Cabbage Fly (Phorbia brassicae): [Characteristics, Detection, Effects and Treatment]

What is the cabbage fly?

One of the most serious enemies of agriculture, at all levels, is the infestation of crops by the presence of the whitefly or cabbage fly, a pest highly resistant to low temperatures that can wreak havoc with great economic losses.

Scientific name Phorbia brassicae, they have a special predilection for the neck of the Cabbages, but in general they attack all cruciferous species.

The characteristic attack method of this pest is the construction of tunnels and galleries in the stems of the plants, in order to suck all the sap, an invasion carried out by the larvae, which can have such lethal power that they end, if we we neglect, leaving the dry, hollow stem, with the usual ruin of the entire crop.

This damage extends to all crucifers, both cultivated and spontaneous, since they are very voracious and can procreate up to three generations in a year, more than enough offspring to ruin entire crops.

How can we identify it?

The so-called whitefly also has the following characteristics and habits. Let’s see.

In the case of cabbages , the attack of the larvae of this fly begins at the neck, where they carve galleries that flood the entire stem to consume all the nutrients, to the point that they leave it empty of content.

But when they attack napiform crucifers like turnips and radishes, then they head for the fleshy root, which is also dried out by the powerful sucking work of the larvae.

Morphology

The larvae have a growth of up to about 10 mm, with a whitish appearance and without legs. 

When they reach adulthood, they measure between 5-7mm and are similar to house flies, but have a grayish-yellowish color and very red eyes.

The species Delia radicum (also attacks the roots of cabbages) has 3 darker lines that cross the abdomen while the Delia platura has a brown dorsal line.

Lifecycle

This species has a life cycle that extends up to about three generations throughout the year.

In the first, it takes advantage of the weeds to grow and multiply, until it jumps, already in the second generation, towards the young plants of the crops, destroying them with direct attacks on roots and leaves, if forceful actions are not taken to destroy them, before they reach the epicenter of the central stem. 

The fly, in its chrysalis phase, protects itself from the effects of winter . But when spring arrives , the first adults will burst, which will hatch to fulfill the massive mission of reproducing and laying eggs in numerous batches, around the roots of the plants and also seeking to do so in the cracks of the earth that gives soil to crops.

The larval stage occurs after 4-8 days of invasion of the roots of the affected cruciferous, until reaching the base of the stem and the petioles of the leaves. Shortly after carrying out this intense task of extracting nutrients, the pupae appear, which rise to the surface of the earth showing a body of about 5 cm.

In summary, the identifying characteristics of the presence of this pest are the following:

1. The leaves acquire a grayish hue that spoils the green color typical of chlorophyll activity. A waxy appearance floods the entire vegetative body, until the plant withers and dies.
2. Another less serious consequence is that the plants stop their growth process and are stunned, they are small.
3. In the case of the roots, the damage is so much appreciated that many sprout, rise to the surface of the earth, because they become necrotic until they rot, due to the attack of the larvae of this very harmful fly, which can also be seen in the soil when they behave like a pest by invading the entire root system of the plant.

What plants does the cabbage fly affect?

How to combat the cabbage fly?

Nothing better than prevention to combat this devastating pest of cabbages.

Some of the most important tips are as follows, but it must always be borne in mind that all this problem begins when weeds are allowed to grow in the crop or garden, because this is the home of the first generation of attackers.

Let’s see where to start defending against this powerful enemy of cabbages.

Soil preparation

It is essential to apply intensive plows when preparing the land for the new crop, because by aerating the soil it is always possible to remove the buried pest.

In this process, it will also be mandatory to remove any traces of the previous crop, to avoid contaminating the new crop. A good granular disinfectant is very useful as a preventive measure. Fenthion, Diazinon and Dimethoate are recommended.

Crop rotation

But it is also good to alternate crops of crucifers, at least once a year. These first actions will have the dipteran at bay, away from the sowing.

Biologic control

In organic farming, a procedure that begins, as we have already said, works very well with the elimination of all weeds on the ground, especially the bad crucifers, because the pests lodge in these spontaneous species. 

It is considered one of the most effective methods, which should be combined with the rotation of crucifers with other compatible crop associations. It is also advisable to eliminate the application of fresh animal manure and use green manures, because they attract the pest.

Other effective measures are:

1. When the presence of the fly is exaggerated, it is necessary to cover the young crops with a protective mesh, a very effective technique in the fight against delia radicum.
2. The fertilization indicated by the specialists and balanced irrigation are also their own practices that prevent the appearance of the insect. That is why the nitrogen- rich fertilizer is the most correct because it accelerates the development
3. Use of yellow chromatic traps, to catch them by sticking to the glue we use, mixed with the paint.
4. Agricultural lime is applied to acidic soils to kill vermin that lodge in the soil, but its application to soils with a pH greater than 7.5 is not recommended.
5. Irrigation with a Neem oil solution also works, applying between 3-4 drops per liter of water for irrigation, trying to pour it into most of the vascular system of the plant to repel pests of any kind. Avoid doing it when the harvest is near.
6.  Finally, if the pest has spread a lot on the plant, unfortunately its total destruction is recommended, without leaving any remains on the ground to prevent the contamination from spreading even more.

What are the best products to eliminate the cabbage fly?

Although care for the environment should always prevail, minimizing the continued use of insecticides of chemical origin, when planting is finished, it is advisable to immediately apply specific agrochemicals, because pesticides are effective in preventing the cabbage fly from doing its thing.

Specific pesticides such as Lambda cyhalothrin 2.5% and Tau-fluvalinate 24% have a very good response to the cabbage fly plague, but must be applied under strict sanitary controls to avoid unwanted effects on crops.