Growing Pierces's Disease Resistant Grapes in Central, South and East Texas

George Ray McEachern, Larry Stein, and Jim Kamas
Extension Horticulturists
Texas A&M University
College Station, TX 77843-2134
March 6, 1997

Grapes are grown throughout central, south, and east Texas almost entirely for home use. Val Verde Winery at Del Rio, Texas and Messina Hof at Bryan, TX are growing Le Noir for Port Wine. A few Blanc du Bois white vineyards have also been planted. There is considerable interest in the possibility of growing grapes for wine and table use. The major limiting factors are Pierce's Disease and fungus diseases associated with the high rainfall and humid conditions in this area of the state during grape fruiting season. Early settlers in this region attempted to grow Vitis vinifera grapes of Europe; however, they could not establish a commercial industry because of these and other limiting factors. Numerous private vineyards have been attempted over the years and most especially after the increased national interest in wine grapes in the 1970's and 1980's. Unfortunately, all of the varieties not resistant to Pierce's Disease died prematurely.

Pierce's Disease entered a large number of Central Texas vineyards in 1996. The long range impact of the problem could prohibit the use of all but PD resistant varieties in the future. The planting of classic wine varieties should be put on hold until the extent and severity of PD is fully understood.

Fortunately, modern grape breeders in the South have developed varieties which are resistant to PD and the opportunity for growing grapes in this area of the state is greater than ever before.

Potential or new grape growers need to understand that grape culture requires a great deal of knowledge, labor, and money. The rewards are good, but the effort required will be far greater than that of other agricultural or gardening challenges. There are numerous cultural practices which must be accomplished , overlooking one practice can bring disaster to the vine or vineyard.

Vineyard Location
The microclimate, soil, and accessibility of the vineyard are critical. A raised elevation with good air movement will help reduce fungus diseases and increase surface water drainage. The soil needs to be well-drained. This can be hard to find in the Gulf Coast area of the state because of the flat nature of the land and the predominance of clay textured soil. A vine simply will not develop new water and nutrient absorbing roots if the soil is not well-drained. Therefore, commercial vineyards must be limited to high sandy ridges. Garden grapes will need to be planted on raised beds to prevent water accumulating in the root zone. Drainage ditches will also be needed in some locations to move the excess rainwater out of the vineyard during periods of high rainfall.

Vineyard accessibility is equally important as microclimate and soil. The vineyard must be checked almost daily and if it is too far to drive, the absence of the owner will result in numerous complications in the management program. The vineyard location should have a good supply of clean irrigation water. Electricity, roads, fences, and other factors can be very important.

Develop a Vineyard Plan Before Starting
The basic considerations for establishing a vineyard need to include market, wine or table, varieties, rootstock, site preparation, trellis construction, irrigation, planting, weed control, vine training system, and irrigation rates. The plan needs to consider learning how to grow grapes, allotting money for establishment and development, scheduling both hand and mechanical labor, a marketing plan, selection of equipment equal to the vineyards needs, pest management, varmint prevention, and other personal needs. All of these factors need to be well thought out and recorded prior to selecting the vineyard site.

Vineyard Size and Economic Risk
Since there are limited commercial grape production areas in Texas, all new vineyards need to be very small to test the economic feasibility of their production. The market may or may not accept new varieties. The risk of fruit diseases or low production could also limit the potential for profits; consequently, all plantings should be very small. It is recommended that the initial planting be only 120 vines or one quarter of an acre. This number of vines allows the owner ample opportunity to learn how to grow grapes without a major economic investment at a very serious risk. A common problem is to plant more grapes than one can properly manage. As a result, one management practice cannot be completed before another is seriously needed and the results are confusion, frustration and poor vine growth.

Varieties
There are numerous wine and tablegrape varieties which have produced well in the dry climate of Central, North, and West Texas; however, they are not resistant to Pierce's Disease. These varieties can be grown as garden grapes with the understanding that they can die at any moment. Vine death can be in one year or fifteen, it is strictly a matter of chance. Planting resistant varieties is the only control for Pierce's Disease. There are no cultural practices, sprays, or rootstocks which will reduce the probability of the disease.

The new and old Pierce's Disease resistant varieties can grow and produce for a long period of time without the risk of vine death. These varieties are described as follows:

'Blanc duBois' is a new white wine grape developed by Dr. John Mortensen of the University of Florida. It is a vigorous vine which seldom requires a rootstock. The clusters are medium-sized weighing 4 to 8 ounces with 45 to 55 round berries and it ripens in late June or July in South and East Texas. The vines can bear up to 5 tons per acre with cane, cordon, or curtain pruning. It is resistant to Pierce’s Disease and Downy Mildew, but susceptible to Black Rot and Anthracnose and will require regular fungicide protection during warm humid conditions. The roots are resistant to nematodes but not well adapted to poorly drained, high pH soils.

