When the first European settlers came to Texas, they brought cuttings of grapevines common to their homelands. Although many vineyards across central and south Texas were successfully established, all eventually died except those that utilized varieties derived from native Texas species. We now known that the cause of widespread vine death was a bacterial pathogen know as Pierce’s disease. Vineyards and wineries flourished in areas settled by Europeans, but most did not survive the economic reality of prohibition.

The Texas grape industry began its resurgence in the early 1970’s. Because of the prospects of high yields, greater field longevity after infection from Pierce’s disease and relative resistance to fungal diseases, French-American hybrids were predominant in the vineyards of this era. When variety trials in several areas of the state indicated that vinifera varieties could produce satisfactory yields with acceptable fruit quality, many existing vineyards chose to replace French-American hybrid acreage in an effort to increase wine quality.

Since that time, new vineyard and winery establishment has continued to expand. Texas has over 3,500 estimated acres and more than thirty wineries. In spite of recent losses to Pierce’s disease, there is continued interest in planting commercial vineyards in the Texas Hill Country. The combination of scenic beauty, moderate temperatures and the prospects of retail sales through tourism have led many to investigate the potential for commercial viticultural ventures.

There are numerous challenges to overcome if grape growing is to succeed on a commercial scale. The single greatest risk to growing Vitis vinifera cultivars is Pierce’s disease. Although once considered a transition zone for Pierce’s disease, it has caused losses in most Hill Country plantings and several vineyards have been completely killed by this pathogen. Before prospective grape growers consider any of the other economic factors crucial to financial success, it is imperative that the risk from Pierces disease be understood. It is impossible within the confines of this text to explain all of the factors that constitute risk, manage that risk or predict potential infection. Every attempt should be made to select a site with the lowest risk potential and a grower must be prepared to follow through with timely cultural practices to manage this disease.

Site selection is also critical for soil depth and drainage as well as minimizing the risk of low temperature injury. Soil fertility levels can always be amended, and alkaline sites can be planted with appropriate rootstocks, but inadequate soil depth, internal soil drainage and air drainage are virtually impossible to overcome. Proper site selection is crucial to the success of a vineyard.

Vine damage from deer browsing can pose a significant threat to the establishment of a vineyard in the Hill Country. Commercial or homemade repellents and hunting can provide partial control, but when other forage is not available, deer browsing can devastate young vines. In most areas, deer-proof fencing is a must. While prices may vary, new growers should use an estimate of $3.50/linear foot as an estimate of the price of deer-proofing a new site.

One aspect of vineyard establishment commonly overlooked by new growers is the time needed to complete all of the tasks in the field. Planting, trellis construction, weed control, water management and vine training all require considerable effort in a timely manner in order for vines to get of to a good start. Grape growing is not simply a weekend activity and growers should seriously consider the of their availability time and the accessibility of additional part-time labor before deciding on the size of the initial planting. Even in traditional agricultural-based economic areas, labor continues to be a major constraint.

In addition to selecting a vineyard site with a reduced risk of encountering Pierce’s disease, there are other criteria that will equally impact the probability of success.

Soils

To support plant growth, soils must contain water, air and nutrients. Irrigation practices can be adjusted to accommodate excessively well-drained soils, but poorly drained soils should be avoided. Under high rainfall conditions, poorly drained soils become waterlogged and can lead to rapid plant death. The ideal soil for any perennial crop is a well drained sandy loam with a well drained sandy clay subsoil located 18"-24" below the surface. Although there are adaptable, well-structured clay soils, a drainage test should be done to ensure the soil would be suitable as a vineyard site. To check for drainage, dig a hole with a hand-held post hole digger approximately 36" deep and fill with water. If the drainage is adequate, the hole should be completely drained within 24 hours. Extremely rocky soils should be approached with caution. Hillsides with caliche outcroppings frequently are indicative of impervious bedrock near the surface. Grapevines can tolerate rocky soils, but the rock must be well fractured in order to allow for root penetration. Rocky sites should be well explored with a backhoe to determine soil depth. Sites with less than three feet of soil above bedrock should be avoided.

A soil analysis should also be conducted on a potential site prior to purchase to provide critical information on pre-plant fertilization needs and rootstock/scion selection.

