step in fumigation. Attention to proper sealing of grain bins before fumigation will often make the difference between success and failure of the treatment. A high degree of air and gas tightness is essential to achieve the required combination of gas concentration and exposure time necessary to kill grain pests.
Metal storage bins are not gas-tight. In fact, many are designed to hold and aerate grain. However, they can be used for fumigation with proper sealing. Bins will vary in tightness, depending upon how well they were built. If the corrugated sections were caulked when put together and bolted tightly, then they will be more gas-tight. Loosely constructed wooden bins may have to be totally covered with a gas-tight tarpaulin to retain enough fumigant to be effective.
Remember, the goal is to confine the gas long enough at the proper concentration to be lethal to the target pests. Sealing is extremely important and demands study and work, but there are a number of techniques that can make the job more effective.
There are several places in a bin where gas can escape. The roof-wall junction may look tight from the outside, but examination from the inside may reveal a gap around the perimeter. This gap is difficult to seal because it is usually dusty and may be damp. Cracks wider than 1 inch are even harder to seal. Before trying to seal these cracks, clean the dust from the surfaces before applying tape or other sealing material. Professionals will clean the surface first and then spray it with an adhesive dispensed from a pressurized can. The gap is then sealed with duct or furnace-cloth tape (which are generally more effective than masking tape). Use at least 2-inch and preferably 3-inch tape when sealing these cracks.
Tape primer is an expensive but useful tool. This comes in pressurized cans, and may be obtained from the fumigant distributor or sometimes from an auto paint store. These materials make the surface tacky and improve the holding quality of the tape. They also can be applied to the adhesive surface of a piece of tape to improve its sticking power.
Polyurethane foams can be used to seal gaps but they are expensive and difficult to remove if the gap is needed for extra grain aeration. Unless insects burrow into the foam and destroy its effectiveness, the seal can last for several years.
Another key area is the gap between the bottom of the wall and the floor. Some manufacturers design the wall base to accept a special sealant that can give a long-term seal. Various materials have been used, including one made with polyurethane impregnated with asphalt. Plain asphalt has also been used on the outside but does not have as much elasticity.
Roof ventilators need to be covered with plastic bags. Bags are less likely to tear against sharp edges if a burlap bag is placed over the ventilator first. The plastic bag should be gathered in at the base and then taped in place.
Bin doors are not gas tight. They can be cleaned and sealed with masking tape, or if not used regularly, they can be sealed with foam-in-place plastic.
Aeration fans and housings must be sealed to avoid gas loss. Normally, polyethylene glued to the air intake will be sufficient. However, the unit should be examined for other potential leaks.
Determine the number of tablets required to treat the volume enclosed by your sealing efforts. Hydrogen phosphide is a very mobile gas and will penetrate to all parts of the storage structure. The dosage must be based upon the total volume of the space you have enclosed by your sealing efforts, and not on just the amount of grain the bin contains. For example, this may include the area below a perforated floor or the volume of aeration ducts in a concrete floor or the head space above the grain mass if you have sealed the entire bin instead of covering the top of the grain with a gas-tight cover.
The dosage listed on the aluminum phosphide label will be in a range. Use the higher rate if the bin cannot be adequately sealed and/or it contains grain in poor condition. Use the lower dosage if the bin is exceptionally gas-tight or contains clean, dry grain. Dosages recommended for the various phosphine-producing fumigant formulations are fairly similar. However, the actual amount of phosphine involved in specific fumigations will vary depending on the type of structure to be treated. Because phosphine distribution is not materially affected by being taken up by the grain, application rates are based primarily on the gas-tightness of the structure and the method of application.
Follow label instructions for dosage increases or decreases.
All fumigant labels provide information on the recommended dosages required to effectively treat stored grain. Using less fumigant than recommended can result in a concentration of gas too low to be effective. Using more fumigant than recommended is illegal, may leave an unwanted residue, adds unnecessary cost, will not increase efficiency and may lead to resistance in the pest insects.
Dosages for aluminum phosphide formulations are expressed in terms of tablets per 1,000 bushels storage capacity or 1,000 cubic feet of space.
Use the following formulas to calculate the number of bushels in a bin.
0.6283 x diameter (ft) x diameter (ft) x grain depth (ft) = the number of bushels in a round bin. (THIS DOES NOT INCLUDE THE AREA ABOVE THE GRAIN MASS)
+ The applicator must post warning signs at all entrances to the fumigated area.
