Adams County Master Gardener
Growing radishes is easy. I thought growing grapes might be too. I like seedless grapes so I bought a white and a red variety and put them
in the ground. I also built a small arbor for them to climb on.
It was just like radishes, the first year. Grapes appeared, they matured, and they looked good. I ate them, they were good. End of year one.
Year two, and things went brown. Actually, they went black. I had just discovered first hand the realities of grape growing. Black rot is just one of the realities. Its not rocket science, actually it's harder. Rocket science revolves around Newton's
laws of motion, and the mathematics are well established and known by hundred's of PhD's. With grapes there are whole families of pestilence that can and surely will occur. There is also a whole army of PhD's that thrive on studying, classifying, experimenting with and
hopefully solving the pestilence problems that abound with the ancient art of growing grapes. Pests mutate and evolve, Newton's laws are constant.
After that rude awakening, I began the search for solutions. The first thing I found is that pruning of grape vines is of the utmost importance. Left unchecked, they will grow and climb forever, or so it seems. We are fortunate that Penn State has
chosen to expand their research laboratory in Biglerville to include grapes. At Biglerville one very cold, very windy Saturday morning in January 2005 I availed myself of the opportunity to learn the art of pruning. Start thinking ruthless, then cut some more. Pruning must
continue through out the growing season as the diseases flourish in the wet and shade, so thinning for sun and moving air exposure is critical.
After a year of growing with pruned vines I soon learned that while necessary, it is not sufficient in our growing region. Fungicide treatment of the mildews and rots is a necessity as a preventative measure, if left until damage is noted its two
How to do this? I needed more information. As a Master Gardener I was made aware of a pesticide applicators course in Lancaster County which I attended. I had the privilege of meeting three of our Penn State PhD's who are at the top of their game and
very knowledgeable. This wetted my curiosity and confidence in Penn State so I sat down at my trusty computer and did some searching.
The bottom line is that an outstanding resource is available on line at:
This is the address for "Small Scale Fruit Production - A Comprehensive Guide" produced by our own Penn State University.
The following chapters are presented as a comprehensive treatment of the various topics.
- The Home Fruit Planting: Getting Started
- Pests and Pesticides in the Home Fruit Garden
- Controlling Wildlife Damage in the Home Fruit Garden
- Pome Fruits: Apples and Pears
- Stone Fruits: Peaches, Nectarines, Plums, Apricots, and Cherries
- Gooseberries and Currants
- Hardy Kiwi
For this article, the focus will be on Grapes. The following topics are addressed. Each should be thoroughly understood before making a selection of plantings, since the best treatment for pests is a resistant variety determined before planting.
- Cultivar Selection
- Purchasing and Planting
- Nutritional Requirements
- Insect and Nematode Pests
- Disease Descriptions and Management
- Pest Management
I selected the seedless cultivar since I like my grapes but not my grape seeds.
Table 6.4. Table and Juice Cultivars for Pennsylvania
Grape Disease Descriptions and Management
Black Rot -Black rot is one of the most serious diseases of grapes in the eastern United States. Crop losses can range from 5 to 80 percent, depending on the amount of disease in the vineyard, the weather, and cultivar susceptibility. The fungus,
Guignardia bidwelli, can infect all green parts of the vine. Most damaging is the effect on fruit. Later fruit infections can destroy many grapes, even the entire crop.
Symptoms - Reddish-brown, usually circular leaf spots first appear on the upper leaf surface. Soon after, the center of the spot becomes tan to light brown. Small black pimple-like bodies appear in the center of the spot, usually arranged in a loose
ring just inside the dark border. Infected grapes become dark and shatter, leaving only the stem. Most serious fruit infections occur when the grape is pea-sized or larger. The final stage is a black, wrinkled mummy.
Disease Cycle - The fungus over winters in mummified berries on the soil or in old berry clusters that hang in the vines. Spores of the fungus are produced within the diseased fruit and infect leaves, blossoms and young fruit during spring rains.
Fruit infections occur from midbloom until the berries begins to color. Mature leaves and ripe fruit are not susceptible. Very few fruit or leaves are infected after late July, and none are infected after the end of August. Black rot infections depend on the temperature and
the length of time the leaves are wet.
Disease Management - Infected prunings and mummified berries should be removed and disked into the soil before new growth begins. In vineyards with susceptible cultivars or where black rot was a problem the previous year, early season fungicide
sprays should be timed to prevent the earliest infections. Should infections become numerous, it is very difficult to protect against fruit rot later in the growing season. It is strongly suggested to plant resistant cultivars. Cultivar selections are presented in Table
Botrytis Bunch Rot -Botrytis bunch rot, or gray mold, is a disease that exists in all vineyards worldwide. The disease is caused by the fungus Botrytis cinerea and is associated commonly with the decay of ripe or nearly ripe grapes. Temperature and
damp climates favor disease development. The bunch rot phase of the disease causes the greatest economic losses.
