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Grapes - Diseases, Pests and Problems



Basic Information



Problem: Asteroid Mosaic
Affected Area: Leaf

Description: Asteroid mosaic disease produces small, star-shaped spots in leaves of affected vines. The spots seem to result when tissues around a veinlet degenerate and the tissue in the center of the spot may be dry. Affected leaves are asymmetrical.

Control: NA


Problem: Bitter Rot
Affected Area: Fruit

Description: The fungus usually invades a berry from the pedicel. Light-colored berries become brownish and often show concentric rings of acervuli and blue berries take on a roughened, sparkly appearance on the surface as the acervuli begin to develop. Within a couple of days, the berry softens and is easily detached and the bitter taste of the berry is most pronounced. Berries that do not shell continue to dry, become firmly attached, and are not as bitter in taste. When shriveled, the rotted berries look much like berries affected by black rot, ripe rot, or the fruit-infection stage of Phomopsis cane and leaf spot.

Control: Bitter rot is generally controlled by the fungicide sprays applied to control more serious diseases, and resistant cultivars.


Problem: Black Rot
Affected Area: Leaf

Description: Young leaf laminae, petioles, shoots, tendrils, and peduncles can be infected. The main symptom on leaves is the appearance of small, tan, circular spots on the lamina in spring and early summer beginning with a small, whitish dot. Lesions on peduncles and pedicels are small, darkened depressions, which soon turn black.

Control: Black rot of muscadine grapes can be effectively controlled by applying protective fungicides.


Problem: Bud Mite Strain
Affected Area: Leaf

Description: Common symptoms include short basal internodes, scarred epidermis of new shoots, flattened shoots, dead terminal buds on new shoots, witches-broom growth of new shoots, zigzagged shoots, and dread overwintering buds. Leaves are usually stunted and wrinkled, and the veins are prominent and drawn together.

Control: NA


Problem: Corky Bark
Affected Area: Leaf

Description: In autumn, affected leaves become rolled and turn uniformly red or yellow, including tissues along the major veins. As buds on this cultivar break in the spring, shoots elongate rapidly but leaves on the shoots remain small, giving the vine a spindly appearance. Leaves that develop on the same shoots a few weeks later are normal in size, and as growth continues, the spindle shoot symptom disappears. In mid or late summer, leaves on affected vines of dark-fruited cultivars may turn yellow before they turn red, the wood at the base of the canes may swell slightly, and the bark may split.

Control: An effective control is the use of propagation stocks from disease-free mother vines.


Problem: Downy Mildew
Affected Area: Leaf

Description: The fungus attacks all green parts of the vine, particularly the leaves. Lesions develop on the leaves that are yellowish to reddish brown, oily, angular, and limited by the veins. Infected shoot tips thicken, curl, and become white when infested with spores and eventually turn brown and die. Similar symptoms are seen on petioles, tendrils, and young inflorescences, which, if attacked early enough, ultimately turn brown, dry up, and drop. The young berries are highly susceptible, appearing grayish when infected and covered with a downy felt of fungus sporulation.

Control: Fungicides are the most important control measure on susceptible cultivars grown in regions with high disease pressure.


Problem: CARPINI E. carpini
Affected Area: NA

Description: The injury it causes is similar to that caused by the Willamette spider mite in California.

Control: NA


Problem: Empoasca Leafhoppers
Affected Area: Leaf

Description: Grape leaves injured by the potato leafhopper are spotted, with yellowed margins that roll or curl downward similar to leafroll and grapevine yellows. Yellow areas may become dry late in the growing season.

Control: NA


Problem: Erythroneura Leafhoppers
Affected Area: Leaf

Description: Vine injury appears first as a white speckling on the upper leaf surface resembling virus infection. The speckling is at first limited to the areas along the main veins and later spreads over the leaf blade and turns a blotchy pale yellow or whitish yellow. Leaves may dry up and drop.

Control: NA


Problem: European Red Mites
Affected Area: Leaf

Description: Injury is characterized by a fine speckling that appears at the base of leaves. The speckling develops into a bronze coloration that soon covers the entire leaf with symptoms resembling leafroll. Continued feeding by the pest may cause leaves to turn brown and fall

Control: NA


Problem: False Spider Mites
Affected Area: Shoot, Rachis, Branches, Pedicels, Leaf, Stem, and

Description: Complete dehydration and blackening of new shoot growth is common. Later, the mites are distributed on the rachis, branches, and pedicels of clusters, where dehydration results in darkened grooves that unite to form large lesions similar to several grape diseases such as Phomopsis cane and leaf spot and stem drying. The stems and berries may completely dehydrate. The foliate loses its green color a concentration of anthocyanins on the lamina of dark cultivars appear reddish.

Control: NA


Problem: Fanleaf Degeneration
Affected Area: Leaf

Description: In the first syndrome, infectious malformations develop and leaves are variously and severely distorted, asymmetrical, and puckered and show acute dents. Yellow spotting may sometimes accompany foliar deformations. In the second syndrome, yellow mosaic, develops on affected vines and bright chrome yellow discolorations appear in the spring that may affect all vegetative parts of the vine. In the third syndrome, veinbanding and chrome yellow flecking is first localized along the main veins of mature leaves and then spreads a little way into the interveinal areas. Fruit set is poor, clusters are straggly, and the yield may be virtually zero.

