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Levi Fredrikson, Patricia A. Skinkis and Ed Peachey

Five vineyard floor management treatments were evaluated for effects on weed control over two growing seasons in an establishing ‘Chardonnay’ (Vitis vinifera) vineyard in the Willamette Valley of Oregon. Four cover crop management treatments and an unplanted treatment were compared to assess the effects on vine row and alleyway weed coverage and densities of broadleaf and grass weeds. A winter annual cover crop was grown in alleyways of the cover-cropped treatments and was mowed in spring. The mowed residue was managed as follows: 1) residue transferred in-row as mulch representing the industry practice of “mow-and-throw,” 2) residue transferred in-row as mulch at three times the rate of the earlier treatment, 3) mowed residue incorporated into alleyways, and 4) removal of mowed cover crop residue from the vineyard. Weed coverage was assessed visually within a 1.0-m2 quadrat placed randomly in alleyways and vine rows, and densities of broadleaf and grass weeds were determined by counting and grouping individual weeds within each quadrat. Vine row weed coverage and densities were lower in treatments with residue mulch at each sampling date in 2009 and 2010, with nearly 100% in-row weed suppression by the heavier mulch treatment. Alleyway weed coverage was lowest when residue was incorporated and highest in the unplanted treatment at some sampling dates. Grass weed densities in alleyways were similar between treatments at all sampling dates. Results of this study indicate that in-row mulch of cover crop residues at fresh weight densities of 2.5–15.0 kg·m−2 provided effective weed control in a non-irrigated vineyard in western Oregon. Also, alleyway weed coverage may be reduced through incorporation of mowed cover crop residues.

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R. Paul Schreiner, Patricia A. Skinkis and Amy J. Dreves

The grape rust mite [Calepitrimerus vitis (Acari: Eriophyidae)] is an important pest of grapevines (Vitis sp.) in grape-growing regions around the world. A rapid method for extracting eriophyoid mites was adapted from earlier studies to provide integrated pest management (IPM) consultants and commercial growers with a practical, efficient, and reliable tool to monitor grape rust mites in vineyards and nursery stock vines. The rinse in bag (RIB) method allows quick extraction of mites from young shoots or from leaves using 35% to 70% ethanol or isopropanol in a sealable plastic bag. The RIB method recovered ≈85% of grape rust mites from single leaves in the first rinse. The method is useful to estimate grape rust mites on young shoots (≤10 cm length), although recovery of grape rust mites (average ranging from 35% to 81%) was lower because of a higher density of trichomes on young shoots as compared with leaf samples. The RIB method was not effective to assess grape rust mites within dormant buds, so a separate method using a blender to disrupt tissues and extract mites in alcohol was developed. The RIB method was used to determine grape rust mite abundance with leaf symptoms in commercial vineyards and nursery stock vines. The earliest visible symptom of grape rust mite damage on leaves in the summer was the development of stippling that is distinct from the type of damage caused by other grapevine pests. The stippling is described as numerous clear zones of small diameter (resembling pinholes) that are visible when a leaf is backlit. The severity of stippling was related to the number of grape rust mites present on leaves, with >600 occurring on leaves with severe stippling symptoms. In commercial vineyard case studies, the RIB method was used over two seasons and revealed that grape rust mite populations remained on leaves until postharvest, and foliar applications of wettable sulfur reduced grape rust mite populations on leaves.

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Alison L. Reeve, Patricia A. Skinkis, Amanda J. Vance, Jungmin Lee and Julie M. Tarara

Vigor and crop level management are important practices for premium wine grape production. The implications of crop thinning ‘Pinot noir’(Vitis vinifera L.) vines of varying vigor were investigated in the Willamette Valley of Oregon in 2011 to 2013 to better understand the relationship between canopy size and yield within the framework of a cool-climate, premium production wine grape vineyard. To manipulate vigor, a competitive grass cover crop (Festuca rubra L.) was grown in both (Grass), alternating (Alternate), or neither side of the flanking alleyways (Tilled). Vines within each vineyard floor treatment had two crop levels applied, including cluster thinning to one cluster per shoot (Half Crop) or no crop thinning (Full Crop). Grass treatment had reduced leaf area and leaf nitrogen (N) concentrations during all years compared with Tilled treatments. Leaf photosynthesis was also lower in Grass treatments despite more light in the canopy interior. Grass treatments had lower yield than Tilled treatments in 2 of 3 years and lower yeast assimilable nitrogen (YAN) concentrations in fruit every year. There was limited impact of floor treatments on total soluble solids (TSS) and pH. Reduced yields through cluster thinning had limited impact on vegetative growth but increased TSS and pH, in 2 of 3 years. There were few floor management by crop level interactions in any year. Grass effectively reduced vegetative growth to moderate vigor levels with cane weights between 20 and 40 g. Using a competitive grass cover crop may be an effective strategy to reduce excessive vine growth and require less labor in canopy management and crop thinning without compromising basic fruit ripeness, although YAN levels need to be monitored.

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Alison L. Reeve, Patricia A. Skinkis, Amanda J. Vance, Katherine R. McLaughlin, Elizabeth Tomasino, Jungmin Lee and Julie M. Tarara

Growers of high-end ‘Pinot noir’ wine grapes (Vitis vinifera L.) commonly reduce yield by cluster thinning with the goal of increasing fruit quality; however, there are no objectively defined yield targets to achieve optimum fruit composition. Canopy leaf area relative to fruit yield can affect total soluble solids (TSS), and recommendations have been established for warm wine grape production regions. However, the relationship between leaf area and photoassimilation differs among climates and training systems. Leaf area to yield (LA:Y) ratios developed in warm, arid regions may not be suitable for cool, wet regions such as western Oregon. A 3-year field study was conducted to elucidate relationships between canopy to yield ratios and berry composition for ‘Pinot noir’. Vegetative growth and fruit yield were manipulated through competitive cover cropping and cluster thinning. Growth was manipulated in three ways: perennial red fescue (Festuca rubra L.) was grown in 1) both (Grass), 2) one (Alternate), or 3) neither (Tilled) of the alleyways flanking the vine row. Within each vineyard floor treatment, fruit clusters were thinned to one per shoot (Half Crop) or vines were left unthinned (Full Crop). Floor management influenced both canopy size and yield because of altered vine nitrogen (N) status. Effects of crop load on berry components were not always consistent between the crop load metrics used [yield to pruning weight (Y:PW) ratio or LA:Y]. In 2 years, TSS reached a maximum at similar LA:Y; however, this did not necessarily produce optimum TSS. Yield had the greatest influence on pH and total anthocyanins (ACY) in the highest yielding, coolest year. Crop load metrics were not reliable predictors of TSS because of the dominant effect of seasonal variation. Relationships between canopy to yield metrics and other berry components were partially explained by tissue N, photosynthetic photon flux (PPF) through the cluster zone, and/or yield. Cluster thinning to adjust yields may not alter source to sink relationships or canopy to yield ratios enough to overcome ripening limitations in cool climates. Only one wine vintage had sensory differences with Alternate-Half Crop and Alternate-Full Crop wines ranked high quality and Tilled-Half Crop and Tilled-Full Crop wines ranked low quality by both consumer and winemaker panels. Therefore, cluster thinning may have limited impact on wine sensory properties.