Vegas Riffle, Nathaniel Palmer, L. Federico Casassa, and Jean Dodson Peterson*
*California Polytechnic State University SLO, One Grand Avenue, Building 11, Room 218, San Luis Obispo, CA 93407 (jdodsonp@calpoly.edu)

“Old” vines are highly sought after by wine industry professionals and consumers due to their rarity and perceived superior wine quality. To evaluate the validity of this assertion, a two-year study was conducted at a single, interplanted Zinfandel vineyard block in California’s Paso Robles AVA. Treatments included Young vines (five to 12 years old), Control (a representative proportion of young to old vines in the block), and Old vines (40 to 60 years old). Vine age had an effect on vine vegetative growth, with Old vines producing shorter internodes (25.5% decrease) and smaller shoot diameters (29.3% decrease) than Young vines. No differences were found in photo- synthetically active radiation or leaf area index between Old and Young vines. Old vines developed more quickly during berry formation and more slowly during berry ripening periods. Due to variation in the timing of sugar accumulation, Old vines were harvested 21 days after Young vines in 2019 and nine days after in 2020. Vine age affected yield, with Old vines producing, on average between both seasons, 3.7 kg more fruit per vine than Young vines. Old vines also produced, on average between both seasons, 22.8 more clusters per vine than Young vines (5.41 tons/acre and 2.64 tons/acre, respectively). Larger vine capacity is attributed to Old vines having more arm, spur, and dormant bud positions per vine than Young vines. Additionally, Old vines had larger trunk circumferences and diameters than Young vines. Old vine fruit had higher Brix, pH, and titratable acidity than Young vines at harvest in 2019 only, with no differences found in 2020. No differences in berry color or phenolics were found between Old and Young vines. These results suggest the potential for greater yield and increased growing season length when extending the longevity of Zinfandel vineyards.

Funding Support: 21-03-101 Agricultural Research Institute, California State University; Cash Matching Funds – Historic Vineyard Society; BK0020 California Polytechnic State University, San Luis Obispo, Baker Koob Endowment; Research Assistant Funding – California Polytechnic State University, San Luis Obispo, College of Agriculture and Environmental Sciences Summer Undergraduate Research Program; In-kind Matching Funds – Dusi Vineyards