Final Report: This is year 2 of a 2 year proposed project for the Washington Grape & Wine Research Program
Date: 25 May 2017

Project Title: Phosphorus Nutrient Management and Comparative Studies Between P-Deficient and Virus Affected Grapevines

Principal Investigator(s): Joan R. Davenport
Collaborator(s): Dr. Naidu Rayapati, Ste. Michelle Wine Estates, Mercer Canyon Ranches
Project Budget Number: 13C-3319-4596

I. Project Summary: Non-technical, 1-3 succinct paragraphs that cover the following points:

  1. What is the current issue and why does it need researched?
  2. What are the basic methods and approaches used to collect data that are used to inform target audience?
  3. What ultimate goals does the project hope to achieve?

Red wine grapes in Washington State often show red discoloration in leave which could be the result of low phosphorus (P) in the vine, a nutritional disorder, or a virus infection with either Leafroll [GLRD] or Red Blotch [GRBD].

When a vineyard is low in P, there are two approaches to applying fertilizer to increase the amount of P in the vines: either soil or foliar application. Because of the chemical make-up of soils used for vineyard production in irrigated Washington, it is unclear if soil applications would be effective, thus this study is designed to compare not only the amount of P needed to remediate a low P vineyard, but also to see if soil or foliar application are equally effective.
Although there is no research that links the red leaf discoloration in virus infected red wine grapes, supplemental P fertilizers are being tested on these vineyards to see if it alleviates some or all of the symptoms.

The ultimate goal of the project is to provide guidelines for P fertilizer management in wine grapes in irrigated Washington.

II. Materials, Methods and Experiments Conducted to Meet Stated Objective(s):

Vineyards that had been soil and tissue tested for P status and virus were chosen for this experiment. There were four vineyards in the study, a non-infected Cabernet Sauvignon plus one with Leafroll, and a non-infected Merlot and one with Red Blotch. Using guidelines from studies on P content of grapevines, P was applied either through direct spray to the foliage (foliar application) or direct application to the soil (simulated as a drip fertilizer application) three times during the growing season (bloom, late fruit set, and veraison) for seasonal total applications of 0, 12, 25 and 37 lbs/A P in replicated plots.

Leaf and soil samples were collected to monitor plant P status at veraison. At harvest, fruit was hand-picked and clusters counted to estimate yield as well as the yield component cluster weight. A fruit subsample was retained to analyze quality parameters as well as fruit P concentration. All vineyards were harvested in 2014, however in 2015, Cabernet Sauvignon site 2 was commercially harvested prior to our harvest.

This was year two of what was intended to be a three year project. While the intent was to conduct this project for three years, the project was conducted on 4 different fields for two growing season, giving a total of eight site years which we have concluded is sufficient to address this trial.

III. Major Research Accomplishments – include the following points:

  1. Explain major activities completed (include timeline)
  2. Describe specific objectives that were met.
  3. Describe significant results achieved and any conclusions (both positive and negative).
  4. Discuss key outcomes realized from this project.

Read more by downloading the full report above.

Pest & Disease // Soil Health // Vineyard Nutrition // Viticulture //