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S. Kaan Kurtural, Geoffrey Dervishian and Robert L. Wample

Three canopy management methods, hand pruning (HP), mechanical prepruning with hand shoot thinning (MP+HT), and mechanical box-pruning with mechanical shoot thinning (MP+MT), were applied with the objective of achieving similar and commercially marketable ‘Cabernet sauvignon’ grape (Vitis vinifera) yields while maintaining vine balance and comparing labor operations costs. Canopy management system labor operation cost estimates indicated a 62% and 80% labor savings with the MP+HT and MP+MT treatments, respectively when compared with HP. The total shoot density of the vines was unaffected by the treatments applied. However, the contribution of count shoots increased with the concomitant addition of mechanization to canopy management. All treatments achieved similar canopy architecture and microclimate. The treatments did not affect photosynthetically active radiation (PAR) intercepted in the fruiting zone of canopy at veraison. All treatments had similar yield, total soluble solids (TSS), juice pH, and titratable acidity (TA) at harvest. Berry skin total phenolics, anthocyanins, and tannins when measured at harvest were also similar among the treatments applied. All treatments tested were within acceptable Ravaz index limits of 5 to 10 lb/lb. However, only MP+MT treatment reached a near optimum leaf area to fruit ratio of 1.2 m2·kg−1 and pruning weight of 1.0 kg·m−1 for warm climate viticulture. The results of this study provide commercially acceptable mechanical canopy management options that may provide labor cost savings for winegrape growers in the San Joaquin Valley (SJV) of California.

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S. Kaan Kurtural, Imed E. Dami and Bradley H. Taylor

Response of yield components and fruit composition of `Chambourcin' (Vitis vinifera × V. rupestris) grapevines to three pruning levels of 15, 20, and 25 nodes retained for each pound of dormant prunings; and three cluster thinning levels of 1, 2, and 2+ clusters per shoot in 2002 and 1, 1.2, and 1.5 clusters per shoot in 2003 were measured at two vineyards in the lower midwestern United States. In both years of the study, there was very little interaction of pruning and cluster thinning. The proportion of non-count shoots increased within the canopy in response to increased pruning severity. Pruning weight means were lower in 2002 across all treatments compared to 2003. Pruning weights decreased with the increase in the number of clusters retained per vine. Pruning influenced yield only in 2003 when the proportion of count shoots decreased below 62% of the total, hence the relationship between number of shoots per vine and yield (R2 = 0.3452; P < 0.0003). In both years of the study, the increase in severity of cluster thinning resulted in yield reduction but an increase in the total soluble solids in juice. Yield compensation was achieved by an increase in cluster weight of 38%, and 25% in response to a reduction of 37%, and 23% in cluster numbers; which translated into a yield reduction of only 10% and 3%, at Vineyards 1 and 2, respectively. Balanced pruning to 15 to 20 nodes per 1 lb of prunings and cluster thinning to 1 to 1.2 clusters/shoot optimized yield (9.7 kg/vine, 13.4 t·ha-1) and fruit composition, and maintained vine size (≥0.3 kg·m-1 of row). These results provide valuable information for growers of `Chambourcin' grapevines in the lower midwestern U.S., as well as in other climates with long growing seasons.

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Matthew W. Fidelibus, Stephen J. Vasquez and S. Kaan Kurtural

California table grape (Vitis vinifera) growers cover the canopies of late-season varieties with plastic (polyethylene) covers to shield the fruit from rain. Green- or white-colored covers are commonly used, but there is lack of information whether either cover might be preferable based on canopy microclimate or fruit quality. In late September, ‘Redglobe’ (in 2011) and ‘Autumn King’ (in 2012) table grapevines were covered with green or white plastic, or left uncovered, and canopy microclimate, fungal and bacterial rot incidence, and fruit yield and quality at harvest, and after postharvest storage, were evaluated. Green covers were more transparent and less reflective than white covers, and daily maximum temperature difference in the top center of the canopies of grapevine with green covers was consistently >5 °C than that of grapevine subjected to other treatments, but covers had little effect on temperatures in the fruit zones, which were not enveloped by covers. Effects on relative humidity (RH) depended on location within the canopy and time of day; RH peaked in early morning and was at a minimum in late afternoon. All cover treatments had relatively similar peak RH in south-facing fruit zones and the top center of the canopy. However, in the north-facing fruit zone, vines with green covers had higher RH at night than vines subjected to other treatments. Both covers consistently reduced evaporative potential in the top center of the canopy, but not in fruit zones. Treatment effects on condensation beneath the covers were inconsistent, possibly due to differences in canopy size, variety, or season, but south-facing cover surfaces generally had less condensation than the top or north-facing surfaces. About 0.5 inch of rain fell on 5 Oct. 2011, but no rain occurred during the 2012 experiment. In 2011, green covers delayed fruit maturation slightly, but not in 2012. Covers did not affect vineyard rot incidence, the number of boxes of fruit harvested, or postharvest fruit quality in 2011, but fruit from covered grapevine had less postharvest rot in 2012 than fruit from noncovered grapevines, even though a measurable rain event occurred in 2011 but not in 2012. In conclusion, our results suggest that white covers may be preferable to green since green covers were associated with higher temperatures in both seasons and higher RH in the ‘Autumn King’ trial of 2012, but otherwise performed similarly.

