Pest & Disease Control for Onion Plants

Fortunately, onions are not prone to many of the pest and disease problems that commonly occur in vegetable gardens—in fact, onions (like garlic) act as a natural pest repellent for the whole garden. Deer, mice and voles will not trouble your onions, and onions' sulphur content is offensive to many insect pests.

NOTE: This is part 7 in a series of 9 articles. For a complete background on how to grow onion plants, we recommend starting from the beginning.

Pests/Diseases

If your onion plants should ever develop a problem, it will most likely be purple blotch, blight, thrips or white rot. Many remedies, both organic and chemical, are available and have all proven effective. Carefully follow all package directions for best results. More is not better!

Purple Blotch and Blight

These two maladies are caused by fungus, and may occur under very wet or humid conditions. Look for small white spots on the leaves that are surrounded by a greenish circle that resembles a halo. Purple blotch is so named because it causes the leaves to develop purplish areas.

Natural Control

Monterey Complete Disease Control
Monterey Liquid Copper Fungicide
Natural Guard® Neem

Chemical Control

Ferti-Lome® Broad Spectrum Landscape & Garden Fungicide
Ferti-Lome® Triple Action

Manual Control

Properly space onion sets when planting to promote good air circulation after the sets sprout and begin to grow.

Thrips

If the leaves on your onion plants are turning gray, you might have a thrip problem. The insects appear as tiny yellow or black specks that can easily go unnoticed. Mites are less of problem, but occasionally appear at the base of the bulb roots and stunt the plant’s growth.

Natural Control

Natural Guard® Neem
Safer® Brand Insect Killing Soap

Chemical Control

Ferti-Lome® Triple Action
Hi-Yield® Vegetable & Ornamental Insect Control

Manual Control

Do not plant Allium genus members (onions, leeks, shallots, garlic) in the same spot the following season.

White Rot

This is another fungal disease that develops during cool weather, affecting the leaf bottoms and roots. Because the spores can survive for several years, rotate your onion-bed location every year and be sure to clean up all fall debris in the bed before winter sets in.

Natural Control

Monterey Complete Disease Control
Monterey Liquid Copper Fungicide
Natural Guard® Neem

Chemical Control

Ferti-Lome® Broad Spectrum Landscape & Garden Fungicide
Ferti-Lome® Triple Action

Manual Control

Completely clean up and dispose of all fall debris (in the trash, not the compost pile) to prevent overwintering of pests and/or disease.

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