Cabbage maggots are tiny insects that can cause great damage on cole crops like cabbage, broccoli, turnips, rutabaga, radishes, cauliflower, and brussels sprouts.

They are destructive insects, and even as tiny as it seems can completely reduce a crop to nothing.

Find more about cabbage maggots and how to control them from wreaking havoc around your garden.

IDENTIFICATION, BIOLOGY, AND DISTRIBUTION

These destructive insects can be mostly found in the northern zones of the United States as cole crops are best grown in cooler climates. This does not mean they cannot be grown in locations with warmer climates since they can also be found in the coastal regions of California with warm climates.

As similar with most maggots, the cabbage maggot are larvae deposits of the Delia radicum known as the cabbage fly, cabbage root fly, root fly or turnip fly. They bear some resemblance with the housefly, but are half the size. 

The egg/larvae deposits of the Delia radicum are white in color, 1/8-inch-long in size, and shaped like torpedoes. They lay their eggs in rows close to the stem of cruciferous vegetables.

Once laid, the eggs can only survive in cool/moist soil. If exposed to temperatures higher than 95°F, the eggs won’t live to survive.

The eggs metamorphosizes to maggots, white in color, about 1/3-inch-long with no legs, and pointed at one end.

LIFE CYCLE

The pests reside as brown pupae all through winter inside the soil close to the roots of crops grown during fall.

During the period of early spring in the north and in California with warmer climate, the flies emerge from the soil. Interestingly, they can travel distance as far as a mile to search for host plants.

They feed on the pollen and nectar of most of the plants they colonize as hosts for 10 days or more before proceeding to lay their eggs near the base of the host plant. It then takes about a week for the larvae to hatch.

The newly hatched larvae then burrow through the soil finding its way close to the root of the plant and start destroying the fibrous roots until there is nothing left of the plant.

In some cases, older larvae may also dig into stems of plants to finish off such plants.

While burrowing through the soil, the larvae metamorphoses into the pupa after it has digested the root of the plant. They emerge from the soil when fully matured (which takes about 2-3 weeks) to repeat the cycle all over again.

DAMAGE

Due to the fact that cabbages and other cole crops best thrive in cooler climates, they need to be cultivated and harvested early enough before the heat of the summer leaves them vulnerable to these destructive pests during springtime.

Therefore, cabbages and other cole crops planted in springtime are likely to encounter visits from these pests than the ones planted in summer.

Cabbage maggots are very tiny and because they reside mostly in the soil, you might not notice their presence until your plants start wilting. Plants that are infested, will likely show signs of wilting during the heat of the summer.

Turnips and radishes in contrast to cabbages do not wilt, thus making it difficult to identify whether or not the plant is infested.

Another sign of plant infestation can be changes in the color. Most times infested plants are slightly blue or yellow foliage.

There are cases where you would even find the larvae on the roots of the plants when you pull them out. Unfortunately, at this stage such plants will eventually die.

In the event where the radish, turnip, and rutabaga plants survive, the damage done by the burrowing larvae to their roots will render them inedible and clearly unmarketable. 

MONITORING

Now that you know that these pests are mostly prevalent during springtime, it is necessary to be conscious of seasonal changes. For instance, the springtime is when the female cabbage fly comes visiting, depositing their eggs near the root of their host plants.

Interestingly, the Barbarea vulgaris known as the wintercress aka yellow rocket, can help you monitor the presence of these pests. When this type of weed starts growing in your area, be on the alert because the flies are close.

You can also adopt the use of sticky cards traps to help attract the flies. To achieve this, suspend the sticky notes slightly above the top of the plant.

A personal inspection of your crops can help you to identify the presence of these pests. Look along the stems of your crops to check for deposited eggs of the cabbage fly and quickly take them out. Also check between groups of 2-5 plants for egg deposits.

Where you find the presence of one egg per stem, then you can be sure that your plants will suffer extensive damage as the pests at this point will begin to grow at an exponential rate. More pests therefore mean more damage.