'Orlando Seedless' is a new white tablegrape developed by Dr. John Mortensen of the University of Florida which is very vigorous and produces long, thin clusters of small, round, light green berries. It is the first seedless tablegrape which is resistant to Pierce's Disease. Fruit size will be a major problem which will require cluster thinning and cluster pruning to correct. Girdling and gibberellic acid may also be needed to bring berries to a commercially acceptable size. The flavor of the berries is excellent; however, the skin does not crunch as with some Vinifera tablegrape varieties. The vines can bear up to 6 tons per acre; however, the most optimum pruning system has not been determined. The cordon pruning system has not proven to be the best, so the cane system is recommended. In addition to being resistant to Pierce’s Disease, it is resistant to Downy Mildew and Powdery Mildew, but susceptible to Black Rot and Anthracnose and will require fungicide sprays.

'Le Noir' or'Black Spanish' is a red wine, juice, and jelly variety which has produced very high yields in South Texas since 1889. The wine is very tannic and acidic which is used by Texas and Mexico wineries to make outstanding port wines. The cluster is large and compact with small, black, seeded berries. The juice is very different in that it is very red rather than clear in color. The vine can be cordon pruned on deep, fertile soil; however, on shallow sands or heavy clays it should be short-cane pruned. It is resistant to Pierce's Disease, but highly susceptible to Black Rot and Downy Mildew. Leaf pruning and frequent fungicide sprays will be essential in preventing fungus diseases. The vine is only moderately vigorous and can occasionally show yellow leaves or iron chlorosis on high pH soils which are poorly drained. The fruit ripens in late July or early August.

'Champanel' is a red jelly variety developed by the legendary T.V. Munson of Denison, TX. It is extremely well adapted to South and East Texas. The cluster is small with large, black, seeded berries which are very acidic until fully ripe. The vine is extremely vigorous and grows well in a wide range of soils; however, it can have serious iron chlorosis problems on some poorly-drained, high pH soils. The vine responds best to cordon or curtain pruning. It is resistant to Pierce's Disease, Black Rot, Downy Mildew, Anthracnose, and Powdery Mildew; therefore, it will not require fungicide sprays. It is also resistant to all insects except the Grape Leaffolder. 'Champanel' is an outstanding garden grape because of its ease of culture and natural resistance to insect and disease pests. It also makes the best arbor variety for the same reasons.

'Favorite' is a seedling of'Black Spanish' which was selected at Brenham, TX. It is very similar to its parent, but has higher quality fruit. Unfortunately, it is not as easy to purchase. 'Favorite' is managed the same as'Black Spanish'

'Roucaneuf' is a French x American hybrid variety from Southern France which is resistant to Pierce's Disease. It is only moderately vigorous and should be planted close in the row and cane pruned. The clusters are small, but long, and produce small, pink berries. It is used for white wine or can be eaten fresh as a tablegrape.

Other Pierce's Disease resistant varieties include Mid South, Miss Blue, Miss Blanc, Daytona, Suwannee, Conquistador, Lake Emerald, Stover, Norris, and Herbemont. All of these can be grown on sandy, acidic soil.

Rootstocks
A rootstock should not be used unless a major disease problem exists. 'Champanel' and 'Dog Ridge' can be used for Cotton Root Rot control and also to improve low vine vigor on clay soils. If a very deep sandy soil is used, SO4 can be used for nematode control. All three of these rootstocks will control the Phylloxera root insect. Garden grapes are almost always grown on their own roots.

Vine Spacing
It is important to coordinate the vine spacing with vine vigor. Deep, fertile, well-drained soil will produce very vigorous vines which need a wide spacing of 12- foot rows with vines planted 8 feet apart in the row. Shallow or poorly-drained, clay soils will not produce as much vigor and the vines can be planted on 10-foot rows with vines 4 feet in the rows. Experience and knowledge of the variety, rootstock, and site will be essential in determining the exact vine spacing and pruning system. Garden grapes can be spaced closer than normal if intensive shoot placement can be practiced. Vines can be placed 4 to 6 feet apart for arbor training and pruning.

Planting
Grape vines should be ordered well in advance of the planting season so quality vines and requested varieties can be purchased. Have the vines shipped as soon as they are dug at the nursery. Heel the roots into the soil in a shady location until planting in late February. Never allow the roots to dry out.

Immediately prior to planting trim the roots to only 1 or 2 inches and cut the top back to only 2 buds on the strongest cane. Remove all other canes. Carry the vines to the vineyard site in a bucket of water. Dig a small hole with a hand-held post digger and pack the same soil back into the hole. Plant the vine next to a stake. Water the vine with two or three gallons of water immediately after planting. As the new buds begin to grow, watch out for cut worm and grasshopper damage. Do not allow weeds to develop and keep the young vine watered once a week or more if it dries out.

