Grapevine Petiole Sampling Standard Method
Gill Giese, NMSU Extension Viticulture Specialist
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| Figure 1. Grape shoot with leaf location to obtain the petiole sample |
Figure 1. Left: grape shoot with the 6th leaf from the shoot tip circled in red. In the drawing on the right the petiole is still attached to the leaf blade.
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| Figure 2. Grape leaf blade with petiole that is kept, processed and submitted. |
1. The petiole, or leaf stem, is submitted to the lab for analysis. Petioles are ideal to handle and store. They do not breakdown/mold as readily as do leaf blades. Petioles are convenient to dry and ship.
2. At collection, break off the petiole where it attaches to the stem/shoot. Immediately separate the petiole from the leaf blade to prevent translocation of sap from petiole into leaf blade. Discard leaf blade.
3. Timing and location: select and collect petioles attached to the leaf opposite a fruit cluster at full bloom. Grapevines are judged to be in “full bloom” when about 60-75% of flower caps are shed. Use the most recent, fully mature leaf. Recently mature leaves are typically located at the fifth to seventh node counting from the shoot tip (refer to Figure 1 above).
4. Collect petiole samples at the same time year to year and at the same time of day (morning preferred).
5. There is no one “best” time to collect petiole samples, as there is no single time that is diagnostic for all possible nutrient disorders and deficiencies. However, nitrate peaks in most grape varieties at bloom and nitrogen is the nutrient most often deficient and most frequently applied. Also, testing for nitrogen in the soil yields less than robust results due the fact that nitrogen is very mobile within and readily leaches from the soil. Consequently, testing for soil nitrogen will indicate different amounts of N at different times of year.
a. Potassium levels decline from bloom to veraison, when grape berries begin to soften, develop sweetness and change color.
b. Boron, if low at bloom, can recover as temperatures warm late in the season.
c. In some regions, i.e. France, California and Oregon, the most recently fully developed leaf is sometimes collected in August and used for analysis.
6. If possible, avoid sampling vines on border rows or adjacent to dusty roads.
7. Gently wash freshly collected petioles with mild detergent water bath (Dreft baby detergent is often used or a detergent that does not contain phosphorous). Transfer petioles to a water rinse and then finish with a final rinse using distilled water. Rinsing is intended to remove dust and/or chemical spray residue. Finally, transfer the washed and rinsed petioles to paper towels to dry. After the petioles are completely dry…place the dried petioles in a paper bag, allow to dry in the open bag for a few days prior to shipment to the lab.
8. Collect separate samples by cultivar and block.
9. Collect 1-2 petioles per vine. The total sample should contain 30 -100 petioles...depending on the size...some petioles are quite large and 30 will be sufficient. But the lab techs cannot complete the analysis if there is not enough biomass.
10. Alternately, collect 5-10 petioles from 10-20 representative vines and flag these for
small fertilizer trials or repeat samples.
11. If you apply nutrients or want to track what is going on in the vineyard over the season,
a 2nd petiole sample can be collected at 70-100 days post-bloom, at veraison (see description of veraison above).
Table 1. Target values for soil, bloom petiole and late summer petiole samplings. THE TARGET VALUES IN THE TABLE ARE GENERATED FROM GRAPE REGIONS OUTSIDE OF NEW MEXICO AND ARE PROVIDED AS ESTIMATES ONLY!
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| Late-summer petiole | |||
Nitrogen | —z | — | 1.2 - 2.2 | % | 0.8 - 1.2 | % |
Phosphorus | 20 - 50 | ppm | 0.17 - 0.30 | % | 0.14 - 0.30 | % |
Potassium | 75-100 | ppm | 1.5 - 2.5 | % | 1.2 - 2.0 | % |
Calcium | *500 - 2000 | ppm | 1.0 - 3.0 | % | 1.0 - 2.0 | % |
Magnesium | 100 - 250 | ppm | 0.3 - 0.5 | % | 0.35 - 0.75 | % |
Boron | 0.3 - 2.0 | ppm | 25 - 50 | ppm | 25 - 50 | ppm |
Iron | 20 | ppm | 30 - 100 | ppm | 30 - 100 | ppm |
Manganese | 20 | ppm | 25 - 1000 | ppm | 100 - 1500 | ppm |
Copper | 0.5 | ppm | 5-15 | ppm | 5 - 15 | ppm |
Zinc | 2 | ppm | 30-60 | ppm | 30 - 60 | ppm |
References:
1. Kamas, J. 2014. Growing Grapes in Texas, Texas A&M University Press, College Station, Texas.
2. Wolf, T.K. editor. 2008. Wine Grape Production Guide for Eastern North America. NRAES, Cooperative Extension Ithaca, NY.
Labs:
1. Waypoint Analytical: http://waypointanalytical.com/PlantTissues
2. Fruit Growers Lab: http://www.fglinc.com
3. A&L Labs Lubbock, TX: http://al-labs-plains.com/
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