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The tell-tale signs are there:
C- shaped notches in leaves; stunted growth; and even yellow,
wilting leaves - a black vine weevil infestation! This insect
infects over 200 plants but the most common include rhododendrons,
azaleas and yew. There are few garden pests that are as difficult
to get rid of as this weevil but by targeting the young and vulnerable
larvae and using a few cultural practices, gardeners can get
good control of this nuisance.
Identification
The adult weevil is a dark, oval-shaped
insect, ½" in length with a blunt snout and distinct
antennae. In North America, all of the adults are females so
every insect has the ability to cause and infestation. Feeding
occurs at night; the adults do not fly but instead need to crawl
up plants. The larvae are off-white in color with dark heads
and can also do extensive damage as they feed on plant roots.
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Life cycle
The adult weevils emerge from
the soil in late May or early June through mid-July. These adults
feed for 4-5 weeks in order to produce the 300+ eggs that are
dropped into the ground under the plant. The eggs hatch within
2 weeks and the larvae then tunnel into the soil where they feed
on plant roots. They then tunnel deeper into the soil to protect
themselves from frost and pupate in the spring. |
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Control Methods
Understanding the lifecycle and
feeding practices of the weevil is the key to keeping the pest
under control. Since adult weevils feed on leaves during the
night and look for dark, moist spots during the day to rest,
trapping them in these areas can be quite effective.
Hand picking
With the aid of a flashlight,
pick-off the adults in the evening as they come out to feed.
Traps
*Simply placing a white drop
cloth under your plant in the evening or early morning and shaking
the leaves will help to catch many of the adults.
*During the day, place a board
under the plant. Check the board for hiding adults and scrape
them off into a bucket of soapy water.
*Place a wrapper around the trunk
of the plant and coat it with a sticky substance such as Tanglefoot.
The wrapper should be at least 6" wide.
Mulching
The eggs and larvae of the black
vine weevil require moisture to survive. If your plants are heavily
mulched, pull back this mulch to allow the surface of the soil
to dry out and do not water plants unless necessary.
Beneficial Nematodes
Rather than attacking the adults,
beneficial nematodes go after the larvae in the soil and are
a safe & natural method of controlling black vine weevil.
A few things are critical in order to get good control:
Timing & Temperature - Beneficial
nematodes require a soil temperature of at least 60 F to work.
Gardeners often miss the critical period in the spring since
the weevil larvae pupate fairly early, before the soil warms.
The late summer and early fall is the best time to apply nematodes.
Moisture - The root zone around
the plant must be moist since nematodes don't swim and require
water to carry them through the soil. Water the area before and
after application. |
