Pest Sprays for Onions

Pesticides

• Traditionally, pest sprays have included chemicals that kill pests. Examples include malathion, carbaryl and diazinon. These are moderately effective at killing plant pests, and may have toxic effects on humans. Synthetic pesticides or pest sprays are classified as Class I, II or III. Class III, which includes malathion, is slightly toxic and Class I is highly toxic.

Organic Pesticides

• Unlike chemical sprays, organic pesticides use natural substances to control insect problems. They include neem oil, pyrethrum, sulfur dust, oil sprays and insecticidal soaps. While these are safe for use around pets and people, they may only be moderately effective in the garden. For best results, apply as soon as you notice pests. Follow the application direction on your specific product, including the dose range and time to wait between applications.

Types

• Major onion pests include the onion thrip and the onion maggot. For thrips, try synthetic pesticides that contain endosulfan, dimethoate or cyfluthrin. Alternatively, try organic pesticides such as pyrethrum, neem oil or insecticidal soap. To control onion maggots, apply a diazinon-based product before planting, or a permethrin- or malathion-based product when you notice a pest problem. Onion maggots are harder to control with natural pesticides, so chemical controls are recommended.

Tips

• To reduce the likelihood of an onion maggot infestation, avoid using a topcoat of organic fertilizer. Thoroughly incorporate any organic matter you plan to use into the soil, because these pests are attracted to moisture and humidity from decaying organic matter. If you planted onions in a double row, each row needs twice the amount of pesticide allotted for a single row. Whether you plan to use organic or synthetic pest sprays, check the plants often and treat at the first sign of an insect presence. Onion pests can also spread to garlic, leek, chive and shallot plants.