Detail account of fumigation techniques in pest management

BY:

JAYANT YADAV, CCSHAU, HISAR, HARYANA

Preface

Current world population is expected to reach 10.5 billion by 2050 (UN March, 2013), further adding to global food security concerns

Food and Agriculture Organization of U.N. predicts that about 1.3 billion tons of food are globally wasted or lost per year (Gustavasson, et al. 2011).

Reduction in these losses would increase the amount of food available for human consumption and enhance global food security

Unsatisfactory control of pests in stored products results in contaminated products that can cause health, financial, legal and aesthetic problems

Fumigants provide effective & economical control where other forms of pest control are not feasible.

A variety of pests may be found in stored commodities and food processing facilities, depending upon geographic location, physical nature of the facility, and the type of food being processed.

Introduction

• Fumigation is the process of introducing a pesticide into an enclosed space in such a manner that it disperses quickly and act in a gaseous state on the target organism.

• A fumigant is a chemical vapor or gas that, when released, penetrates objects or enclosed areas in concentrations that are lethal to pest organism.

Toxicity of fumigants to insects

• fumigants enter the insect mainly by way of the respiratory system.

• To enter insect eggs, gases diffuse through the shell (chorion) of the egg or through specialized "respiratory channels"

• poisoning of an insect by a fumigant is influenced by the rate of respiration of that insect; any factor that increases the rate of respiration tends to make the insect more susceptible

Impact of environment on fumigants

1. EFFECT OF TEMPERATURE

• most important environmental factor

• range of normal fumigating temperatures from 10 to 35°C

• the concentration of a fumigant required to kill a given stage of an insect species decreases with the rise in temperature.

• At temperatures below 10°C, increased sorption of the gas by the body and also the resistance of insects may be weakened by the effects of exposure to low temperatures.

2. EFFECT OF HUMIDITY

• it is not possible to make any general statements about the influence of humidity on the susceptibility of insects to fumigants

3. EFFECT OF CARBON DIOXIDE

• Carbon dioxide may stimulate the respiratory movements and opening of spiracles in insects.

• With flammable fumigant like ethylene oxide and methyl formatecarbon dioxide may work to advantage both by reducing the fire or explosion hazards and by increasing the susceptibility of the insects.

4. PROTECTIVE NARCOSIS

• Some fumigants can produce paralysing effects on insects

• hydrogen cyanide (HCN) , if certain species are exposed to sublethal concentrations before the full concentration is applied, the resulting fumigation is less effective than one in which the insects are subjected to the full concentration from the very beginning

• Similar in case of phoshine in introduced at higher conc.

Dosages and concentrations • The dosage is the amount of fumigant applied and is usually expressed as

weight of the chemical per volume of space treated and expressed as g/m3 or g / quintal of grain

• While concentration is the actual amount of fumigant present in the air space in any selected part of the fumigation system at any given time .

• CALCULATIONS FOR CONVERSION OF DOSAGE INTO CONCENTRATION VALUES

Example. To convert 1g/m³ of PH3 (molecular weight 34 approximately)• (1x22.4)/34 = .659 cm³per litre

= 659 parts per million by volume CONCENTRATION X TIME (c x t) PRODUCTS Most fumigation treatments are recommended as grammes per cubic metrefollowed by a statement of the length of the treatment in hours.For eg - to kill 99 percent of larvae of Tenebroides mauritanicus (L.) at 20°C, a concentration of 33.2 milligrammes per litre of methyl bromide must be maintained for 5 hours. The product 33.2 milligrammes per litre x 5 hours = 166

-milligrammes per litre x hours is known as the concentration x time product needed to obtain 99 percent control of this insect and expressed as mg h/ lt

ADVANTAGES OF FUMIGATION

• Fumigants are usually quick acting and can result in total eradication of the pest.

• Fumigant kill all insects irrespective of the type of their mouth parts or their mode of feeding

• Fumigant are toxic to all forms of life ,therefore it is possible to control all life stages of the pest

• Reduced residue problems in treated areas

• Because fumigants are gases, they diffuse through all parts of the structure or commodity being treated and can reach pests control materials or techniques.

• For certain commodities, fumigation is the only practical way to control pests.

DISADVANTAGES OF FUMIGATION

• The control achieved through fumigation is temporary i.ethere’s no residual action from fumigants. Where untreated populations of the pests remain, re-infestation of the treated site can take place quickly.

• Fumigants are toxic and often highly hazardous to the applicator, requiring special precautions during application

• Some commodities or pieces of equipment may be damaged by certain fumigants and must be removed or otherwise protected.

• Fumigant activity may be greatly affected by temperature.

TYPES AND NATURE OF FUMIGANTS

1. Methyl Bromide Methyl bromide is a colorless, odorless

and tasteless gas and it is usually formulated with a small amount if chloropicrin as a warning agent.

Against insects, methyl bromide appears to exert its principal toxic effect on the nervous system.

Methyl bromide is also used as a soil fumigant to control fungi, weeds, nematodes and insects.

Methyl bromide is sold as a liquid pressure. Upon release, it vaporizes to form a gas that is about 3.3 times heavier than air.

Methyl bromide reacts chemically with sulfur products and should not be used to fumigate materials such as avocado, soybean flour, flours , baking powder ,rubber and woolen goods.

2. Chloropicrin

Chloropicrin fumigants include products marketed under the names Chlor-O-Pic, Lavacide 100 and Quasar. These products contain nearly 100-percent chloropicrin and are marketed as liquids .

Chloropicrin volatilizes to form a dense gas that is about 5.7 times heavier than air.

Chloropicrin is highly toxic to insects, vertebrates, and many soil microbes, such as fungi. It’s highly irritating to eyes and is powerful “tear gas.”

