INCREASING BERRY SIZE OF IDAHO ORGANIC TABLE GRAPES
A USDA Specialty Crop Grant administered by the Idaho State Department of Agriculture
Performance Report 9/30/2011

I. Activities Performed

All the planned sizing activities were performed during the summer; second and third reporting periods 2011 starting with "shoot thinning" in late June, followed by "cluster thinning," "cluster stretch," "bloom thinning," girdling, "cluster tipping," sizing spray, and ending with berry measurements in early September.

1. Shoot thinning: The number of shoots for the Alborz should be reduced to 20 to benefit berry size and quality. Better control needed next season to maintain the shoots at or below the maximum goals.
2. Cluster thinning: Hand thinning, leaving one cluster per shoot, proved to be important. Next season Alborz should be thinned from 20 clusters per plant to 16, and Glenora thinned to one cluster per shoot with maximum of 24 clusters per plant.
3. Cluster stretch: "Stretching" the clusters with Gibberellic Acid (GA) was beneficial and improvements to this technique should be implemented next season. The Red Globe responded negatively to stretching with GA. Glenora needs to be stretched next season.
4. Bloom thinning: The one-time application of the heavier dosage of the GA was the most effective and economical means of bloom thinning used in the project. Hand-brushing each cluster worked (ideal for gardeners) but was too time consuming and lacked consistency.
5. Girdling: Full circular cuts around the trunk were more effective than the partial 2/3 cuts. Hand-girdling was the most expensive sizing technique used in the project. Next year a closer comparison should be done on the GA sizing technique with and without girdling.
6. Tipping: Tipping was successful in achieving the largest berries on clusters to fit into the standard 2 lb. bag for packaging. Next season the Glenora should be tipped since larger berries will be pursued.
7. Sizing:Repeated spray applications of GA was the most influential activity to maximize the berry sizes. Kelp increased the size of the berries but not enough to meet the standard goals.
8. Berry measurements: The resulting berry size was determined by averaging 10 berries from each row. One cluster was used from 5 plants and one berry from the top and one from the bottom of the cluster was measured. Tony McCammon, University of Idaho Horticulture Educator, verified the size differences of the Emeralds while the grapes were on the vine. John Davis, commercial table grape grower with "The Dirt Doctor" inspected the Emeralds, Alborz, and Red Globe when the berries were at full size.

II. Breakdown of Specifications on Activities Performed by Grape Varieties (see attached PDF spreadsheet).

III. Summary of Results by Grape Variety

1. Emerald: The most impressive accomplishments of this project to date have been with the Emeralds. They normally produce very large clusters with small round berries. The technique used in the Blue Row significantly increased the berry size and developed interesting and appealing oval-shaped berries. Furthermore, each cluster easily fitted the standard 2 lb zip bag. This packaging improvement is ideal for commercial table grape growers. Next season the accent should be on fine-tuning the Blue Row technique plus try to meet the size goal without the expensive girdling procedure.
2. Alborz: The sizing techniques used on the Yellow Row achieved the size goal set for the Alborz grape. The clusters, however, did not color well. One advantage of the Idaho Alborz is their full, rich red color. Next year the procedure used on the Yellow Row should be modified so that the berry size increase is more impressive. A new goal of 20 mm is realistic. Emphasis, however, should be on reaching a "full color" with the larger berries.
3. Glenora: The size goal was not met but the plants responded well to the sizing techniques. Glenora normally has very small berries and are popular because of their uniqueness. The berries resemble blueberries and have a delightful special taste. It is worth trying to impress the market with a larger, blue grape. The project results indicate that Glenora should be able to handle a more aggressive sizing methodology and realistically reach the high size goal of 19 mm. Importance should also be placed on developing a full rich color for the much larger than normal berry.
4. Red Globe: This variety responded very negatively to the sizing methods used in the project. The control row had impressively large and uniform berries simply by not over-cropping, and most importantly, by cutting each cluster in half at berry set. Red Globe are naturally large grapes because they are seeded. Unfortunately, the seeds are the reason "Globes" are no longer popular or grown locally. This variety should be eliminated from this project and accent directed to the remaining commercial red, green, and blue seedless grape varieties.

IV. Participation by Project Partner and Other Experts

Partner John Davis, The Dirt Doctor, inspected the project grape varieties twice. He was consulted on all phases of the operation. John stated that his goal with most of his table grapes is growing 2 lb. clusters. Therefore, a sub-goal was set for the project of producing the maximum size berry for 2 lb clusters. Regarding the Red Globes, he firmly concluded "that whatever (Rocky Fence Vineyard, Inc.) was doing, STOP!" Red Globe, as previously mentioned, should be removed from the project. He was also impressed with the Emeralds, and thought the Alborz needed better color.

Tony McCammon, U of I Horticulture Educator, toured the project. Mike Medes, Lead Partner, relied heavily on Tony to research sizing information especially on canopy management.

Dr. Essie Fallahi, U of I Pomologist, suggested hand brushing to bloom thin the Emeralds, shoot and cluster thinning techniques, and canopy management.

Peter Rathan, factory representative for Gibberellic Acid supplier, and Tom Tankersly, Helen Chemicals Co., both suggested mix rates for GA.

V. Problems, Delays

Rocky Fence Vineyard, Inc. experienced severe Powdery mildew in the vineyard including the project's Emeralds and Alborz. Consequently, the planned Field Day was cancelled. The grapes were not in show condition and the lead partner had to dedicate the vineyard labor to controlling the mildew problem. The field trip is rescheduled for next September, 2012. Red globe should be removed from this project. They are no longer a commercial grape in Idaho and respond negatively to advanced sizing techniques. They grow large naturally and the size and quality can be improved by simple thinning and tipping demonstrated during the first year of this project.

VI. Future Project Plans

Pertinent information from this performance report will be distributed this next reporting period to Ariel Agenbroad, U of I Extension Educator; Jennifer Miller, NW Center for Alternative to Pesticides; and to Tony McCammon, U of I Horticulture Educator. Mike Medes, Lead Partner, will assist them in communicating the findings of this project to the public and table grape growers including the Snake River Table Grape Growers Association.

Over this winter, 2011-2012, the lead partner will consult with the project partner, support authorities and agricultural experts to formulate an improved work plan for next year. By the end of the second reporting period, Mike Medes will provide a breakdown of the revised activity specifications to meet or exceed the project goals in the 2012 season.

Emerald Grapes 2011 Target Berry Size: 19 mm Maximum Size Achieved, (Row "Blue"): 21 mm (Tony McCammon, U of I Horticulture Educator)
Alborz Grapes 2011 Target Berry Size: 19 mm Maximum Size Achieved (Row "Yellow"): 19.5 mm; (John Davis, "The Dirt Doctor")
Glenora Grapes 2011 Target Berry Size: 19 mm Maximum Size Achieved (Row "Blue"): 18 mm
Red Globe 2011 Target Berry Size: 21 mm Maximum Size Achieved, (Row "Control"): 24 mm