Foliar testing for assessing vineyard nutrition

Early veraison is the most accurate time of year for sampling grape petioles to determine vine nutrient status.

There is a poor relationship between soil and plant nutrient levels. In general, foliar analysis is more reliable than a soil test for judging the nutrient status of the vine. The best option is to test both the soil and the petioles and compare results to determine not only the nutrient levels in the soil, but how they are being utilized by the vines. Petiole testing can actually save growers money by allowing the application of fertilizers according to how they are utilized by the plant, instead of according to levels present in the soil.

We will soon be at veraison, which is considered to be the most accurate time of year for assessing grapevine nutrient status. Detailed information classifying the element levels in grape petioles (deficient, below normal, normal, above normal and excessive) can be found in Table 1 below.

Table 1. Specific element recommendations for grapes from petioles.

Element*

Deficient

Below normal

normal

Above normal

Excessive

Nitrogen %

0.3-0.7

0.7-0.9

0.9-1.3

1.4-2.0

2.1+

Phosphorus %

0.12

0.13-0.15

0.16-0.29

0.30-0.50

0.51+

Potassium%

0.5-1.0

1.1-1.4

1.5-2.5

2.6-4.5

4.6+

Calcium %

0.5-0.8

0.8-1.1

1.2-1.8

1.9-3.0

3.1+

Magnesium %

0.14

0.15-0.25

0.26-0.45

0.46-0.80

0.81+

Manganese (ppm)

10-24

25-30

31-150

150-700

700+

Iron (ppm)

10-20

21-30

31-50

51-200

200+

Boron (ppm)

14-19

20-25

25-50

51-100

100+

Copper (ppm)

0-2

3-4

5-15

15-30

31+

Zinc (ppm)

0-15

16-29

30-50

51-80

80+

*Values may differ among species for optimal growth. Values from leaves will vary significantly. For petioles taken between July 15th to August 15th. Source: Fertilizing Fruit Crops, Ohio State University Extension; bulletin 458

The University of Minnesota (UMN) has a good factsheet on how to do petiole sampling in vineyards as well. Here are some suggestions from both Cornell and UMN on how to do it right. Tissue analysis should begin once the vine starts producing (usually the third year) and be repeated yearly until the yields stabilize and fertilizer needs are determined. Mature vines can be sampled every 2 to 3 years. A single sample should represent no more than 5 acres. Make note of previous cropping levels.

  • For samples collected at veraison, select petioles from the most recently developed mature leaf.
  • For each sample, use 25-50 typical vines.
  • Be consistent. For routine sampling, collect samples at the same growth stage each year- either bloom or early veraison.
  • Vines should be of the same age, variety and rootstock, growing on a relatively uniform soil of the same fertility. If these conditions are not met, divide the vineyard into uniform blocks and sample separately.
  • Monitor the same areas in specific vineyards or blocks each year. Flag specific rows within a block and revisit them yearly.
  • Collect 60 to 100 petioles from 2 to 3 leaves on the vine. Don’t pick more than one leaf per shoot. Keep the petiole- discard the leaf blade.
  • Don’t collect leaves for sampling if they have disease, insect or mechanical damage.

Cornell University has a short YouTube video about how to collect petiole samples from vineyards and prepare them for the testing lab. View the video on YouTube.

Here are some of the recommendations from the video: Detach each petiole from the leaf blade immediately after picking and place in a paper bag. Label each sample and keep your own record of the following: varieties sampled; vineyard block where the samples are collected; sampling date; and conditions of vineyard. Before sending samples in for testing, allow them to dry at room temperature in a well-ventilated place until they are crisp. The petioles can be washed to remove spray residue and dust if they are dirty. Dip them in a weak detergent solution (2-3 cups of deionized water with a couple of drops of Tide, etc.) for one minute or less, then rinse with clean water one minute or less. Blot dry with paper towels or a clean dish towel and place them loosely in a paper bag to dry.

References:

Petiole Analysis as a Guide to Grape Vineyard Fertilization Dr. Carl Rosen, Professor, Department of Soil, Water and Climate, University of Minnesota.

Lake Erie Regional Grape Program, Vine Nutrition and Soils.

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