Fertilizing grapes

June 13, 2014

As we all see our grape canopies exploding with growth at this time of year it is important to consider that the vines have their greatest need for nutrients to support shoot development and blossom fertilization. Without knowing your soil or petiole values, specific recommendations are hard to offer, but here are a few items to consider:

Nitrogenmay only rarely be needed in most mature vineyards, but young vines can often benefit from modest applications. Generally no more than 30 lbs actual N per acre, and more likely 20, will suffice. Let your experience with the vines dictate this, and if you have sufficient growth and crop yield, lay off the nitrogen. Calcium or Ammonium nitrate are good sources.

Potassium may often be deficient, and is most often seen on basal leaves as marginal yellowing or reddening of leaf tissues.

Boron is important for fruit set and calcium transport in grapes, and is frequently deficient in Vermont soils. However, it is very easy to over apply boron, which may lead to toxicity. All nutrient applications should be based on soil and/or plant tissue analysis, but this one is especially important. Boron is often supplemented in vineyards with Solubor, which contains 20% boron by weight. Amounts applied per acre are typically low, 1-3 pounds boron (or 5-15 pounds Solubor) per acre, and may best be applied in irrigation or herbicide water. Foliar applications of boron are very good at correcting deficiencies in the short-term, and may be applied with pest management sprays, If using pesticides in water-soluble bags (like Rally), the boron will prevent dissolution of the bags, so they should be thoroughly mixed until the bag is completely dissolved before adding boron to the tank. Typical rates of foliar boron should be no more than 0.5 pounds of boron per (or 2.5 pounds of Solubor) acre per application.

Magnesium deficiency is common in many vineyards, and is typically pronounced on many of the cold-hardy cultivars. Magnesium is an essential component in chlorophyll, and deficiency symptoms often appear as interveinal chlorosis (yellowing, or sometimes reddening) at leaf margins and between leaf veins. Symptoms are most readily observed on older leaves. Short-term correction of magnesium deficiency can be had with foliar applications of magnesium sulfate (Epsom salts) applied at 5 to 10 pounds per acre. This may be applied with pest management sprays. These sprays may be made 2-3 times at two-week intervals beginning immediately after bloom. Correction of magnesium deficiency in soil may be performed with application of 300 to 600 pounds per acre of magnesium sulfate. If potassium is also low sul-po-mag fertilizer will supply both of those nutrients. In the long-term, if soil pH is low (below 6.2 or so), then dolomitic lime may be applied .

All nutrient additions should be guided by soil and plant tissue analysis. Soil analysis may be conducted at any time, and samples sent to the UVM Agriculture and Environmental Testing Lab.

Petiole analysis may be conducted at two times, and growers should select one and stay consistent in order to compare year-to-year results. Sampling at veraison is the most common and preferred method, but bloomtime sampling may be preferable if there is a suspected nutrient deficiency that may be corrected in the present growing season.

The closest analytical lab for grape petiole analysis is the Cornell Nutrient Analysis Laboratory . Please note that they now have partnered with Agro-One Services. It is recommended that you contact them before you send any samples to confirm that recommendations will be sent along with the analysis and to confirm costs.
Video about petiole sampling: https://www.youtube.com/watch?v=8EHbojLfXek

Dr. Joe Fiola from the University of Maryland summarized bloom petiole sampling in a recent Timely Viticulture newsletter:

Tissue Sampling

Some early varieties in many vineyards are just starting to bloom. This is a critical time for taking tissue/petiole samples to assess the nutritional status of your vines. The following are some timely considerations.

  • Grape petiole analysis is recommended along with soil samples and visual observations as part of a complete nutrient management program.
  • A three year cycle of sampling all of the varieties in a vineyard is typically recommended.
  • Tissue/petiole analyses reveal the actual nutrients in the vines.
  • Tissue samples are needed when doing your mandatory Nutrient Management Plan.
  • Spring tissue sampling is a good time to sample, as you can make nutrient adjustments to the vineyard that will influence this year’s crop quality.
  • Nitrogen status is best evaluated with tissue sampling not soil sampling.
  • The time to take spring tissue samples is during full bloom of a particular variety.
  • Bloom time samples may show more accurate levels of boron and zinc, but are less accurate indicators of potassium status. Where bloom-time analyses indicate borderline potassium nutrient levels, a second sampling is warranted in late summer (70-100 days post bloom).

Some specifics on sampling:

  • Each sample should be less than 5 acres; less if there are major changes in soil or topography
  • Sample different varieties separately. Samples should represent plants that are planted on the same soil type and are of the same age, variety and rootstock.
  • Vines should represent that portion of a block that is maintained under the same cultural practices, i.e. fertilizer, irrigation and vigor control practices. For example, irrigation blocks are not to be combined with non-irrigated blocks even if they are on the same soil type.
  • Do not sample vines on the border of the block or near dusty roads.
  • For the bloom-sampling period, sample the petiole of the leaf petiole OPPOSITE the 1st blossom/cluster (see detail on fact sheet linked below).
  • About 50-75 petioles are needed from varieties with large petioles and about 75-100 petioles are needed from varieties with small petioles.
  • Gently wash petioles with water and gentle detergent, pat dry and place in OPEN paper bag (lunch, #6 size) to dry for a few days.
  • There are many labs that can analyze tissue samples (see detail on fact sheet linked below). Call the laboratory to determine current pricing and submission information. http://www.grapesandfruit.umd.edu/Grapes/Pages/SoilTestingLabs.doc


Terence Bradshaw, UVM Tree Fruit and Viticulture Specialist

Where trade names or commercial products are used for identification, no discrimination is intended and no endorsement is implied.
Always read the label before using any pesticide.
The label is the legal document for the product use.
Disregard any information in this newsletter if it is in conflict with the label.

The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM Grant, and USDA Risk Management Agency Funds.