Trellis Construction
The permanent trellis should be constructed prior to planting. It consists of a farm fence T-post at each vine. Wires are set at 18, 42, 52, and 66 inches from the ground if a 7-foot post is used for cane and cordon pruned vines. Single curtain vines will need wires at 18 and 66 inches from the ground. If a shorter fence post must be used, lower each wire so that the upper wires are still the same distance apart as they were with the 7-foot post. End posts need to be over 8 feet long, over 4 inches wide , and pressure treated to prevent decay. Old railroad ties and landscape timbers do not make good end posts because they rot prematurely.

All perennial weeds need to be killed down the row immediately after construction of the trellis with a contact herbicide. The drip irrigation system needs to be attached to the trellis and made operative prior to planting.


Figure 1.
Click image for larger view.

Grape Arbors
Garden grapes can also be trained onto an arbor as an excellent landscape plant. Figure 2 illustrates a typical grape arbor. Do not use net wire on the top of the arbor because it will make pruning impossible.


Figure 2.
Click image for larger view.

Vine Training
The objective the first year of the vine's life is to develop a strong root system; hence, no training is performed. It is very important, although, to tie the developing shoots onto the stake to keep them off the ground and allow weed control up to the vine. A farm fence post makes the most optimum stake. The second year, just prior to bud break, the vine is pruned back to only two buds on the strongest cane. All other canes and buds are removed. This combination of root development for one full year and heavy pruning forces very rapid and strong growth the second year. As a result, training is very easy. Weak, slow-growing vines are impossible to train. When all of the shoots are over 18 inches long, select the strongest and very carefully tie it to the stake. Do not remove other shoots until the strongest shoot is successfully tied. These shoots break off very easily.

Pruning Systems
Grapes can be trained and pruned to a number of systems. The four discussed here are Bilateral Cordon, Cane, Short Cane, and Single Curtain. Stated in the most simple of terms, grapes are pruned by removing 95% of the canes in late winter just before bud break. If too much wood is removed, the vine will be excessively vigorous. On the other hand, if too little wood is removed, the vine will overbear. It is better to remove too much wood than not enough, because overbearing will weaken the vine as well as produce lower quality fruit. Tablegrapes should always be over-pruned to increase the fruit size.

As a general rule, the vines are pruned to only two buds of second year's growth, eight to twelve buds prior to the third year’s growth, and twenty to thirty buds prior to the fourth year's growth. These buds can be on canes for cane pruned vines or two bud spurs on the cordon pruned vines. Each bud will produce a shoot with two to three clusters of grapes.

Bilateral Cordon
This is the most common system used in Texas and California. A horizontal trunk is trained onto the 42-inch wire left and right of the stake. Seven spurs with two buds are selected on each side during the second and third growing seasons. This system is for moderate to vigorous vines. If the shoots are weak and less than 3/8 inch in diameter, switch to the cane system, which requires fewer buds. If the shoots are extremely vigorous and too long, switch to the single curtain, which require more buds.


Figure 3.
Click image for larger view.

Cane
The cane system is gaining popularity throughout the commercial wine and tablegrape industry because of the flexibility in pruning level. To cane prune, remove all of the one-year-old canes except one on each side of the stake. Select the two canes which are approximately 3/8 to 1/2 inch in diameter and 4 to 6 feet long. Arch the two canes over the wire that is 52 inches from the ground. There should be 6 to 12 buds on each cane. The end of the cane should always be at least 3/8 inch in diameter. Also, leave two very short one-bud spurs on the trunk as renewal spurs. They will produce next year's production canes.


Figure 4.
Click image for larger view.

Short Cane
Low vigor vines of less than 12 buds should be short cane pruned. Select the two strongest canes on the vine and prune back to only 1 to 6 buds each. Remove all other canes. It is very important to prune large clustered varieties to the short cane system.


Figure 5.
Click image for larger view.

Single Curtain
Extremely vigorous vines should be trained to the single curtain system. This is a horizontal trunk or cordon at the top of the wire, going left and right from the stake. Spurs are selected each winter 6 inches apart with 1 to 6 buds each, depending on the vigor level. If last year’s growth was weak, leave fewer buds, if it was overly vigorous, leave more buds.


Figure 6
Click image for larger view.

Pruning Theory
In growing grapes, for home or commercial, it is important to maintain a healthy balance between vine growth and fruit production. This will result in strong vines and top quality fruit. Shoot and cane size is the best index for determining how vines are performing. At harvest, the canes should be 3/8 to 1/2 inch in diameter to be optimum. Each shoot should have 15 to 22 mature leaves at harvest. If the shoots are not of this optimum size, vine vigor can be controlled by increasing or decreasing the number of buds left on the vine after pruning.

