Answer: The cabbage maggot (Delia radicum) is most likely the problem, says Van Bobbit, home horticulturist with Washington State University in Puyallup. The 1/4-inch-long gray adult fly emerges from the soil in early spring and lays white, oblong eggs on or just below the soil surface within two inches of the stems of any cabbage-family plants. Within a week the creamy white maggots migrate to the roots to feed and grow for three to five weeks. Then they pupate in the soil and later emerge as adults. There are usually three to five generations a year in western Washington. The feeding maggots often cause enough root loss that young plants eventually die. Older plants seem to be able to withstand the feeding. Young plants are most susceptible to being killed by the larvae, notes Bobbit. Barriers are the easiest way to prevent damage. Cut a piece of tar paper four inches square, and slit it to the center on one side so that the paper can slip over and fit snugly around the cabbage stem. This will stop theadult fly from laying eggs at that plant, Bobbit explains. You can also prevent egg-laying with floating row covers such as Reemay, placed over transplants and newly seeded beds. The covers should extend at least six inches away from the plants. Be sureto check weekly for any flies that emerge under the floating row cover. Once maggots are feeding on the roots, there is little you can do to control them other than pulling up the plants and destroying them, he adds.
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