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Grape
Grapes are among the oldest cultivated plants in the
world. Human history and grape culture have
been intertwined for eons.
Leading producers of grapes are: Italy, France,
former Soviet Union, Argentina and U.S.
California produces about 90% of US grapes
Most grapes are used in wine production
~90% of raisin grapes are grown in Fresno County
Grape
Family Vitis has 11 genera and 600 species
Genus Vitis is the only food-bearing genus
About 30 species are native to North America
There has been much interbreeding to give
rise to current cultivars
**Images and lecture material were not entirely created by J. Bond.
Some of this material was created by others.**
Economically important species
Vitis vinifera -European grape—the basis of the
world wine, raisin and table grape industries.
Includes ‘Thompson Seedless’
V. labrusca (Fox grape) Blue grapes primarily used
for juice ‘Concord’ is leading cultivar
V. riparia (Riverbank grape) Blue grapes ‘Beta’,
‘Marechal Foch’, ‘Baco Noir’
V. aestivalis (summer, pigeon or winter grape)
‘Norton’
V. rupestris (rock or mountain grape) ‘St. George’
Muscadine grapes V. rotundifolia, V. munsoniana &
V. popenoei
Principal grapes grown in North
America
European grapes—for wine, raisins and table
use
American blue grapes—for juice and jelly
French American hybrids—primarily for wine
in areas with cold winters
Muscadine grapes—in the south
Grape vine anatomy
• Roots - Grapes root readily from hardwood cuttings. Most
European grapevines are propagated on specific rootstocks
• Trunk - May be single or split. This is usually maintained as
part of the perennial structure of the vine. It may be trained
vertically or in a J fashion.
• Cordon - Horizontal permanent stems. Not all training systems
have cordons
• Canes - One year old wood. May have 5-10 nodes. Current
season growth is also called canes.
• Spurs - Canes pruned off short, usually 2-3 buds. May be
fruiting spurs or renewal spurs
• Tendrils - Twining structures borne opposite leaves or clusters.
Helps hold grapes to trellises
Diseases
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Crown gall
Downy mildew
Black rot
Pierce’s disease
Crown Gall
Caused by the bacterium Agrobacterium tumefaciens.
This bacterium has the widest host range of any plant
pathogen. It is capable of causing tumors, or "galls,"
on virtually all plant species, except the monocots. A
similar bacterium, Agrobacterium rubi, causes galls on
the canes of brambles
Serious problem, freeze injury locations are worse.
Rod shaped bacteria non-motile and motile., biovars –
3 is found on grape
Crown Gall
All fruit crops grown in Illinois are susceptible.
The disease is particularly destructive on brambles (raspberries
and blackberries) and grapes.
It can also cause severe problems on apple, pear, blueberry, all
stone fruits and on ornamentals.
The bacteria induce galls or tumors on the roots, crowns, trunks
and canes of infected plants.
These galls interfere with water and nutrient flow in the plants.
Seriously infected plants may become weakened, stunted and
unproductive.
Symptoms
The disease first appears as small overgrowths or galls on the
roots, crown, trunk or canes.
Galls usually develop on the crown or trunk of the plant near the
soil line or underground on the roots.
Above ground or aerial galls may form on canes of brambles and
highly susceptible cultivars of grape.
Although they can occur, aerial galls are not common on fruit
trees.
In early stages of development the galls appear as tumor-like
swellings that are more or less spherical, white or fleshcolored, rough, spongy (soft) and wart-like.
Symptoms
They usually form in late spring or early summer and
can be formed each season.
As galls age they become dark brown to black, hard,
rough, and woody. Some disintegrate with time and
others may remain for the life of the plant.
The tops of infected plants may appear normal.
If infection is severe, plants may be stunted, produce
dry, poorly-developed fruit, or show various
deficiency symptoms due to impaired uptake and
transport of nutrients and water.
Symptoms
Disease Cycle
The bacteria overwinter inside the plant in galls, or in the soil.
The persists for long periods in the soil and plant debris.
When they come in contact with fresh, wounded tissue of a
host, they enter the plant and induce gall formation. The
bacteria are most commonly introduced into a planting site on
or in planting material.
