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The top five threats to vineyard health.

As California's vineyard industry grows and matures, we will begin to see what happens when you grow the same crop in the same place over time. Growers in Europe have considerable experience with this topic, since some vineyards have occupied the same space since the age of the Roman Empire and before. There are strategics that can be used to lessen potential problems. In this column I will discuss what I consider to be the most worrisome vine health issues and what you can do to avoid, address or control the maladies that can visit and blight your plantings.

1. Nematodes

Nematodes comprise such a broad group of organisms that this is potentially the most perplexing issue for viticulturists. As with having fungi in your vineyard, some are innocuous, some are pathogenic and some are probably beneficial. Plant pathogenic nematodes are problematic because they impair roots from water and nutrient uptake. Mostly they feed on the smaller feeder roots that grow in spring and fall and are not very suberized (woody). Feeding injuries may also allow secondary pathogens into the root system such as Fusarium oxysporum, which aren't necessarily "reel hot" but over time will do damage.

Preplant fumigation is helpful, but it will nor complete!) eliminate the nematodes. You ma; also treat existing vineyards with the fumigants fenamiphos and sodium tetrathioearbamate (Enzone), but these treatments have only temporary effects. There are some new biological materials being tested, but at this time they are not evaluated well enough to know how effective they are, and for which nematode species. Similarly, there is probably some benefit from resting ground and cover cropping with rye grass, certain mustards and vetches that will suppress nematode populations but nor eliminate them. Here are some of the most problematic nematodes to have in your vineyard:

Dr. Andy Walker from UC Davis has released five rootstocks, numbered GRN 1 -5, which all have different parentages based on native grapevine species from the United States. Nematode-resistant parents in the group include MuscadinLi rotimdifoluh Vitis rufotomentosa, Vitis champmii (Dog Ridge and Ramsey) and Vitis uionticola. Propagation of some of the new roorstocks can be tricky--especially GRN-1 which has a high amount of Muscadniia rotinidifolia in its parentage. No one rootstock has broad resistance against all nematodes, bur individual stocks show enhanced resistance to dagger, cirrus, ring, lesion and root knot nematodes. More testing is definitely needed.

2. Fanleaf degeneration

Xipbenema index transmits the fanleaf degeneration virus and is a scourge once the virus and nematode are found in a vineyard. Infected vines produce very poorly if at all. Infestations of both problems often came from contaminated nursery stock many years ago, before the disease was understood (another reason to be very careful where you source budwood and rootstock materials for new plantings.) It is mostly a problem where multiple generations of vineyard have been planted. Presently; only one rootstock is known to impart resistance: 039-16, an old hybrid between Musaidinni rpiundifolw and Yitis mmifem (Alinerm.) The rootstock evidently allows feeding by the nematodes and infection by the virus, but somehow the symptoms are not manifested. 039-16 is only recommended for fanleaf sites, as if tends to invigorate whatever scion is grafted to it, and it also may cause increases in potassium in the fruit, making winemaking more difficult. Additionally, there is some concern about phvlloxera, since the rootstock has Vitis vinifera in its parentage. Newer rootstocks that Dr. Walker is breeding are fairly resistant to Xipbenema index feeding, but it isn't clear whether they will prevent fanleaf degeneration infections. Both Vitis rufotomentosa and Muscadinia rotund7folia are the principal sources of resistance to Xipbenema index in the parentage of the rootstock. GRN 1 and GRN 5 are particularly resistant.

3. Phylloxera

Phylloxera-resistant rootstocks are well understood, and we have had effective selections in use for more than 100 years. Recent concerns about 101-14 and 5C center around the ability of phylloxera to feed on small roots and cause nodosities, or swellings. There has been no sign of tuberosi-ings, which are large lesions that indicate the rootstock is failing. However, drought conditions combined with the presence of phylloxera can cause great stress to the vines, and these two rootstocks should not be used where very dry conditions or limited water is likely to occur. Regulated deficit irrigation strategies should be used carefully if you are on either of these root-stocks and phylloxera is known to be present in the vineyard.