Symptoms - Buds and young fruit infected in early spring turn brown and dry out. Prior to bloom, large reddish-brown patches appear on the leaves. By the end of bloom, the fungus develops on aborted berries that are attached to or trapped in the
fruit clusters. From ripening onward, the grapes are infected directly through the epidermis or through wounds. Eventually, the entire cluster becomes moldy. When weather is dry, infected berries dry out; in wet weather, they tend to burst and a brownish-gray mold forms on
Disease Cycle -Botrytis bunch rot also infects numerous wild hosts and cultivated plants. The fungus can live on these alternate hosts as a saprophyte on dead tissue. The pathogen over-winters on bark and in dormant buds. In the spring, spores are
produced by the fungus and infect leaves and young grape clusters. Spores on decaying and dead vegetation are moved about mainly by air currents. Water is necessary for germination, but this requires only 1 to 4 hours, depending on the temperature. High relative humidity
allows infection to take place after the spore has germinated. Any break in the skin of ripening grapes provides an ideal entry point for the Botrytis fungus as well as a moist medium in which the spore can germinate.
Disease Management - At least two fungicide sprays are suggested on very susceptible varieties during the bloom period. The sprays will reduce the number of infected flower parts and the incidence of young fruit infection. Any practice that reduces
skin cracking or skin punctures near harvest helps control ripe fruit rot. Preharvest fungicide applications are also recommended. Plant disease resistant grape cultivars when possible. Cultivar selections are presented in Table 6.3.
Crown Gall - Crown gall occurs on over 600 species of plants. The disease is characterized by galls or overgrowths that form on the roots, trunk, and arms of grape vines. V. vinifera cultivars are more susceptible to crown gall than V. labrusca
cultivars. These galls are found mostly on the lower trunk near the soil line. Large galls can develop rapidly and completely girdle a young vine in one season. When galls are numerous, or when they are located on major roots or on the root crown, they disrupt the
translocation of water and nutrients, leading to poor growth, gradual dieback, and sometimes the death of the vine. In general, affected plants are more susceptible to adverse environmental conditions, especially winter injury.
Symptoms - The major symptom of the crown gall disease is the fleshy galls. Current-season galls appear in early summer as white, fleshy growths that usually develop near injured vines. By late summer, the galls turn brown. In the fall, they become
dry and corky and might fall off the vine in a few years.
Disease Cycle - The disease organism is the soil-borne bacterium Agrobacterium tumefaciens. The bacterium survives for long periods of time in vineyard soil, within galls and within infested vines. A fresh wound is required for gall formation to
start in the grapevine. Contaminated planting material (nursery stock) is another source of the disease.
Disease Management - Because the bacterium lives in the soil, it cannot be controlled by chemical sprays. It is necessary to examine new plants before planting and discard any that have galls. In the vineyard, remove large galls on the upper parts of
the trunk or on the arms by pruning the arm or trunk below the affected tissue. Then, renew the vine by means of a shoot from the base of the vine.
The development of crown gall is closely correlated with wounding and freeze injury. Practices that reduce wounding, especially during pruning and machinery operation, are useful in managing the disease. Preventing freeze injuries also is important.
In some areas, growers bury young vines in the fall to reduce this type of injury.
Downy Mildew - Downy mildew occurs wherever it is warm and wet during the growing season. There is some cultivar resistance, with V. vinifera cultivars being the most susceptible and V. rotundifolia being the most resistant.
Symptoms - The pathogen attacks all green parts of the vine, especially the leaves. Lesions on leaves are angular, yellowish, sometimes oily, and located between the veins. As the disease progresses, a white cottony growth can be observed on the
lower leaf surface. Severely infected leaves will drop. If enough defoliation occurs, the over-wintering buds will be more susceptible to winter injury. Infected shoot tips become thick, curl, and eventually turn brown and die. Young berries are highly susceptible,
appearing grayish when infected. Berries become less susceptible when mature. Infected berries remain firm compared to healthy berries, which soften as they ripen. Eventually, infected berries will drop.
Disease Cycle - The disease is caused by the fungus Plasmopara viticola, which overwinters as spores in fallen leaves. This fungus has two types of spores, both germinating to give rise to swimming spores. These spores swim to the stomates (breathing
pores) of plants and cause infection. Water is necessary for the spores to swim and to infect, so outbreaks of the disease coincide with periods of wet weather. Downy mildew is favored by all factors that increase the moisture content of soil, air and the plant, with
rainfall being the principal factor for infection. The frequency of rain and the duration of wet periods correlate with the number of additional infections during the growing season. Downy mildew infection can become a severe problem when a wet winter is followed by a wet
spring and a warm summer with a lot of rainfall.
Disease Management - Some control can be achieved by preventative management practices such as making sure soils are well-drained, reducing the sources of over-wintering inoculum (fallen leaves), and pruning out the ends of infected shoots.
Fungicides, however, are the most important control measure, especially on susceptible cultivars. They should be applied just before bloom, 7 to 10 days later (usually at the end of bloom), 10 to 14 days after that, and finally, 3 weeks after the third application. For
cultivars very susceptible to downy mildew, or where the disease was severe the previous season, an additional application is suggested about 2 weeks before the first blossoms open.
