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Returning to American roots routs disease and brings flavor-bursting grapes back within the organic grower's reach.
Rots, blights and insect pests--the wrath of grapes. Grappling with grape growing can indeed be a challenge for the organic gardener. But home growers have an advantage: the ability to use small-scale techniques that many large-scale growers do not. This flexibility can be the key to grape success in the home vineyard.
"Gardeners need to get away from the idea that the only table grape is like the THOMPSON SEEDLESS," says David Gadoury, Ph.D., a plant pathologist at Cornell University's New York State Agricultural Experiment Station, Geneva, N.Y. "If they would just be willing to try some different varieties, disease wouldn't be such a problem.
"And, if gardeners are going to grow grapes without pesticides in areas where disease Is a problem, then resistant varieties are a must."
Most seedless table grapes are derived from Vitis vinifera, the European wine grape. The problem for home gardeners is these European grapes succumb easily to American disease. But native American grapes, most notably V. Labrusca, generally are hardier and more resistant. (There are exceptions, though. CATAWBA, an American wine grape that is almost pure V Labrusca, is highly susceptible to downy mildew and other fungal diseases.)
The drawback of most American varieties is their poor fruit quality compared to the more refined European types. Fortunately, plant breeders are working to create hybrids that combine European quality with American grit. And good varieties descended from a number of native species are available now.
In field trials at the University of Arkansas and other locations where researchers have used standard cultural practices and a minimum of chemical disease controls, MARS consistently has resisted disease problems usually associated with seedless table grapes. The variety
has exhibited its strongest resistance to black rot, downy mildew, powdery mildew and anthracnose, the four most damaging fungal diseases of grapes and those most act to strike the home vineyard.
"We released MARS primarily because of its disease resistance," says the University of Arkansas' Jim Moore, Ph.D., developer of the variety. "The grape was targeted at home gardeners who, as a rule, don't spray very much."
This blue, seedless table grape has the characteristic "crispness" of European or California table grapes, combined with the desirable strong flavor and aroma characteristic of V. Labrusca. MARS also seems cold hardy and is recommended for much of the country as far south as North Carolina and north Georgia.
RELIANCE, another seedless variety developed at the University of Arkansas, will suit northern gardeners because of its cold hardiness. The variety resists most diseases, but is somewhat prone to black rot and downy mildew. Downy mildew, however, shouldn't be a severe problem in northern states, and black rot can be controlled largely through cultural practices.
Gardeners who aren't bothered by seeds have a broader- range of choices. CONCORD, the most common and highly resistant Eastern variety, is a hardy, deep-purple to black, aromatic grape that produces large fruit clusters late in the season. It has long been used for jelly and juice, but also is a fine table grape for the home vineyards.
CONCORD is recommended throughout the Northeast and as far south as Maryland. It can be prone to black rot in some areas, but this usually can be controlled, again, by attention to cultural details. (.A seedless CONCORD is available, but it lacks the disease resistance and productivity of the standard.)
Other- seeded varieties with a high, degree of disease resistance were developed in the early 1900s by T.V. Munson, a Texas grape breeder. Because Munson used several American grape species, not just V. labrusca, many of the cultivars are widely adapted and still available.
Several Munson varieties such as XLANTA and CHAMPANEL, have very good eating quality" says Lon Rombough, a private grape breeder and consultant for the Grape Test Group of the North American Fruit Explorers. "Table grapes then were softer and juicier than modern varieties, but I think they are just as good."
YES, YOU CAN GROW GRAPES IN THE SOUTH
Grape growing in the South can be especially trying. The region's hot, humid climate creates an ideal environment for a wide range of disease and pest problems. Of greatest concern to Deep South growers is Pierce's disease, a bacterial ill spread primarily by sharpshooter leafhoppers. Until recently, it made successful production of bunch grapes a near impossibility in much of the region.
Thanks to an aggressive grape-breeding program at the University of Florida, Southern grape fanciers now can grow their own. Released in 1983, CONQUISTADOR is a good quality, disease-resistant, seeded grape similar to CONCORD in taste and appearance, and it resists Pierces disease. Like its forerunner BLUE LAKE, CONQUISTADOR was developed especially for the home vineyard and is suited for making juice, Wine and jelly, and for eating fresh.