+ These signs must contain:
the words: DANGER/PELIGRO"
the SKULL AND CROSSBONES symbol in red,
"area and/or commodity under fumigation,
"DO NOT ENTER/NO ENTRE."
"This sign may only be removed after the commodity is completely aerated (contains 0.3 ppm or less phosphine gas). If incompletely aerated commodity is transferred to a new site. The new site must also be placarded and workers must not be exposed to more than 0.3 ppm phosphine."
+ date and time fumigation begins,
+ date fumigation is completed,
+ names of a fumigant used,
+ name, address, and telephone number of the applicator.
Divide the total number of tablets needed by four to place in each pie-shaped quarter of the bin. For example, if the total number of tablets required for the bin is 280, the number for each quarter is 280 divided by four which equals 70. Typically, five tablets are applied at each probe site, so the number of tablets needed for a quarter of the bin (70) should be divided by five to determine the number of probes needed. In this example, each section would be probed 14 times and with five tablets deposited in each probe.
When placing the tablets in the probe, place the first one when the probe is down 5 feet, then raise the tube one foot and drop the next tablet . Continue until five tablets are placed. The last tablet should be about 6 inches from the surface.
As many as 20-50 tablets may be released at one probe site; however, releasing all the tablets at once may slow the release of gas and may cause an explosion. Arrange for enough applicators and other workers to complete the job quickly enough to avoid excessive exposure to hydrogen phosphide gas. The production of gas during application can be reduced by opening the flasks out-of-doors and conducting fumigation when temperature in the bin is lowest.
APPLICATORS SHOULD WORK IN PAIRS AND BE PROPERLY FITTED WITH RESPIRATORY DEVICES.
If gas monitoring equipment is available, the permissible gas concentration ranges (based on eight hours, Time Weighed Average) for various types of respiratory protection devices are:
| Gas Concentration | Respiratory Protection |
| Less than 0.3 ppm | None required |
| 0.3 - 15 ppm (or escape from levels up to 1,500 PPM) | NIOSH/MSHA approved full face gas mask - hydrogen phosphide canister combination. |
| More than 15 ppm | NIOSH/MSHA approved self- contained breathing apparatus (SCBA) |
If monitoring equipment is not available and the gas concentration is unknown, an NIOSH/MSHA approved self-contained breathing apparatus is required.
If monitoring equipment is not available on a farm and application cannot be done from outside the structure, an approved canister respirator must be worn during application from within the enclosed indoor area.
After all sections of the bin have been probed, close the bin and seal the access point with masking tape or plastic glued into place. This seal prevents the fumigant vapors from venting to the outside and prevents the wind from drawing the fumigant out of the grain. Gas loss can be reduced by placing a polyethylene sheet cut to size over the grain before sealing the door. Fasten a rope to this sheet so it can be removed safely after the fumigation to prevent moisture condensation problems. Remove the plastic immediately after the fumigation is complete to prevent moisture condensation and avoid hindering aeration. Use proper respiratory protection when removing the plastic. The rest of the bin still needs to be well sealed for best results.
If the grain temperature is considerably warmer than the outside air, or if the grain is more than 12-15 feet deep, the professional fumigator may place as many as 25 percent of the tablets in the aeration system. Tablets or pellets should never be stacked on top of each other. Never place aluminum phosphide on a wet surface or in standing water since it would evolve the gas too fast and could possibly ignite or explode. Once aluminum phosphide tablets or pellets have been exposed to air, they should not be resealed since they may ignite or explode spontaneously. Be sure to seal fan opening.
The amount of time for exposure of the gas to the grain must be long enough to provide for adequate control. Lengthen the time at lower temperatures because insects are more difficult to kill under these conditions.
Temperature |
Pellets |
Tablets |
Below 40 degrees F |
Do Not Fumigate |
Do Not Fumigate |
40 - 53 degrees F |
8 days |
10 days |
54 - 59 degrees F |
4 days |
5 days |
60 - 68 degrees F |
3 days |
4 days |
Above 68 degrees F |
2 days |
3 days |
1As a rule-of-thumb a minimum of one day should be added to the exposure time listed above for each 10 feet the gas must penetrate downward. It is preferable to add two days for each 10 feet.
