What you need to know is that while many green "spray" pesticides work on contact, they have little to no effect once they dry. In other words, they don't persist in the environment for very long; that's part of what makes them "environmentally friendly!" So if you're using a natural or green spray pesticide, for best results, you need to spray the bug directly. This is okay if you're dealing with an occasional cricket, ant, or other insect that wonders in. But in some cases, you may need to use a pesticide that persists a little longer.
Some of the naturally derived dusts, such as boric acid and diatomaceous earth, do have a long-lasting effect (if they are not displaced after application). But NEVER use pool grade diatomaceous earth; it is an inhalation hazard and should only be used for swimming pools. To be sure you're using the right product, only use pesticides registered with the EPA. And you should always use caution when applying dusts. Follow the label instructions carefully and always wear gloves and a dust mask. Indoors, dusts should be applied in cracks & crevices and voids, NOT along baseboards or other open places. Many dusts can be applied outdoors as well, but again, follow the label instructions. To avoid drift, never apply dust in windy conditions.
Many of the synthetic pesticides also have longer residual activity. There are certain instances when it's necessary to use a pesticide that will persist in the environment for some time. For example, with pests like cockroaches, which spend most of their time hiding in cracks and crevices, a longer-lasting pesticide will most likely be necessary. After all, how can you spray roaches directly with a green pesticide if you never see them?
Really, it's a delicate balancing act. So, here's my advice when it comes to using pesticides, whether it be green or synthetic (really, it's just using IPM):
- First, take steps to eliminate potential food and water sources, limit harborage areas, and pest-proof buildings to keep pests out.
- Use insect baits preferentially over other pest management products (when dealing with roaches and ants).
- "Green" spray insecticides can be used as contact sprays to apply directly to insects.
- "Green" insecticidal dusts can be used in cracks & crevices and voids. Always apply dust in a thin, even manner - don't dump it in piles - insects will actually avoid piles of dust.
- If you deem it's necessary to use a conventional, synthetic pesticide, ALWAYS read and follow the label instructions carefully. Try to limit your applications to cracks & crevices and avoid broadcast applications indoors (remember, crack and crevice applications are also exempt from notification). This will limit the potential risk of exposure to students and staff.