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Studies continue to evaluate the Pierce’s Disease (PD) resistant, predominantly European grape ‘502-20’ developed by the UC Davis breeding program in central Alabama. The major goal is to assess the vinegrape vegetative and cropping potential when vines are planted at three different planting distances and trained to a highly efficient ‘Watson’ trellis system which features divided canopy training for a better air movement and reduced risk of foliar disease development, while providing ease in canopy management and crop harvesting.

Figure 1. Crop load and fruit quality of PD resistant predominantly European grape ‘502-20’
trained to a ‘Watson’ trellis system, grown at the CREC in Clanton, AL, 2022.

Planting Distance

Data is being collected to determine vine phenology, total yield, fruit quality and vigor of ‘U0502-20’ grape at each planting distance. Annually, the experimental vines are dormant pruned to 12 spurs per vine (6 spurs/cordon) with two buds per spur retained for a total number of 24 buds per vine.

The ‘U0502-20’ vines produced the first commercial crop during the 2019 season. Our results for total yield per vine and the total number of clusters per vine in 2022 indicate ‘502-20’ grape produced the highest yield and cluster number per vine at planting distance of 8 feet by 12 feet, while results were significantly lower at planting distances of 7 feet by 12 feet and 6 feet by 12 feet (Table 1).

Tabel 1. Effect of planting distance on yield per vine and number of clusters/vine of '502-20', 2022

Planting DistanceYield/vine, kgNumber of clusters/vine
6' x 12'9.6 38
7' x 12'12.6 44
8' x 12'17.4 53

Study results on cumulative yield per vine (Table 2) for the period of plant establishment (2019-2022) are demonstrating the vines planted at a distance of 8 feet within the row were the most productive and resulted in 46.8 kg/vine. We estimated the average annual yield per acre based on the number of vines at each planting density and found out that the highest crop per acre (5.3 MT/acre) was produced at distance of 8 feet by 12 feet, followed by vines planted at 6 feet by 12 feet (5.2 MT/acre), and 7 feet by 12 feet had 4.9 MT/acre.

Table 2. Effect of planting distance on cumulative yield per vine and average yield per acre, 2019-2022

Planting DistanceCumulative yield/vine, kg, 2019-2022Average yield per acre/year, MT
6' x 12'34.35.2
7' x 12' 38.14.9
8' x 12'46.85.3

Mean cluster weight varied between 540.0 g and 441.0 g based on planting distance, with vines planted at 8 feet by 12 feet producing the largest clusters this season. However, cluster size was statistically similar for ‘502-20’ grape at all planting distances. Planting distance had no significant effect on soluble solids content, juice pH and acidity during the current season (Table 3).

Table 3. Effect of planting distance on soluble solids content, pH and titratable acidity of '502-20' grape, 2022

Planting distanceSoluble Solids Content (%)pHTitratable Acidity
6' x 12'
7' x 12'
8' x 12'







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