Spray the outside of the bin following fumigant application and after sealing is completed. Use premium grade malathion, methoxychlor, or Reldan, and spray to point of runoff. Follow instructions on the container label for mixing rates.
If the area is to be entered after fumigation, it must be aerated until the level of hydrogen phosphide gas is 0.3 ppm or less. Remove the plastic covering from the grain surface immediately after fumigation even if the bin is not to be aired out. The area or site must be monitored to insure that liberation of gas from the treated grain does not result in the development of unacceptable levels of hydrogen phosphide. Do not allow the re-entry into treated areas by any person before this time, unless protected by an approved respirator.
Fumigants do not provide any residual control. After the bin is aired out, you may wish to consider spraying the grain surface with a recommended grain protectant to reduce insect reinfestation and fogging the space above the grain to kill flying insects.
At the end of a phosphide fumigation, the powdery residue of tablets or pellets will contain a small amount of undecomposed aluminum phosphide for several additional days. Under normal circumstances of grain handling, these residues do not present a hazard, but inhalation of the powder should be avoided.
Determining concentrations - It is very important to monitor the fumigant concentration to determine any losses due to sorption or leakage so that adjustments can be made if necessary. It may be necessary to reseal an area, add more gas, or lengthen the exposure period to give the proper concentration of fumigant for the necessary time. After the fumigation is over, it is equally important to be able to know that the gas has been reduced to a level below the 8 hour Time Weighed Average (0.3 ppm) to insure worker safety upon reentry.
There is no single device that can economically and efficiently measure all fumigants at all normal levels. Various devices can be used depending on the gas being measured and whether a high reading during the fumigation or a low-range reading for compliance with the Time Weighed Average after the fumigation is needed. Follow instructions for the particular device you use.
Detection tubes are probably the most versatile tools available for measuring gas concentrations. They are available for many industrial gases, as well as almost all fumigants. The equipment used with the tubes is well-built, durable, and manufactured by a number of suppliers. The initial cost of the equipment is moderate and can be amortized over hundreds of uses and many years. For most gases, they are sufficiently accurate.
The disadvantage to using these tubes is that they are designed for a single use on a single type of fumigant. Their cost of over $4 per tube can be burdensome when many readings are needed.
They are not available for both high and low readings so separate tubes of different capacities must be used. The tubes have a limited shelf life and are not reliable after the expiration date. In addition, they have limited accuracy on some gases.
Plastic tubing must be placed so that air within the bin may be sampled from outside the bin.
All fumigants are dangerously when improperly used. Follow the cautions listed on the container label and use only in strict accordance with label directions.
Wear respiratory protection approved by NIOSH/MSHA for the level of hydrogen phosphide gas to which you will be exposed to.
The effective life of a gas mask canister is limited. Keep an accurate account of the time that a canister is used and replace it after each use, if you smell fumigant, or the canister is out-dated.
Self-contained breathing apparatus requires a refilling source. Your local fire station or rescue squad may be a refill source.
Never fumigate a bin by yourself. Have another person on site to help if you get into trouble. The helper must also be properly fitted with approved respiratory protective devices. Devise a code so that you can communicate with each other. Make sure gas and electrical connections are turned off. Have the telephone numbers of the police and fire departments, hospital, physician, and rescue squad available.
Do not drink alcoholic beverages for a day before, during, or after exposure to grain fumigants. Do not think that because you might have gotten away with fumigations without these precautions before that you can always get away with disregard to safety. Fumigants demand respect if you want to avoid injury or death.
If there are differences in statements in this guide and the aluminum phosphide label, follow the label instructions.
Grain in flat-storage, machine-shed type buildings should be covered with a tarpaulin for maximum effectiveness.
Avoid falling or coming in contact with electrical wires when doing this.
Peters, Leroy L. 1992. Fumigating Farm-Stored Grain with Aluminum Phosphide. CES, University of Nebraska, Lincoln, Nebraska
Leesch, J.G., G. Cuperus, J. Criswell, J. Sargent and J. Muller. Practical Fumigation Considerations. In. Stored Product Management. V. Krischik, G. Cuperus and D. Galliart eds. CES Circular No. E-912. Jan. 1995.
Pedersen, John R., Randall Higgins, F. Robert Hernderson and Charles Lee. Stored Products Pest Control. Pesticide Applicator training Manual, Cat.7B. CES. Manhattan, KS. 1996.