“Fumigation shall be scheduled when insect population has grown above the ‘control threshold’ triggering a corrective action. Several corrective actions may be used to lower insect population but the value of fumigation cannot be compared to spraying, fogging and cleaning. On the day after the fumigation, grain will start coming into the mill. It is obvious that his grain must be free of insects. Good planning will combine grain fumigation with mill fumigation.”
Mill fumigation is an expensive and important procedure for most mills. It helps to zero the insect population in the milling lines, in the empty bins and in the mill building. The mills stop for a few days to get a fumigation and usually combine it with thorough cleaning and equipment maintenance.
When is fumigation needed?
Fumigation shall be scheduled when insect population has grown above the “control threshold” triggering a corrective action. To monitor insect population, a mill needs a complete system of pheromone and UV traps that collect insects in various locations. Insect traps should be able to catch all potential stored product insects that are expected in a mill including the following species: Tribolium, Sitophilus, Rhyzopertha, Oryzaephilus, Plodia interpunctela, Efestia elutela, Trogoderma, Psocids and mites (mites are not insects, they are small arthropods belonging to the class Arachnida).
A complete monitoring system shall have traps in all floors and areas and the traps shall be regularly inspected at a frequency of not less than monthly. An average number of 1-2 insects caught per trap per month could be regarded as acceptable with no need for corrective action. When this number grows, action is needed.
Several corrective actions may be used to lower insect population but the value of fumigation cannot be compared to spraying, fogging and cleaning.
Fumigation planning must include several aspects like:
Emptying the bins. Mill bins and silos may be left full only if the fumigant label allows it. In the case of heat treatment, all bins shall be empty. A bin left full or partly full, may allow insects to hide in the grain or flour and survive the heat.
Remove ingredients, packed product, empty packaging and anything else that may be negatively affected by the treatment. In the case of heat treatment remove fire distinguishers, bottles under pressure and flammable material.
Make a thorough cleaning.
Seal the mill if using a fumigant. Sealing is the most important part of fumigation. At the end of sealing make a pressure test. Do not start the fumigation until the pressure test is satisfactory.
Check the weather forecast. If wind is expected, postpone the fumigation or do not use fumigant. Make a heat treatment. If the temperature is low check the fumigation protocol. It may not be allowed to proceed with the fumigation unless you use heaters to increase the ambient temperature in the mill.
Fumigant: sulphuryl fluoride
Check the label and use the proper dosage. Use many monitoring lines. Use fans to distribute the gas in the building. Have additional gas, to cover leakage. Monitoring shall be carried out using the appropriate equipment and software.
Phosphine shall not be used to fumigate mills as it reacts with copper. Electrics and electronics will be corroded.
When heat is used, sealing the building is not necessary. Sensors shall be placed in many areas to monitor the treatment and identify under or overheated points. Monitoring shall be carried out using the appropriate equipment and software.
All fumigants and heat are covering the inside part of the building. It is extremely possible that insects are moving also on the outside walls. This is heavily expected during heat treatments as adult insects try to escape the heat and may find an opening through a window or else. Spraying on the outside walls with contact insecticides is not an additional option. It shall be part of the fumigation. Special lifting trucks may be needed to spray on a tall building –like most mills are. The weather shall be also checked to avoid rain.
Fumigation of grain
On the day after the fumigation, grain will start coming into the mill. It is obvious that his grain must be free of insects. Good planning will combine grain fumigation with mill fumigation. Monitoring of silo fumigation is necessary as well as gas recirculation.
Before entering the mill fumigators must be sure of gas concentration. Aeration is equally important as fumigation. Calibrated sensors must be available and report form each area of the mill. Before allowing workers to get in, a thorough inspection with the right meter must take place by a senior fumigator. Fans shall be available to help pushing the fumigant out. There is no reason to take risks.
Follow up inspection
Every fumigator must make a thorough inspection of the mill when a fumigation is over. The inspection may reveal gaps and mistakes that shall be noted in order to be avoided in future treatments. Ideally this inspection will be made together with a mill representative.
The role of the mill managers
A fumigation weekend shall not be a weekend on the beach for the mill personnel. A mill employee with training on IPM must follow the fumigation process with the fumigators to evaluate their work and help by pointing out the mill weak points. Pest management shall always be a combined effort of fumigators and industry people.
Failing a fumigation is easier than succeeding it.