Black vine weevil (Otiorhynchus sulcatus) adults feed on susceptible plant foliage, leaving notched edges, while the larvae feed extensively on roots. Damage causes in excess of £30m in annual losses for this sector.
Some of the key insecticides are granule formulations mixed into the compost before potting to prevent infestation by larvae. They can be used at any stage up to final potting (non-edible crops only) but there is no guarantee of total control if untreated liners are potted on into treated media because larvae can survive around the roots.
Parasitic nematodes can be drenched into soil/growing media and work effectively down to 5°C soil/growing media temperatures.
O. armadillo and O. salicicola, discovered in the UK in 2002, are thought to have arrived on nursery stock from southern Europe. Black vine weevil control measures are likely to be effective against them.
How to recognise it
O. sulcatus adults are about 1cm long with roughly textured black bodies, slightly speckled by tufts of yellow hairs. They have no wings and are nocturnal, hiding in crevices and leaf litter during the day and generally feeding at night. O. armadillo and O. salicicola look similar but can be distinguished by a tooth-like protrusion at the top of their legs.
O. salicicola is also larger (1.2cm).
Larvae are white and legless with glossy orange/brown heads. Fully grown, they are 1-1.5cm long, plump, often curled into a "C" shape and sometimes discoloured.
In northern Europe, adult black vine weevils occur only as females, so the species reproduces by unfertilised eggs. In unprotected crops, adults emerge from pupae in May/June. About four weeks later, they start to lay eggs on the surface of the soil or growing media, close to the host plant, until September/October. Some estimates suggest they can lay as many as 1,500 eggs during that period, but not all the eggs are viable.
Larvae hatch after about two weeks and, when young, feed on peripheral roots of plants. In time, they can digest woodier tissue and will graze on the bark of woody stems, burrow into root systems and mine into fleshier parts, such as cyclamen corms, when they become more difficult to control.
Larvae overwinter in a dormant state, in cells in the soil or growing media, resuming feeding when temperatures rise in spring. They pupate in May and June, with adults emerging three or four weeks later. Some adults can also overwinter in glasshouse structures or debris and may start laying eggs earlier.
There is usually only one generation but in the warm conditions of interior landscapes and heated glasshouses, where the life cycle is speeded up, there may be several generations and all stages may be present at the same time.
• Adult feeding leaves distinctive half-moon notching around leaf margins (pictured).
• Larval damage can show as stunted growth. Infestations can go unnoticed until leaves wilt suddenly — control is then too late.
• With a wide host range, adult weevils may feed and lay eggs using different plant species so some plants displaying leaf notching will not necessarily have larvae too.
Treatment: biological control
Several products are available based on nematodes, applied as a suspension through conventional spray equipment, irrigation systems (maximum pressure 3 bar) or even as a drench with a watering can or through a Dosatron. The nematodes attack larvae in the compost or soil, releasing bacteria that kill the pest and break its tissue down for the nematodes to digest.
A new generation of nematodes is produced inside the larva’s body and they leave in search of more larvae. Apply from August to November when larvae are young and from March to May before they pupate. Nematodes can persist for four-to-six weeks in moist soils and composts.
Larvae attacked by Heterorhabditis spp. (Nemasys H or Larvanem) nematodes change colour to red/brown. They require soil/compost temperatures above 12°C. Larvae attacked by Steinernema kraussei (Nemasys L) do not turn a different colour. Nemasys L requires soil/compost temperatures above 5°C.
Metarhizium anisopliae, an insect-killing fungus against vine weevil larvae and adults, is also available and can be compost-incorporated or applied around established plants. AHDB Horticulture has fact sheets available (01/03, 02/03 and 18/10) on vine weevil recognition, control and host plant range.
AHDB Horticulture project CP 111 provides further insight into vine weevil feeding habits, effects of growing media types on vine weevil activity and pest management. Chemicals Regulation Directorate (CRD) project PS2134 looked at the cockroach trap Roguard (BASF) and isolates of Beauvaria bassiana. Other projects are looking at nematode distribution using refuge traps (CRD project PS2140).
Treatment: cultural control
• General hygiene, such as disposal of old stock, weed control and cleaning up plant debris.
• Check newly arrived plants for signs of infestation or damage.
• Strategic placement of plants that are particularly attractive to adult weevils can help monitoring.
Treatment: chemical control
Active ingredient Chlorpyrifos
IRAC code 1B
Action(s) Organophosphorus insecticide — compatible with some biological controls.
Active ingredient Indoxacarb
IRAC code 22A
Formulation Explicit*, Rumo* or Steward* (DuPont)
Action(s) Contact and ingested insecticide — compatible with some biological controls.
Active ingredient Lambda-cyhalothin
IRAC code 3
Formulations Various including Hallmark WZT*
Action(s) Contact-acting insecticide — incompatible with biological controls.
Active ingredient Metarhizium anisopliae strain F52
Formulation Met52 granular bioinsecticide* (Fargro)
Action(s) Effective on vine weevil pre- and post-incorporation into soils and growing media — compatible with biological controls.
Active ingredient Thiacloprid
IRAC code 4A
Formulation Exemptor (Everris)
Action(s) Granular formulation (growing media incorporation) for non-edible crops — compatible with some biological controls.
Active ingredient Imidacloprid
IRAC code 4A
Formulations Couraze (Solufeeds), Imidasect 5GR (Fargro)
Action(s) Granular formulation (growing media incorporation) for non-edible crops with additional label restrictions under the current neonicotinoid ban — compatible with some biological controls.
Fully updated by Dove Associates
Use plant protection products safely. Always read the label and product information before use.
* Extension of Authorisation for Minor Use (EAMU) required for use in ornamental plant production outdoors and/or under protection.
Dove Associates shall in no event be liable for the loss or damage to any crops or biological control agents caused by the use of products mentioned.