Uses of chloropicrin on foodstuff have been restricted in recent years.

3. Aluminum Phosphide Aluminum-phosphide fumigants include products marketed under the

trade names Detia, Fumitoxin, Gastoxin, Phostex and Phostoxin. These products contain aluminum phosphide in combination with inert

ingredients such as ammonium carbamate and urea. The formulated material is a solid molded into pellets or tablets.

The active ingtedient, aluminum phosphide, reacts with atmospheric water to produce hydrogen-phosphide gas. This gas is known as phosphine. Phosphine is a colorless gas with an odor that smells different to different people.

Phosphine has an inhibitory effect on insect respiration and is unique in that it is only toxic to insects in the presence of oxygen - in the absence of oxygen it is not absorbed and is not toxic to insects .

Phosphine is only slightly heavier than air, about 1.2 times heavy and it is reactive and very corrosive metals, especially copper, silver, gold, and platinum.

3. Magnesium Phosphide

Magnesium phosphide is similar to aluminum phosphide, releasing hydrogen phosphide gas in reaction with water. Release of the gas is faster than occurs with aluminum phosphide.

Common magnesium phosphide products contain the solid magnesium-phosphide material attached to a strip or blanket that can be put in place very quickly.

Magnesium-phosphide fumigants can be used effectively for warehouse and processing plant fumigation.

Techniques of fumigation for stored grains

1. DIRECT MIXING (VERTICAL STORAGE)

By this method, the fumigant is applied to the grain so that it is distributed as evenly as possible from the beginning of the treatment.

Direct mixing is often employed when infestation is general throughout the mass and when there is access to the grain stream during filling or transfer from one bin to another

Only solid or liquid-type fumigants are used in this way.

Aluminium phosphide tablets or pellets can be inserted in the grain stream by hand or with an automatic dispenser calibrated to deliver a dosage appropriate to the rate of loading in the bin and Calcium cyanide is usually discharged from an automatic applicator.

Storage bins of the vertical type usually have manhole covers in the ceiling and these are usually closed immediately to prevent loss of fumigant

2. SURFACE APPLICATION (FLAT STORAGE)

The surface application method has so far been used mainly with liquid type fumigants.

The liquids are sprayed evenly over the top surface of the grain and the vapours slowly evolve and diffuse downward through the bulk

Carbon tetrachloride has given good distribution in grain in deep bins, carbon disulphide has been used in many countries, although its tendency to burn or explode is well known, Propylene oxide has been used in France and Algeria.

(a) Larqe Bulk Fumigation

The liquid-type fumigants are usually applied to the surface of bulk grain by means of sprayers and the nozzles are removed to facilitate the rapid application of the liquid to the surface of the grain

A method for treatment of high vertical bins of grain by applying methyl bromide with carbon dioxide has been developed by Calderon and Carmi (1973) . The carbon dioxide acts as a carrier and will take the methyl bromide down through the grain mass to the bottom of the bin.

• In flat storage units, in which the depth of the grain does not exceed 10 m (about 30 ft), tablets, pellets or sachets containing aluminium phosphide may be used.

• The fumigant is usually applied by probing into the grain

3. SURFACE INFESTATION

With certain species of insects, such as the Indian meal moth, Plodia interpunctella infestation may be confined to the top of the grain. This problem cannot be solved by the usual method of surface application of fumigants because the vapours diffuse down through the grain.

In silo bins or other storage units, which can be made air tight surface infestations can be treated with materials such as dichlorvos to obtain control

It should also be pointed out that incipient surface infestations of insects may be arrested by using pyrethrum, malathion or other approved materials applied as a fine mist in the space over grain

4. HOT SPOT FUMIGATION

Treatment of localised areas in a grain mass is often a useful

technique for dealing with incipient infestation

These spots are usually recognised and defined by local rise in

temperature

Liquid type fumigants are applied through tubes .

Aluminium phosphide tablets are the best materials in use

Enough fumigant is applied to maintain the required lethal

concentration not only in the region of infestation ,but also in

the margins surrounding it for 1 or 2 m

5.TENT FUMIGATION

A tent ( polythene or nylon

impregnated with vinyl chloride ) is

constructed to cover sacks of grains

Tent can be conveniently stretched

The fumigant is introduced in to the

tent through hoses connected to the

preparing equipment

Most commonly HCN is used as

fumigants

6. VACUUM FUMIGATION

This is done in the case of cotton bales, imported products likely to be infested by insects, packaged food .

The article to be fumigated is placed in a tight sealing steel chamber from which the air has been sucked out to produce a partial vacuum

A fumigant heated 120°F

Due to the partial vacuum the fumigant is able to penetrate the deeper layers of the bales .

The reduction in the oxygen content due to partial vacuum forces the insects to breathe in toxic gas more readily

Today, the technique is used chiefly in plant quarantine work and for fumigating tobacco and other materials, such as compressed bales of jute bags and pressed dates which are difficult to penetrate at atmospheric pressure.

Fumigants -Ethylene oxide/carbon dioxide mixture , Methyl bromide , Hydrogen cyanide

Vacuum fumigator

Fumigation for rodents control

Most commonly employed chemical control measures inclidepoison baits and fumigation.

Initially poison baits are employed for control like Zinc phosphide(2%), Racumin bait, norbormide etc.

But to control the residual population of rodents fumigation is necessary to kill more than 90% of population, otherwise they breed so fast that population reaches the same level within months. For this

Fumigation with Aluminium phosphide tablets, 2 tablets of 0.6 g or half of 3g per burrow have been found effective.

After introducing a tablet into live burrow, the opening is closed tight with soil.

Soil moisture is essential to produce deadly phosphine gas.