Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Black
Vine Weevil (and
other root weevils) .
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The
black vine weevil, has been reported as being accidentally imported from
Europe and was first detected in Connecticut in 1910. However, there is
evidence in the scientific literature that this species was actually detected
in the 1830's. It was probably introduced along with some plant material
brought from Europe. Mainly through movement of ornamental plants, the black
vine weevil has been spread across much of northern North America from Maine
to the Carolinas and west to Washington and Oregon. It occurs in all counties
in Ohio. |
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There
are two close relatives of the black vine weevil, the strawberry root weevil,
and the rough strawberry root weevil. All of these weevils are collectively called
root weevils because their larvae feed on a variety of plant roots. The
strawberry root and rough strawberry root weevils are often found in seedling
nurseries, nursery poly-houses and occasionally in small fruit farms. Neither is
very important in the landscape in Ohio.
Plants Attacked
Adult
black vine weevils will feed on over 100 different kinds of plants including
trees, shrubs, vines and flowers. The preferred hosts seem to be Taxus (yews), hemlock and various rhododendrons. Taxus capitata seems
to be particularly susceptible to attack. This pest is- often called taxus weevil by the nursery.
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Damage Adults
that feed along leaf margins produce typical crescent shaped notches. Careful
searches should be made to try and locate specimens since several other
weevils and some caterpillars can produce this same type of notching.
Moderate to light notching seems to have little effect on-plant health. The
legless larvae prefer to feed on young tender roots of Taxus,
rhododendrons and hemlock. If young roots become scarce or the soil becomes
overly moist the larvae will move to large roots near the base of the plant.
Large larval populations or moist soils cause feeding on the plant stem and
the plant may be girdled. |
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Injury
to Taxus has appeared throughout Ohio, particularly
in northeastern counties where nurseries are located on sandy loam soils. This
pest can also reach epidemic populations in polyhouses where liners and
perennials are being
grown. Occasionally, hundreds of field grown plants are killed with dramatic
suddenness. Perennial producers occasionally open their polyhouses in the
spring, only to find that many of the plants are dead because all of their root
systems have been eaten away.
Description and –Life Cycle
Black
vine weevils are oblong oval in shape, about 1/2-inch long and have a short,
broad snout with elbowed
antennae.
The body is slate grey to blackish brown and the wing covers have numerous
small pits and short hairs. This pest is difficult to distinguish from other Otiorhynchus weevils. The strawberry root weevil is usually
half the size of the black vine weevil, and more brown in color. The rough
strawberry root weevil is only slightly smaller than the black vine weevil but
the collar just behind the head, the pronotum, is
heavily pitted. Only females are known in North America, and only one generation
occurs outdoors annually in Ohio.
Female
weevils emerge from soil pupation chambers late May to early July. These
weevils must feed on plant material for 21 to 45 days before they are ready to
lay eggs. After the preoviposition period has passed,
the females place several eggs each day into the soil or leaf litter nearby
suitable host plants. The weevils hide during the daytime at the base of plants
or in mulch and leaf litter near food plants. Adults may live 90 to 100 days
and usually lay 200 eggs during this time. The eggs hatch in two to three weeks
and the small C-shaped; legless larvae feed on plant rootlets. The larvae grow
slowly over the summer, molting five to six times. By late fall the larvae have
matured and are about 5/8-inch long. The mature larvae enter a quiescent prepupal stage in an earthen cell and pupate the following
spring. A single generation occurs each year.
These
weevils can not fly but they are very active walkers. They are easily transported in potted plants
or transplants using a soil root ball.
Control Hints
These
weevils are difficult to control once established because of their nocturnal
behavior, the subterranean habits of the larvae, and the lack of natural
predators or parasites.
Strategy 1: Habitat Modification - Egg and larval survival is
helped when soil moisture is moderate to high in July and August. Heavy mulches
also help maintain critical moisture levels, Remove excessive mulch layers and
do not water plants unless necessary.
Strategy 2: Biological Control
Using Parasitic Nematodes- The entomopathogenic nematodes, Steinernema and Heterorhabditis spp., have been effective for controlling black vine weevil
larvae, especially in potted plants. Sufficient water must be used during
application to wash the infective nematodes into the soil and root zone. If the
nematodes are to be used in landscape plantings, remove as much of the mulch as
possible and thoroughly wet the remaining thatch and soil before and after the
nematode application.
Strategy 3: Soil Drenching with
Insecticides -
This technique has not worked well for larval control unless moderately
soluble, long residual insecticides are used. Most pesticides get bound up in
the organic matter under plants and never reach the larvae.
Strategy 4: Foliar Sprays of
Insecticides -
Since the adults are active after dark, the most common method of control is to
place a stomach poison on susceptible plant foliage. Because adults are active
for a long period, several sprays may be needed. Early applications are
encouraged so that adults are affected prior to their egg laying period.
Information obtained through the Ohio State Extension Factsheet HYG-2016-95
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES