Look for
You can often spot these black, wingless, beetle-like creatures on the leaves of indoor and outdoor plants. The signature semi-circular-shaped notches along the sides of leaves, caused by adults as they feed, are another tell-tale sign of a vine weevil infestation. The pale cream-coloured larvae meanwhile feed on the roots of plants destroying the root system and causing them to wilt and die.
Plants affected
- Both the adults and their larvae can be one of the most destructive pests to shrubs, small trees, garden and house plants. They can be a particular problem in pot grown plants and adults seem particularly keen to lay their eggs in peat based compost.
About Black vine weevil
- Adult vine weevils are 1cm in length and wingless. They’re dull black with light-coloured patching running down their backs.
- Adults are mainly nocturnal and only feed at night.
- Adult vine weevils appear between March and April from the soil of indoor pots, and between May and June from outdoor pots and borders.
- After mating, each female lays between 500 to 1, 500 eggs into the soil around their favourite host plants.
- Eggs hatch ten-15 days later into white C-shaped larvae with brown heads, which begin feeding on roots, tubers, corms and the lower stems of susceptible plants. They grow to around 1.5cm in length.
- The larvae remain in the soil until they emerge as adults.
- Most adults will die in late autumn when cold weather sets in. Although those in houses can often survive into the next year.
- Overwintering larvae will feed on the deep roots in the soil and pupate around late April to early May.
Treatment
Chemical
Products containing the following chemical ingredients are all effective on Black vine weevil
- Thiacloprid (in liquid form as a soil drench)
Note: It is important to read manufacturer’s instructions for use and the associated safety data information before applying chemical treatments.
Organic
- Check plants every week to prevent vine weevil infestations becoming out of control and deal with early signs immediately.
- Remove and destroy newly-hatched adults to reduce the numbers of eggs laid in the soil. This is best done at night, with a torch, when the weevils are most active.
- Use netting and fleeces to stop adults moving between plants and laying eggs within pots.
- Replant perennial pot plants in the spring and look for and remove any vine weevil larvae you find.
- Use commercially available nematodes (microscopic worm-like creatures) Steinernema kraussei and Heterorhabditis megidis that can be watered into pots or surrounding soil to control vine weevil larvae. The nematodes seek out and kill vine weevils.
Prevention
- Quarantine or dispose of any soil from pots where vine weevil have been found. Don’t reuse this or throw on the garden because it may still contain vine weevil eggs, larvae or pupae.
- Remove plants that have unexplainably wilted and died and examine the roots. If they appear eaten, then search the surrounding soil and destroy any vine weevil larvae that you find.
- Look for leaf edge notching on garden plants to indicate where adult vine weevils are feeding. Then treat the surrounding soil with nematodes during the summer months to control any larvae that appear.
- Avoid using broad spectrum insecticides which will kill soil-dwelling predators of vine weevil larvae, such as centipedes and carab beetles.
- Encourage insectivorous birds by hanging feeders in winter and provide nesting boxes in spring.
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