Two-Wire Horizontal Trellis for Thompson Seedless Raisin Production

¹ University of California Agricultural Extension Service, Fresno County, Fresno, California.

Field trials were conducted in 4 Fresno County Thompson Seedless raisin vineyards to compare a 22-inch horizontal trellis about 48 inches aboveground with a standard one-wire trellis at the same height. Raisin yields, average berry weights, soluble solids, and total acid determinations were taken for 3 years.

Raisin yields were usually significantly increased with the horizontal or flat-top trellis. In one test, increased yield was partially due to higher soluble solids. The increase in yield was probably due to a greater number of berries which would result from more clusters and/or larger clusters.

The increase in the number of berries might be due to more mature renewal fruit canes. Shoots used for renewal canes are supported by the wires in a horizontal trellis and thus are better exposed to light than with a one-wire trellis, where these shoots hang downward and are often shaded.

Expanse of the leaf area is greater with a horizontal or wide-top trellis than with a single wire trellis. The horizontal trellis also spreads and supports the shoots, which should provide for better leaf exposure.