Fumigation is a method of pest control that uses gaseous pesticides to suffocate or poison pests within an enclosed area. It involves sealing an area, releasing a fumigant gas, holding the gas for a period to kill any infestations, then ventilating to remove the gas. Common fumigation methods include direct mixing of solids or liquids into grain/materials, surface application of liquid fumigants, spraying large bulk storage areas, sealing and gassing small farm storage areas, targeting surface infestations, and treating localized "hot spots" of infestation. Fumigation remains widely used and technological developments have improved procedures, though some highly hazardous fumigants have

1. Fumigation

2. DEFINITION
Fumigationis a method of pest controlthat
completelyfills an areawithgaseouspesticides
or fumigants—to suffocateor poisonthe pests
within. It is used to controlpests in buildings
(structural fumigation), soil, grain, and produce,and
is also used during processing of goodsto be imported
or exportedto prevent transfer of microorganisms.
In modern terminologya fumigant is a chemical
which, at a requiredtemperature andpressure, can
exist in the gaseous statein sufficient concentrationto
be lethal to a given pest organism. This definition
implies that a fumigant acts as a gas in the strictest
sense of the word.

3. This definition excludes aerosols, whichare particulatesuspensions of liquids or solidsdispersed in air,
and whichare popularlyreferredto as smokes, fogs or mists.
It is important to make this distinction at the outset because it emphasizesone of the most important and
useful properties of fumigants:as gases theydiffuse as separatemolecules.
This enables them to penetrateintothe materialbeingfumigatedand to diffuse awayafterwards. On the
other hand, aerosols are unable to penetrateevena short distance intomaterials because theirparticles
are deposited at the outer surfaces.

4. PRESENT STATUS OF FUMIGATION
Fumigantsare stillwidelyused for the controlof insects and other pest organisms. Because of their
unique characteristicsand the great adaptabilityof the fumigationtechnique, fumigants can often
provide effective, economical control where other formsof pest control are not feasible.
In manycasestreatments can be carriedout on infested material without disturbingit in anyway.
The development of lightweight plastic sheetsto enclose spaces or materials requiringfumigationhas
extendedthe use of fumigants and made control procedureseasier andmuch more adaptable.
Several modern technological developments, includinginstrumentation for gas detection and analysis,
improvedformulations as well as increaseddemandfor effectiveand economicalpest control measures,
havedone muchto improve fumigation procedures.

5. Modern technologyand researchhave also brought to light certainproblemswith
fumigants that were previouslyunknown.
In some cases fumigants withexcessive hazard potential have been restrictedor prohibited
so that theyare no longerwidelyused for pest control in some countries.
Fumigant use is, more and more, beingdetermined on a risk-benefit basis, where materials
withunusual hazards are usedonlybecause no effective substituteis available.
Whensuch materialsare used, the fumigator should take additionalprecautions to avoid
anyhazard.
Misuse or accidents that generateadverse publicitycan do muchharmto the practice of
fumigation and may jeopardize publicacceptance of other fumigantsnot havingsuch
effects.
Great care shouldbe taken to ensure that fumigants are always used wiselyand carefully.

6. PROCESS
Fumigationgenerallyinvolves the following phases:
First the areaintended to be fumigatedis usuallycoveredto createa sealed environment;next the
fumigant is releasedintothe space to be fumigated;.
Then, the space is heldfor a set period while the fumigant gas percolates throughthe space and acts on
and kills anyinfestationin the product,.
Next the space is ventilated so that the poisonous gases are allowedto escape from the space, and render
it safe for humans to enter.
If successful, thefumigated areais nowsafe and pest free.

7. METHODS
OF
FUMIGATION

8. 1. DIRECT MIXING
The fumigant is applied to the grainso that it is distributed as evenlyas possible fromthe beginningof
the treatment. Direct mixingis oftenemployed when infestation is general throughout the massand
when there is access to the grainstreamduring fillingor transferfromone binto another.
Onlysolidor liquid-type fumigants are used in this way. Fairlyevendistribution of the gas withgood
controlof the insects can usuallybe obtained. The solid-type fumigants usedfor this treatment are
aluminiumphosphide tabletsor pellets evolving phosphine and granular calciumcyanide evolving
hydrogencyanide.
Aluminiumphosphide tabletsor pellets can be insertedin the grainstreamby hand or withan
automatic dispensercalibrated to delivera dosageappropriateto the rate of loadingin the bin.
Calciumcyanide is usuallydischarged froman automaticapplicator. Also, aluminiumphosphide
powder formulation in paper bags may be added to grainas bins or silos are filled. In thiscase, it is
necessaryto provide for removal of the bagsafter fumigation is complete.

