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Pierce Disease Resistant grapes

Figure 1. Pierce’s Disease resistant 94% Vitis vinifera selection ‘502-20’ trained to a Watson system.

Building upon information previously reported in Pierce’s Disease Resistant Grapes In Alabama, new plot studies are underway to study a new generation of pierce disease resistant 94% European grapes (Figure 1.). The goal of this new study is to determine the cropping potential and fruit quality of 94% V. vinifera grapevine ‘502-20’ in Alabama when trained to a highly efficient Watson trellis system. The study also looks to determine the optimal planting distance for this genotype.

It is hoped that the information documented throughout this project will aid in the development of best management practices and production system recommendations for Alabama grape producers. It is also hoped that this information will prove vital for the establishment of a sustainable modern grape industry in the Southeast.


To compare the total yield, fruit quality, and to determine the best planting distance for this variety, vines are planted in a replicated study at an in-row planting distances of 6, 7, and 8 feet intervals with 12 feet between the rows. The highly efficient divided canopy Watson trellis system provides better air movement and reduces the risk of disease development by allowing faster drying conditions for the vine canopy.

Observations are on-going to determine differences in vine phenology, cropping potential, and fruit quality at each planting distance. While dormant, vines were pruned in February to 12 spurs per vine (6 on each cordon) with two buds per spur retained for a total of 24 buds per vine. Shoot thinning was conducted early in the season to maintain the desirable shoot number. Additionally, cluster thinning was applied to adjust the crop load to one cluster per shoot.

Figure 2. Total yield of Pierce’s Disease resistant 94% European grapes ‘502-20’.

Figure 2. Total yield of Pierce’s Disease resistant 94% European grapes ‘502-20’.


Figure 3. Planting distance of 7’ X 12’ resulted in the largest average cluster size.

Figure 3. Planting distance of 7’ X 12’ resulted in the largest average cluster size.

Results indicate that vines planted at a distance of 8’ X 12’ produced the highest total yield with 19.5 pounds per vine. Those vines planted at 7’ X 12’ showed a yield of 19.4 pounds per vine. The grapes planted at 6’ X 12’ had a smaller total yield that the other distances and produced a yield of 18.4 pounds per vine (Figure 2).

Other results indicated the following:

  • Vines planted at 8’ X 12’ had the highest number of clusters per vine (31.6), (Table 1.).
  • Average cluster size varied between 367.2 g for vines planted at 6’ X 12’ to 394.3 g for vines planted at 7’ X 12’ (Fig. 3).
  • Average berry size for all planting distances was slightly above 2 grams, with vines planted at a distance of 6’ X 12’ producing the sweetest berries with a 18.7 percent brix average.

Table 1. Effects of Planting Distance on Pierce’s Disease Resistant Grapevines*

*Grown at the Chilton Research & Extension Center

**Measured in grams.
Planting DistanceTotal Number of Clusters per VineMean Cluster Weight**Mean Berry Weight**Brix Percentage
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