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close this bookVector Control - Methods for Use by Individuals and Communities (WHO, 1997, 425 p.)
close this folderChapter 9 - House-spraying with residual insecticides
close this folderInsecticides for residual spraying
View the document(introduction...)
View the documentCharacteristics of good residual insecticides
View the documentResistance
View the documentFormulations
View the documentDosages and cycles
View the documentType of sprayed surface
View the documentCommonly used insecticides
View the documentPreparation of insecticide suspension

Preparation of insecticide suspension

If the standard spraying procedure (see p. 376) is adopted the spray liquid will be applied at a rate of 40ml per m2 or one litre per 25m2. This amount of suspension normally stays on the surface without run-off.

Water-dispersible powder

One litre of spray suspension can be prepared using the following formula:

where:

X = weight of water-dispersible powder required (g)
Y = recommended application rate (g/m2)
C = concentration of active ingredient in formulation (%).

Example

DDT (75% water-dispersible powder) is to be sprayed at a dosage of 2g/m2.

For an eight-litre tank, the amount of water-dispersible powder needed is:

8 × 66.6 = 533.3g

The insecticide should be packed in small bags containing 533.3g each. In the field, put water in a mixing bucket until the eight-litre mark is reached. Mix the contents of one bag with the water, using a wooden paddle. Pour the solution into the sprayer through a funnel with a screen, close the tank and shake it.

Emulsifiable concentrate

To prepare an insecticide suspension from an emulsifiable concentrate, use the same formula as for the water-dispersible powder, with:

X = amount of emulsifiable concentrate needed (ml)
Y = recommended application rate (g/m2)
C = concentration of active ingredient in formulation (%).

To prepare one litre of suspension, add X ml of emulsifiable concentrate to (1000 - X) ml of water.

Example

DDT (25% emulsifiable concentrate) is to be sprayed at a dosage of 1g/m2.

To prepare one litre of suspension, add 100ml of emulsifiable concentrate to 900ml of water. For an eight-litre tank, add 800ml of emulsifiable concentrate to 7200ml of water.