Relative Risk of Pierce’s disease

Removal of wild grapevines, immaculate weed control and establishing a weed-free perimeter around a vineyard provide the best strategy to manage Pierce’s disease, but there are additional factors that should be considered when selecting a vineyard site. Sharpshooters need water to survive and reproduce. Avoiding sites adjacent to creeks, streams, ponds or even depressions that retain rainwater will reduce the likelihood of consistently high leafhopper populations.

When choosing a new vineyard site, be prepared to buy more land than will actually be planted. By creating a large (at least 150 ft.) buffer zone around vineyards, growers can either chemically or mechanically create an environment that is not favorable to insect populations. Growers should also understand that when hay fields adjacent to a vineyard are cut, large numbers of insects will be seeking alternative habitat and feeding sites. Insect monitoring and insecticide applications should be considered when insects move into the vineyard.

Air Drainage

Selecting a site that is topographically higher than surrounding areas is an important factor in avoiding damage from spring frosts. Because cold air is more dense that warm air, it settles to low-lying areas on cold, still frosty mornings. There can be at least a 10'F difference between the top and bottom of a hill on frosty mornings. The dilemma of the hill country is that where there are great soils, there is commonly poor air drainage and where there is great air drainage, there are rarely deep soils. Good sites are there, but they are the exception rather than the rule. Prospective growers should avoid the temptation of planting a vineyard on a parcel just because they own it. Many factors must come together if the vineyard is going to be successful.

Vineyard Layout

Row orientation is a topic of debate, and there are numerous factors that will impact a grower’s final decision. Aligning rows to run parallel with the prevailing wind during the growing season has several advantages. With a full canopy of leaves, a trellis will encounter tremendous stress from wind during late spring and summer storms. Aligning with the wind may help to prevent trellis wire breakage. Another benefit of orienting rows with the winds is improved airflow through the vineyard. Increased airflow will reduce canopy-drying time after a rain and will reduce pressure from fungal diseases.

A second factor to consider in row orientation is ease of equipment operation. Numerous vineyard tasks will necessitate the movement of a tractor and some type of implement up and down vineyard rows. It takes far less time to transverse a vineyard with long rows as opposed to making many more row-end turns with short rows.

Row & Vine Spacing

In the last century, spacing between rows was a function of how much room was needed for a team of horses and a plow to move between rows of grapevines to cultivate weeds. The same principle really applies today, and the distance between rows is a decision reached largely on the equipment available to a grower. In the east, rows have been traditionally spaced nine feet apart, but in the west, ten-foot rows are the norm. Rows can be spaced as close as six feet apart if compact equipment is available, but vigorous vine growth can result in a dense canopy that grows together and is very slow to dry after rains. Such a situation frequently results in severe fungal disease pressure.

Distance between vines will depend on a number of factors. Vigor of a given variety, vigor imparted by a rootstock and soil type will all impact vine size. In shallow soils, vines are typically placed more closely together than on deep alluvial soils. The ultimate goal is to fill the trellis with a canopy of healthy leaves that are well exposed to the sun. Because of these variables, no single in-row spacing can be universally recommended.

How many vines will I need?

To determine how many vines will be needed for a new site, multiply the row width x distance between vines. Divide 43,560 (sq. ft./acre) by that number and it will tell you how many vines will be needed.

Example- Rows 9-ft. apart, 8-ft. between vines. 9 x 8 = 72. 43,560 / 72 = 605 vines per acre.

Trellis Design There are many options open to growers in choosing a trellis design. A trellis basically has two functions- to facilitate light interception into the canopy, and to support a crop where it can be harvested. Again, there are different standard practices in eastern and western growing regions of the United States, so many variations of trellis construction can be found. The following photo reflects an example of trellis that has been constructed to facilitate vertical shoot positioning. This technique increases fruit quality, increases bud fruitfulness on canes, and assists in disease control by facilitating canopy drying.

