Weeds consume valuable resources that include water, they reduce harvest efficiency and they harbor insects, pathogens and vertebrates, said Kurt Hembree, UC weed specialist for Fresno County.

And their presence can be critical during certain times in establishment of a vineyard.

Hembree looked at pruning weights, trunk growth and bunch counts in plots where weeds were permitted to grow for various lengths of time compared to weed-free plots.

“The longer the weeds were let go, the greater the effect on recovery of the vine and rodent damage,” Hembree said. “Even at three to six months, there was damage in terms of reduced growth. If weeds were there more than nine months, we had critters move in that chewed the bark. A weedy period of only three months reduced pruning weight and trunk growth for two years.”

Long canes not good

Matthew Fidelibus, a UC researcher on table, wine and raisin grapes, cautioned that allowing canes to grow too long can cut down on fruitfulness in some raisin varieties and can lead to too much shade.

He added that soluble solids (brix) in clusters can decline closer to the tip of the cane. His studies are looking at 15 and 20 node canes.

Fidelibus said some growers have canes with 40 to 45 nodes and “are over-cropping the cane, much less the vine.”

Internode length varied among varieties studied, including DOVine, Thompson Seedless, Fiesta and Selma Pete.