4. Wood-rotting organisms

Various cankers and trunk diseases become problematic as vines age and the permanent structure of the vine increases. Eutypa dieback and hot canker (Botryospaeria sp.) are two of the most troublesome groups of wood pathogens. The diseases are easily confused by symptoms. To tell the diseases apart, and some other canker organisms that are closely related, you must use lab techniques including plating on selective media or biotech approaches such as PCR (polymerase chain reaction.) Both diseases are caused by fungal organisms that have alternate hosts commonly found near the vineyards including fruit trees, willows, ceanothus 'and buckeye trees among others. The infection periods for the disease are in the winter, when the fungi sporulate and enter vines through pruning wounds. Fruiting bodies form on old, dead wood on the trunk and cordons, and spores are emitted during wet weather. Bot canker spore releases also may occur during sprinkler frost protection. The degree of susceptibility varies among winegrape varieties to these diseases, with Cabernet Sauvignon, Sauvignon Blanc and Petite Sirah among the most susceptible. Long-term preventative approaches include cane pruning to minimize the amount of wood in the vine, pruning late and double-pruning where wood is left long until fust before bud break ro minimize the amount of time that the pruning wounds are available to spores discharged during wet weather. Research also has shown that lime sulfur applied during winter at the rate of 10-15 gallons per acre will kill over-wintering fruiting bodies of these fungi and others that may be a problem, including powdery mildew. (This course of action is recommended for powdery mildew only when you have had severe problems in previous seasons.) Treating wounds with selected fungicides also is possible (refer to UC IPM Guidelines.)

Esca (black measles) and young vine decline (Petri disease) are very perplexing diseases caused by a complex of fungi including Phaeoacremonium sp. and Phaeomoniella sp. When young vines are affected, their vascular tissue is colonized and the vines often grow poorlv or die due to lack of water. The vines can come from the nursery already infected, or they might become infected if not properly irrigated or otherwise stressed. Older vines typically show chlorotic and red interveinal areas on the leaves known as "tiger stripes." Severe infections may cause leaf drop and stem dieback. Fruit may show dark spots and shrivel. The fungi act very similar to fungal canker diseases by sporulating from fruiting bodies in dead tissue and infecting pruning wounds during winter rains. However, the infection period is wider, and these fungi can enter most any time following pruning. The overwintering stages of this disease also can be prevented with lime sulfur sprays.To avoid young vine decline, be very careful where you obtain your vines and propagation material.

5. Pierce's disease

This bacterial disease tends to occur episodically following warm, wet winters when there is lush growth in riparian areas where the causal agent Xylella fastidiosa builds up large amounts of cells that are then transmitted by sharp shooters feeding on lush green growth infecting nearby vines. Glassy-winged sharpshooters are potentially more harmful than native sharpshooters, as they can infect vines by feeding directly on woody stems for a longer period. There are strategies to control these pests, but ultimately disease-resistant vines would be very helpful. Dr. Walker has been developing a group of hybrid vines with a resistant gene taken from native American grapes and crossed back into standard wine varieties. Seedlings are screened with bio-techniques to be sure that the resistant gene is present; if so, the seedlings are placed into trials to determine if PL) resistance is adequate and fruit quality is also suitable for fine winemaking. Walker and his lab presently are screening the latest generation of vines that are 97% vinifera. There are promising resistant selections that can be used to plant in areas prone to Pierce's disease that will be suitable for making qualify wine. He also is starting a similar program to develop resistance to powdery mildew.

Conclusions

Long-term vineyard health is being enhanced by a modest investment in research and plant breeding that has the potential for enhancing the productive life of grapevines. The longer the vineyard lasts, the longer the initial investment can be paid for. Advances in the past 10 years by hard-working scientists will make a big difference for our industry in the near future.w&v

Glenn McCourty is the UC Cooperative Extension winegrowing and plant science advisor for Lake and Mendocino counties. He is the technical editor for the "Organic Winegrowing Manual" published by the University of California Agricultural and Natural Resources division. He also tends a I-acre vineyard of the aromatic Italian winegrape variety Arneis on his property along the Russian River near Ukiah, Calif

Highlights

* Older vineyards need special attention to avoid problems.

* Nematodes are unseen root pests that are difficult to prevent with a single resistant roorstock.

* Wood-rotting organisms infect vines in the winter, and lime sulfur sprays are an important control technique.

* Phylloxera and Pierce's disease are long-term problems best controlled with resistant plant materials.
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Title Annotation:Grounded Grapegrowing
Comment:The top five threats to vineyard health.(Grounded Grapegrowing)
Author:McGourty, Glenn
Publication:Wines & Vines
Date:Apr 1, 2012
Words:1587
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