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S. Kaan Kurtural, Lydia F. Wessner and Geoffrey Dervishian

A trial in the San Joaquin Valley of California investigated how the interaction of pruning systems and mechanical shoot thinning affected canopy performance, yield components, fruit phenolic composition at harvest, and production efficiency of a procumbent cultivar in a warm climate grape-growing region. Two pruning systems and three shoot thinning treatments were arranged factorially in a randomized complete block design with four replications. The pruning methods were applied by either hand-pruning to a target of 25 nodes/m or mechanically hedging and retaining a 100-mm spur height. The shoot density treatments were applied mechanically at a modified Eichhorn-Lorenz scale, stage 17 to retain 40 or 45 shoots/m of a row, or left unthinned. The contribution of count shoots to total shoots increased when mechanical box pruning replaced spur pruning. The contribution of percent count shoots to total shoots was greatest with 40 shoots/m and unthinned treatments. The percent photosynthetically active radiation (PAR) transmission and percent canopy gaps increased with mechanical box pruning and also with the decrease in shoot density per meter of row. Berry and cluster size decreased with mechanical box pruning application. However, because mechanically box-pruned vines carried more clusters, yield per meter of row increased. There was a quadratic response to shoot thinning where berry skin phenolics, anthocyanins, and tannins decreased with the 45 shoots/m treatment when compared with 40 shoots/m and unthinned treatments. Pruning weight per meter of row and leaf area-to-fruit ratio decreased, whereas Ravaz Index (kg yield/kg pruning weight) increased with mechanical box pruning. Shoot thinning treatments did not affect pruning weight per meter of row or leaf area-to-fruit ratio. Increasing amount of PAR and percent canopy gaps by shoot thinning resulted in vegetative compensation from a sparsely populated grapevine canopy, thereby negating its purported effects. The 40 and 45 shoots/m treatments repopulated the canopy rapidly with non-count shoots thereby increasing the pruning weight per meter of row at the end of the season. In the absence of a physiological response, shoot thinning in a procumbent cultivar is not recommended. Mechanically box pruning to a 100-mm spur height and slowing down vegetative growth by irrigating to 50% of daily evapotranspiration (ETo) variance between fruit set and veraison have resulted in a Ravaz Index window (5 to 10 kg·kg−1) and is recommended for procumbent red wine grape cultivars for the region with similar or better berry skin phenolic accumulation than spur-pruned vines.

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Joseph Masabni, S. Kaan Kurtural, Dwight Wolfe and Chris Smigell

The effect of cropload (kg yield/kg pruning weight) on yield components and fruit composition of 17 eastern European grapevine cultivars was evaluated from 2000 to 2004 in a vineyard, at the research station in western Kentucky, characterized by a long and warm season. There was a cubic relationship between number of clusters retained per vine and the cropload (R 2 = 0.6374, P < 0.0001). Similar relationship was evident between yield per vine and cropload (R 2 = 0.5908, P < 0.0001). Of the observed variation in cluster weight, 28% was attributed to variation among predictions, based on the value of cropload in a quadratic relationship (P < 0.0001). As cropload increased, pruning weight per meter of row decreased (R 2 = 0.4513, P < 0.0001). However, there was very little effect of cropload on the percentage of total soluble solids and juice pH measured at harvest. Optimum cropload values fell in between 13–18 (kg yield/kg pruning weight) depending upon cultivar evaluated, based on optimum ranges for pruning weight per meter of row for optimum vine balance in the lower Midwest.

