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Tissue sampling grapes at veraison – too late or getting in early for next season?

16 January 2012 | Categories: grapes, sampling, plant tissue, veraison

While petiole sampling of grapevines at full bloom is the most common method of tissue analysis employed by viticulturists and advisors, it is by no means the only time that tissue samples can be taken.

Sampling can also be carried out at veraison or berry colouring / softening.

There are several reasons why sampling could be carried out at veraison.

- Sampling was not carried out at full bloom  (70-80% capfall) so there is no gauge as to how the vines are faring except for visual observation.

- Any nutrients which were in the low or just adequate range at flowering can be re-checked as can the response to any treatments applied to adjust for such situations.

- Potassium was low or borderline but not deficient at flowering and another check on tissue K is required. This will determine if K deficiency is   developing at fruit ripening, a more common occurrence. Mg could also fall into this category.

- Other problems or symptoms may have manifested themselves between flowering and veraison and a check is warranted.

 -If excess Na or Cl problems in the tissue are suspected.

There may still be time to apply corrective treatments for next season in the post-harvest period – this is the case for sub-tropical areas and there may be a small window of opportunity in temperate areas.

Having decided there is a need or benefit to be gained by tissue sampling at veraison, the next choice we have to make is which part to sample – the petiole or the leaf blade as calibration data exists for both.

Australian researchers, Weir and Cresswell, as well as many other researchers recommend petioles be used when checking K, Na or Cl levels. In the case of Na and Cl, these elements accumulate in the petioles even though the leaf blades may show the symptoms. If B toxicity is suspected, sampling leaf blades is recommended. For a general look at overall tissue levels either petiole of leaf blade analysis can be used.

Having decided on petiole or leaf blade, the next thing to consider is the position of plant part to sample as it differs depending on whether you choose petioles or leaf blades (different origins of the data meant different position of plant parts were selected by researchers).

Petioles - Sample petioles from recently mature, fully expanded leaves located 6 to 7 leaves from the shoot tip.  Collect one or two petioles per vine.  Sample from minimally shaded, normal growing shoots on both sides of the vine canopy. Collect 60 – 100 petioles per sample.

Leaf blades (without the petiole) - Leaf blades (lamina only) from leaves opposite bunch at base of shoot. One leaf per vine from a single variety x rootstock planting. Collect 50 leaves per sample.

Then of course there is trouble shooting when an unknown problem has shown symptoms. Here you may have to forget the good advice above and instead sample the affected plant part from affected vines and the matching plant part on non-affected vines for comparison.  When there are no reasonable clues as to what the problem is, it is suggested both leaves and petioles be sampled and analysed separately, that is leaves and petioles of affected plant parts and leaves and petioles of matching plant parts from non-affected vines – four samples in all to give best chance of solving the problem. You do not have to wait until veraison in such situations – sample when the abnormal appearance is observed. Here you will be relying not so much on published standards but on the comparison between good and poor samples for the solution to the problem.

To avoid the need for trouble shooting, tissue sampling should be conducted regularly over a number of years as part of the management program.

So while it is true that sampling at veraison is too late for the current season, it could be argued it is getting in early for next season, much earlier than sampling at next season’s full bloom.