To increase the vigor of weak vines, leave fewer buds at pruning. To decrease the vigor of rapidly growing monster vines, leave more buds at pruning. The balance between vigor and fruiting can be measured two ways, by cane pruning or by pruning wood weight.

The cane count system is very simple; count the number of canes which are 3/8 to 1/2 inch in diameter at pruning time. Reduce the number 10% and this is the number of buds to leave on the vine after pruning. For example, if a vine has 20 mature canes over 3/8 inch in diameter, subtract 2 and this indicates 18 buds should be left on the vine after pruning, nine on the left and nine on the right. The buds can be on cane, cordon, or curtain pruned vines.

The wood weight system is conducted by weighing the pruning wood. The wood should weigh .5 to .7 pounds for each foot of vineyard row, regardless of the pruning system or vine spacing used.

Irrigation
South and East Texas receive a great deal of rainfall; however, the early summer can be very dry. Grapes require one inch of water per acre per week. Shallow or heavy clay soil will need supplemental irrigation when rains do not occur. Vines should not be allowed to go more than three weeks without water. When a drought occurs, apply 28 gallons of water per vine per week until a rainfall. This volume should be reduced 50% for young vines.

Drip irrigation is essential for commercial production of grapes. Attach a 1/2-inch plastic irrigation line to the 18-inch irrigation wire. Place one emitter at each vine, 12 to 18 inches from the trunk.

Garden grapes should not be sprinkler irrigated with city water because it can burn the foliage. Do not irrigate vines after the month of August because it can stimulate late season growth and freeze injury.

Fertilizer
Grapes are usually vigorous and require no fertilizer. Weak growing vines on well-drained soil may respond to a very low rate of nitrogen fertilizer. Never fertilize grapes after June because it can stimulate late-season growth and freeze injury. Never use phosphorous fertilizer because it can tie up zinc and iron in the soil.

Grapes growing on heavy, poorly-drained, clay soil frequently have yellow or white leaves. This problem is called iron chlorosis. It is corrected by improving drainage and by applying 1/8 ounce of Fe 138 Iron Chelate to each vine in one gallon of water as soon as the yellow color occurs.

Weed Control
Grapes cannot grow in weeds. Weed control is the most important cultural practice in the production of grapes. If left uncontrolled, weeds simply kill the vines by using all of the soil water and nutrients.

The ideal system is to keep the vineyard middles mowed close, just like a lawn. Kill the weeds under the vines down the row with a contact herbicide. The weeds on one acre or less can be easily controlled with a three-gallon backpack sprayer.

Insect Control
There are a number of insects with can attack grape vines. However, the vines should not be sprayed until damage is obvious and the insect is seen. Phylloxera is a small root insect which has the potential of completely killing all vines in an area or region. Since it has not been identified in Texas, no precautions are taken for its control. There are a number of rootstocks which are resistant to Phylloxera should it become a problem.

Disease Control
High temperature and humidity are ideal conditions for fungus disease development. Black Rot, Downy Mildew, Bunch Rot, and Anthracnose can occur when conditions are optimum. They can be prevented by spraying the clusters with fungicides. Removing the leaves which cover the clusters in early May will help prevent fungus diseases by increasing air circulation and better fungicide contact with the clusters.

Pierce's Disease is a bacteria-like pathogen which is moved to the grape vine from grass host plants by a small leafhopper. The only control is resistant varieties. It occurs only in the warm, humid area of Texas south of the 800 hour chilling below 45 degree line. It is identified by irregular margin leaf burn followed by general vine decline. It usually takes two to four years for the vine to die after infection.

Cotton Root Rot can be a very serious problem on poorly-drained, high pH soils. It can be prevented by proper site selection or resistant rootstocks, such as Champanel and Dog Ridge. It is identified by rapid vine death in July right before or during harvest.

Increasing Tablegrape Fruit Size
Tablegrapes can be enlarged by heavy pruning, cluster thinning, berry thinning, girdling, and gibberellic acid sprays to thin berries from the cluster and sprays to enlarge the fruit size.

The easiest way to increase fruit size is to prune heavy and allow only one cluster per shoot. Remove the other clusters immediately after fruit set or when the berries are BB size. In addition to this the number of berries in a cluster can be reduced by sniping some of the berries when they are BB size. If the cluster has a long tail, simply cut the tail off or if the cluster has a shoulder, simply cut the shoulder off. Large mature tablegrape vines should not produce more than 20 clusters, smaller vines should produce less.

Harvest
Grapes ripen very early in South and East Texas, from late June for tablegrapes to early August for Black Spanish. Varieties not recommended for the area frequently produce clusters with uneven ripening fruit. Birds and other animals can be a serious problem at harvest time. Netting is the only sure way to prevent fruit loss.

Tablegrapes are harvested when they taste good or when the sugar level is above 16%. Wine grapes are harvested before the juice pH reaches 3.4.