Under the soil surface, there is an unbelievable world of tiny creatures. A lof of these critters are a critical part of creating healthy soil. Beneficial nematodes and soil microbes are a key part of a balanced environment.
Other creatures can cause financial loss, crop damage, and stress. Vegetable root maggots are one such pest. These larvae feed on the roots of all kinds of veggies and can destroy your crop.
Read on to get to the root of your root maggots problem.
What We’ll Discuss
What Are Vegetable Root Maggots?
Vegetable root maggots are the larvae of onion flies (Delia antiqua), turnip root flies (D. floralis syn, D. florilega), radish root flies (D. planipalpis), seedcorn maggot flies (D. platura), and cabbage root flies (D. radicum).
They are part of the Anthomyiidae family, which also includes true flies. On a wide scale, this incorporates approximately 640 recognized species and 39 genera in North America. Delia species are pests that attack vegetables, destroying your crop.
Some flies are considered useful in the garden, carrying out roles attributed to pollinating, cleaning or assisting with decomposition. But vegetable root flies aren’t in the useful category. Technically, it’s not the adults that are bad news, but the larvae.
They feed on food crops, damaging the roots and slowing growth. Large infestations can even destroy your harvest.
Identifying Vegetable Root Maggots
The adult of vegetable root maggots looks like a smaller housefly at about a quarter inch long. They lay the eggs that hatch into the larvae that overwinter in the soil.
One of the most notable characteristics of the larvae is the elongated, cylindrical body shape. This sets them apart from your average horse, bottle, or housefly larvae.
The maggots are white or transparent and range in size, averaging around a quarter inch in length. They have a tapered front end and a flat, blunt posterior. The tapered front allows them to burrow through soil, roots, and the other underground portions of vegetables.
Another distinguishing feature is the presence of a pair of small, dark-colored mouthparts that look like hooks at its front end. These mouthparts are called mandibles and enable the maggot to burrow and feed.
The mouthparts have sharp hooks that allow the vegetable root maggot to efficiently tear and consume plant material.
As they age, the legless larvae turn dark brown before pupating.
The physical characteristics reflect the vegetable root maggots’ specialized adaptability for their life in the soil. As effective tunnellers, they penetrate the outer layers of roots to get to the nutrition inside.
All of the adults and larvae look similar regardless of the species. The best way to tell them apart is to look at the plant they’re consuming. Each species sticks to specific plants.
Lifecycle Of Vegetable Root Maggots
The lifecycle of the vegetable root maggot begins when adult flies lay their eggs at the base of susceptible plants. They often target young seedlings or recently transplanted seedlings.
Within three-10 days, those eggs hatch, and the tiny maggots immediately burrow into the soil. This is where they overwinter or, during the summer, they immediately begin feeding on the roots of the plant.
Vegetable root maggots undergo several molts and growth stages over two to four weeks from hatching.
This length of the larval stage depends on the environmental conditions. When favorable, the maggot grows quickly.
Once full size, they pupate in the soil, forming little brown chrysalis. It transforms into the adult fly form inside this chrysalis and will tunnel out of the soil and fly off and mate.
The vegetable root maggot can overwinter in its pupae form, if necessary, continuing its lifecycle in spring when conditions are more favorable.
This lifecycle can repeat multiple times throughout a growing season. Some areas can have four or five cycles while some might only have one.
They are active in temperatures from 40°F upwards, but there is evidence to suggest they can survive much lower temperatures in a dormant state.
Which Plants Do They Eat?
Understanding their behaviors is crucial for the gardener and the farmer alike to combat this destructive pest.
Some of the vegetables that are particularly interesting to the vegetable root maggot are staples we grow in our backyards.
Different root maggot species only feed on specific crops. An onion root maggot won’t eat cabbage and a cabbage root maggot won’t eat onions, for example.
Onion flies (Delia antiqua) eat alliums like onions, garlic, chives, shallots, and leeks.
Turnip root flies (D. floralis syn. D. florilega) feed on cabbages, turnips, rutabaga, and radishes.
The radish root fly (D. planipalpis) is a pest of radishes, broccoli, cabbage, cauliflower, and canola.
Seedcorn maggots or bean root flies (D. platura) beans and peas.
Finally, cabbage root fly (D. radicum) attacks brassicas, including Brussels sprouts, broccoli, kale, collards, beets, and cabbage.
Regardless of the species, they will continue to feed on the roots and underground stems until they’re ready to pupate.
Signs of a Vegetable Root Maggot Infestation
The trouble with this pest is that unless you have cameras underground, an infestation is hard to spot until the plant shows signs above the ground.
Once infested, vegetables may become weak, diseased, and stunted. When symptoms show, it’s usually too late to resolve things and your crop is likely useless.