Wounds that commonly serve as infection sites are those made
during pruning, machinery operations, freezing injury, growth
cracks, soil insects and any other factor that causes injury to
plant tissues.
Bacteria are abundant in the outer portions of primary galls,
which is often sloughed off into the soil.
In addition to primary galls, secondary galls may also form
around other wounds and on other portions of the plant in
the absence of the bacterium.
Control
Obtain clean (disease free) nursery stock, and avoid planting
clean material in sites previously infested with the bacteria.
Any practice that reduces wounding is highly beneficial.
Preventing winter injury (especially on grapes) is also
beneficial.
On grapes, the double trunk system of training may be a useful
system for minimizing losses due to crown gall. If one trunk is
infected, it can be removed.
Galls on the upper parts of the trunk or on canes can be
removed by pruning.
Control
A biological control agent for crown gall is available for apple,
pear, stone fruit, blueberry, brambles and many ornamentals. It
is not effective on grape.
The agent is a nonpathogenic strain of bacterium (Agrobacterium
radiobacter strain 84) that protects the plants against infection
by the naturally occurring strains of pathogenic bacteria in the
soil.
Nursery stock is dipped in a suspension at planting time. The
antagonistic bacteria act only to protect disease free plants from
future infection by the crown gall bacterium; they cannot cure
infected plants.
Downy mildew
A major disease of grapes throughout the eastern United
States.
The causal agent Plasmopara viticola, causes direct yield losses
by rotting inflorescences, clusters and shoots.
Indirect losses can result from premature defoliation of vines
due to foliar infections. This is a serious problem because it
predisposes the vine to winter injury.
It may take a vineyard several years to fully recover after
severe winter injury.
Symptoms and Signs
On leaves, young infections are very small, greenish-yellow,
translucent spots that are difficult to see. With time the lesions
enlarge, appearing on the upper leaf surface as irregular paleyellow to greenish-yellow spots.
On the underside of the leaf, the fungus mycelium (the "downy
mildew") can be seen within the border of the lesion as a
delicate, dense, white to grayish, cotton-like growth.
Infected tissue gradually becomes dark brown, irregular, and
brittle. Severely infected leaves eventually turn brown, wither,
curl, and drop.
The disease attacks older leaves in late summer and autumn,
producing a mosaic of small, angular, yellow to red-brown spots
on the upper surface. Lesions commonly form along veins, and
the fungus sporulates in these areas on the lower leaf surface
during periods of wet weather and high humidity.
Symptoms and Signs - Fruit
Most infection occurs during 2 distinct periods in the growing
season.
The first is when berries are about the size of small peas. When
infected at this stage, young berries turn light brown and soft,
shatter easily, and under humid conditions are often covered
with the downy-like growth of the fungus.
Generally, little infection occurs during hot summer months.
As nights become cooler in late summer or early fall, the second
infection period may develop. Berries infected at this time
generally do not turn soft or become covered with the downy
growth. Instead, they turn dull green, then dark brown to
brownish-purple. They may wrinkle and shatter easily and, in
severe cases, the entire fruit cluster may rot.
These infected fruit will never mature normally.
Symptoms and Signs - Fruit
Symptoms and Signs -
Shoots and
Tendrils
Early symptoms appear as water-soaked, shiny depressions
on which the dense downy mildew growth appears.
Young shoots usually are stunted and become thickened
and distorted.
Severely infected shoots and tendrils usually die
Disease Cycle
The fungus overwinters in infected leaves on the ground and possibly in
diseased shoots.
Oospores germinates in the spring and produce a sporangium. These
sporangia are spread by wind and splashing rain.
The sporangia release zoospores, which also are spread by splashing
rain, either will produce a germ tube and enters through stomates.
Once inside the plant, the fungus grows and spreads through tissues.
Infections are usually visible as lesions in about 7-12 days.
At night during periods of high humidity and temperatures above 55
degrees F (13 degrees C), the fungus grows out through the
stomates and produces sporangiophores on the lower leaf surface.
The small sporangiophores and sporangia make up the cottony, downy
mildew growth.
