Leaf Area and Conductance, Internode Length, and Root Structure of Five Cultivars of Vitis vinifera Treated with Paclobutrazol

¹ Department of Horticulture and Landscape Architecture, Washington State University, Pullman, WA 99164-6414.

Rooted cuttings of five cultivars (Grenache, Chardonnay, White Riesling, Gewürztraminer, and Sauvignon blanc) were treated with 0, 2.5, 5.0, and 10.0 mg active ingredient (ai) per plant of paclobutrazol dissolved in a mixture (50:50) of 80% ethanol and Regulaid^TM. All treatments were stem-applied on the same day. All plants had approximately four expanded internodes at the time of treatment. Significant reductions in internode length and leaf area were recorded for all five cultivars and showed a concentration-dependent response in some cultivars. The time required for initial response, as well as the effective period of inhibition, was variable between cultivars. There was no significant effect on leaf conductance. A change in root structure was observed and is discussed.