What is the pest that eats little notches around my Bergenia
and Heuchera? What can I do to prevent this?
It is possible your Bergenia and Heuchera are being nibbled by black vine
weevils or strawberry root weevils. Usually you would begin to notice the
damage in mid-spring. The notches won’t kill your plants, but if you have
a lot of black vine weevils and plants appear to be wilting, you may want
to attempt to control the larvae. Spraying beneficial nematodes
(Steinernema) on the surrounding soil may also help.
Below are links to information about weevils:
Black Vine Weevil from UMass Extension
Black Vine Weevils from University of California’s Integrated Pest Management site
Strawberry Root Weevil from the Pacific Northwest Insect Management Handbook
A document about Black Vine Weevil (and other root weevils) from Ohio State University Extension
Excerpt:
“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.
“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.
“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.
“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. Excessively damp soils in the fall
also force larvae to move up the base of the plant where girdling can
occur. Properly maintain rain down spouts and provide for adequate
drainage of soil around plants.
“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 a much of the mulch as possible
and thoroughly wet the remaining thatch and soil before and after the
nematode application. Applications of the nematodes in landscapes has
produced variable results.”