Site Preparation

Once a site has been selected, a new grower should set aside one full growing season to prepare the new site. It is common to experience a one- or two-year waiting period for propagation of the desired variety on the appropriate rootstock. Ideally, a site should be cleared from trees and brush two to three years before vines are planted. In fields with annual and/or perennial weeds, the field should be deeply disked in the spring and ripped if a hardpan is present. Once vegetation emerges, the field should again be disked about the first of May. This should eliminate many of the annual grasses and broadleaf weeds that will germinate during the first year of preparation. A non-selective contact herbicide such as glyphosate (Roundup®) should then be applied in mid-summer after a rain when remaining perennial weeds are not under drought stress. A second glyphosate application in late September will probably be needed to eliminate perennial weed pressure. Weed control will always be a problem, but every effort should be made to control as many perennial weeds as possible prior to planting. A fall cover crop such as annual rye grass or oats is commonly recommended to prevent soil erosion and to provide a source of additional organic matter to the new vineyard site. Cover crop height should be maintained by mowing throughout the fall and winter. In early spring, two to three weeks prior to planting, the cover crop should be sprayed with glyphosate or disked in a six-foot band down the vineyard row and closely mowed in the row centers in order to create an easy planting environment.

Irrigation

The suitability of a potential vineyard site is entirely dependent upon an available supply of high quality irrigation water. Surface water (ponds) can be used, but a large, deep pond will be required to hold enough water for any length of time. In addition to quantity limitations, surface water will require a more elaborate filtration system to insure that irrigation emitters do not clog.

In most cases, sub-surface wells are used to provide supplemental irrigation in vineyards. Consult area well-drillers or an Underground Water Conservation District Office to obtain an estimate of well capacity that can be expected in a given area. Growers should plan new vineyards based on the greatest future needs- the water needed by a mature, bearing vineyard in the heat of summer. As a rule of thumb, a well capacity of 5 gallons per minute per planted acre is sufficient to supply ample water to mature vines.
Drip irrigation systems are normally used to supply supplemental water in a commercial vineyard. This system consists of a pump, a series of underground main pvc lines, which connect to one half to three quarter inch diameter polyethylene lines running down the row. In a young vineyard, one emitter per vine, spaced about one foot from the trunk, is sufficient to provide supplemental water to immature vines. Typically, once vines enter into their third or fourth growing season, the line is pulled to re-position the original emitter to about two feet from the trunk, and a second emitter is placed on the other side of the vine. While there are numerous kinds of emitters with variable discharge rates, most growers choose to use one gallon per hour emitters that have the ability to be cleaned. High calcium bicarbonate levels commonly found in ground water in the Hill Country typically leave behind precipitate that can clog emitters. Most growers also choose to run the lateral irrigation line on a low trellis wire (~12" high) to facilitate weed control measures, to discourage rodents from damaging lines and to aid visual inspection of lines.
 

Choosing Varieties & Rootstocks

Before a vineyard is planted, prospective growers should have plans for how the grapes they grow will be utilized. If a winery is included in plans for the vineyard, extensive market research should be done to determine the line of products that will be offered at your facility. If you plan on selling to an existing winery, take the time to visit with a number of owners to gauge what the needs of the future will be.

As previously mentioned, grape varieties are categorized as either susceptible or tolerant to Pierce’s disease. In sites where Pierce’s disease is probable, growers may opt to plant tolerant varieties and eliminate the disease from their set of worries. As a general rule, the demand of tolerant varieties such as ‘Blanc du Bois’ and ‘Lenoir’ is considerably less than for susceptible vinifera varieties and consequently, revenues for the production of these varieties will be lower. With in-state winery sales increasing and the unpredictable trends in consumer preferences constantly changing, it is impossible to predict the demand for specific vinifera varieties. The following list includes some of the vinifera varieties planted throughout the different production regions of Texas. Lists are in descending order by acreage.

Whites

‘Chardonnay’
‘Sauvignon Blanc’
‘Chenin Blanc’
‘Riesling’
‘Muscat Canelli’
‘Semillon’

Reds:

‘Cabernet Sauvignon’
‘Merlot’
‘Ruby Cabernet’
‘Zinfandel’
’Pinot Noir’
‘Cabernet Franc’
‘Barbera’

There is considerable interest in planting varieties originating from warmer regions such as ‘Sangiovese’ and ‘Shiraz’, but production potential and wine quality have not accurately been determined. Again, winery contacts are in the best position to project varietal needs.

There is little empirical data on the performance of modern rootstocks in the Hill Country of Texas. Rootstocks are used to impart a particular level of vigor, to overcome specific soil limitations such as phylloxera, nematodes, high soil lime content, and Cotton Root Rot. On acid or mildly alkaline soils SO4 & 5C are stocks commonly used in the Hill Country. These stocks are tolerant to phylloxera (an insect that feeds on both root and foliage).
 

The following is a list of rootstocks currently in use or that hold promise for vineyards in the Hill Country.
 

