Directions for Collecting Petiole Samples

DIRECTIONS FOR COLLECTING PETIOLE SAMPLES

SELECTING THE VINES:

1. SELECT AN AREA containing at least 30 vines of the variety to be sampled if possible. These 30 vines should be representative of: (a) a problem area, or (b) the average of the vineyard. The final fertilizer suggestions will apply ONLY to the area represented by the selected vines.
2. SELECT 30 VINES to represent the sample. If more than one area or block is being sampled, give each area a REFERENCE NUMBER and record this NUMBER for future reference. If you have the fields identified with either a number or a letter, this may be used for the reference number. When the diagnosis sheet is returned, it will refer to this field number/name.

COLLECTING PETIOLE SAMPLES:

1. TIME OF COLLECTION. Collect petiole samples 70 - 100 days after bloom (this is typically late August or early September). Samples should not be taken after harvest.
2. MATERIALS NEEDED. A 2 or 3 pound stamped bag is provided in the kit.
3. PROCEDURE. Select the youngest mature leaf from a bearing primary shoot which is well exposed to light. The youngest mature leaf is somewhat difficult to define. It is the youngest leaf on the shoot to obtain full leaf size and is best identified by having brown pubescence on the underside of the leaf instead of white pubescence. SELECT 2 leaves from each plant. REMOVE AND DISCARD the leaf blade and keep ONLY the petiole. The 60 petioles constitute the sample. Place the 60 petioles in the paper bag and mark the IDENTIFICATION NUMBER on the bag.
4. WASH THE PETIOLES before they wilt to remove spray residue and dust. This may be done by dipping the petioles in a weak detergent solution (Dreft, Tide, etc.) and then rinse quickly with clean water. Don't allow the petioles to remain in the detergent or rinse water for more than one minute. Shake the excess water from the petioles and place them loosely back into the bag. With the tops of the bags open, allow the petioles to dry at room temperature until they become crisp.