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R. Paul Schreiner

Grapevines grown in low-phosphorus (P) soils typical of western Oregon vineyards may benefit from additional P applied to the canopy using foliar sprays. Alternatively, vines may be negatively affected by foliar P sprays because lower root colonization by arbuscular mycorrhizal fungi (AMF) could reduce uptake of other nutrients or increase vine water stress. The impact of foliar P sprays on vine growth, vine nutrient and water status, AMF colonization, and fruit yield and quality was studied in two ‘Pinot noir’ vineyards with a history of low vine P status over 3 years. Three foliar spray treatments [phosphite, phosphate, water (control)] were applied to vines three times each season using a standard air-blast sprayer at a commercial vineyard. Two foliar spray treatments (phosphite, water) were applied using a hand sprayer at a smaller research vineyard. Phosphite sprays increased leaf blade and petiole P concentrations and reduced arbuscular colonization of roots at the research vineyard, but neither phosphate nor phosphite significantly affected these variables at the commercial vineyard. Foliar P sprays had no effect on vine growth, vine water relations (leaf water potential and stomatal conductance), yield, or fruit quality attributes at either site. These results indicate that there is little benefit to spraying the canopy of grapevines with P, even in vineyards with low P status.

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R. Paul Schreiner and Jungmin Lee

‘Pinot noir’ grapevines were grown in a pot-in-pot system using a red-hill-soil where volumetric soil water content (θv) was carefully controlled. Four-year-old vines were supplied with one of two irrigation regimes (wet or dry) between véraison and fruit maturity and the experiment was repeated over 2 years. From véraison to harvest, vines in the wet treatment received irrigation whenever θv approached ≈15% maintaining leaf water potential (Ψleaf) above –1.0 MPa. Vines in the dry treatment received irrigation when θv approached 11% to 12% and experienced significant water stress (Ψleaf ≈–1.4 MPa) before water was re-supplied. Vines were destructively harvested at véraison and at fruit maturity to determine biomass and nutrient content in the current season’s above-ground tissues. Fruit yield, maturity indices, and must nutrient composition were measured at maturity. Irrigation did not influence vine growth in either year nor did it influence yield or fruit maturity indices. Irrigation also had no influence on leaf, whole cluster, or must mineral nutrient concentrations. Vine growth, yield, and nutrient status in leaves and musts varied by year. Vegetative growth was greater in 2007 than 2008, whereas yield and cluster weights were greater in 2008. Also in 2008, whole clusters obtained a greater proportion of dry matter and nutrients after véraison when differing irrigation treatments were imposed. Nonetheless, irrigation did not affect must chemical composition. These findings suggest that periodic post-véraison water deficits that are moderate to severe have little effect on berry nutrient and sugar accumulation in ‘Pinot noir’ cropped at typical levels for this variety.

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R. Paul Schreiner and Carolyn F. Scagel

An interplay between carbon and phosphorus is known to regulate root colonization by arbuscular mycorrhizal fungi (AMF); however, it is unclear whether plant C or plant P status plays a bigger role in controlling the abundance of arbuscules (the primary site of nutrient exchange in AMF symbiosis) in roots. In this study, ‘Pinot noir’ grapevine (Vitis vinifera) was grown in an unsterilized vineyard soil and colonized by indigenous AMF in two experiments, where photosynthetic capacity (defoliation or shading) and shoot nutrition (foliar fertilizer) were manipulated. Temporal changes in root colonization by AMF and plant growth and nutrition were determined. Foliar fertilizer application increased P and K uptake, but reduced Cu uptake in both experiments. Decreasing the photosynthetic capacity of shoots due to defoliation or shading rapidly reduced arbuscules in fine roots (within 7 to 14 days). In contrast a 3-fold increase in shoot P status from foliar fertilizer only reduced arbuscules after a more prolonged time (28 to 56 days). The combination of shading (15% of full sun) and foliar P application reduced arbuscules more than shading alone within the first month, whereas foliar P use in full sun had no influence on arbuscules within a month. Returning plants to full sun after 28 days in shade resulted in a resurgence of arbuscules in roots regardless of plant P status. Arbuscules in grapevine roots are regulated by the interaction between plant C and P status, such that high shoot P reduces arbuscule formation or maintenance more when combined with reduced plant photosynthesis. This indicates that grapevines do not reduce AMF nutrient transfer as an immediate response to elevated shoot P as long as plants are maintained in a high light environment.