SO4 (V. berlandieri x V. riparia) Vigorous rootstock popular among growers on neutral or mildly alkaline         sites. Good nematode and phylloxera tolerance. Most cultivars are widely available on this stock.

Kober 5 BB- (V. berlandieri x V. riparia) A vigorous rootstock suited to areas where scion vigor is a problem. Moderate nematode resistance. Very resistant to phylloxera and perhaps has some resistance to Cotton Root Rot.

Teleki 5C- (V. berlandieri x V. riparia) A stock, somewhat more vigorous than SO4, being planted on Hill Country sites with acidic or mildly alkaline soils. High resistance to phylloxera and nematodes. There has been widespread confusion in the nursery industry between 5C and SO4.

110 Richter- (V. berlandieri x V. rupestris) Vigorous stock that tends to delay maturity. This stock is drought tolerant and tolerant of up to 17% lime in the soils. Not extensively planted, but holds promise for moderately high pH sites.

1103 Paulsen- (V. berlandieri x V. rupestris) A vigorous stock (similar to 110 R) adaptable to clay-lime soils. 1103 P is also reported to be somewhat salt tolerant. Not extensively planted to date.

41 B- V. berlandieri x V. vinifera) A moderately vigorous stock which imparts somewhat early fruit maturity. Chief characteristic is its exceptional resistance to high-lime soils.

Dogridge- An extremely vigorous stock with good resistance to nematodes, but only moderate tolerance to phylloxera and high-lime soils. Difficult to propagate so may have limited availability in nurseries. High level of suckering is a commercial drawback.

Champanel- (V. champini) A native cultivar sometimes used as a rootstock where high pressure from Cotton Root Rot is encountered. Not tolerant to nematodes. While graft transmission has not been proven, its tolerance to Pierce’s disease may make it a potential carrier in combination with a susceptible scion.

As a general rule, new growers should consider a small planting the first year to have a better idea on the amount of labor and materials that will be needed for a larger planting. In other words, make your mistakes on a small scale first. It is common to underestimate the time and resources needed in establishing a vineyard. Considering the investment, it may be wise for prospective growers to plan on planting a large parcel over a period of years.

Grapevine Nutrition

Maintaining a nutritional balance in the vineyard is essential to proper vine growth, productivity and optimal fruit quality. Extensive soil sampling should be conducted prior to planting in order to understand soil pH and nutritional limitations. Elements such as potassium, and to a greater degree, phosphorus should be applied to a new site prior to planting and incorporated to place the nutrients in the area where the root systems of vines will be developing.

As vines become mature, petiole (leaf stem) analysis is a far greater predictor of vine needs. This sampling reflects the plant/soil interaction as opposed to simply what is in the soil.

While soil sampling can provide information on initial nutritional needs, mature vines are best managed through the use of tissue testing. Petioles (leaf stems) can be collected at specified times during the growing season, analyzed, and the information can be used to provide guidance into needed fertilizer inputs.

Soils in the Hill Country are typically low in nitrogen. For young vines, small, frequent applications of nitrogen are necessary for healthy vine establishment. Trellis fill and leaf color can provide guidance for nitrogen needs as vines mature.

Crop Load Management

In order to remain a profitable enterprise, vineyards should be guided toward producing an average yield of 3.5 to 5.0 tons per acre. Notions that low yields necessarily constitute higher fruit quality should be dispelled. In other grape growing regions of the world, law prescribes sustainable grape yields. These laws are the result of centuries of trial and error and are largely a function of soil and climatic limitations. Texas is not France, and there are no price supports in place that make low-yielding vineyards a profitable venture.
 
 

PIERCE’S DISEASE

The single greatest threat to the long-term survivability of susceptible cultivars is Pierce’s disease. Pierce’s disease (PD) is caused by a xylem-limited bacterium that clogs the vascular tissue of susceptible grape cultivars. The causal organism is a gram-positive, rod-shaped bacterium named Xylella fastidiosa that is indigenous to the Gulf Coast region of the United States. Although different races of this organism cause similar diseases in other crops, they appear to be host specific, i.e., the grape strain does not appear to infect peach and the peach strain does not appear to cause symptoms in grape. Grapevines become infected when a sharpshooter that carries the bacterium feeds on tender tissue. These insect vectors are very efficient at transferring the bacterium during feeding and infection is likely.