BLUE LAKE, though somewhat less tasty table grape' makes superior jelly and is more resistant to anthracnose. Either grape is a good choice, providing plenty of quality fruit, while resisting diseases.
A number of other Southern grapes have been developed in recent sears, including the University of Florida's recent released ORLANDO SEEDLESS. Unfortunately, they are targeted for commercial production and in most areas require intensive management to control diseases. Their quality is high, but their disease and pest resistance is not.
Southern growers do have an advantage, however, in their ability to raise muscadines, V. rotundifolia a group of native American grapes that were the source of a thriving Southern industry before the turn of the century. Recent breeding efforts could pit several muscadine varieties against conventional table grapes (See "'The grape of choice for hot, sultry summers,). Muscadines resist the diseases that plague most grapes, making them the grape of choice for many Southern gardeners.
"If you can get past powder! mildew, downy mildew. black rot anthracnose, and Piercer's disease in the South, the other diseases you may encounter are basically minor" Cornell`s Gadoury says. Of course, all diseases are a problem and a crop can be lost to any of them. High humidity and wet weather combine to create an environment ideal for downy mildew and black rot, two fungal diseases that without fungicides can be difficult to control in susceptible varieties. .Anthracnose can be particularly troublesome in the Mid-Atlantic region.
Few areas outside of California's Central Valley and parts of the Southwest are suitable for producing European grapes and grape hybrids without chemicals. Powdery mildew is the only significant disease problem in those two areas. and it can be controlled quite well using sulfur dust.
''Vinifera grapes do nicely because downy mildew simply doesn't exist in those areas," Gadoury says. Unfortunately that's not the case anywhere else in the United States.''
THE KEY TO CULTURAL ACCEPTANCE
For success without chemicals start with resistant varieties and then adhere to good cultural practices with particular attention to diligent sanitation. Be sure to remove rotten fruit and leases' as well as any mummified (dry, shriveled) berries. preferably before leaf fall. These plant materials harbor diseases in winter that will attack the next year's crop. Burn or bury them. Weed regularly throughout the season and always be aware of potential disease problems. Pinch or pull off leaves marked with spotty lesions. These could signal anthracnose, a serious fungal disease of grapes and other fruits and vegetables.
Removing mummified berries from vines infected with black rot is one of the best methods for controlling that disease. Berries are the prime source of disease spores, so pull them immediately. Martha Owens, owner of Owens Vineyard and Nursery, has controlled black rot by growing vetch around vines. Black rot spores on the soil's surface seem unable to penetrate the dense 1-foot-tall mat formed be the vetch, and do not infect the vines. Common vetch (Vicia angustifoila) is suitable for most areas.
Viticulturists typically recommend establishing a permanent sod between the rows. Choose a low growing grass adapted to your region. Maintain a 4-foot strip of bare soil around the vines. If you mulch, remove it yearly and replace with fresh mulch.
To control spores of powdery mildew and other fungal diseases that may remain on the bark from the previous season' use a cleanup spray of lime sulfur before vines leaf out in spring. During the growing season wettable sulfur is an effective fungicide if applied at berry set and again about 10 days late. In humid areas sulfur can be used every other week if needed, though early application usually will solve a problem. Sulfur does leave an unsightly residue on fruit and can discolor house siding, so use it carefully.
To protect individual grape clusters, bag them with small paper sacks during application. This will minimize sulfur residue on the fruit. Good air circulation limits fungal disease, so proper pruning is crucial. Be sure to sterilize pruning tools between each cut when removing diseased wood . Mix one part household bleach with nine parts water to make a good strelizing solutions.
Controlling disease is not the home viticulturist`s only task. Pest control is no less important.
insecticidal soaps, superior- oil and Bacillus thuringiensis will control most grape pests. Bt can be used effectively against the grape berry moth and other lepidoptera pests' while soaps and superior oils control leafhoppers and other sucking insects. Some pests, such as the green June beetle, can be effectively controlled with bait traps.
