Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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NOVEMBER/DECEMBER 2009
GRAPE GROWING
What causes a BUD to produce a BUNCH OR NOT?
 
The compound bud (CB) above the leaf scar (LS) at each cane node consists of a primary bud flanked by two secondary buds.
The path to fruitfulness may be visualized as a series of processes beginning at bud break the year of bud formation and ending at bud break the following year when the buds sprout and produce flower clusters:
Inflorescence initiation — Formation of flower clusters begins within each developing bud when certain tissues begin to form either an inflorescence primordia or a tiny tendril. This occurs early in the spring, when the bud is only a few nodes away from the growing tip.
Plant-mediated necrosis — Some time after inflorescence initiation in some buds, the inner section dies above an apparent abscission layer. This is clearly a physiological process initiated by the plant. The plant “decides” that a bud is not worth the metabolic cost, and “tells” the bud to die. Secondary buds on either side of the primary bud usually survive. This kind of necrosis seems to peak in the first couple of months following bloom.
Injury-related necrosis — Injurious environ- mental factors such as pathogens, heat, water stress or frost might damage a bud and cause it to eventually die.
Bud mites — A strain of the Erineum mite, Colomerus vitis, grape bud mites infest only buds. These tiny worm-shaped mites move from old to new buds during the first couple of weeks after bud break, andmultiply all year. During inspection in the following winter, we may find hundreds in a bud, where they can damage or destroy the inflorescences.
Inflorescence Initiation
The “bud” which occurs at each node on a cane is actually a compound bud typically composed of three simple buds: a primary bud in the middle and a secondary bud on each side. For most varieties, under California conditions, the primary bud may have up to three flower clusters, or inflorescences, but more typically there are two. Thompson Seedless buds usually have one inflorescence, sometimes two.
The secondary buds often have no inflorescence, but sometimes have one or rarely two; these being smaller than those in the primary bud. Inside each of the three buds is a 6- to 12-node compressed shoot with primordial leaves, flower clusters and tendrils. Buds that push at bud break become shoots.1,3,4
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BY
Devin Carroll,
Advanced Agricultural Services, Inc.
Hanford, CA
O
rape fruitfulness is defined as the percentage of buds that produce one or more flower clusters per shoot. Fruitfulness is determined within developing buds during the year prior to a crop. First, primordial clusters, called
inflorescences, either do or do not initiate in each bud. Later, the fruitful buds may be lost through plant-mediated necrosis or from various injurious processes.
Fruitfulness may be estimated prior to pruning by inspection of a sample of buds, allowing a grower to optimize fruit load by leaving the best combination of spur length and spur or cane numbers.