In the Garden:
Southern California Coastal & Inland Valleys
August, 2008
Regional Report

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2863

Different onion varieties mature at different times.

Onion Family Disease and Pest Problems

Fall is a good time for planting onion family crops like chives, garlic, leeks, onions, and shallots. There are some nasty diseases and pests that can damage these plants, so to help you figure out what the problem is and what to do about it, here are some tips for identification and treatment.

Problem: Fluffy white rot begins at the base and spreads to the foliage, and bulbs have a soft watery rot.
Solution: Destroy diseased plant immediately. Rotate crop to new soil.

Problem: Onion maggots tunnel cavities in the lower stem and bulb, and plants may wilt and die. Susceptibility is greatest with white varieties, less so with yellow ones, and the least with red ones.
Solution: Plant seeds or sets throughout the garden, rather than in one area. Add sand or wood ashes to the top layer of the planting area. Spray the soil with an oil-and-soap mixture. Dust with diatomaceous earth. Destroy the affected plant before the maggots mature into flies and lay a new generation of eggs.

Problem: If plants are stunted and roots are pinkish or red, shriveled, and rotted, the plant is infected with pink root fungus. It is encouraged by heavy, wet soils.
Solution: Plant tolerant and resistant varieties on well-drained soil. Incorporate organic matter to improve drainage. Once the soil is infested, do not grow any bulb crops.

Problem: Rust infection is manifested by long pustules of bright orange spores on the leaves.
Solution: The fleshy parts are usually safe for eating, but the foliage must be destroyed. Rotate crops to soil that is not as rich in nitrogen.

Problem: Black spots on leaves and between the sections of bulbs indicate a smut infection. Young plants may have twisted leaves.
Solution: Plant healthy, resistant varieties.

Problem: Bulbs that are soft and have thin skins, thick necks, and leaf tips that turn brown are deficient in potassium.
Solution: Incorporate a high-potassium fertilizer.

Problem: Bulbs with thin skins are deficient in copper.
Solution: Incorporate manure.

Problem: Outer layers of harvested bulbs that become bleached, soft, and slippery demonstrate sunscald damage. This occurs when bulbs are harvested and set out for their initial curing in direct sun on very hot, dry days.
Solution: Shield bulbs from direct exposure to the sun during curing.

Problem: Mature bulbs and sets develop sunken, spongy areas around their necks when they are infected by neck rot fungus. White varieties are extremely susceptible. The fungus is encouraged by insufficient curing and fertilizer that is applied late in the season.
Solution: Plant healthy sets of early-maturing, thin-necked varieties. Pungent varieties are less susceptible than mild-tasting ones. Do not apply fertilizer late in the season. Incorporate organic matter. Cure bulbs thoroughly at warm temperatures with good ventilation but out of direct sun. Store them in a cool, dry area with good air circulation. Examine the bulbs frequently, and remove those that are spoiled. Store thick-necked varieties separately from thin-necked ones, and eat them soon after harvest, as they will not cure sufficiently for long storage.


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