Sporangia cause secondary infections and are spread by rain.
The optimum temp. for disease development is 64 to 76 degrees F.
Control
Any practice that speeds the drying time of leaves and fruit will reduce the
potential for infection.
Sanitation is important. Remove dead leaves and berries from vines and the
ground after leaf drop.
It may be beneficial to cultivate the vineyard before bud break to cover old
berries and other debris with soil. Cultivation also prevents overwintering
spores from reaching developing vines in the spring.
To improve air circulation, control weeds and tall grasses in the vineyard and
surrounding areas.
Grape varieties vary greatly in their susceptibility to downy mildew. In general,
vinifera (Vitis vinifera) varieties are much more susceptible than American
types, and the French hybrids are somewhat intermediate in susceptibility.
A good fungicide spray program is extremely important. Downy mildew can be
effectively controlled by properly timed and effective fungicides.
Black rot
Caused by the fungus Guignardia bidwellii
The the most serious disease of cultivated and wild grapes in
Illinois and is one of most important disease of northeast
US, Canada, EU, SA
The disease is most destructive in warm, wet seasons.
Crop losses range from 5 – 80%
The fungus attacks all green parts of the vine – the leaves,
shoots, leaf and fruit stems, tendrils, and fruit. The most
damaging effect is to the fruit.
Black Rot
Infections early in the growing season destroy blossom
clusters or cause developing berries to "shell off" the
cluster and fall to the ground.
Later infection periods can destroy a high percentage of
the berries, turning them into hard, black, shriveled
"mummies."
Unsprayed fruit on very susceptible varieties may become
almost completely rotted by harvest time
Symptoms - Leaves
Reddish brown and circular-to-angular spots appear on the
upper surface of the leaves starting in the late spring.
As spots coalesce, they form irregular blotches that are reddish
brown. The number of spots or lesions per leaf varies from 1
to more than 100
The center of the leaf spot turns tannish brown and is
surrounded by a black margin.
Pycnidia that are speck sized and black are arranged in a
definite ring just inside the margin of the spot.
Only young, rapidly growing leaves are susceptible.
Symptoms - Leaves
Symptoms - Fruit
Fruit infections can take place shortly after the calyx (flower petal)
falls, but most infections occur when the fruit is half to almost
full size.
A small spot appears that is circular and whitish tan, often
surrounded by a brown ring.
The spots rapidly enlarge, darken, and may cover half or more of
the berry within 48 hours.
The center of the spot rapidly becomes sunken, wrinkled, and
dark. Within a few days, the entire berry becomes coal black,
hard, and mummified.
The diseased fruit 'shell' or shatter and drop early. The surface of
the withered fruit is covered with minute, black pycnidia that are
often arranged in circular zones.
Symptoms - Fruit
Symptoms - Shoots, Leaf and Fruit
Stems, and Tendrils
The lesions on these parts are dark purple to black, oval to
elongated, and somewhat sunken.
The speck-sized black pycnidia are scattered over the
surface of the lesions.
As the canes grow, the bark tends to split along the length
of the lesion. If the berry stem is infected early, the flow
of sap is shut off, and the berry shrivels and fails to
develop.
Disease Cycle
Overwinters in canes, tendrils, and leaves on the grape vine and
on the ground.
Mummified berries on the ground or those on vines become the
major infection source the following spring. During rain,
ascospores are shot out of numerous, perithecia and are
carried by air currents to young, expanding leaves.
Ascospores slowly germinate, often taking 36 to 48 hours,
penetrate the young leaves and fruit stems (pedicels).
The infections become visible after 8 to 25 days. Spots appear
first on the lower leaves. When the weather is moist,
ascospores are produced and released throughout the entire
spring and summer, providing continuous primary infection.
The fungus requires warm weather for optimal growth; cool
weather slows its growth. A period of 2 to 3 days of rain,
drizzle, or fog is also required for infection.
Disease Cycle
Each older leaf spot contains a number of pycnidia, each of which
produces hundreds of summer conidia that ooze out in winding
tendrils during wet weather.
Raindrops spreads these spores to other leaves and to young fruit.
The conidia germinate in 10 to 15 hours and penetrate young
tissue.