Once a grapevine is infected, the bacteria multiply and colonize the xylem, or water conducting tissue of the plant. This vascular constriction inhibits the movement of water through the grapevine and often results in first visible symptoms noted during periods of heat or drought stress.

Electron micrographs of Xylella fastidiosa in xylem vessels of grapevine
Photos by: Dr. Doug Cook

It is important to distinguish between two groups of grapevines: susceptible cultivars and tolerant cultivars. Once a susceptible cultivar is infected, there is no known, approved method of treating the infection and the disease will most probably be fatal to the vine. Cultivars vary in the length of time it takes the pathogen to cause vine death. Tolerant cultivars appear to have internal mechanisms of suppressing bacterial numbers to the point that the vine can live and be productive even in the presence of the bacteria. There is preliminary evidence that some non-susceptible cultivars may in fact be resistant to infection. All native Texas species of Vitis are believed to be tolerant of PD, which potentially makes them carriers of the bacterium. As a consequence, removal of adjacent, wild grapevines is imperative to disease management.

Disease Cycle

Pierce’s disease infection is dependent upon the presence of a susceptible host, a source of the bacteria, and an insect vector to inoculate the susceptible host. In addition to native grapevines, there are other indigenous plant species that harbor the bacteria without visual symptoms. Surveys in California have identified several alternate host, but in our area, where the disease is endemic, there are undoubtedly many more plant species capable of supporting the causal agent.

Vector Management

Although a serious problem to commercial grape growers on the West Coast, PD is not native to California, but was probably

introduced from the Gulf Coast through infected grapevines. Three or four species of sharpshooters are believed to be the most important vectors in those areas. It is likely that there are numerous species of sharpshooters that can potentially transmit the bacteria in Texas. Work continues to identify these insects, determine their preferred habitat, and understand population dynamics. Sharpshooters do prefer certain habitats. Bermudagrass, perennial rye, fescue grass, blackberry, willow, and elderberry provide important food sources or egg-laying sites for some sharpshooters. Sources of water are also essential to supporting sharpshooter populations, so choosing sites away from these rivers, creeks or ponds can aid in insect management.
 

   Images of several Sharpshooters know to transmit PD.

Most, if not all, sharpshooter species go through five larval, or instar stages in which they apparently loose the ability to transmit the disease with each molt. In areas of rampant infection, it is assumed that alternate sources of the bacterium are widely available. Keeping vineyards and adjacent areas free of potential alternate hosts is essential for long-term management of Pierce’s disease. Monitoring insect populations, especially after habitat disturbance such as cutting of adjacent hay fields, can greatly assist growers in the judicious use of insecticides.

Symptoms

There are numerous symptoms expressed by susceptible cultivars after infection. The first symptom is usually uneven marginal leaf necrosis that often appears near the point of infection. Since the disease inhibits water movement in the vine, symptoms often appear during heat stress or near veraison (color change) in the cluster.

Leaf scorch caused by PD

The clusters of heavily infected vines may actually collapse during this time of high water and carbohydrate movement.

Cluster collapse at veraison caused by PD

Another diagnostic symptom of PD is the abscission of leaf blades from shoots with retention of leaf petioles. In addition, as winter approaches, new shoots become woody and develop periderm on one-year-old shoots. This periderm formation usually begins at the basal portion of a shoot and progresses toward the growing tip. In infected grapevines, periderm formation is not uniform, usually resulting in green "islands" at the nodal area while the internodal portion of the stem becomes brown.

Irregular patches on infected stem tissue.

While each of these symptoms can be confused with one or more other non-related factors, the occurrence of several symptoms together provides strong suspicion of infection in a susceptible host.

Pierce’s disease Probability in Texas

In the mid 1970’s, Dr. Ron Perry published a bulletin entitled A Feasibility Study for Grape Production in Texas which included the following figure detailing the expected presence of Pierce’s disease in Texas.

Expected Probability of Pierce's Disease in Texas

At that time, it was postulated that the range of the disease was limited by the natural range of insect vectors. Cold temperatures have been shown to be therapeutic to plants infected with Xylella, but exact duration and absolute temperatures have not been identified. It is now believed that P.D. is limited to areas which do not receive severe winter temperatures. After a series of warm winters in Texas, outbreaks of PD were confirmed in vineyards previously thought to be in low probability areas.

