Demon WP is a wettable powder insecticide that you mix with water and spray to control ants, cockroaches, spiders, crickets, and dozens of other common pests. It works both as a contact killer and a residual treatment, meaning it continues killing insects that cross treated surfaces for several weeks. Here’s everything you need to know to mix, apply, and reapply it correctly.
Mixing Ratios
Demon WP comes in small water-soluble packets. For standard pest control, mix one packet per gallon of water. This creates a 0.1% concentration that handles most routine maintenance treatments around your home.
For heavy infestations or stubborn pests, double it to two packets per gallon. This stronger 0.2% mix is useful when you’re dealing with an established cockroach problem, large ant colonies, or a first-time cleanout where pest pressure is high. Once you’ve knocked the population down, you can drop back to the one-packet ratio for follow-up treatments.
Use a pump sprayer with a clean tank. Before adding the Demon WP, wash the sprayer thoroughly with water and detergent to remove any residue from previous products. Do not mix Demon WP with oil-based products. Fill the sprayer partway with water, drop in the packet, then add the remaining water and agitate well. The powder needs regular shaking during application to stay suspended, so give the sprayer a few pumps and swirls every couple of minutes while you work.
Where and How to Apply
Demon WP is labeled for use in, on, and around buildings and structures. That includes homes, commercial buildings, parks, athletic fields, and the lawns and landscaping surrounding them. The three main application methods are general surface spraying, crack-and-crevice treatment, and outdoor barrier treatment.
Indoor Application
Focus on cracks and crevices where insects travel and hide: along baseboards, behind appliances, around door and window frames, under sinks, and where plumbing or wiring enters walls. Spray a light, even coating rather than soaking surfaces. You’re not trying to drench anything. A fine mist along a crack line is enough for the residual powder to do its job once the water evaporates.
Only apply indoors in well-ventilated areas. Do not use it as a space spray (meaning don’t fog a room with it). Avoid applying to overhead surfaces unless you’ve covered the floor and furniture below with plastic sheeting. Never spray near aquariums, as this product is extremely toxic to fish and reptile pets.
Outdoor Barrier Treatment
To keep pests from entering your home, spray a band of soil and vegetation 6 to 10 feet wide around the building’s perimeter. Also treat the foundation itself up to 2 to 3 feet high, concentrating on areas where pests are active or could find entry points. Apply as a coarse spray that thoroughly wets the band area. A general guideline is 1 to 5 gallons of mixed solution per 800 to 1,600 square feet of treated ground.
Pay extra attention to door frames, window frames, weep holes, and utility entry points. For carpenter ants, spray around any area where they enter or hide. For bees, carpenter bees, and wasps, spray nests directly in late evening when insects are at rest, treating the nest entrance and surrounding surfaces where they land.
What It Controls
Demon WP targets a broad range of household and structural pests: ants (including carpenter ants), cockroaches, crickets, spiders, bees, carpenter bees, wasps, and many other listed insects. It’s a versatile general-purpose insecticide rather than a specialist product, which is why it’s popular for perimeter and indoor treatments alike.
How Long It Lasts
Residual control from Demon WP typically lasts several weeks. Once the spray dries, it becomes rainfast for that period, though outdoor conditions like heavy rain, direct sun, and irrigation will break it down faster than a sheltered indoor application.
Plan to reapply once a month for outdoor treatments to maintain a consistent barrier. The minimum reapplication interval is 21 days. Indoors, you may not need to reapply as frequently since the powder residue is protected from weather, but inspect treated areas periodically and retreat when you notice renewed pest activity.
The White Residue Problem
Because Demon WP is a wettable powder, it leaves a visible white film when it dries. On light-colored baseboards and concrete foundations, this is barely noticeable. On dark surfaces like stained wood, dark tile, or black trim, the residue can be obvious and look like staining.
This is the most common complaint with the product. If you need to treat dark-colored surfaces, consider a liquid concentrate insecticide instead, which dries clear. If you’ve already applied Demon WP and want to clean up visible residue, scrub the area with hot water and soap, then rinse with plain water. The product won’t damage paint or varnish, but the white powder can be stubborn on textured surfaces.
Safety During and After Application
Wear the personal protective equipment specified on the product label when mixing and spraying. At minimum, this means chemical-resistant gloves, long sleeves, long pants, and shoes with socks. If the label calls for protective eyewear, use goggles, a face shield, or safety glasses with side protection. Read your specific label carefully, as PPE requirements can vary by application type.
Keep children and pets out of the area while you’re spraying. Once the product dries, which usually takes about 30 minutes, treated areas are safe for people and pets to re-enter. After drying, the concentration is only strong enough to affect small insects. That said, store unmixed Demon WP packets out of reach. A dog getting into a jar of concentrated powder is a different situation than walking across a dried treated surface.
Do not spray near fish tanks, ponds, or any body of water. Demon WP is extremely toxic to aquatic life. Avoid applying where runoff could reach storm drains, streams, or other surface water. Never spray electrical equipment like junction boxes, switch boxes, or motor housings with the water-based mixture due to shock hazard. Do not apply to edible crops, in greenhouses growing food, or in warehouses storing raw agricultural products.
Tips for Best Results
- Agitate frequently. The powder settles fast. Shake your sprayer every few minutes to keep the mixture uniform.
- Treat entry points first. Doors, windows, pipe penetrations, and foundation cracks are where pests get in. Prioritizing these gives you the most immediate impact.
- Apply on a calm day. Wind carries spray mist where you don’t want it, especially near gardens, water features, or pet areas.
- Time evening applications for stinging insects. Bees and wasps are least active and most likely to be in the nest after dark.
- Stay on schedule. A monthly outdoor reapplication keeps the barrier consistent. Gaps in treatment give pest populations time to rebuild.