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The small cabbage weevil and the cabbage pod weevil belong to the weevil family. The larvae as well as the adult beetles infest numerous plants from the crucifer family and can cause high yield losses due to their feeding activity.

Biology

There are several species of weevils whose larvae live on a wide variety of cruciferous plants. The most common is the cabbage stem weevil.

In addition, the large cabbage stem weevil or rape stem weevil(Ceutorhynchus napi Gyllenhal, 1837), the cabbage pod weevil(Ceutorhynchus obstrictus Marsham, 1802; formerly C.assimilis Paykull, 1800) and the cabbage weevil(Ceutorhynchus assimilis Paykull, 1792, formerly C. pleurostigma Marsham, 1802). The black cabbage stem weevil(Ceutorhynchus picitarsis Gyllenhal, 1837) is also occasionally mentioned. The lifestyle of these species is similar and they only produce one generation per year.

Small cabbage stem weevil

The adult beetles overwinter in sheltered places, such as in the ground litter of bushes, forest edges or hedges. As soon as the air temperature exceeds 12 °C in March, the females begin to fly and seek out their host plants. After about ten days of maturation feeding, holes are gnawed into the near-stem area of leaf veins to lay eggs. Three to four eggs are then laid in each of these cavities. The tissue then heals again. The transparent eggs are completely concealed in the leaf tissue. Each female lays an average of 150 eggs in this way.

After about six days, the larvae hatch and begin to feed inside the stems. They create feeding tunnels in which they slowly work their way towards the ground. The larvae leave their host plant and pupate in a small, self-dug burrow. In June of the same year, they hatch into beetles, which do not reproduce until the following year. While the main mass of weevil larvae develops on oilseed rape in early spring, stragglers can be found somewhat later in the year on cabbage, radishes or horseradish.

Cabbage pod weevil

This weevil species only flies from the flowering time of oilseed rape. It lays its eggs in the pods of cruciferous plants after a ripening feed. The larvae feed on the seeds and, after developing, bore their way out of the pod wall to pupate in the soil. After hatching in summer, the beetles feed on flowering cruciferous plants before going to their winter quarters. The cabbage pod weevil favours infestation by the cabbage pod gall midge(Dasineura brassicae).

Large cabbage stem weevil

In contrast, the cabbage stem weevil flies a few days earlier and lays one egg in each feeding hole in the stem of its host plant, not in the leaf stalks. When laying the eggs, each female secretes a substance that stimulates the plant tissue to proliferate. The beetles only hatch after overwintering and not in early summer.

Cabbage gall weevil

Unlike its related species, the larvae of the cabbage gall weevil live in pea-sized growths (galls) in the root collar or on the main root of young plants. The beetle usually overwinters here and lays its eggs in the spring after maturing. However, it is also said that the females lay eggs in the autumn so that the larvae overwinter in their galls. Arrow cress is also a possible alternative host.

Black cabbage stem weevil

The black cabbage stem weevil begins laying its eggs in autumn. The damage to the plants is caused by the larvae over the winter months.

Host plants

Cabbage shoot weevils feed on a wide variety of cruciferous plants (canola, cabbage, mustard, radish, turnip, radish, garden cress, and many others). However, which ones are attacked depends primarily on their availability: for example, in early spring after overwintering, mainly winter rape and cabbage seed bearers are available. Plants such as cabbage vegetables, horseradish or radishes, on the other hand, are only attacked later by "stragglers".

Distribution

Cabbage shoot weevil and cabbage pod weevil are widespread and alternately frequent in all cultivation areas of rapeseed, cabbage vegetables and horseradish in Austria.

Economic importance

The feeding activity can cause yield losses of up to 20-30%. Cabbage is particularly affected in the vicinity of rapeseed fields where the beetles had previously developed en masse, as they can still cause considerable damage here before they visit their overwintering sites.

Prevention and control

• Chemical control of adult beetles is possible with products against the cabbage stem weevil/rape stem weevil/cabbage pod weevil or biting insects (see list of plant protection products authorised in Austria)
• The best time for application is in early spring as soon as the first beetles fly but have not yet laid eggs. Eggs or larvae in the rapeseed stalks are very well protected and cannot be chemically controlled. If the treatment is carried out too early, a second treatment may have to be carried out.
• Yellow traps are used to determine when the beetles start to fly:
  • Set up at field edges and in the crop and check daily for beetles.
  • It is recommended to add a few drops of washing-up liquid and spirit - this reduces freezing on cold nights.
  • Observe threshold values for spraying measures.
• As a preventative measure, cultivate cabbage as far away from oilseed rape as possible and choose a later cultivation time to avoid the flight period of the beetles.
• When planting seed carriers in early spring, covering them with close-meshed fly screen or fleece has proven to prevent the beetles from flying in.
• Cultivation of early-shooting rapeseed varieties.
• Promote rapeseed development in the juvenile stage.

Links

Pests in oilseed rape - fall and spring monitoring by the Chambers of Agriculture

Services

Plant Health Services