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Anil Shrestha, S. Kaan Kurtural, Matthew W. Fidelibus, Geoffrey Dervishian and Srinivasa Konduru

Weed management is an important problem faced by organic grape (Vitis vinifera) growers as there are few effective and economic options available. However, new organically acceptable weed control products have become available in recent years. Several studies were conducted to compare the efficacy of two mechanical weed control methods (French plow and Bezzerides tree and vine cultivator) with steam, and an organic herbicide (d-limonene) in organic raisin and wine grape vineyards. The experiments were designed as split plots with the aforementioned treatments as main plots with additional weed control treatments (handhoeing and no handhoeing in the raisin grape vineyards; hoeing, no hoeing, steam, and d-limonene in the wine grape vineyard) one month after the main plot treatment as subplots. The plow provided the greatest level of weed control among the treatments followed by the cultivator. The time required to hoe mechanically cultivated plots was also generally lower than the other treatments. Steam and herbicide only suppressed weeds for 2–3 weeks, and the time needed to hoe plots in these treatments was generally similar to the untreated control at all sampling dates. The mechanical treatments also were two to four times more cost-effective than steam or herbicide. Therefore, mechanical treatments were the most effective and economical weed control methods, though none of the treatments affected vine growth, midday stem water potential, petiole nitrate concentration at bloom, grape yield, or quality.

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Patsy E. Wilson, Douglas D. Archbold, Joseph G. Masabni and S. Kaan Kurtural

Canopy architecture, yield components, berry composition, pruning weight, Ravaz Index, and midwinter primary bud cold hardiness of own-rooted ‘Vidal blanc’ (Vitis vinifera × Vitis rupestris) were measured in response to balanced pruning formula treatments of 20, 30, or 40 nodes retained for the first 454 g of dormant pruning weight and an additional 10 nodes for each additional 454 g and three cluster thinning levels of one, two, and two+ clusters per shoot in 2006 and 2007. Although the pruning formula affected the distance between shoots along the canopy, and the number of count shoots per hectare, the canopy leaf layer numbers were unaffected in either year. Application of the pruning formula did not affect components of yield in either year. However, the number of clusters and yield per vine were affected by cluster thinning treatments where they increased linearly with the decrease in its severity, explaining 73% and 77% of total variance in yield in 2006 and 2007, respectively. Pruning formula or cluster thinning did not affect berry composition substantially. Cluster thinning improved the percentage of mature nodes on shoots before a killing frost in both years. Cluster thinning to one or two clusters per shoot also improved the lethal temperature killing 50% of the primary buds compared with no cluster thinning in both years of the study. Mature wood weight and total pruning weight displayed a quadratic response to cluster thinning where two clusters per shoot had the greatest weight for both, whereas pruning formula had no effect on pruning weight. Optimum fruit weight–pruning weight ratio was achieved with the 30 + 10 pruning formula and two clusters per shoot cluster thinning treatments in both years of the study. The results of this study provide valuable information for growers of interspecific hybrids such as ‘Vidal blanc’ in the lower midwestern United States as well as in other regions with long, warm growing seasons. Balanced pruning to 30 nodes per 454 g of dormant prunings and cluster thinning to two clusters per shoots optimized yield, maintained fruit composition, improved primary bud cold hardiness, and achieved an optimum fruit weight-to-pruning weight ratio of 10.0 kg·kg–1. Thus, this approach should be used for ’Vidal blanc’ in the lower midwestern United States to sustain production.

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S. Kaan Kurtural, Andrew E. Beebe, Johann Martínez-Lüscher, Shijian Zhuang, Karl T. Lund, Glenn McGourty and Larry J. Bettiga

A field study was conducted for three consecutive seasons in the hot climate of central California to assess the performance of ‘Merlot’ grapevine (Vitis vinifera) grafted onto ‘Freedom’ [Fresno 1613-59 × Dog Ridge 5 (27% V. vinifera hybrid)] during training system conversion to facilitate mechanization. The traditional head-trained and cane-pruned (CP) system was either retained or converted either to a bilateral cordon-trained, spur-pruned California sprawl training system (HP), or to a bilateral cordon-trained, mechanically box-pruned single high-wire sprawling system (SHMP). After the conversion, SHMP sustained greater yield with more clusters per vine and smaller berries without affecting the canopy microclimate. This was due to a higher number of nodes retained after dormant pruning. The SHMP canopies, compared with CP and HP; filled allotted canopy space earlier based on photosynthetically active radiation (PAR) transmitted through the canopies, populating the space allotted per vine, favoring higher production efficiency. There were no adverse effects of training systems on berry composition or flavonoid concentration, during or after conversion to mechanical management. However, experimental year effect was obvious on anthocyanin composition of ‘Merlot’ berries, increasing trihydroxylated (i.e., delphinidin-based) anthocyanins in the latter years of the experiment. Our results also provided evidence that earlier canopy growth coupled with sufficient reproductive compensating responses allowed for increased yields while reaching commercial maturity without a decline in anthocyanin content with the SHMP. Converting CP to SHMP reduced labor operations costs by 90%. Furthermore, the SHMP had greater gross revenue and resulted in greater net income per acre even when the conversion year was taken into account. Therefore, SHMP is recommended for growers within the hot climate of the central San Joaquin Valley as a means to maintain productivity of vineyards while not sacrificing berry composition at the farm gate.