Malathion is sold as a concentrated liquid, typically at 57% active ingredient, that you dilute with water before spraying. The exact mixing ratio depends on what you’re treating: mosquitoes, garden pests, or ornamental plants each call for different dilution rates. Getting the ratio right matters for both effectiveness and safety.
Understanding the Concentrate
The most common formulation available is Malathion 57 EC (emulsifiable concentrate), which contains 57% malathion and roughly 5 pounds of active ingredient per gallon. When mixed with water, it forms a milky emulsion you can apply with a standard pump sprayer, backpack sprayer, or power fogger. The “EC” designation means the concentrate already contains emulsifiers that help it blend with water, so no additional surfactant is needed.
Your product label is the definitive guide for mixing rates. Concentrations vary between manufacturers, and labels carry legal weight. The ratios below apply to the standard 57% (5 lb/gallon) concentrate, which is the most widely sold formulation.
Mixing Rates for Common Uses
Mosquito Control
For outdoor mosquito fogging or area sprays, you’ll mix a 2% to 5% solution. A 2% spray uses 1 part malathion concentrate to 28 parts water. A 5% spray uses 1 part concentrate to 11 parts water. The lower concentration works for light infestations or routine prevention, while the higher rate is better for heavy mosquito pressure. You can repeat applications as needed.
Garden and Ornamental Plants
For aphids, spider mites, mealybugs, scale crawlers, thrips, tent caterpillars, lace bugs, and leaf miners on ornamental plants, apply when pests first appear. Use enough water volume for thorough, uniform coverage of all plant surfaces, but stop before the spray starts dripping off the leaves. Larger shrubs and dense plantings need more spray volume to reach interior foliage.
Be aware that malathion can injure certain plants. Known sensitive species include crimson maples, crassula, holly, African violets, petunias, sabina and canaerti junipers, and several fern varieties (Boston, maidenhair, and pteris ferns). Young plants of any species are more vulnerable than established ones. If you’re unsure about a particular plant, spray a small test area and wait 48 hours before treating the whole plant.
How to Mix Step by Step
Fill your sprayer tank about halfway with clean water first. Then add the measured amount of concentrate. Finally, top off with the remaining water and agitate gently. Adding concentrate to water (rather than water to concentrate) prevents the emulsion from clumping and ensures even distribution throughout the tank. If your sprayer sits idle for a while between uses during the same session, give it another shake before resuming.
Mix only what you need for the job. Diluted malathion breaks down relatively quickly and loses effectiveness over time, so leftover spray sitting in a tank for days is both wasteful and harder to dispose of properly. Measure your treatment area beforehand and calculate the volume you’ll actually use.
Protective Gear You Need
Malathion is an organophosphate insecticide that can be absorbed through skin, so direct contact during mixing is the highest-risk moment. Wear chemical-resistant gloves, long sleeves, long pants, and closed-toe shoes. Silver Shield is one material specifically recommended for glove protection against malathion, though any chemical-resistant glove rated for organophosphates will work.
For eye protection, use splash-resistant goggles with indirect vents, not just safety glasses. If you’re pouring concentrate or working in a confined space, add a face shield over the goggles. Do not wear contact lenses while handling malathion, as they can trap the chemical against your eye. Put all protective clothing on before you open the concentrate, and wash everything separately from household laundry when you’re done.
Where Not to Use It
Malathion 57 EC labels explicitly state: do not use inside the home. It is strictly an outdoor product. EPA risk assessments have found potential concerns for fish, aquatic invertebrates, birds, mammals, amphibians, and beneficial insects like pollinators, so keep spray away from ponds, streams, and other water sources. Avoid spraying on windy days when drift could carry the mist beyond your target area. The EPA has proposed mandatory spray drift language for certain application methods, and geographically specific use limitations are available through the agency’s Bulletins Live! Two website.
Do not spray near beehives or when pollinators are actively foraging on flowering plants. Early morning or late evening applications reduce contact with bees.
Disposing of Leftover Spray
The best disposal strategy is not having anything to dispose of. If you do have a small amount of leftover diluted spray, apply it to a labeled use site following the same label directions. You can also offer unused concentrate to a neighbor who has a similar pest problem.
For concentrate or mixed spray you truly cannot use, check with your local solid waste authority or health department for household hazardous waste collection programs. Many communities run periodic collection events for pesticides and other chemicals. Never pour leftover malathion down a drain, into a storm sewer, or onto bare ground near water.