[Formulation Review] Dusts: When More is Not Better

Whether you’re dusting with a bulb duster or a power duster, the concept is the same. You want to apply a thin film of dust into voids, cracks and crevices. If it looks like drifting snow, you’ve applied too much. You want cockroaches and other pests to walk through the dust. Then when they groom themselves, they swallow it. If cockroaches are faced with "snow drifts" of dusts, they’ll walk around them. Heavy dust applications actually repel pests.

Over application of dust can cause other problems besides poor control. Pesticide dusts drift easily. If you’re blowing lots of dust into a wall void, there is the risk that it will end up where you don’t want it, i.e., coming out of an outlet into the next room or drifting through a vent in a kitchen.

Dusts are very effective at controlling pests in voids because they cling well to surfaces and last a long time in these protected sites. But these same qualities can pose a risk for electricians, renovators and others who may later be exposed to excessive applications and also can increase the inhalation risk for you, the applicator.

Follow these tips to ensure you don’t over apply pesticide dust:

Turn off fans, ventilators, furnaces and other air circulation equipment that could blow the dust into non-target areas.

When treating voids or areas other than attics or crawlspaces with a power duster, use a lower pressure to reduce the chances of the dust drifting into non-target areas. (Make sure you wear a NIOSH-approved respirator when dusting in attics, crawlspaces or other enclosed spaces.)

Fill a hand-held duster only half full. You need the remaining empty space in the duster so that air can mix with the dust to give you a fine application. If there is too much dust in the duster, you’ll apply clumps.

Don’t remove the screen inside the duster (unless the pesticide label says so) since it helps keep the dust from clumping.

Shake a hand-held duster lightly before each application to mix the dust and air, and to keep clumps from forming. Add a couple of small ball bearings, marbles or coins to your duster. This not only helps to agitate the dust inside but also gives the dust an electrostatic charge so it sticks better to surfaces. Certain power dusters are also designed to "charge" the dust.

For most hand dusters, it’s important that the base of the spout be above the level of the dust in the duster. If the base of the spout is buried in dust, the air in the duster can’t mix with the dust.

Squeeze the duster lightly to apply a thin film. When a hand-held duster is squeezed correctly, you will just barely be able to see the dust coming out of the tip. The larger the crack or void being treated, the harder you will have to squeeze to force dust onto all surfaces.

Pull the nozzle away from the crack or opening before you completely relax your squeeze. This prevents sucking dust or moisture back into the duster.

Carry a damp cloth to wipe up any excess dust that spills onto surfaces.

Editor’s note: This article was adapted from Techletter, a biweekly publication from Pinto & Associates, Mechanicsville, Md. To subscribe, visit www.techletter.com, or call 301/884-3020.
 

*****

When to Choose a Granular Formulation

Granular pesticides are dry formulations like dusts, except that the particles are larger and heavier. The granule particles are made from an absorptive material like clay, or ground up corn cobs or walnut shells. The pesticide active ingredient is either coated onto the outside or absorbed into the granule itself.

The amount of active ingredient in granular insecticides is relatively low, ranging from 1 to 15 percent.

Granules most often are used as a soil application to control weeds and pests living in or on the soil (ants, fleas, earwigs, crickets, millipedes, sowbugs, etc.), or applied to standing water to control mosquito larvae. They’re also used as outdoor baits for carpenter ants, fire ants and other ants, as well as crickets and cockroaches. Some granular baits are even registered for indoor use in areas inaccessible to children or pets.

Advantages of granular insecticides:

• Packaged ready to use; no mixing needed
• Low drift hazard compared to dusts and sprays due to the heavier particles
• Low hazard to applicator compared to dusts and sprays
• Can be applied through foliage and will drop to the ground below
• Application equipment is simple (seeders, lawn spreaders or hand-held shakers)

Disadvantages of granular insecticides:

• Do not stick to foliage if foliage is the treatment site
• May be more expensive than other formulations
• May need to be incorporated into the soil by watering or raking