Canola
Rape Beetle
Brassicogethes aeneus
Insect
In a Nutshell
- Shiny black beetles around flowers of cabbage or canola.
- Holes in buds.
- Podless stalks under severe circumstances.
Can also be found in
Canola
Symptoms
The most obvious sign of attack is the presence of shiny black beetles crawling around the flowers of the host plant. Holes in the buds indicate where adults have fed on or laid their eggs in the buds. Severe damage to buds can cause the buds to drop leaving podless stalks. Feeding in the flowers is restricted to the pollen-bearing stamens and few visible symptoms are apparent.
Recommendations
Organic Control
Formulations of Bacillus thuringiensis have been used with some success against B. aeneus.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Broccoli and cauliflower plants can be used as trap crops, sprayed with an insecticide, usually deltamethrin. Some trials showed that almost complete protection was possible, but this depends on being able to produce a trap crop in bloom before the main crop, which can be hard to time. Pyrethroid insecticides can also be used for control of B. aeneus if there are no known cases of resistance to the chemical. However, pyrethroid insecticides also affect predatory organisms. Consider neonicotinoids, indoxacarb or pymetrozine as alternatives to pyrethroids. Do not spray after flowering starts.
What caused it?
Adults emerge in spring after overwintering in woodland and other sheltered uncultivated sites. They fly actively when temperatures exceed 12-15°C, often feeding on the pollen of any available flowers before locating their breeding hosts. Eggs are laid in buds at least 3 mm long. The larvae feed on pollen in flowers, taking 9-13 days to complete two larval instars. The full-grown larva then drops to the ground, burying itself in the soil. The new adults emerge later and feed on pollen from any available flowers before once more seeking overwintering sites. The spatial distribution of B. aeneus on crops is usually complex and irregular.
Preventive Measures
- Avoid deep ploughing, which may kill parasites of B.
- aeneus.
- Monitor plants regularly for presence of beetles or holes in buds.
- Do not spray insecticides after flowering starts; the pollen beetles migrate to open flowers, away from the buds, and become pollinators rather than pests.
- Use baited traps or online pollen beetle migration forecasts.
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