Eutypa Dieback -Eutypa dieback is the name for the trunk and arm phase of what was once known as the dead arm disease. It is one of the most destructive diseases on the woody tissue of grapes. The fungus causing this disease has a wide host range,
which includes at least 80 species in 27 botanical families. Most of its hosts are tree species that are common in natural forests.
Symptoms -The earliest symptoms of the disease are cankers formed around pruning wounds. The cankers are hard to detect, since they are concealed by old, dead bark, which can become somewhat flattened. A cross-section of the infected area might show
a wedge-shaped area of darkened wood coming to a point in the center of the trunk. Symptoms of Eutypa dieback are apparent after the canker has become well established, perhaps 2 to 4 years after the infection of the pruning wound. As new shoots develop on the trunk or arms
above the cankered area, vine growth appears stunted and the internodes become shortened. Symptoms are not readily visible until late spring, because affected shoots usually are covered up by healthy shoots. Infected leaves are small, yellow, and crinkled. Symptoms on the
foliage of diseased arms become more extensive each year until eventually the diseased arm fails to produce shoots in the spring. Clusters on affected shoots can have a mixture of both large and small berries.
Disease Cycle - The disease is caused by the fungus Eutypa lata. This disease is entirely different from that responsible for Phomopsis cane, leaf spot, and fruit rot. Rain is necessary for the spread of this disease, and infections occur on freshly
made wounds. The susceptibility of wounds decreases as they become older (2 to 4 weeks after pruning). The disease is slow to develop on grapes and usually is not seen until the third or fourth season. By this time, a canker usually is present, along with symptomatic
foliage. Several more years might elapse before the diseased arm or trunk is killed.
Disease Management - No grape cultivars are known to be immune to this disease. Also, none of the chemicals routinely used to control other grape diseases provides protection against this fungus. Some evidence indicates that the manual treatment of
individual wounds with benomyl at the time of pruning can provide a barrier against the fungus and prevent it from invading the wounds. It is suggested to treat all wounds in wood two years of age or older, especially large wounds. Sanitation practices also will help
control this fungus. Since the fungus survives in vines remaining on the tree or as prunings in the vineyard, affected vines should be pruned when leaf symptoms appear. Single-trunk vines should be cut off at the ground line; double-trunk vines should be cut off at the
junction of the second trunk. Affected prunings must be removed from the vineyard immediately and destroyed. One or more suckers can be retained for vine renewal.
Phomopsis Cane, Leaf Spot, and Fruit Rot - Phomopsis cane, leaf spot, and fruit rot is one of two distinct diseases that used to be referred to as "dead arm," and is widely distributed in vineyards. The disease can weaken vines, reduce yields, and
lower fruit quality.
Symptoms - This disease was often the first disease of the growing season to appear in the vineyard. Infections on new shoots first appear as reddish spots about 1/16-inch in diameter. These are most common on the first 8 inches of new shoots, and
they can be seen when the shoots are about 18 inches long. Infected portions of the leaf turn yellow then brown. When infections on shoots are numerous, they often run together and form dark blotches that crack. Cluster stems can blight and become brittle if infections are
high. These clusters usually break and the fruit is lost. This fungus also causes a fruit rot. Infected fruit will turn brown, shrivel, and eventually drop. In winter, cane infections can be observed.
Disease Cycle - The disease is caused by the fungus Phomopsis viticola. The fungus overwinters in bark and leaf petioles. In the spring, especially under wet conditions, spores produced by the fungus exude from infected tissue and are splashed onto
shoot tips. Only very young tissues are infected. In summer, the fungus becomes inactive, but by fall it resumes activity. Infection in the vineyard is localized because disease is spread mostly within the vine rather than from vine to vine. If the disease is not
controlled, with each increasing year it will become more severe in the vineyard.
Disease Management - Phomopsis cane and leaf spot can be controlled by a combination of sanitation and fungicide application. At pruning, remove dead and diseased wood. Destroy prunings and debris by burning, burying, or plowing them into the soil.
The cane and leaf infections can be prevented by one or two early-season fungicide sprays. The number of new shoot infections during the previous two years and the frequency of prolonged rainy periods during the current year are indicators for performing none, one, or two
fungicide applications. Fruit and cluster stem infections occur from bloom until the fruit are pea sized. Regular fungicide applications are necessary to prevent disease.
What Fungicide do I use?
This is what makes growing grapes harder than rocket science. Use same one too often, the bad guys develop resistance. Use too much and it can kill the grapes. Use too little and you don't get the benefit. What to do? Go to the local suppliers and
see what's on the shelf. The really dangerous stuff is outlawed for us non-professionals. The next year, use something different. Follow the directions to the letter and make sure you wear a mask and change clothes immediately, and hit the hot showers, hard. End of article.
New subject, Surprise Lilies and pecan tree tubes.
In previous articles I offered lilies free and pecan tubes for a price. Guess what, lots of takers for the lilies, about 24. They are coming up now and when they go dormant in May I will mail them out. If you moved or sent me an email and changed
your address, resend. Tree tubes are still available at $15 for 5, including 10 stratified pecan nuts. Devlinw1@aol.com
Read other articles on growing fruits, herbs, and vegetables
Read other articles By Bill Devlin