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R. Paul Schreiner and Carolyn F. Scagel

Grape growers rely on tissue tests of leaf blades or petioles for routine monitoring of vine nutritional health and for diagnosing potential nutrient deficiency or toxicity. There has been a long-standing debate as to which tissue better reflects the nutrient status of vines. A comparison of leaf blade and petiole nutrient concentrations was carried out to investigate which tissue better relates to vine growth, yield, and must nutrient responses of ‘Pinot noir’ grapevines to varying levels of nitrogen (N), phosphorus (P), and potassium (K) supply using data from a pot-in-pot vineyard over 4 years. Leaf blades and petioles were collected at 50% bloom and 50% veraison in each year and N, P, and K concentrations were assessed as predictors of leaf area at veraison, pruning mass at dormancy, yield, and must nutrient concentrations at fruit maturity. Data from commercial ‘Pinot noir’ vineyards were also used to investigate the relationship between leaf blade and petiole N concentrations with must N levels. Results indicated that leaf blades were superior to petioles in predicting vine growth, yield, and must yeast assimilable nitrogen (YAN) responses across a wide range of vine N status at both sampling times. Leaf blade N was a better predictor than petiole N in predicting YAN using data sets from both the pot-in-pot vineyard and commercial vineyards. Relationships between leaf blade and petiole concentrations of P and K and vine response variables generally did not differ and both tissues appeared to be equally effective in predicting P and K effects on growth, yield, and must P or K levels. Although petiole P was slightly better than leaf blade P at bloom in predicting must P levels, and models including both leaf and petiole K simultaneously as predictors relied only on leaf K. For all three nutrients, sampling at bloom and veraison had a similar predictive strength for response variables. Based on these findings, we recommend using leaf blades as opposed to petioles for diagnosing the N, P, and K status of ‘Pinot noir’.

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R. Paul Schreiner, Carolyn F. Scagel and John Baham

The nutrient uptake and distribution patterns for N, P, K, Ca, and Mg were determined in mature (23 to 24 year old), field-grown, rainfed grapevines (Vitis vinifera L. `Pinot noir') growing in a red hill soil in Oregon in 2001 and 2002. Biomass, nutrient concentrations, and nutrient contents of all plant organs, including roots, were determined on 14 sampling dates over 2 years. There was no seasonal change in the standing biomass of primary roots (fine feeder roots), small woody (<4 mm diameter) or large woody (>4 mm diameter) roots. Trunk biomass also did not change during the 2 years, but all other vine organs showed significant seasonal changes in biomass. The rate of N uptake was greatest at bloom, when remobilization from reserves was also high. Nitrogen was also taken up after leaf fall in 2001, but not in 2002, when an early frost occurred before soil moisture recovery by fall rains. Uptake of N, K, and Ca from soil was similar between years, even though canopy demand for N and K was greater in 2002 (significantly larger crop). Phosphorus uptake from soil was lower in 2002 than in 2001, which was most likely due to the drier conditions in 2002. A greater quantity of canopy N, K, and especially P was supplied from stored reserves in the drier 2002 growing season. About 50% of canopy requirements for N and P were remobilized from reserves in the trunk and roots by the time of fruit maturity in 2002. Only 15% of canopy K and <5% of canopy Ca or Mg came from stored reserves in 2002. Our findings indicate that nonirrigated grapevines grown in Oregon acquire nutrients from soil earlier in the growing season and have a greater reliance on stored reserves of N and P than reported in previous studies from other growing regions. Replenishment of nutrient reserves occurred to large extent during the postharvest period. Rainfed vineyards in Oregon may require different nutrient management practices than irrigated vineyards, since low soil moisture may limit summer uptake of P.

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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.