PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Black vine weevil (BVW)
Scientific name
Otiorhynchus sulcatus (Family Curculionidaae).
Do not confuse this weevil with the vine weevil
(Orthorhinus klugi). Other weevils damage plants
in a similar manner to BVW, eg
Fruit-tree root weevil (Leptopius squalidus)
Fuller’s rose weevil (Asynonychus cervinus)
Garden weevil (Phlyctinus callosus)
Whitefringed weevil (Graphognathus leucoloma)
Host range
Ornamentals, eg numerous greenhouse and
outdoor plants, begonia, cyclamen, geranium,
impatiens, orchids, maiden hair fern, woody
ornamentals (azalea, conifers, fuchsia, pittosporum,
rhododendron, rose), containers, nurseries.
Fruit, eg apple, blackberry, blackcurrant,
gooseberry, grape, strawberry.
Vegetables, eg seedlings, and some Weeds.
Description & damage
Adult weevils are 10-12 mm long with an
elongated snout. They are shiny black with faint
yellow spots on their backs. Adult females are about
9 mm long, black with rough wing cases, which are
relatively rounded with parallel ridges running
length-wise with patches of yellowish hair. Antennae
are long, slender and elbowed. Adults feed at night,
hide during the day under mulch, clods of earth or
debris on the soil surface, or rest on the plant in dark
protected places. If disturbed on the plant during the
day they drop to the ground as if dead. Eggs are
each about 0.7 mm in diameter, roughly spherical
and white initially before turning brown. Larvae are
white, curved, legless, about 10 mm long when fully
grown and have brownish heads. Newly hatched
larvae have straight, pinkish white bodies with brown
heads. Pupae are 8-10 mm long, milky white
initially with large spines on the head, legs and
abdomen. As they mature they darken until almost
black. They are hard to find in the soil.
Leaves. Adults feed at night chewing large
ragged notches from flower and leaf margins. They
may eat whole leaves, leaving only the midribs and
main veins. Damage may be unsightly but usually
not significant on most perennials.
Stems and stalks. Adults feed on stems of
seedlings and host plants at, or just below, ground
level. They may also chew fruit stalks of grapes
and sometimes feed on fruit.
Roots, corms. Larvae feed on roots eating
smaller ones and ring barking larger roots or the
main stem just below the surface. Large larvae
may bore into crowns or corms. Look for larvae
2-40 cm down in the soil near roots. Severe root
damage may cause infested plants to suddenly
wilt and die. It is the root damage that is serious.
General. Plants may grow poorly in spring due
to larvae feeding on roots. Others may die after
planting out, which can be embarrassing for
contractors and purchasers. BWV can cause
substantial losses in container-grown perennials.
Slow growing species cannot compensate for the
European strawberry weevil (Tas.)
loss of root tissue and suffer most damage. In hot
weather plants that appear healthy may deteriorate
when subjected to the slightest water stress.
Diagnostics. Detection of either adults (which
are active at night) or larvae is difficult, and
infestations are sometimes overlooked for years.
Adults. Do not confuse with other weevil
pests, eg garden weevil (Philistines callous)
which may be confused with BVW. It is smaller
(6-7 mm long) and dull gray with a pale ‘V’ on
the upper elongated snout. Adults of both species
rest during the day under leaves or plants and so
are seldom associated with damage.
Larvae. Do not confuse with scarab grub larvae
which have 3 pairs legs on the thorax and are
larger.
Damage. Tell-tale notching on leaves by adults
is distinctive, look for adults during the day under
pot rims, etc, or on the plants at night. Root and
stem damage by larvae may be mistaken for
Phytophthora root rot. Look for larvae near roots.
Pest cycle
There is a complete metamorphosis (egg,
larva, pupa and female adult) with 1 generation over
1-2 years. In glasshouses there may be 2 generations
per year, all stages may be present at the same time.
Female weevils emerge in early spring and feed for
about a month, then can lay up to 1000 fertile eggs
without mating, during their life (about 1 year) in
the soil near the base of plants. Peak emergence is
Jan-Feb and again in Aug-Sept. Adults may lay
200-400 eggs in the 1 st year and 400+ eggs the
next. Eggs hatch in 15-21 days; larvae feed for
3-4 months then pupate a few centimeters below the
soil surface. Pupal period lasts 18-20 days.
‘Overwintering’
Usually as larvae but all stages can 'overwinter'.
Fig. 74. Black vine weevil (Otiorhynchus sulcatus)
Above: Corm damage by larvae, leaf damage by adults.
Below: Larva (9 mm long) and adult (12 mm long)
106 Insects and allied pests - Coleoptera (beetles, weevils)