New infections continue into late spring and summer during
prolonged periods of warm, rainy weather. The conidia are
capable of germinating and causing infection several months after
being formed.
During August, the pycnidia are transformed into an overwintering
sclerotia that, in turn, gives rise to perithecia which produce
ascospores in the spring.
Control
Space vines properly and choose a planting site where the vines will
be exposed to full sun and good air circulation.
Prune the vines each year during the dormant period. Remove the
prunings, excess growth, diseased and overwintering berries,
leaves, and tendrils
Keep the fruit planting and surrounding areas free of weeds and tall
grass.
Where feasible, cultivate the vineyard before bud-break to bury the
mummified berries.
Use protective fungicide sprays, which are needed in wet seasons, to
protect the developing new growth.
Pierce's Disease
A lethal disease caused by the bacterium Xylella fastidiosa
First detected in 1880s when it decimated vineyards in the LA
Basin and again in the 1930 and 1940s.
Pierce's disease is only known from North America through
Central America and has been reported from some parts of
northwestern South America.
It is present in some California vineyards every year, with the
most dramatic losses occurring in Napa Valley and in parts of
San Joaquin Valley. During severe epidemics, losses may
require major replanting.
Pierce's Disease
The bacterium that causes Pierce's disease lives in the xylem and is
spread from plant to plant by sap-feeding insects that feed on the
xylem.
Symptoms appear when a significant amount of xylem becomes
blocked by the growth of the bacteria.
Insect vectors for Pierce's disease belong to the sharpshooter and
spittlebug families. The blue-green sharpshooter the green
sharpshooter and the red-headed sharpshooter are important as
vectors of this disease.
Other sucking insects, such as grape leafhoppers, are not vectors.
Pathogen in Host
Voracious,
aggressive flyer and
feeds and breeds on
133 host
Spreads Pierce’s
disease with
astonishing speed.
Spring Symptoms
In vines that are infected in spring, symptoms of
Pierce's disease first appear as water stress in
midsummer, caused by blockage of the waterconducting system by the bacteria.
New leaves on PD vines are stunted, more yellow than
normal, and deformed in shape.
Interveinal areas of leaves may be more yellow than
normal leaves, much like zinc deficiency symptoms.
Spring Symptoms
Summer Symptoms
The combination of these three symptoms is a definitive
indication that PD is present:
1) Leaves become slightly yellow or red along margins in
white and red varieties respectively. As the disease
advance leaf margins progressively dry or die (turn
brown) in concentric zones.
2) Scorched leaves dry down and the blade falls, leaving
the petiole attached to the cane.
3) Wood on new canes matures irregularly, producing
patches of green, surrounded by mature brown bark.
Symptoms
Type and extent of symptoms
vary:
1. Grape variety
Highly susceptible are Barbera, Chardonnay, Fiesta, and Red Globe.
Less susceptible varieties are Chenin blanc, Flame Seedless, Riesling, and
Thompson Seedless. Cabernet sauvignon, Merlot, are intermediate" in
susceptibility.
2. Date when the vine was infected.
3. Vine age - The younger the vine, the faster severe symptoms
will appear and the less chance that it will recover over the
next winter.
4. Climate
5. "Variability".
For unknown reasons, different vines of the same age, location,
and variety will develop somewhat different symptoms.
6.Other constraints mimicking Pierce's Disease
Zinc deficiency, measles, salt burn
Control
Removal of wild grapevines, immaculate weed control and establishing a
weed-free perimeter around a vineyard provide the best strategy to
manage Pierce’s disease.
Sharpshooters need water to survive and reproduce. Avoiding sites
adjacent to creeks, streams, ponds or even depressions that retain
rainwater will reduce the likelihood of consistently high leafhopper
populations.
By creating a large (at least 150 ft.) buffer zone around vineyards,
growers can either chemically or mechanically create an environment
that is not favorable to insect populations.
Growers should also understand that when hay fields adjacent to a
vineyard are cut, large numbers of insects will be seeking alternative
habitat and feeding sites.
Insect monitoring and insecticide applications should be considered
when insects move into the vineyard.