Delaying Bud Break in ‘Edelweiss' Grapevines to Avoid Spring Frost Damage by Using NAA and Vegetable Oil

Delaying bud break is an approach to avoid spring frost damage. A field experiment was conducted during the winter of 2009 at James Arthur Vineyards, Raymond, Nebraska to study the effect of spraying NAA and vegetable oil (Amigo Oil, Loveland Industries, Greely, CO) on delaying  bud break in ‘Edelweiss’ grapevines to avoid such damage. The experiment consisted of five treatments: NAA (500, 750, and 1000 mg/l), oil applied at 10% v/v which consisted of 9.3% oil and 0.7% emulsifier, and the control which was not sprayed. There were four application dates: Jan. 6, Feb. 3, Mar. 3, and Apr. 1, 2009. Randomized complete block design was used with three blocks of 20 vines each. Each vine was sprayed with approximately 0.33 L. Two canes on each vine were randomly selected and bud break was evaluated throughout spring until each cane reached 60% bud break. During harvest, the number of clusters/cane and weight of clusters/vine were recorded. Berry samples were analyzed for pH, °Brix, and titratable acidity (TA). An additional experiment was conducted using forcing solution (Read et al., 1984) on ‘Edelweiss’ canes collected on the same dates of the field experiment. For each date, 20 canes were headed back to the first five buds, then cut into five single-bud cuttings and the bases immersed in forcing solution. The same previous treatments were applied by adding on drop on each bud. Days to bud break and shoot length one week after bud break were recorded throughout the study. Buds that didn’t show bud break were longitudinally sectioned and examined under a stereomicroscope to determine bud viability and any treatment phytotoxity. Oil and NAA at 1000 mg/l significantly delayed bud break 2-6 days compared to the control. Treatment and month interactions were only found for bud break delay and pH. Treatments had no significant effects on yield, cluster weight, °Brix, and TA. The forcing solution experiment showed a month, position, and treatment interaction regarding bud break delay. No interaction was found regarding shoot length effect. Oil caused phytotoxity on 10% of the buds examined, while NAA at 1000 mg/l delayed bud break at the fifth bud position. Both experiments show that NAA at 1000 mg/l has the potential of delaying bud break in ‘Edelweiss’ grapevines without affecting the quantity or quality of production. It is proposed that grape growers may use NAA to delay bud break and possibly avoid spring frost damage.