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 Bud
feeders: Climbing
cutworms is a general term applied to a large number of moth
larvae that feed on grape buds. These night feeding larvae attack
developing buds, young leaves and shoots, devouring all of the tissue.
Damage is usually spotty, although it can be serious. Flea beetle
adults (first generation) attack swelling buds usually at the very
beginning of bud swell, earlier than cutworms. These beetles bore
into buds, hollowing out the inside. Vines near wooded areas are
more susceptible. Larvae and summer adults feed on young foliage,
avoiding the leaf veins, leaving behind a kind of skeleton. Unless
bud feeders are a perennial problem (cause major crop loss), control
measures are usually not warranted. Foliage
feeders: In
addition to flea beetle larvae and summer adults,
Japanese beetles also feed on grapevine foliage. Most people
are familiar with the shiny, metallic green beetle. Generally, infestations
are spotty and do not hurt the vines. Heavy infestations, however,
can literally defoliate young grapevines. In this case, control
measures would be necessary. Damage appears to be more frequent
in areas bordered by turf or pasture, since these are also feeding
grounds for the beetle grubs.
Leafhoppers damage leaves by sucking out the liquid contents
of cells. The potato leafhopper usually shows up in June in New
England. It is yellowish in color, wedge-shaped, very mobile and
about 1/8-inch in length. It can be found on leaf undersides and
moves sideways when disturbed. Damage appears as a marginal yellowing
of the leaf. The grape leafhopper is similar in appearance but has
three black spots and does not move sideways. During the summer,
grape leafhopper 'skins' can be found on leaf undersides. Damage
appears as a yellow speckling, especially along veins. Growers do
not usually treat for leafhoppers. Aphids,
another group of sucking insects, are common pests on many plants.
Most are less than 1/16-inch long and can be distinguished by the
presence of two 'tailpipes' or projections on the back of the aphid.
In some years, the dark brown grapevine aphid has literally blanketed
shoot tips of vines. Usually, grapes are sufficiently vigorous to
tolerate attack and treatment is not necessary. Finally,
the European red mite has become
a concern for New England grape growers. Tiny red mites can be found
mostly on leaf undersides, from mid-May through September. The mites
also ingest the contents of cells, leading to a bronzing of infested
foliage. Severe bronzing, especially early in the season, can result
in a reduction in photosynthesis. This has implications for vine
health and for fruit quality. When scouting in June, if you find
more than two to three mites per leaf, treatment may be necessary.
Vines can tolerate higher mite populations later in the season. Fruit
Feeders: The
grape berry moth is by far the worst insect pest of Northeastern
grapes. This tiny (1/4-inch) moth lays its eggs primarily on newly
formed berries. Eggs hatch in four to eight days, yielding larvae
that feed on young berries, often inside a protective webbing. Generally,
three to ten berries will be webbed together. Soon after fruit-set,
the larvae will bore into the berry and feed internally. One larva
may attack up to seven or so berries. Look for a purplish discoloration
on berries, usually accompanied by a small entrance hole. This entrance
hole has been shown to be a starting point for the Botrytis fungus.
This pest will have several generations, so they are a concern from
fruit-set (June) until harvest. Vines near wooded areas are more
at risk. If more than just a few clusters have berry moth damage,
control measures may be warranted, starting around the post-bloom
stage. Pests
that damage leaves and shoots: A
number of pests can attack grape leaves and shoots. Usually, damage
is spotty and does not seriously hurt the vine. A heavy infestation
of any pest, however, can damage the health of the vine. Grape
cane gallmaker: In May or June, the female of this snout-nosed
beetle hollows out cavities in a green shoot, then lays her egg.
The resulting gall is apparent in six to eight weeks and is found
just above a node. It is twice as thick as the node, has a deep
longitudinal scar and is reddish in color. The yellowish larvae,
with light brown heads, may be found within the gall until August.
Damage is usually not serious enough to warrant treatment. Grape
cane girdler: In late May-June, this shiny black beetle lays
its eggs in a green shoot. The female then proceeds to girdle the
cane just above the egg and just below the egg. This section of
shoot either dies back or breaks off. A shoot which snaps all of
a sudden, perhaps hanging by a thread, has been attacked by the
cane girdler. Damage is usually minor. Grape
tumid gallmaker: A
small fly by this name lays its egg within an unfolding bud or shoot
tip. Maggot-like larvae hatch and feed on vine tissue. A small (1/8-1/4
inch) reddish gall forms around the larvae as it feeds. Galls can
be found on leaf undersides, clusters and petioles. Treatment is
not recommended, except in extreme situations. Insect
and Mite Control Many
types of insects cause damage to grapevines. The damage is often
only cosmetic and does not hurt the vine. A central theme to the
insect and mite control is scouting. Scouting is the systematic
evaluation of foliage and fruit on a timely basis. This allows identification
of the pest, an assessment of the damage and will help in deciding
whether treatment is warranted. Recognizing insect or mite damage
is relatively easy with a basic understanding of each potential
pest. For the smaller grower, scouting simply means checking the vines weekly or bi-weekly for any signs of damage. With only a few vines, this is easy. With 30 or more vines, it is too time-consuming to check every vine; representative samples must be taken. Use the following guidelines when scouting:
Adapted from the Cornell Cooperative Extension, 2001
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