Vegetable troublemaker - root maggots

Yellow or wilted leaves on cole crops, onions, or radishes are often the first sign of damage by vegetable root maggots. By the time damage is visible, it may be too late to save the plants. But prevention can keep the maggots away.

In spring and fall, small gray flies lay their eggs at the bases of the plants and in the surrounding soil. When the eggs hatch, the white 1/4-inch-long maggots tunnel through stems and migrate down to feed on roots.

On onions, radishes, and turnips, the maggots damage the edible part of the plant directly. On broccoli, Brussels sprouts, cabbage, and cauliflower, the tunnels in the stems cut off the supply of water and nutrients to the tops of the plants, causing them to wilt and die.

The best time to control this insect is at planting time, before the adults can lay their eggs. If you had a problem last season, don't plant in the same area. Floating row covers (see "Miracle blankets for vegetables?' on page 86 of the February 1987 Sunset) or fine-mesh screen provide the most effective controls. Make sure plants are completely covered so flies can't get inside.

Some gardeners have controlled cabbage maggots using dursban or diazinon at planting time and watering it in well (make sure it's registered for this use in your state), but this method usually doesn't provide complete control. If plants become infested, remove them, tie them in plastic bags, and discard.

Photo: Entire broccoli plant (right) wilted and turned yellow after 1/4-inch-long vegetable root maggots (above) girdled and bored into stem, fed on roots