Also keep a close eye in wetter/moist parts of your garden which are very conducive spots for depositing their eggs.

CULTURAL CONTROL

There are cultural methods that you can adopt to reduce the risks of infestation of your crops.

BE CAREFUL WHERE YOU PLANT

One of the methods that can be adopted to reduce the infestation of your crop by these pests is to avoid planting your cabbages in the same areas where cole crops were previously planted. Cabbage maggots are attracted to cole crops, therefore planting your cabbages on a different portion far from other cole crops, will help reduce the presence of these pests.

You should also avoid planting your cabbages in areas that previously contained decaying matter.

USE FLOATING ROW COVERS

Install floating row covers around your plants to help protect them from infestation by these insects. This can be done as soon as you plant your seeds or after transplanting.

Most importantly, do not use floating row covers in areas where cole crops were previously grown as the plants can still be infested from under the row cover.

You can take off the row cover once the soil warms up and the plants are large and strong enough.

PILE SOIL AROUND STEMS

Pile soil around the stems of your plants. This is done to enable plants to grow strong roots deep into the soil capable of withstanding any form of infestation and compensate for any root loss.

TILL CROP RESIDUE UNDER

Always endeavor to till crop residue under the crop after harvesting as to destroy any of these insects that may want to take abode under such residue till the next planting season. 

Tilling the crop residue under the harvested plant, will help expose the pupae to sunlight which it can’t survive under.

ORGANIC CHEMICAL TREATMENT

There is an organic plant-based treatment known as Ecotrol G and recommended by the UMass Amherst Center for Agriculture, Food, and the Environment for treating soil infested with these insects.

The product comes in the form of plant oils, which when applied can repel the insects,

BIOLOGICAL CONTROL

You can as well adopt the following biological methods to keep these pests away from your plants:

BENEFICIAL NEMATODES

It has been shown that the application of beneficial soil nematodes called Steinernema feltiae repels these pests from plants.

The juvenile nematodes can be applied to the transplants in water, or can be sprayed on it before or after transplantation.

In case the adult emerges from the soil in less than a week after transplanting, you will be required to treat the plants to further protect them from infestation. The recommended concentration to be used in treating your plants is between 100,000 to 125,000 juveniles per transplant.

The soil in which the nematodes are applied should be kept moist to enable their survival.

NATURAL ENEMIES

Apart from using the aforementioned methods, there are natural enemies of these pests that can help reduce their reproduction around your plants.

The beetle species known as Aleochara bilineata that reside in the soil can kill a large number of the eggs larvae, and pupate by laying its eggs on the surface of the maggots.

Other enemies of these pests include the predatory mites and parasitic wasps which feasts on the maggots.

A natural occurring fungus can also attack the maggots destroying a large percentage of its population. This happens when there is an abundance of flies in relative high humidity.

The disadvantage of this is that the fungus can equally attack your plants.

CHEMICAL PESTICIDE CONTROLS

Insecticides although not completely effective can be used to control the population of these pests around your crops.

However, if the soil temperature is above 95°F over a few days in a row, then there is no need to apply the insecticide.

Chemical pesticide control includes diazinon and cyantraniliprole.

The insecticide should be targeted more on the seed furrows, or at the base of the plants. You also need to apply a lot of water to the soil to enable easy penetration of the insecticide, following the product’s application instructions closely.

In situations where the insects are already established, applying the insecticide will yield little or no result. The insecticide will be also ineffective when there are no maggots in the tunnels, a stage where they have metamorphosed into pupae.

MONITOR AND TAKE ACTION

It is very important you pay close attention to your plants as cabbage maggots may not be noticed at the early stage until the damage has been done.

A close observation of your plants regularly will help to monitor and control their presence, thereby preventing them from growing exponentially and causing great damage to your plants.

If you have experienced a cabbage maggot infestation on your plants, share your experience on how best you tackled the situation.