By Matt Gibson
If you are seeing large groups of flies around your brassicas and root crops, and/or noticing the fruits on these crops starting to turn yellow, it might be due to an infestation of root maggots in your garden. Root maggots are the larvae of several different species of root maggot flies. Though multiple species of root maggots exist, they all look practically identical, and each species is treated using the same prevention and control methods.
Root maggot populations are more dense in certain geographical areas on the globe than in others, but any climate suitable for growing root vegetables or cole crops is, unfortunately, suitable for root maggots as well. Fortunately, there are many ways to prevent root maggot infestations, as well as treatment methods for controlling root maggot infestations, once you are aware of their presence in your veggie garden.
In this article, we will discuss how to identify root maggots, what symptoms of root maggot infestations are, which plants are at risk of an attack, how the life cycle of the root maggot fly progresses, how to prevent root maggots, which organic and inorganic treatment options we recommend.
Identification of Root Maggots
Root maggots are small, white, worm-like creatures that measure about a quarter of an inch long. Root maggot infestations often go unnoticed until after a good deal of damage has already been done, as root maggots feed by chewing through the roots and tubers of vegetables that remain underground until harvest time.
Though small infestations typically don’t show any visible signs of internal damage, there are several signs of internal root maggot presence that are noticeable in severe cases of infestation. Heavily compromised plants may start to wilt, shrivel, or yellow due to serious root damage. The roots of affected plants are usually riddled with worm holes, or tunnels, which wind and twist their way through the roots and tubers of infested plants. Occasionally, root maggots damage the taproots of affected plants, quickly killing the plants by chewing through their most vital structures.
If you don’t mind eating food that has a little bit of cosmetic damage, you can still reap the rewards of harvests that have suffered from root maggot infestations. Though these crops may not be the most attractive of the season, there is nothing unsafe about eating the portions of damaged fruits or vegetables that are free of root maggot tunnels. Simply cut away the damaged areas of the fruit and eat the rest.
Plants Affected by Root Maggots
Root maggots commonly target root vegetable crops and cole crops in the vegetable garden. They are most commonly found in home gardens.
Commonly targeted root vegetables include:
Commonly targeted cole crops include:
Life Cycle of Root Maggots
In late spring or early summer, adult root maggot flies begin to emerge from the soil after breaking free from their wintertime pupal cocoons. Just after emerging, male and female root maggot flies partner up and mate, and females begin laying between 50 and 200 tiny white eggs. The eggs are deposited in plant stems at the soil line or into cracks in the soil right next to the plant’s stems. Eggs begin to hatch just a few days after being deposited, and larvae burrow their way into the ground to reach the plant’s root system. Newly hatched root maggots start by feeding on the plant’s smaller roots, germinating seeds, and root hairs. As they grow larger, they begin to eat tunnels and holes as they travel through the roots. After feeding on roots for up to three weeks, root maggots start to pupate in the plant roots or the soil surrounding the plant. There can be multiple generations each year.
Prevention Methods for Root Maggots
Crop Rotation – Practicing regular crop rotation can go a long way towards preventing garden pest and soil-borne disease issues. Alternate the garden location where you plant each type of crop, making sure to never grow the same crop in the same location for three to four years. If you grew onions in a particular bed last season, do not use that same bed for onion crops for the following three to four years. Additionally, take care to avoid planting your crops in a location where runoff water from neighboring gardens or farms can find its way into your beds or fields. This can be especially damaging if the neighboring farm or garden runoff water is from crops that you are currently rotating off of.
Healthy Growing Environment – If you provide your crops with their preferred growing environment and are supplying them with sufficient water and nutrients, you will have a garden full of healthy plants. Healthy plants are much less likely to become infested with pests, and healthy plants with no pests are much less susceptible to contracting soil-borne diseases. If you have developed a healthy growing environment for your plants, they will be much better equipped to fight off pests and diseases.
Keep Garden Area Tidy – Keep your garden beds clean and free of trash and plant debris. Soil-borne diseases are caused by fungus spores and bacteria that tend to hide out in plant debris, laying in wait to reinfect newly planted crops. Keeping your garden free of infected plant debris can greatly reduce the possibility of reinfecting newly planted crops with last season’s infection.
Reduce Organic Material/Manure in Soil – Root maggots prefer to lay their eggs in soil that is high in organic content, especially manure. If you have ongoing problems with root maggots, you may want to reduce the amount of organic matter that you add to your soil between growing seasons, or use a manure-free compost to amend your soil.
Soil Solarization – If root maggots are a continuing problem in your garden, or in particular garden beds, you may want to consider solarizing problem beds during the summer. Learn more about how to solarize your soil here [https://www.gardeningchannel.com/soil-solarization-method-explanation/].
Control Methods for Root Maggots
Organic Control Methods
Floating Row Covers – Installing floating row covers over seedlings or young plants will keep root maggot flies from being able to lay their eggs on the plants. Once plants mature, floating row covers can be removed, as root maggots tend to lay their eggs on young plants so that their larvae will be able to feed on small, tender, immature roots.
Paper Collars – Heavy paper collars can be installed around transplants at the base of the plants in order to prevent root maggot flies from laying their eggs on the stems at soil level.
Yellow Sticky Traps – Placing yellow sticky traps all around your vegetable garden will trap adult root maggot flies before they are able to mate and lay their eggs on your veggie crops.
Beneficial Nematodes: You’re probably familiar with the root knot nematodes that can be such a problem for many crops, but beneficial nematodes, such as Heterorhabditidae or Steinernematidae nematodes, have the opposite impact in the garden. These roundworms eat root maggots as well as fungi, bacteria, and other potentially harmful organisms.
Rove Beetles: You can purchase and deploy beneficial insects to fight many of the insects that will strike plants, and rove beetles are particularly effective against root maggots. That’s because these black and brown winged beetles, under one inch long, prey on root maggots as well as aphids, mites, mealybugs, and other soft-bodied garden troublemakers.
RotoTiller Treatment: Use a RotoTiller after harvesting a crop or pulling up seasonal plants in an area where you’ve had trouble with root maggots. Doing so destroys the areas where root maggots spend their winters: in plant debris or soil near the habitats where they live during the warmer seasons.
Diatomaceous Earth: Diatomaceous earth is a natural pesticide consisting of diatoms, which are ocean creatures whose fossilized bodies are sharp, which is why they deter many soft-bodied garden pests. To use diatomaceous earth, sprinkle it in the area of your garden where you have seen root maggots (as well as caterpillars, mites, and many other common nuisance insects). You can rest assured that diatomaceous earth is safe to use in areas where pets or children play.
Non Organic Control Methods
Pesticides – Pesticides are often avoided when treating root maggots, as they only target root vegetables and cole crops, both of which are cultivated for culinary use. Gardeners are understandably hesitant to spray plants down with chemicals, when they intend to ingest the affected crops, and share them with their families.
Pesticides are also ineffective treatments for managing root maggots, unless they are applied during the first eight to ten weeks of spring. This is because it is difficult for pesticides to reach the pests once they have burrowed into the root system. A pyrethrin drench can be a highly effective way to rid your garden of root maggots, but should only be used as a last resort due to the environmental damage that pyrethrin can cause.
Root maggots are a serious problem for many vegetable gardeners who are cultivating their own root vegetables and brassicas. However, being aware of the symptoms and the various prevention and control techniques for root maggots will help you devise a plan to handle these very annoying and destructive garden pests.