Prepared by Mike Ellis Professor and Extension Specialistand Omer Erincik Graduate Research Assistant Department of Plant Pathology The Ohio State University OARDC/OSUE Wooster, OH, 44691
Black rot Symptoms: On leaves • Brown to reddish brown lesions with irregular margins. • Minute, black, spherical fungal fruiting bodies (pycnidia) form within the lesions. • Pycnidia often are arranged in a ring pattern just inside the margin of the lesions. • Similar lesions also develop on young shoot, cluster, stems and tendrils.
Black rot Symptoms: On Fruit • Small, round, light-brownish spots develop on fruit. • Tissue in the spot softens and becomes sunken. • Spots enlarge quickly rotting the entire berry in a few days. • Infected berries eventually shrivel into small, hard, black and wrinkled (mummies).
Black rot Disease Development: • Caused by the fungus Guignardia bidwellii. • The fungus overwinters on infected plant parts in the trellis or on the ground. • In spring, the fungus produces spores on plant parts infected the previous year. • The fungus spores are spread by splashing rain, and a film of free water on the vine surface is necessary for infection.
Black rot Disease Development: • Berries are susceptible to infection from bloom until several weeks after bloom. Berries become resistant to infection as they begin to ripen. Ripe berries are resistant. • The disease can result in complete crop loss under warm, humid environmental conditions.
Downy mildew Symptoms: On leaves: Early season infections: • Irregular pale-yellow to grayish-yellow spots appear on the upper leaf surface. • White to grayish cotton like fungal growth develops within the border of the lesions on the lower surface. Late season infections • Small, angular, yellow to red-brown spots develop on the upper surface. • Lesions commonly form along the veins. • The fungus sporulates (produces downy growth) on these infected areas
Downy mildew Symptoms: On fruit • Infected young berries turn brown and soft, shatter easily, and often are covered with a downy like growth of the fungus. • Late season infection results in berries that are dull green, then dark brown to brownish –purple. They are generally not covered with the fungal growth.
Downy mildew Disease Development: • Caused by the fungus, Plasmopara viticola • The fungus overwinters on infected plant parts in the trellis or on the ground. • The fungus is spread by wind, splashing rain, and by handling wet plants. • When plant parts are covered by a film of water, the fungus infect leaves through stomates (natural openings) on the lower leaf surface. • All common species of wild and cultivated grapes are susceptible.
Powdery mildew Symptoms: On leaves: • Small, white or grayish-white patches of fungal growth appear on the upper or lower leaf surface. • These patches usually enlarge until the entire upper leaf surface has a powdery, white to gray coating. On shoots: • Dark-brown to black patches develop on young shoots and dormant canes.
Powdery mildew Symptoms: On fruit: • Infected berries are misshapen or have rusty spots on the surface, and are usually covered by a powdery growth of the fungus. • Severly infected berries often split open. • Late in the season tiny black specks may develop on the surface of infected areas.
Powdery mildew Disease development: • Caused by the fungus, Uncinula necator • The fungus overwinters in bark crevices on the vine. • The fungus is spread by wind throughout the growing season. • Unlike most other grape diseases, powdery mildew is considered a “dry-weather” disease, and does not require free water on the plant surface to infect. • The disease is generally more severe in dry areas or during dry seasons at temperatures between 65 and 80 °F.
Phomopsis cane and leaf spot • Symptoms: • On leaves: • Small light-green irregular spots with star-shaped margins develop in early spring. • Later in the growing season, these spots turn black and have a yellow margin. • Usually only the lower 1 to 4 leaves on a shoot are affected. On shoots: • Small, black spots develop at the base of developing shoots. • These spots may grow together to form irregular black crusty areas. • Under severe conditions, shoots may split and form cracks in the cortex.
Phomopsis cane and leaf spot Symptoms: On cluster stem: • Small black spots develop on cluster stems, eventually the entire cluster stem may be blighted. On Fruit: • A light-brown fruit rot develops close to harvest. • Black spore-producing structures (pycnidia) develop on the surface of infected berries. • Fruit rot develops only on ripening or ripe fruit. Green fruit are resistant to fruit rot.
Phomopsis cane and leaf spot Disease development: • caused by the fungus, Phomopsis viticola • The fungus overwinters on infected plant parts in the trellis. • The fungus produces spores in early spring, and the spores are spread by splashing rain; thus, spreading the disease. • Most infections occur early in the season under cool and wet conditions. • Fruit rot symptoms do not develop until fruit starts to ripen.
Botrytis bunch rot Symptoms: • Infected berries first appear soft and watery. • Later, they become covered with a grayish brown, dusty mass of fungus spores. • Rotted berries generally shrivel with time and turn into hard mummies.
Botrytis bunch rot Disease development: • Caused by the fungus, Botrytis cinerea. • Berries are usually infected by the fungus during bloom or near harvest. • Disease is favored by warm and moist weather. • Any wound on the berry provides an excellent infection site for the fungus.
Management of leaf and fruit rot diseases of grape(Black rot, Downy mildew, Powdery mildew, Phomopsis cane and leaf spot, Bortytis bunch rot) • Free water (wet conditions) is required for most fungal pathogens (except Powdery mildew) to infect plants. Any practice that promotes faster drying of fruit and foliage is beneficial for disease control. • Many cultural disease control methods are aimed at promoting faster drying of plant parts.
Management of leaf and fruit rot diseases of grape • Site selection • Plants grapes in sunny, open areas that allow good air movement. • Do not plant in shaded areas • Maintain good weed control beneath vines • weeds can reduce air movement and result in slower drying time. • Proper pruning practices, • opens the canopy for increased sunlight penetration • creates good air circulation for faster drying. • Sanitation • Destroy fruit mummies and remove all diseased plant parts during dormant pruning, or early in the spring before bud break.
Management of leaf and fruit rot diseases of grape • Use of disease resistance varieties: • Unfortunately, the grape varieties that are commonly grown in the midwest do not have good resistance to most diseases. Disease management for grapes depends mostly on the cultural practices previously mentioned, and the use of fungicides (chemical control) if necessary.
Using Fungicides For Grape Disease Control • Fungicides are very important for disease control in commercial grape production, and can be useful in backyard grape vineyards; however, the emphasis for disease control in backyard vineyards should be placed on the use of the various cultural practices previously mentioned. • Effective fungicides are usually difficult or impossible for backyard growers to obtain. • If not used properly, they are generally not effective.
Using Fungicides For Grape Disease Control • If diseases such as black rot or downy mildew become established in the vineyard, fungicides may be required in order to “clean up” the planting. • There are a few fungicides available for homeowners that should be useful in backyard vineyards.
For backyard growers that do wish to use fungicides in the disease management program, fungicide recommendations are available for grapes in Bulletin 780 “Controlling Disease and insects In Home Fruit Planting”.
Selected literature for backyard fruit production and plant health management: • Bulletin 591. “Growing and Using Fruit at Home” • Bulletin 780. “Controlling Diseases and Insects in Home Fruit Planting” • Bulletin 815. “Grapes Production, Management and Marketing” • Bulletin 861.“Midwest Small Fruit Pest Management Handbook” These can be obtained through your county extension agent or the Extension Publications Office, The Ohio State University, 385 Kottman Hall, 2021 Coffey Road, Columbus, Ohio, 43210-1044
To get more information about plant diseases visit the websites below. http://www.ag.ohio- state.edu/~plantdoc/extension.php http://www.ohioline.ag.ohio-state.edu