Conversion to Mechanical Pruning in Vineyards Maintains Fruit Composition while Reducing Labor Costs in ‘Merlot’ Grape Production

Abstract

<jats:p>A field study was conducted for three consecutive seasons in the hot climate of central California to assess the performance of ‘Merlot’ grapevine (<jats:italic>Vitis vinifera</jats:italic>) grafted onto ‘Freedom’ [Fresno 1613-59 × Dog Ridge 5 (27% <jats:italic>V. vinifera</jats:italic> 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 (<jats:italic>PAR</jats:italic>) 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.</jats:p>

Proximal Sensing of Soil Electrical Conductivity Provides a Link to Soil-Plant Water Relationships and Supports the Identification of Plant Water Status Zones in Vineyards

“…Previous research suggested that to reach the maximum level of maturity, a leaf area to fruit ratio between 0.8 to 1.2 m 2 /kg was required for a single-canopy trellis system (Kliewer and Dokoozlian, 2005). In our study, there was no difference of leaf area to fruit ration between two water status zones and the first year had overall leaf to fruit ratio lower than 0.8 m 2 /kg consistent with previous findings that mechanically managed vineyards in warm regions may ripen fruit to technological maturity at lower values (Kurtural et al, 2019).…”

Optimal Ranges and Thresholds of Grape Berry Solar Radiation for Flavonoid Biosynthesis in Warm Climates

“…Dormant pruning weight was collected during the dormant season (16 December); and crop load was calculated as the ratio between yield per vine (kg) and the pruning mass (kg) of each vine. Labor operations costs and gross income per hectare were calculated based on yield and net returns per hectare (California Department of Food and Agriculture, 2020; Kurtural et al, 2020) and methods presented elsewhere (Kurtural et al, 2019). Anthocyanin productivity (unit cost to produce anthocyanin) was calculated as reported by Cook et al (2015).…”

Mechanization of Pruning, Canopy Management, and Harvest in Winegrape Vineyards

“…Dormant pruning is one of the most labor-intensive practices in vineyards 1,8 . It is estimated that about 80% of all labor operations costs in vineyards can be attributed to the combination of pruning and harvesting practices 27 .…”

“…Research in interior and coastal California 1,8,27,[36][37][38] has shown that using one of the pruning management strategies described above would save between 60% to 80% of labor operation costs per acre compared to manual pruning alone 1,8,27,38 . In a study comparing traditional Guyot cane pruning, manual spur pruning and complete mechanization in Madera, CA researchers found that converting traditionally farmed systems will save 80% of labor operations cost without any differences in berry primary and secondary metabolites.…”

“…In the case of downward growth habit grapevines, the canopy is quickly repopulated thereby negating any effects of higher amount of solar radiation received, resulting in poor berry development. In cultivars such as Syrah 23 , Merlot 1 and Zinfandel 29 mechanical box-pruning followed by mechanical shoot thinning resulted in less than ideal yield:pruning weight ratio and poor anthocyanin accumulation 23 . Crop load management in procumbent grapevines may be limited to pre-pruning pass with a mechanical pruner and hand shoot removal follow up and mechanical harvest.…”