Muscadine Grape Diseases and Their Control
Fruit Disease Information Note 12
W.O. Cline, Extension Plant Pathologist
[General Information] [Symptoms] [Control]
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The muscadine grape (Vitis
rotundifolia) is a native grape species found in the southeastern United States. It
grows wild throughout North Carolina and will survive in areas where other grape species
will not. The fruit is generally harvested as single berries rather than in bunches. As
the species name implies, the leaves are round and unlobed, though serrated at the edge.
Both purple-fruited "black" and bronze-fruited "white" muscadines are
seen in the wild. Since the early 1950s, many improved cultivars have been developed for
commercial production of fresh fruit and for winemaking.
Although far more resistant to most
diseases than are bunch grapes (V. labrusca, V. vinifera), muscadines can
suffer extensive losses in commercial plantings if diseases are left unchecked. Fruit
rotting diseases can reduce yields and make berries unmarketable for either wine or fresh
sales. Fruit grown for fresh consumption must be adequately sized and free of blemishes
caused by disease.
Symptoms of Major Diseases of
spot (Mycosphaerella angulata) is an important leaf disease. The symptoms of
angular leaf spot first appear as faint, light yellow spots on the leaves. As the yellow
spots become more noticeable, irregular brown flecks develop in the center of the spots.
As the growing season progresses, the disease often increases and causes extensive
defoliation by harvest. If heavy defoliation occurs, the total yield and also the quality
of grapes are reduced.
rot (Greeneria uvicola, syn. Melanconium fuligineum) can be a very
destructive fruit disease. Infection occurs shortly after bloom. Just before harvest,
infected berries turn black with spore-bearing structures (acervuli) erupting through the
skin of the fruit. Rotted berries may or may not fall to the ground before harvest. The
fungus infects fruit stems, leaves and young shoots.
Powdery mildew (Uncinula necator) attacks berry clusters
and young berries just after flowering. Infected berries are covered with a white fungus
growth. As the berries enlarge, the fungus growth disappears, but the grapes become
rough-skinned (russetted) and may crack. Loss of yield results from both berry drop and
reduced size of berries.
Ripe rot (Glomerella cingulata; imperfect stage Colletotrichum
sp.) Also causes a berry rot near harvest and in recent years has
become the most damaging fruit rot disease. Rotted berries turn uniformly
dark brown over part or all of the berry and have pink or orange spore
masses on the surface. Ripe rot infections can occur at any stage of fruit
development, but fruit infected in the green (unripe) stages does not
rot until it begins to ripen. Once infected grapes begin to rot
and produce spores in the vineyard, the disease can spread rapidly to
other ripe fruit. The most devastating losses to this disease occur
on susceptible cultivars during rainy harvest seasons. Generally speaking,
dark skinned cultivars (Noble, Pride) are more resistant, while bronze
cultivars (Carlos, Scuppernong, Magnolia) are more susceptible.
rot (Botryosphaeria dothidea) causes small, sunken, black fruit spots that are
round with distinct edges in the early part of the season. As harvest approaches, these
spots may develop a greasy-looking soft rot around the initial lesion. A halo develops
around the black spot and the entire fruit may rot just before harvest. Infections are
sometimes not visible until the soft rot stage occurs.
Black rot (Guignardia bidwellii f. muscadinii)
causes a circular brown leaf spot and a black scab on berries. Occasionally, lesions occur
on the young stems and tendrils. Black rot seldom causes much damage in sprayed vineyards.
Pierce's disease (Xylella fastidiosa) is the primary disease
limiting production of bunch grape species (V. labrusca, V.
vinifera) in the southern U.S. This bacterial pathogen is of little
importance on most muscadine grapes, occasionally causing a marginal leaf
burn on susceptible cultivars such as Carlos. The cultivar Pride is highly
susceptible and may be killed by the bacterium. Growers should avoid propagating
from symptomatic vines. Chemical control is not available. For
more information on Pierce's disease on bunch grapes, see the
at Texas A&M.
Crown Gall (Agrobacterium sp.) is a disease caused by a
bacterium which has frequently been associated with gall formation on grape vines. Galls
are fleshy, irregularly shaped growths. The disease usually occurs in association with
freeze injury, and galls may form all along the length of the trunk and cordons. Fall
planting exposes new vines to freeze injury and should be avoided. Symptoms of crown gall
are far less severe on muscadine grapes than on bunch grapes.
establishing a planting, investigate the possibility of using disease-resistant cultivars.
For instance, among large-fruited bronze cultivars, 'Fry' is very susceptible to ripe rot,
while 'Triumph' is not. As mentioned earlier, dark-skinned cultivars tend to have less
Cultural Practices. Home
and commercial growers alike can reduce diseases through cultural practices. Mowing or
otherwise reducing undergrowth near vines will improve air movement through the vineyard.
Timely harvesting along with removal of leftover fruit at the end of the season should
also help reduce fruit rots. Avoiding excess late-season fertilizing can reduce both
disease and the likelihood of winter injury to cordons and trunks of vines.
Fungicides. Results from
experimental tests for control of muscadine grape diseases have shown that a regular spray
program with an effective fungicide plus an insecticide is highly beneficial and
profitable. An effective disease control program is essential to produce the high yields
of quality grapes that are possible with the newer varieties. In new vineyards, the
disease control program should begin in the second or third season after planting.
Repeated early season applications of fungicides (May-June-July) are the most effective.
In home plantings, fungicides are generally not necessary.
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Recommendations of specific
chemicals are based upon information on the manufacturer's label and performance
in a limited number of trials. Because environmental conditions and methods
of application by growers may vary widely, performance of the chemical
will not always conform to the safety and pest control standards indicated
by experimental data. All recommendations for pesticide use were legal
at the time of publication, but the status of registration and use patterns
are subject to change by actions of state and federal regulatory agencies.
Published by the North Carolina Cooperative Extension Service
Distributed in furtherance of the Acts of Congress of May 8 and June 30,
1914. Employment and program opportunities are offered to all people regardless
of race, color, national origin, sex, age, or disability. North Carolina
State University at Raleigh, North Carolina A&T State University,
U.S. Department of Agriculture, and local governments cooperating.
Last update to information: April, 2000
Last checked by author: April, 2000
Web page last updated on 07 April 2000 by A.V