The Texas Hill Country, long thought to be a transition zone between high and low probability for PD, experienced several warm winters in the mid 1990’s after which several vineyards were found to be completely infected. Prospective growers should realize that this disease is cyclic and that infections are likely to occur. Vineyard survival will ultimately depend on site selection, cultural practices that reduce the risk of widespread economic loss, weather and to some degree, luck.

1996 Positive Elisa Tests Results for Pierce's Disease

Diagnostic Detection

Conventionally, an" ELISA", or antiseral reaction test is used to confirm suspected cases of Pierce’s disease in Texas. Problems encountered a few years ago were due to defective antiserum distributed by the manufacturer. This procedure is still recommended for growers wishing to confirm Pierce’s disease infection in grapevines.

For research purposes, polymerase chain reaction technology (PCR) is used detect the presence of the causal bacteria. This test, which is approximately 10,000 times more sensitive that the ELISA test will be helpful in confirming suspected insect vectors and alternate hosts of the bacteria.
 

MANAGEMENT OF PIERCE’S DISEASE OF GRAPE

Acknowledge Risk

Because there is no known control for Pierce’s disease, the act of planting susceptible cultivars in areas where P.D. is known to exist assumes an inherent risk.

Remove Wild Grapevines

In Texas, wild hosts of the grape pathogen have not been identified. In other states, grape strains of Xylella fastidiosa have been isolated from wild grape, ragweed, alfalfa and almond trees. As a precaution, it is recommended that wild grapes be removed from around the vineyard

Remove Diseased Vines

Based on foliage and cane symptoms confirmed by laboratory diagnosis, diseased plants should be immediately destroyed. Regardless of varietal tolerance, any vine with symptoms of this disease should be pulled up or cut off at the ground and removed from the vineyard. Since observations indicate that the disease can spread from vine to vine within the vineyard, removal of diseased vines reduces the potential sources of inoculum that could be transmitted by insect vectors.

Vector Management

The disease is vectored by certain kinds of xylem-feeding insects, mainly the leafhopper group known as sharpshooters. All of the insect species responsible for vectoring PD in Texas are not known at this time. There are species of leafhoppers that inhabit Texas vineyards and adjacent wild hosts that look like sharpshooters that are not known to vector P.D. Sharpshooters tend to be significantly larger than other species of leafhoppers found in and adjacent to vineyards.

The difficulty of vector management as a means to manage P.D. is the inability to identify all potential vectors within and adjacent to the vineyard, so chemical control of vectors is tenuous at best. Nonetheless, the current thinking in California is that vector transmission occurs primarily from host plants adjacent to the vineyard, so California growers practice vector control in areas adjacent to the vineyard. Growers should use caution when choosing insecticides to insure that specific pesticide labels permit such use.

The pattern of PD spread in Texas more closely parallels that observed in Florida where significant vine-to-vine spread of the disease occurs. This would indicate that insecticidal control of vectors within the vineyard may also be needed..

Based on the best information available, the following vector control recommendations are suggested:

Establish and maintain a 150 foot buffer (minimum) around the vineyard through mechanical or chemical mowing or cultivation.

The California experience would indicate that the greatest danger from transmission of PD through sharpshooter vectors is shortly after budbreak and decreases as the season progresses. Starting at budbreak and continuing for 6 weeks, sample the vegetation in the area outside and adjacent to the buffer, or in the absence of a buffer, sample the vegetation adjacent to the vineyard.

Sampling consists of using a standard sweep net and taking a minimum of eight 25-sweep samples at least twice a week. If adult sharpshooter numbers exceed an average of 1 per 25-sweep sample, insecticidal treatment may be justified.

Treat a 65-foot band adjacent to the buffer or a 130-foot band adjacent to the vineyard in the absence of a mowed buffer. If it is not possible to treat adjacent vegetation, it might be appropriate to treat the vineyard itself. The problem with this approach is that if the alternate host reservoir for the sharpshooter vectors is large and the buffer is small or absent, then within vineyard treatments may be ineffectual in keeping sharpshooters out. Twice a week spraying for 4 to 6 weeks following budbreak may be necessary, but only if sweep samples indicate that a threshold population has been reached.

Care should be exercised in judiciously using insecticides. Unfortunately, the greater the number of sprays, the more likely secondary pest outbreaks will be created, especially with spider mites.

