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Thomas J. Zabadal

Field grafting of the Concord variety (V. labruscana) when using t-bud, chip bud or sidewhip grafting is typically less successful than when these grafting methods are applied to several European (V. vinifera) and European-American hybrid varieties. Sap flooding is one cause of failure of field grafts. Although trunk slashing basal to field grafts is used to control such sap flooding, it was not effective on Concord vines. Therefore, a strategy to reduce sap flooding of graft unions on Concord vines by increasing transpiration was evaluated. Additional leaf area was retained at the time of field grafting by using the following approaches either alone or in combination: (a) delaying trunk decapitation until several weeks after grafting, (b) retaining a trunk renewal cane and (c) retention of a second, ungrafted trunk. All treatments significantly increased the success rate for the t-bud (88% vs. 63%), chip bud (85% vs. 36%) and sidewhip (90% vs. 48%) grafting methods. Concord vines develop modest leaf area from base buds at the time of field grafting when compared to many other grape varieties. These results suggest that this factor influences the application of certain field grafting methods to this variety.

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Thomas J. Zabadal

The effect of cane girdling, in combination with the common commercial practices of gibberellic acid applications and/or other crop control, on vine size and fruit characteristics was measured over 3 years for `Himrod' grapevines (Vitis ×labruscana × V. vinifera) grown in central New York state. Cane girdles 4 mm wide between the second and third node from the base of each fruiting cane resulted in vines that were capable of sustaining vine size while enhancing several aspects of fruit quality. When added to several vine-manipulation regimes, cane girdling increased cluster weight as much as 106%, berries per cluster as much as 138%, and berry weight as much as 17%. Although cane girdling increased yield as much as 66%, it consistently reduced fruit soluble solids concentration (SSC). Therefore, for cane girdling to contribute to sustained production of quality `Himrod' table grapes in a cool-growing-season climate, it will be necessary to practice it in combination with a level of crop control that will ensure acceptable fruit SSC.

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Thomas J. Zabadal and Thomas Dittmer

Producing the cold-tender wine grape Merlot is a major challenge in the cool-climate viticultural region of southwestern Michigan. Merlot grapes produced in this region provide a strong market opportunity; therefore, several strategies for preserving the fruiting potential of vines through the winter were evaluated over 5 years. Vines were managed with frequent trunk renewal so that they were pliable and capable of being laid near the ground. One treatment was (A) a control. Three treatments involved pruning vines in the late fall to two to four canes, which were then (B) laid on the ground without any cover, (C) attached to a wire near the ground and covered with straw, or (D) attached to a wire near the ground and covered with 20 cm of soil. The fifth treatment (E) involved arching unpruned vines to place canes near the ground but without any covering. Pruning was completed in spring, and vines were tied using fan training. Vines were adjusted to a maximum of 40 live nodes per vine. Winter minimum temperatures averaged 1, 8 and 16 °C warmer than the air temperature at 1.5 m above ground when measured at 0.3 m above ground (B and E), under the straw mulch (C), and under the soil (D), respectively. Very low ambient air temperatures of –27 and –28 °C were experienced in two of the winter periods. C, D, and E consistently provided greater node survival through the winter than control vines. B was inconsistent in performance. The lowest annual yields for A through E for the 5-year period were 3.1, 0.7, 8.3, 6.7, and 9.0 tons per hectare, respectively. These data indicate that treatments C, D, and E were capable of reliable annual production of Merlot grapes even in years with episodes of low winter temperatures. Projects are under way to develop commercial capability for the vine burial and mulching techniques used in this study.

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Thomas J. Zabadal and Thomas W. Dittmer

Varying amounts of vegetation-free area (VFA) were established around newly planted `Niagara' (Vitis labrusca L. × Vitis vinifera L.) grapevines to determine their influence on vine growth during the first growing season. VFAs were either circular with radii from 0 to 5 ft (0 to 152 cm) in one experiment or in bands from 0 to 8 ft (0 to 244 cm) in width in a second experiment. VFAs were maintained with biweekly manual weeding for the entire growing season. Leaf, shoot and root dry weights as well as the number of primary shoots and the length of the longest root were measured at the end of their first growing season. The thresholds for maximum vine dry weight biomass accumulation occurred with a circular VFA of 4 ft (122 cm). When banded VFAs were used, total vine dry weight biomass continued to increase up to the widest treatment of 8 ft (244 cm). Therefore, no threshold was attained. These are greater VFAs than typically established around vines in commercial plantings. Therefore, growers who desire to maximize vine growth of newly planted vines, should consider larger VFAs around vines than has been traditional unless such a practice is likely to cause surface soil erosion.

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Thomas J. Zabadal and Thomas W. Dittmer

Cluster compactness can affect fruit quality by influencing pesticide spray penetration into clusters and by predisposing berries to cracking and subsequent decay. Compactness of clusters can be altered through gibberellic acid sprays, flower cluster thinning and pruning severity. Assessment of cluster compactness has often been performed using a visual rating system which may not provide adequate quantitative measurement. Evaluation of cluster compactness by insertion of wedges between randomly chosen pairs of berries on a cluster revealed a high correlation with a visual rating system and a more sensitive measure of cluster compactness than the visual rating system. Several pruning severity treatments were applied to table grape cultivars to determine their influence on cluster compactness. It was possible to measure statistically significant differences in cluster compactness among these treatment using this wedge measurement technique.