Control: The best forms of control are resistant cultivars and fumigation for nematode vectors.


Problem: Fleck
Affected Area: Leaf

Description: Fleck disease is characterized by yellow, translucent spots that usually appear in the third and fourth order veins of young and medium aged leaves. Leaves with numerous flecks are twisted and wrinkled.

Control: NA


Problem: Grape Rust Mite
Affected Area: Internodes, Leaf, and Fruit

Description: Buds are killed, internodes are shortened, foliage becomes dense, and fruit production is reduced. Clusters are damaged when flowers are injured. Feeding on the surface of leaves of white grape cultivars causes a yellowing that closely resembles the appearance of leaves slightly injured by spider mites.

Control: NA


Problem: Grapevine Yellows Diseases
Affected Area: Shoot and Leaf

Description: The characteristic symptoms appear in the summer and the vine adopts a weeping posture and the shoots bend down as though made of rubber. The leaves harden, roll slightly abaxially, and tend to overlap, giving the shoot a characteristic snakelike appearance. The brittle leaves first become golden yellow in white cultivars and red in black cultivars on all parts most exposed to the sun.

Control: The best form of control is resistant cultivars if they are available. To control by insecticidal treatments, insecticides should be applied during the egg hatching period.


Problem: Leaf Blotch
Affected Area: Leaf

Description: Leaf lesions generally appear after mid-season and are small and have distinct, dark margins, while larger ones show distinct, light-colored zonate rings or arcs. Synnemata are produced within three or four days of the appearance of a lesion.

Control: NA


Problem: Leaf roll
Affected Area: Leaf

Description: Affected plants are slightly smaller than healthy ones. In the spring, leaves on diseased and healthy vines appear similar, but as the season progresses, the diseased leaves turn yellowish or reddish, depending on the specific cultivar. By late summer, the leaves roll downward starting with leaves at the base of the shoot and the disease delays fruit ripening.

Control: The best form of control is to use disease-free vines.


Problem: Peach Rosette Mosaic Virus
Affected Area: Leaf and Vine

Description: The usual symptom in older vineyards is a circular pattern of missing or dead vines. Infected vines usually exhibit an umbrella-like growth habit due to shortened and crooked shoot internodes. Leaves are commonly deformed.

Control: The most efficient control is to have the soil tested for nematodes.


Problem: Sharpshooter Leafhoppers
Affected Area: Leaf and Stem

Description: Feeding by sharpshooters on leaves and cluster stems results in wilting and eventual drying of the affected parts.

Control: NA


Problem: Treehoppers
Affected Area: Shoot and Leaf

Description: The treehoppers injure grapevines by feeding directly and depositing eggs on the shoot. Shoots fed upon by the buffalo treehopper show a brownish girdling involving the epidermis and cortex and a thick, red or yellow, downward rolling of the leaves away from the girdle.

Control: NA


Problem: Twospotted Spider Mite
Affected Area: Leaf and Fruit

Description: The first symptoms of attack are yellow spots caused by feeding on lower leaf surfaces where dense colonies thrive. Later, defoliation is likely to affect berry maturation and quality. Twospotted mites also attack berries, producing dark spots on the skin.

Control: NA


Problem: Willamette and Pacific Spider Mites
Affected Area: Leaf and Vine

Description: Plants infected with Willamette and Pacific Spider Mites have yellow, cupped foliage, a bronze discoloration, and heavy webbing. Pacific spider mite injury in vineyards is spotty and tends to occur on weaker vines or in water-stressed areas. Both Pacific and Willamette spider mite populations are favored by dusty vineyard conditions.

Control: NA


Problem: Yellow Speckle
Affected Area: Minor

Description: NA

Control: Viral Disease


Problem: Leaf miners
Affected Area: Leaf

Description: Small whitish maggots feed between the leaf surfaces. Damage appears as winding trails in leaf tissue. As mines enlarge, they may merge and from large, light-colored blotched areas. Feeding lasts 1 to 3 weeks. They may pupate in the leaf or in the soil and 1/4" long, gray, flies emerge in 2 to 4 weeks.

Control: For the most part, these pests do not harm the grape plant. Floating row covers may screen out the fly. Control host weeds like lambs quarter to reduce local populations.


Problem: 2,4-D damage
Affected Area: Leaf

Description: Leaves emerging when 2-4,D is used as an herbicide on nearby plants, become curled and twisted with veins taking on a parallel pattern. Older leaves may turn yellow or browned.

Control: Grapes are highly susceptible to 2-4,D damage and may be affected by drift and volatilisation from some distance away. Avoid spraying lawn areas and gardens near the plants especially when temperatures are expected above 85? F within the next few days. Minute quantities of vapors drift to the plants and cause small and deformed leaves.


Problem: Powdery Mildew
Affected Area: Leaf

Description: White powdery substance on leaves.

Control: Not usually a serious problem and seldom requires the use of pesticides. Use surface or underground watering methods to avoid wetting leaves.





Grapes

Tips

Do not over water or over fertilize grapes. After they are established, they require little irrigation and little fertilizer.

 

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