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.
