Factors that affect Fumigation for the control of Store insects and pests

1.     Types of Fumigation

Chamber and vault fumigation

2.      Vacuum chamber fumigation

3.      Vehicle fumigation: railroad car, truck or van

4.      Tarpaulin fumigation

5.      Spot fumigation

6.       Structural fumigation

7. Empty building fumigation: warehouse, grain elevator, food processing plant, mill,  restaurant

8.Shipboard, in transit ship  fumigation

9.      Farm grain storage fumigation

10.   Rodent burrow Fumigation

Factors that Modify Fumigant Effectiveness

fumigants are used in various formulations and dosages according to the nature otthe commodities and pestsinvolved. Factors that modify fumigant effectiveness that must be considered when selecting a formulation include the following:

1.      Pests to be controlled 

2.      Temperature

3.      Moisture

4.      Structure area fumigated

5.      Method of application

Pests to be controlled.

A pest's susceptibility to fumigants depends on the species, its stage of development, and-its habitat. In general, fumigant gases reach the insects' tissues through the respiratory system. Most insects breathe through a series of openings, called spiracles, in the outer skeleton. Once inside the insect's body, oxygen from the air and fumigant gases are diffused through the insect's thin cell membranes. Some primitive insects and mites, close relatives of insects, breathe by taking in air through the cuticle, which covers the whole body. The life stage of the insect that is least active metabolically (e.g., pupae, hibernating adults) is the most difficult to kill by fumigation. Fumigant labels give dosages needed for different species of insects and different life stages of those species. For this reason, a fumigators should know some pest biology. Insects that have been fumigated with methyl bromide die slowly. At first, they may be unable to walk or fly normally. They usually come to rest on their backs and eventually are unable to recover from that position; however, they may move their heads, legs, or antennae for as long as several days before they finally die. (Some fumigants may anesthetize insects so that they appear to be dead shortly after fumigation only to revive and resume normal life.) Persons accustomed to seeing a quick kill are sometimes disappointed by observing insects that have been exposed to lethal dosages of slowacting fumigants. Such insects are doomed to die eventually.

Temperature.

 Sub-lethal concentrations of the fumigants gas may result if fumigation is done at abnormally high or low temperatures. At low temperatures, the fumigant vaporizes and diffuses slower. Insect activity and metabolism are likewise slower. These factors tend to retard killing action, especially at temperatures below 10° C (50°F); thus, at lower temperatures, you must use higher dosages and longer exposure time for a successful fumigation. Conversely, at excessively high temperatures, fumigants vaporize faster and may dissipate too soon for lethal concentrations to be maintained long enough to kill pests, especially if the seal of the fumigation site is not perfect. In the range of normal fumigating temperatures (60° to80° F), the fumigant concentration needed to kill a given stage of an insect species decreases with the rise in temperature; this is mainly due to the insects' increased respiration rate, in response to the rise in temperature. Death occurs faster in the higher end of the normal  temperature range. fumigant labels generally warn not to use the product at temperatures below 40° F (5° C); some soil fumigants also set an upper boundary.

Moisture.

 Adequate moisture is required for release of the actual toxicant, phosphine, in aluminum phosphide and magnesium phosphide products. At relative humidities below 25%, or gram moisture below 10%, release of phosphine requires more time. Excessive moisture may interfere with fumigant action by reducing fumigant concentration within a commodity, or by retarding aeration during soil fumigation. Do not fumigate extremely dry soils because a certain amount of moisture is needed so that weed seeds will germinate and can be killed while actively growing. Thus, as in the case of temperature, there is an optimum for moisture. Product labels give appropriate information on the effects of moisture.

Air Movement.

Fumigate when there is little air movement. Regardless of how well the enclosure to be fumigated is sealed, wind can create problems due to

leaks. Leaks in an enclosure are the single most likely cause for fumigation failures.

Structure, Site or Commodity.

The most important step in a structural fumigation is the proper sealing of the structure the more tightly sealed the structure, the more efficient the fumigation. Because wood is porous, wooden structures, even well-sealed ones, will not retain fumigant gases as well as those made of metal, plastic, masonry, or concrete. Cement blocks are also porous and likewise are a problem for efficient fumigation. Increased dosages and exposure times can compensate for the loss of gas through diffusion into porous building materials. Tarpaulin Fumigation using a gasproof sheet or cover is more effective than sealing a building with paper or tape and holding a fumigant within structural walls. Tarpaulin fumigation has the advantage of reaching the exterior wood areas (doors, sills, etc.) which may be infested. Ideally, a fumigant should not change the quality of or damage the treated commodity in any way, or leave any hazardous residue during processing of the commodity that could be harmful to the consumer. In fumigation, as in any pesticide treatment of a raw agricultural commodity or packaged food product, the "tolerance" must be considered. The tolerance, or tolerated residue, is the amount of the pesticide's active ingredient that is considered safe to consume and is legally permitted to remain in the commodity. Tolerances are expressed in parts per million, which is the same value as milligrams per kilogram (1,000 grams). On methyl bromide product labeling, the tolerances are given for the raw agricultural commodities for which the chemical has an established tolerance, along with the stored product pests to be controlled, dosages, and exposure times. Follow dosages and exposure times in order not to exceed the legal tolerances in the commodity fumigated. Grain fumigation can be affected by type and condition of the grain: size, shape and permeability of the kernels, and the amount of dockage (chaff, dust, etc.) in the grain. "Sorptive capacity" of stored grain refers to adsorption, the adhesion of the fumigant gas molecules to theexternal surface of the grain, plus absorption, the holding of gas molecules within the kernel by capillary action. Other factors being constant, sorptive capacity of a grain increases with a decrease in kernel size and a

corresponding increase in surface area. Permeability of seed coat is also a factor. Increased sorptive capacitymeans less gas fumigant in the surrounding air; hence, recommended dosages are generally higher for smaller grains such as wheat, rye, or sorghum than they are for corn. A more complete discussion of the factors affecting grain fumigation accompanies this fumigation training manual. Persons planning to fumigate stored food commodities should carefully read this manual.