Gardening Articles: Care :: Plant Care Techniques
by National Gardening Association Editors
Pests and diseases can ruin an onion crop. Here are ways to avoid these problems.
Onions in the North aren't usually bothered by insects like onion thrips or onion maggots, but if you live in the South you'll have to deal with them.
Thrips are very tiny insects that feed on the leaves of the onion plant. The plants weaken, and the yield of the crop can be reduced quite a bit. Spraying or dusting with insecticidal soap and hanging yellow sticky traps around the plantings is usually all it takes to control thrips. Follow spray directions on all sprays carefully when you use them.
The onion maggot is the offspring of a small fly that lays its eggs near the base of the plant, or late in the season right on the bulb itself. The small maggots kill the plant by burrowing into the stem and the bulb. Pull up and destroy any plants with maggots before the maggots mature into flies.
There are some insecticides that can handle a bad case of onion maggots, but an easier control is to cover the newly set out plantings with a floating row cover to prevent the adult fly from laying eggs on your onions.
Neck rot is probably the most common onion disease. It often hits just after the harvest or while the bulbs are in storage. All onion varieties can develop neck rot, but the mild-flavored, thick-necked Bermuda-type onions are especially susceptible. Drying the onions at warm temperatures with good ventilation can help prevent this disease.
There are some fungus diseases such as pink root, mildew, and bottom rot that are carried in the soil itself, but rotating the onion plot and growing resistant varieties are just about all a home gardener has to do to avoid these.
It's a good idea to spread out your onions, planting them in several sections of the garden. You not only reduce the chance of onion disease, but, because onions repel many insects, you create a kind of defense network that protects your other vegetables.