9. 2. SURFACE APPLICATION
The surface applicationmethodhas so far been usedmainlywithliquidtype fumigants. The liquids are
sprayedevenlyover the top surface of the grainand the vapours slowlyevolve and diffuse downward
through the bulk. Thismethodis usuallyemployed onlywhenthe graincannot convenientlybe turned
or as an emergency measure.
Diffusion may be slowand distributionwithsome fumigantsis often not uniform. Carbon tetrachloride
has given good distributionin grainin deep bins.
Less hazardoussubstitutes for carbontetrachloride, such as methyl chloroform, maybe used for this
type of treatment in the future. Unmixed carbondisulphide has been usedin manycountries, although
its tendencyto burn or explode is well known.
Propylene oxide has been usedin France and Algeria. In this type of treatment, the grainis usuallynot
aeratedand the vapours remainin the grainuntil dissipated by leakage.

10. 3. LARGE BULK
FUMIGATIONThe liquid-type fumigants are usuallyapplied to the surface of bulkgrainby means of sprayers. If the
surface areais large,powersprayers may be used. If possible,application shouldbe made fromoutside
the binor storage througha manhole, roof hatch, windowor door.
With all types of sprayer, the nozzlesare removedto facilitatethe rapid applicationof the liquid to the
surface of the grain. For larger bulks, adequatehose and a pump capable of throwinga streamis used.
The spray nozzles may be placedon a spray boommounted on the sledandadjusted to distributethe
required dosage in an even spray on bothsides as the sledis pulled acrossthe storage by meansof a rope
or chain.
If the storage space is wide,two or more sleds shouldbe pulled simultaneouslyacross the surface so that
the operatorscan leave the buildingimmediatelyafter the fumigant hasbeen applied.

11. 4. FARM STORAGE
FUMIGATIONThe gas tightness of the structure is particularlyimportant in small storages, because the mass of grainis
not large enoughin itself to retain vapours once leakagebeginsat any point.Steel, concreteor tight
wooden structures are usuallysatisfactorywithout alterations.
For small cracks or openingsa caulking gun maybe used to applycompounds that willgive a semi-
permanent gas-tight seal. Most wooden storagesare leakyand it maybe necessaryto line the floor and
wallson the inside withstout roofingpaperor plastic sheetingand to nail boards overany visible
openingsin the walls.
Experience has shownthat results are not usuallyas good in small bulks of grainas in largebulks. One
reasonis that there is oftena poor kill on the top surface. Also, in small bulks goodcontrol is more
difficult throughthe massin grainthat is "tough" or has excessive dockage.

12. The use of aluminiumphosphide tablets has proved effectivefor the treatment of small storages.
If aluminium phosphide is used, it is recommendedthat a tarpaulin or polyethylene sheet be placed
carefullyoverthe surface of the grainafter the tabletsare applied.
The best wayto applya liquidfumigant to small storages is by spraying the surface from the outside of
the buildingwiththe aid of a stirruppump. Some liquid fumigants, suchas chloropicrin, are supplied
in cans or bottles.
In some applications, it is convenient and satisfactoryto puncture the cans or openthe bottles, invert
themand thrust the openingabout belowthe surface of the grain. It is recommendedthat the
openingsbe stuffedwithwads of cotton or cellu-cotton to prevent too rapid loss of the liquid, but
looselyenoughto produce a wick effect that willallowthe liquid to flowgraduallyinto thegrain.
This method permits accurate and economicaldistribution of the dosage since the requirednumber of
containers maybe spacedevenlyon top of the grain.

13. 5. SURFACE INFESTATION
With certainspecies of insects, suchas the Indian meal moth, infestation maybe confinedto the top of
the grain. Thisproblemcannot be solved by the usual method of surface application of fumigants
because the vapours diffuse down throughthe grain, and it would thus be necessaryto treat the whole
mass at great expense in order to deal withgrainnear the surface.
Also, turningthe grainonlyspreadsthe infestationthroughout the entire bulkof grain. In silobins or
other storage units, whichcan be made air tight above the grainsurface by closing manholesand other
openings, surface infestations can be treated withmaterials suchas dichlorvos to obtain control,
particularlyinfestations of some of the moths.
Slowrelease resinstrips havebeen found to give satisfactorycontrol of moths in granaries. Surface
sprays of dichlorvos may alsobe used.
For storages withventilators, where dichlorvosvapour maybe lost,an aerosol emission systemhas been
found superiorto the slowrelease strips.

14. 6. ‘HOT SPOT’ FUMIGATION
Treatment of localized areas in a grainmassis often a useful technique for dealing withincipient
infestations. These "spots" are usuallyrecognized and defined by a local rise in temperature.Liquid-type
fumigants applied throughtubes or aluminiumphosphide tablets are the bestmaterials to use. In this
type of work the tendencyis to underdose.
Enoughfumigant should be appliedto maintain the requiredlethal concentration, not onlyin the region
of infestation, hut also in the margins surrounding it for I or 2 m (3 to 6 ft) in everydirection to the spot
itself.
(Note: Results are improved if the marginal applications are made first in a ring surroundingthe ‘hot
spots’)
The vapours fromthe marginal treatmentstend to slowdown diffusionof the fumigant fromthe
infestedspot.