Grape Disorders

1. Q. The leaves on my grape vines are turning brown and dying. Is this the dreaded Texas disease of grapes called Pierce's or is it the dry weather?

A. It is hard to diagnose Pierce's Disease on grapes without a sample and even with a sample, an exact diagnosis is difficult without a laboratory analysis. Pierce's Disease is native (meaning it is here all the time!) in this area of Texas and will sooner or later kill susceptible varieties. The only readily available resistant varieties are Champanel and Black Spanish. Pierce's Disease is characterized by death of leaf margins and tissue between leaf veins. The damage may occur 1-3 years before the vine dies. Grape leaves can also be damaged by a foliage disease called black rot, which can be identified by reddish brown spots in the leaves. Earlier applications of benomyl (Systemic Fungicide) or bayleton (FungAway) could have prevented this foliage damage as well as the dried fruit which is also a symptom of the disease. Black rot will normally not kill a vine unless severe infections occur on a yearly basis. Keep the vine well watered, pest free, actively growing and hope that you don't have Pierce's. Next time, plant recommended, adapted varieties.

2. Q. My grape vine is enormous but not very productive. Why?

A. For grapes to be most productive, they should be pruned rather severely. The two most common for the home garden are the vertical trellis and the overhead arbor. Both of these are satisfactory in the home planting if kept well pruned.

Pruning may be done anytime after the vines become dormant. In areas where there is danger of winter injury, pruning may be delayed until early spring. Vines pruned very late may bleed excessively, but there is no evidence that this is permanently injurious. Certain vines in the wild will never bear fruit as they are male vines.

3. Q: When is the best time to take cuttings to propagate a grape vine? What is correct propagation procedure?

A: Most grape cultivars are propagated by dormant hardwood cuttings, which root readily. Cutting material should be collected during the winter from healthy, vigorous, mature vines. Well-developed current season's canes should be used; they should be of medium size and have modertely short internodes.

4. Q: Two year old grapevines leafed out alright, then they began to dieback and turn black. There is a mossy looking white fungus on the leaves. Sprayed with wettable sulphur and spread powdered sulphur around the roots of plants.

A:Black rot,powdery mildew and downy mildew can all be problems on grapes. Spray at recommended intervals with fungicides such as Benomyl and/or Captan. Bayleton fungicide also works well but it is hard to find in small quantities.

5. Q. I planted grapevines last year. Now they are loaded with many bunches of grapes. Should I leave all of these grapes on the plants?

A. Remove all of the grape clusters. Overcropping is a serious problem with grapes and must be corrected to insure healthy vines, quality grapes and regular production. Too much fruit too early can severely weaken a grapevine. Even older three-year-old vines should fruit only 16 to 24 clusters. Mature vines should carry 40 to 60 clusters depending on cluster size and vine vigor. The point is to prevent overcropping.

6. Q: What is the correct grafting procedure for grapes and muscadines. I have uncessfully attempted to graft cultivated varieties of both onto wild established and vigorous rootstock in an attempt obtain productive vines early. I normally have good success using normal grafting techniques on plums, mayhaws, and pecans. A different technique may be needed for grapes. Any advice or alternate source of information you can provide would be appreciated.

A: The best way to graft grapes is to use a "T" bud. It can be used on both old as well as young vines. The key to making the technique work is to make a "bleed cut" about one to two inches below the "T" cut. In this way the vine bleeds at this cut and not at the "T" above. If the vine bleeds at the "T" cut, the bud cannot heal.

The "T" or shield bud is outlined in detail at the following site: This technique is best used in early to mid-spring; do not try too early though as the sap from the vine will be excessive. You will need to cut and store buds in January or February.

7. Q: I've got 5 two year old grape vines. I put them up on a Geneva Double Curtin trellis. The branches that come off of the main trunk running down the trellis tend to grow long and wrap around the main trunk. I've tried to prevent this. Now, should I be cutting these back to a certain length, or should they be growing long and toward the ground? I didn't get a single grape this year. 3 of the 5 vines were self-fertilizing. At first bloom it appeared that there were some tiny clusters, but these seem to disappear.

A: It sounds like your grapes are doing extremely well. Many people have trouble getting plants to grow vigorously, but this is not the case for you. Normally we let the vines grow at will the second year once we have them established on the trellis. If you are growing table grapes we want the plants to be vigorous forever. Whereas with wine grapes we want them to slow down to improve the grape and subsequent wine quality. So depending on which type you have, either continue the same fertilization program or discontinue it in '97. We only want about 4 to 5 feet of growth on wine grape varieties. Decreasing or eliminating the fertilizer will help slow the vines down. Still if you are not fertilizing or if the plants continue to grow vigorously, you will need to leave more buds when you prune this winter. This will allow more shoots to develop which should slow down the vine. Also, you may need to pinch out the terminals of the more vigorous shoots. You may have to do this several times a growing season.

As far as fruit goes, the vines are still young and in reality we don't want them to produce a lot of fruit until they are well established. More than likely they were still growing too vegetatively to produce grapes in '96. I am sure you will have a lot more fruit in '97. Only leave about 6 to 10 clusters per vine though as it is easy for vines to overproduce early on and never recover. They should be able to handle a full crop in '98.

| Parson's Archive Home | Aggie Horticulture |