Use an insecticide registered for use for the target area. In most cases (and for all sites external to the vineyard), sharpshooters are not listed as a target pest on the label. Specific use restrictions for grapes and alternate hosts will be found on the label.

Vineyard Floor Management

Because there is limited information as to other species may serve as a source of the P.D. organism, many growers are utilizing clean cultivation to eliminate any possible inoculum source within the vineyard. Weed growth under the trellis can be controlled with cultivation, or herbicides, but management of the vineyard floor between the rows has become problematic. Clean cultivation can have serious drawbacks such as the potential for serious soil loss due to erosion. The use of cover crops in vineyard row centers has several advantages over cultivation including increased equipment mobility, the preservation of soil structure within the vineyard and erosion control.

Because at this point we do not know what plant species constitute propagative alternate hosts of Pierce’s disease, the decision on what plant species growers should plant or encourage on the vineyard floor is still only a guess. In light of these considerations, it may be wise to plant (drill or no-till seed) cool season, annual cover crops such as annual rye grass or oats in October and encourage cover crop growth during the months that grapevines are dormant. These annual plants have a low probability of contracting the causal bacterium and would be growing during a period when transmission to grapevines is not believed to occur.

Cover crop height can be managed by mowing and is easily controlled during the spring with low rate glyphosate applications. This practice keeps cover crop roots in place to support equipment traffic, helps reduce erosion and establishes an organic material layer that inhibits the germination of indigenous weed species. When annual rye grass is used for this purpose, additional suppression of weed seed germination may be observed due to the allelopathic properties of rye. Additional applications of glyphosate or glufosinate can be used throughout the growing season to keep developing weed populations in check. Pre-emergence herbicides can also be incorporated into a vineyard floor management program.
.
The Management program was formulated by the Pierce s Disease Advisory Panel. This is an interdisciplinary working group, made up of representatives from the commercial grape industry, as well as members of the Department of Plant Pathology and Microbiology, Department of Entomology and Department of Horticulture, Texas A&M University.  To view  a copy of the October 2000 Management of Pierce's Disease Publication.
 

BLACK ROT

Black rot of grape is an important fungal disease of American origin that was probably spread to the Old World through the importation of phylloxera resistant rootstock. Primary infection usually arises from infected fruit from the previous season and all green tissue of the grapevine is susceptible to infection. Brown circular lesions appear on infected leaves and within a few days, black fruiting bodies are formed within the lesions. These leaf lesions then become the primary source of infection to developing
fruit clusters. An infected berry first appears light brown, soon the entire berry turns dark brown, and black pycnidia develop on its surface. Infected berries shrivel, turn hard and black and are called mummies. The black rot organism overwinters in mummified fruit on the vine and on the ground. Spring rains trigger the release of airborne ascospores from mummies and subsequent infection of susceptible tissue takes place if temperature and duration of leaf wetness are conducive.

Pycnidia form within lesions and produce pycnidiospores that are spread by rainfall. Leaf lesions are capable of producing spores and causing secondary infection approximately five to seven days after they first appear. Control of black rot is based on properly timed applications of fungicides.
 

Black Rot Infection Chart
 

Temperature  'C	Temperature 'F	Hours of leaf wetness required for infection*
7.0	45	No Infection
10.0	50	24
13.0	55	12
15.5	60	9
18.5	65	8
21.0	70	7
24.0	75	7
6.5	80	6
29.0	85	9
32.0	90	12

*R.A. Spotts, Ohio State University
*Note that at 55'F, it takes 12 hours of leaf wetness for infection to occur, but only 6 hours at 80'F. Most fungicides are protectants and must be applied before an infection period to provide effective control. Fungicides that provide "reach-back" properties must be applied within a specific time period after the infection period starts. Site selection, row orientation and canopy management techniques that increase airflow and decrease canopy-drying time can be beneficial in a black rot management program.

POWDERY MILDEW

Powdery mildew, (Uncinula necator), can infect all green tissue of the grapevine. Cluster infection at or shortly after bloom can lead to a reduction in set or cause berry damage leading to cracked, damaged fruit at harvest. Infection of the foliage can cause a reduction in vine growth, fruit yield and quality and a reduction in winter hardiness. In eastern U.S. growing regions, the fungus overwinters as cleistothecia on bark, but in California, powdery mildew overwinters as hyphal strands on dormant buds where infection takes place very shortly after budbreak. In Texas, the best evidence is that the fungus overwinters as cleistothecia. Sulfur is an integral part of the powdery mildew control program, but under some environmental conditions can become problematic. Sulfur is ineffective when ambient air temperatures are below 50 'F and can be phytotoxic to grapevine foliage when temperatures exceed 95'F. Sulfur residue on fruit can also interfere with fermentation, so use of this product is suggested in late spring and for post-harvest applications. There are several systemic fungicides that can be used during the growing season to prevent fruit yield and quality losses as well as protecting foliage.
 