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Thomas J. Zabadal and Thomas W. Dittmer

Sunlight-exposed clusters of Vitis vinifera L. cv. Chardonnay at twelve positions on a N-S oriented, single curtain trellis were monitored for temperature to determine their patterns of heat summation and diurnal temperature.

Diurnal patterns of temperature differed greatly among these clusters. These differences reflected the solar insolation on individual clusters. Point-in-time measurements among clusters during mid-day varied as much as 12°C. 24-hour heat summation for these clusters revealed little difference among them. Heat summations for periods of daylight or solar insolation indicate more heat accumulation for clusters on the top of the trellis, at ground level and on the west side of the trellis than on the east side of the trellis. These differences might be usefully exploited when training vines to maximize aspects of fruit maturation in relatively cool climates.

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Thomas J. Zabadal and Thomas W. Dittmer

Three vine management systems were evaluated on `Chardonnay' grapevines under Michigan growing conditions for five growing seasons to determine their influence on yield, fruit quality, cluster compactness, and the incidence and severity of fruit rot. These systems used mid-wire cordon (MWC) vine training, Umbrella Kniffin (UK) vine training, and a combination of those (UK/MWC). Over four growing seasons the UK and UK/MWC treatments had higher fruit soluble solids and higher yields than the MWC treatment. These higher yields were attributed to higher yields per node and the ability to retain more live nodes per vine than was possible with the MWC treatment. The UK and UK/MWC treatments also had less fruit rot than the MWC treatment in some years, which was related to reduced compactness of clusters. The UK and UK/MWC treatments produced greater numbers of mature canes per vine than the MWC treatment, and the locations of the canes allowed full cropping the season following an extremely cold winter.

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Thomas J. Zabadal and Thomas W. Dittmer

Three vine management systems were evaluated on `Chardonnay' grapevines under Michigan growing conditions for five growing seasons to determine their influence on yield, fruit quality, cluster compactness, and the incidence and severity of fruit rot. These systems used mid-wire cordon (MWC) vine training, Umbrella Kniffin (UK) vine training, and a combination of those (UK/MWC). Over four growing seasons the UK and UK/MWC treatments had higher fruit soluble solids and higher yields than the MWC treatment. These higher yields were attributed to higher yields per node and the ability to retain more live nodes per vine than was possible with the MWC treatment. The UK and UK/MWC treatments also had less fruit rot than the MWC treatment in some years, which was related to reduced compactness of clusters. The UK and UK/MWC treatments produced greater numbers of mature canes per vine than the MWC treatment, and the locations of the canes allowed full cropping the season following an extremely cold winter.

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Thomas J. Zabadal and Martin J. Bukovac

The effects of CPPU [forchlorfenuron, N-(2-chloro-4-pyridinyl)-N-phenylurea] on berry development of Vitis labrusca and V. labrusca × V. vinifera cultivars was evaluated under field conditions. A concentration response was initially established by spraying clusters of `Himrod' at a mean berry diameter of about 5 mm with 0, 5, 10, or 15 mg·L–1 CPPU. Berry enlargement was monitored (16, 30, 44, and 59 days after treatment) during development. Cluster mass, number of berries per cluster, berry mass and firmness, and °Brix were determined at harvest. Berry mass was dramatically increased (2.3 versus about 3.6 g/berry) at harvest by all concentrations of CPPU. Cluster mass and compactness were also increased and berry firmness was linearly related to CPPU concentration (r 2 = 0.997). There was no significant effect on number of berries per cluster (79 to 86). °Brix, rachis necrosis at harvest, and berry abscission after 30 days of refrigerated storage (1 °C) were significantly reduced. Effect of time of CPPU application (0, 5, and 10 mg·L–1) was established by treatment of clusters at mean berry diameters of about 4, 5, 7, and 9 mm. Response was indexed by following berry enlargement at 14, 28, 42, and 56 (maturity) days after treatment. Maximum berry size for both 5 and 10 mg·L–1 was obtained from applications at 4 to 7 mm berry diameter. Relative response of seedless and seeded cultivars was compared by application of CPPU at 0, 5, 10, or 15 mg·L–1 to clusters (4 to 6 mm berry diameter) of seedless `Vanessa' and `Lakemont' and seeded `Concord' and `Niagara'. Bioresponse was determined by a time course of berry enlargement and berry and cluster mass, number of berries per cluster, and rating cluster compactness at maturity. Except for `Lakemont' at the 5 mg·L–1 concentration, CPPU at all concentrations increased seedless berry diameter significantly from the first measurement at 14 through 56 days after application. Berry and cluster mass and cluster compactness were significantly increased in `Vanessa'. In contrast, the only effect of CPPU on the two seeded cultivars was an increase in berry size in `Concord' and an initial increase in berry size 14 days after application in `Niagara'.

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Thomas J. Zabadal, Gary R. VanEe, Thomas W. Dittmer and Richard L. Ledebuhr

Functional leaf area is the basis for vineyard productivity. Therefore, the leaf area displayed on a trellis will determine the productive potential of a vineyard. A device that uses a series of infrared sensors was constructed to quantify vineyard trellis fill. A vertical row of sensors on a moving over-the-row vineyard trailer recorded the interception of infrared light beams through the trellis. These values were related to the total time of measurement to calculate a percentage of trellis fill. Our device was used to quantify differences among training systems applied to `Chardonnay' grapevines. This system is quick, easy, and at least as accurate as currently used visual methods. This technique should be useful for determining the influence of various cultural practices on the development of grapevine canopies.