Look for things like:
- Wilting, discolored, or collapsing foliage
- Slow or stunted growth and development
- Holes in bulbs, tubers, and underground stems
- Rotting or dying off of plant parts above soil level
- Maggots visible when soil disturbed
- Sudden onset of disease
- Poor or lack of seedling emergence above soil level
- Rotting bulbs, tubers and rootstock
Look out for the presence of a large number of flies in or around your vegetables, particularly on the soil. This can be a sign of both emerging new adults or the laying of fresh eggs.
Prevention and Management
Prevention is the best weapon against the vegetable root maggot. It’s hard to treat these pests with conventional sprays and deterrents because they hide underground. Plus, once they start feeding, the plant is already damaged.
Make the Soil Uninhabitable
Tilling the soil and garden debris after harvests and before replanting may interrupt any potential developing maggots, pupae, and overwintering spots. This will also expose the maggots to predators like birds.
Keep in mind that tilling disturbs the soil’s environment, which can cause long-term issues. But sometimes, it’s necessary, especially when dealing with repeated maggot infestations.
Avoid spreading fresh manure near and around seedlings or established vegetable plants as this is particularly attractive to the adult fly in which to lay eggs. You should never spread fresh manure near plants anyway since it can burn them. Always use well-rotted manure.
Soil temperatures over 95°F destroy any eggs close to or recently laid on the surface. Solarize your soil to kill off these pests.
Biological Control
When devising your garden plan, be sure to account for encouraging beneficial creatures. For example, predatory insects assist in keeping the vegetable root maggots and adult flies to a minimum.
Soil-dwelling beetles, such as some rove (staphylinid) or ground (carabid) beetles, are natural predators of the vegetable root maggot.
Predatory mites and parasitic wasps can come in handy when it comes to controlling numbers as well. Partridge pea (Chamaecrista fasciculata), yarrow (Achillea millefolium), dill (Anethum graveolens), sweet alyssum (Lobularia maritima), lemon balm (Melissa officinalis), and marigolds (Tagetes spp.) all attract beneficial insects.
Biological control using beneficial nematodes can be effective. Nematode species Steinernema feltiae and Heterorhabditis bacteriophora can be used individually or separately.
These nematodes effectively kill the larvae in the soil. You can buy a pack of 10 million S. feltiae at Amazon and 5 million of H. bacteriophora at Amazon.
There is evidence to suggest that some soil-borne fungal diseases may be able to keep maggot numbers down by preventing the proper development of the pupae.
Maintaining a balanced garden and letting nature work with you can reduce the need for tougher measures. This means avoiding tilling, having lots of diversity, including natives, and removing any weeds.
Crop Rotation
Don’t grow the same plants in the same area year after year. Crop rotation is the process of placing different species in an area at least once every three years or so. This denies pests and pathogens a host and the ability to build up over time.
Adult flies can travel up to a mile, but making the vegetable planting less predictable can reduce their success.
Rotating crops also supports the soil’s ability to feed and nurture the plants in it without depleting specific nutrients and increasing the biodiversity of the beds. And, as we discussed, biodiversity is key.
Companion Planting
Planting intermittent rows of or interspersing herbs that are less attractive and stronger smelling may also reduce infestations. There isn’t a ton of evidence that this works, but it certainly doesn’t hurt.
Interplant with:
Covering Plants
Protect growing plants from the adults by using floating row covers, cloches or tightly netted garden sheeting.
This can help deter the adults from laying eggs in the first place, but you must be sure to weigh and pin down all of the ends to prevent the flies from getting underneath.
You shouldn’t cover plants if you know you already have larvae in the soil. If the eggs or larvae are already in the soil, the adult flies will hatch inside the cover and they will have a nice, protected area to feed on your plants.
Garden Hygiene
Be sure to keep up with weed maintenance throughout the year. Weeds give this pest a place to overwinter and they attract the adults at laying time. A tidy garden can give you a head start in preventing them in the first place.
Any infested plant debris or plant matter needs to be disposed of. Don’t put it in the compost pile unless you hot compost and your pile reaches temps over 95°F. Otherwise, put them in a garbage bag, seal it, and toss it out.
Treatment
Preventing adults from laying eggs in the first place is the best method of treatment. Again, except for nematodes, it’s pretty much impossible to treat the larvae.
Dust the surrounding soil and plant foliage with diatomaceous earth. You can also use wood ash so long as you use caution. Wood ash is usually best added to compost, but if you apply it directly to the soil, don’t let it touch the plants and don’t use too much.
Using insecticides directly on the soil and plants could be effective. But beneficial insects and micro organisms are likely to be affected by this treatment tactic as well. Insecticides should be the last resort.
Adult flies are attracted to bright yellow. Yellow sticky fly traps near the soil surface helps you monitor fly numbers and may catch a few adults.