 

DOWNY MILDEW

Downy mildew (Plasmopara viticola) has a complicated life cycle, but inoculum comes from previously infected leaves that overwinter on the ground.
Extended leaf wetness during dark conditions is needed for primary infection that can result in unnoticeable subtle foliage lesions. Greatest pressure usually comes about with extended rainy periods in late spring or early summer. Again all green portions of the vine are susceptible to infection. Infection in the canopy can lead to premature defoliation and fruit or rachis infection can cause crop loss. When the rachis, or fruit stem becomes infected, the infection can become systemic within the cluster which is virtually uncontrollable. Again, control of downy mildew is focused on the early to mid-season use of preventative fungicides.
 

COTTON ROOT ROT

Phymatotricum omnivorum, or Cotton Root Rot is a soil-borne fungal disease that affects over 250 known crop plants. While grapevines are not as susceptible as apples or alfalfa, they can succumb to this disease under high-pressure conditions. The disease is favored by high soil pH levels (above 7.4) where it has the ability to reproduce sexually and cause widespread vine loss. Own-rooted vines are more at risk than those grafted on a more vigorous root system. It is reported that the V. champini rootstock Champanel is tolerant to Cotton Root Rot. Using this stock potentially brings with it other potential risks (see rootstock section). Other stocks such as 5BB, SO4 and 5C can provide some additional vigor, but may succumb under high-pressure situations. Avoiding heavy, high pH sites is the best measure of caution against Cotton Root Rot.

OTHER BACTERIAL DISEASES

In addition to Pierce’s disease, (Agrobacterium vitis) or Crown Gall is a bacterial disease of grapevines that can cause a loss of vine vigor, which can eventually results in death. Like Pierce’s disease, there is no effective control of this bacterial disease once vines are infected and are exhibiting symptoms. It was once thought that the bacteria primarily entered vines through freeze injury sites, but it is now believed that freeze events simply initiate the galling process. Selecting a reputable nursery and planting disease free vines is the best way to prevent losses from crown gall.
 
 

Virus diseases of grapevines are numerous and usually result in vines that become less vigorous and productive. While there are different ways virus diseases spread within vineyards, the best approach to managing the disease is to rogue infected vines once they are identified. Vines that are suspect may be tested via commercial laboratories to confirm or refute infection status. Purchasing certified virus-free nursery stock is the best way to avoid contaminated plant material.

In addition to sharpshooters, there numerous insects that may feed on grapevine foliage or fruit. Below are a few of the most common insect pests encountered in the Hill Country.

Grape berry moth is a lepodopteran insect with three or four generations per year that can damage flower clusters or fruit.

Eastern grape leafhopper is one of several species of insects that feed on the underside of foliage reducing overall photosynthetic capacity of the canopy. These insects are phloem feeders and are not believed to be capable of transmitting Pierce’s disease.

Grape leaf Folder and Grape Leaf Roller are larvae of two separate moth species that feed on foliage after rolling or folding themselves inside a leaf.

Phylloxera- is a "root louse" insect that can feed either on foliage or, more damaging, on the roots of susceptible grape species. Own rooted V. vinifera are especially at risk. Rootstocks with V. berlandieri parentage are used to overcome potential root damage.

Growing any perennial crop is an exercise in patience that can be emotionally and, at times, financially rewarding.The key to producing profitable yields is growing healthy vines. Water, weed control and proper vine nutrition are essential to growing vines capable of producing good yields of high quality fruit.

The greatest limiting factor to the production of susceptible V. vinifera cultivars is Pierce’s disease. Understanding this risk, and more importantly, following through on site selection, insect control and habitat management will provide new growers the greatest probability of success.

In the best sites, managing excessive vigor may itself be a challenge and can be accomplished by setting an appropriate crop whereby vine size dictates crop load. Proper canopy management will ensure optimal fruit quality and stable vine vigor.