Spring root maggots are not whimsical
“A maggot is the larval stage of a winged creature; as is the written text, at least in the writer’s hope.”
— John Fowles, “A Maggot,” 1985
John Fowles, who is best known for his novel “The French Lieutenant’s Woman” (1969), set the plot of his sixth book, "A Maggot," in the 1700s when “maggot’’ also meant "a whim, fancy or quirky idea." During that time period, people apparently believed maggots squirmed around the brains of living human beings, and a bite could evoke a profound or creative thought.
The title of Fowles’ novel refers to a fanciful image he had of a group of travelers riding on horseback across a deserted landscape. Fowles wrote in the prologue, “What follows may seem like a historical novel; but it is not. It is maggot.”
Today, we have no whimsical meanings for maggots. We know them only as little, whitish worms that forensic scientists get excited about, and gardeners hate. Root maggots can be especially troublesome for early spring plantings because they thrive in cool, wet soil. Particularly susceptible to root maggots are onions, leeks and vegetables such as radishes, turnips, cabbage, kale, broccoli and cauliflower.
Root maggots are the larvae of cabbage flies (Delia radicum) and onion flies (Delia antiqua). The adults are gray and a little smaller than a housefly. In spring, they emerge from the soil where they’ve been overwintering and begin laying 50-200 eggs in the stems of host plants, or at the soil line near the stems. The eggs hatch in a few days, and the larvae then burrow in the soil to feed on plant roots and germinating seeds.
After three or four weeks, the larvae have eaten their fill and wiggle their way back up to the surface where they pupate, hatch and start the process of laying eggs all over again. Several generations of flies emerge every year.
Since the damage to garden plants from root maggots occurs underground, it can be difficult to detect the problem. However, affected plants will look stunted and the leaves may wilt or turn yellowish. If a damaged plant is lifted from the ground, its exposed roots will be partially eaten away. Onions, leeks, radishes and turnips may have tunnels where maggots have eaten through the bulbs.
There are several strategies for dealing with root maggots in the garden, although no chemical treatment is available. One recommendation is to cover seed beds and seedlings with floating row cover to prevent adult flies from laying eggs on the plants. A lightweight fabric should be used that lets in plenty of sunlight and moisture. The problem with this strategy has to do with timing; adult flies will be trapped inside if they haven’t yet emerged when the cover is placed.
Some gardeners recommend sprinkling diatomaceous earth around the plants. Produced from silica, the skeletal remains of tiny marine organisms called diatoms, particles of diatomaceous earth have sharp edges that penetrate the body of an insect and then dry it out. Although diatomaceous earth is approved for organic gardening, it can irritate skin and eyes and has been shown to be a health hazard if breathed in large quantities. Gloves, glasses and a face mask should be worn during application.
Another way to get rid of root maggots is to introduce beneficial nematodes. These parasitic worms contain bacteria that kill insects when released inside the insect’s body. Nematodes can be purchased at garden supply stores.
Cabbage and onion flies are partial to specific host plants, so rotating garden crops every year is a good way to prevent root maggot infestation.
There’s no whimsy when it comes to protecting spring crops from root maggots, just good gardening sense. For more about early spring garden pests, check out my blog at http://blogs.esouthernoregon.com/theliterarygardener/.
— Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at firstname.lastname@example.org.