Traditional use of insect pheromones is controlling the grape berry moth in Northeastern vineyards. And another method, developed by researchers at Cornell University may allow growers to significantly reduce the use of chemicals insecticides in commercial vineyards. Unlike standard traps-- which mimic insects` sexual scents and lure them into the trap--Shinetsu pheromones "twisties" are tied to trellis wires throughout the vineyard to create a pheromone 'fog`' that reportedly disorients male grape berry moths and interrupts the mating process.
Unfortunately, researchers report that this method is not applicable for small, home vineyards because large areas--at least an acre-- are needed to create the fog. The pheromone technology should have a tremendous impact on the nation's commercial grape industry .
Another pest control measure gaining favor among commercial producers, and one that can be equally effective in the home vineyards, is the use of narrow - range superior oils. Unlike heavy dormant oils that are traditionally sprayed on fruit trees during the winter, superior oils are lightweight, extremely pure mineral oils that can be sprayed in low volume in both winter and summer. These oils suffocate pests, and have proved especially effective in controlling grape leafhoppers When sprayed during summer. Superior oils are somewhat more powerful than insecticidal soaps, but either- can be used to provide good control.
Planting to attract insect predators also plays a role in pest control. Studies in California have found that blackberry bushes planted around vineyards attract parasitic wasps that are natural enemies of the grape leafhopper. And, of course, you get to eat the blackberries, too.
SOIL: ph between 6 and 7. To adjust, use dolomitic limestone on acid soils and sulfur on alkaline soils. After planting topdress with well-rotted manure or compost at monthly intervals until midsummer.
SITE AND SPACING: A southern slope protected frolic northwest winds is best. For most bunch grapes, 10 feet apart on level ground, 12 feet apart on hills. Straight rows are best for level or slightly rolling land. Contour rows are recommended for hilly terrain. Southern muscadine grapes are more vigorous and require 16 to 20 feet between plants with 10 to 12 feet between rows
LIGHT: Full sun.
WATER: Keep well-watered and weed free.
PLANTING: Prepare a hole large enough to accommodate a vine s entire root system in its natural spread (about four times the diameter of a root ball). Set the plant at or slightly lower than the level it grew in the nursery. Fill the hole, tamp firm and settle with water. Plant in northern regions as late in winter or early in spring as possible. In southern areas, plant in fall. Cut back the vine to a single stem with two or three good buds. When growth begins in the spring, select the strongest of the shoots formed from these buds for the main trunk of the vine.
HARVEST: Usually begins third season after planting. First full harvest in fourth season.
Muscadines a group of native American grapes with long history and promising future, are considered the grape of the choice by many Deep south gardeners. For good reasons too. They thrive in the region's hot , humid climate and their disease resistance is unparalleled. Popped into mouth, a muscadine's thick slip-skin and tough pulp may intimidate the uninitiated. But the full flavor will win over even the most skeptical eater. Plant breeders at the University of Georgia have developed a muscadine variety with a crisp, plum-like texture and earlier work at North Carolina state University produced an experimental seedless muscadine bunch-grape hybrid.
An unnamed variety combining seedlessness and crisp texture currently is being developed at the University of Florida. Release of the variety is still a couple of years away, but plant breeder John Morteson, Ph.D.,says that when it does arrive, the South will have a grape in great demand nation wide.
"We've been able to combine the size of some Georgia varieties - notably FRY, SUMMIT and TRIUMPH- with high quality, productive and self-fertile varieties." Mortenson says. "These traits have been bred into single selections which are now on trial for eventual release".
Unfortunately for grape growers in other regions of the country, muscadines are limited in their hardiness range. Some varieties can be grown as far north as coastal Virginia, but the line usually is drawn around Atlanta. Recommended varieties for home gardeners include Bronze- DIXIE, DOREEN, TRIUMPH; Black - ALBEMARLE, COWART, ALACHUA, NESBITT, SOUTHLAND; Red - LOOMIS (outstanding grape requires a polinator ).
Copyright © 1991 Organic gardening. All rights reserved.
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