Tulare County

Researchers routinely measure berry weight when evaluating the effect of a cultural practice or pest management strategy on fruit development. Berry weight is easy to determine: a sample of one to two hundred berries is randomly collected per plot, counted, weighed, and then berry weight is reported as grams per berry.

However, growers, fruit brokers, and retailers usually characterize berries by diameter or length rather than berry weight. For example, they would describe a box of Thompson Seedless as having berries mostly 11/16 inch in diameter rather than as having mostly 5 gram berries. There is a strong linear correlation between berry weight, diameter, and length. Tables 1 to 5 give berry weight and corresponding values for berry diameter and length for Flame Seedless, Thompson Seedless, Red Globe, Fantasy Seedless, and Crimson Seedless. Also given is the number of berries per pound for different berry weights.

Berry weight and size are affected by numerous factors including gibberellin, girdling, soil type, irrigation, rootstock and the weather. The average berry weight of Flame Seedless, Thompson Seedless, and Crimson Seedless ranges from 4 to 6 grams. Fantasy Seedless berries are larger ranging from 6 to 8 grams, and Red Globe berries are 10 to 13 grams.

The berry shape of these five varieties varies from round to cylindroidal. Flame Seedless is round with berry diameter the same as berry length. The Red Globe berry is almost round but berry length is slightly greater than diameter. Thompson Seedless table grapes, Fantasy Seedless, and Crimson Seedless have elongated berries.

Cultural practices that increase berry diameter result in a significant increase in berry weight and yield. Table 6 summarizes theoretical yield response to an increase in berry diameter.