Thomas W. Dittmer

The Maintenance of Fruiting Potential Through the Winter for ‘Merlot’ Grapevines Grown in Southwestern Michigan

Abstract Several cold-tender Vitis viniferawinegrape varieties afford wine marketing opportunities in cool climate viticultural regions. However, in some of these regions, their survival through the winter is a major challenge. The ‘Merlot’ variety, as it is grown in southwest Michigan, presents such a situation. Therefore, ‘Merlot’ vines on C3309 rootstock were evaluated on a southwest Michigan farm for a 5-year period to determine the ability of several treatments to preserve the fruiting potential of vines through the winter. Vines were managed with a combination of the fan training system and renewal spurs near the graft union so that trunk renewal canes near the graft union were capable of being laid along the ground. Treatments were: (a) Control-no fall vine manipulation, and pruning performed in the spring; (b) Canes Near Ground (CNG)-vines pruned to two-to-four trunk renewal canes per vine in the fall and tied to a trellis wire 20 cm above ground; (c) Straw Mulch (SM)-same as CNG except canes were covered in the fall with straw; and (d) Bury Canes (BC)-same as CNG except canes were covered in the fall with approximately 10 cm of soil. Fall vine manipulations were performed as soon as vines were fully dormant. Canes that were overwintered near the ground were attached to trellis in early spring and adjusted to a maximum of 40 live nodes per vine after growth began. Annual winter minimum temperatures at 0.2 m above ground (CNG treatment), under the straw mulch (SM treatment), and under the soil (BC treatment), respectively, averaged 1, 8 and 16°C warmer than the ambient air temperature (1.5 m above ground) over the 5-year period. Very low ambient air temperatures of -27°C and -28°C were experienced in two of the five winter periods of this study. Subsequent to those low-temperature episodes, vines managed with SM and BC had significantly greater survival of nodes and greater yields than control vines. CNG was inconsistent in performance. The lowest annual yields for the control, CNG, SM and BC treatments for the 5-year period were 3.1,0.7, 8.3 and 6.7 t/ha, respectively. These data indicate that the SM and BC treatments provided more reliable production than the other treatments. Projects to commercialize the straw mulching and vine burial techniques used in this study are now underway.

Influence of Weed Control, Nitrogen Fertilization, Irrigation and Pruning Severity on the Establishment of ‘Niagara’ Grapevines

Abstract Strong consumer demand for white grape juice has encouraged growers to plant significant new acreages of the variety ‘Niagara’. However, the 4-year time period required to grow a newly-planted vineyard to its full productive capacity is a major factor influencing the profitability of new vineyards. Therefore, the influence of weed control under the trellis, nitrogen fertilization, irrigation and pruning severity on the development of newly-planted ‘Niagara’ grapevines was evaluated. Weed control had the greatest impact on the development of vine size. Without weed control under the trellis, no combination of nitrogen fertilization, irrigation and pruning severity was capable of producing acceptable vine size. Weed control under the trellis, followed by nitrogen fertilization, irrigation and pruning severity, exhibited a descending order of influence on vine size development. Therefore, growers should apply these practices in that order of priority when establishing new ‘Niagara’ vineyards.