Wine grape growers cannot financially afford to fallow ground for too long between plantings, if at all, Walker says. Un-fallowed ground or not practicing crop rotation can result in severe biological consequences. A partial solution is to rotate grape rootstocks at replant and fallow the ground as long as possible.

How long should a grower fallow ground to decrease pests? Walker says it’s very difficult to remove all pests in a fallowed vineyard.

“It probably is not possible to get rid of all nematodes in a fallow process,” Walker said. In fact, “A short fallow period can largely reduce the population to effectively establish the vines. That is the key.”

Walker then discussed California water supplies and its potential impact on vineyard replanting.

“We will not have enough water in the next 30 years. It (water) will politically become unavailable,” Walker said.

Using overly-weak rootstocks in a relatively dry-and-warm climate is probably not the best strategy in most situations, Walker concluded.

Consultant Stan Grant of Progressive Viticulture, Turlock, Calif., shared several “take-home messages” about vineyard replanting. “Purchase CDFA certified grape vines for the vineyard,” Grant emphasized.

These vines target the elimination of specific grapevine diseases, including leafroll, fanleaf, corky bark, stem pitting, and fleck which can spread from vine-to-vine by grafting and/or vegetative propagation.

Walker’s second, take-home message was, “Replant the vineyard with a rootstock with a different parentage than the previous rootstock.”

This is critical since soil-borne inhabitants in an older vineyard may have adapted resistance mechanisms to the current rootstock.

Conduct a systematic rootstock selection process, Walker recommends. Consider pests issues first, vigor second, followed by other adaptations which could be useful.

Financial planning for replanting was discussed by the ‘banker’ on the panel —Scott Smith, chief financial officer, Silverado Premium Partners, Napa, Calif. The company has vineyards along the California coast.

“My role as a finance manager is (to determine) whether we are maximizing (financial) return from the vineyard,” Smith said. “I am not wedded to which variety is planted. I just want to make money.”

Silverado develops a five-year replanting schedule for vineyards more than 20 years old. The plan is revised annually based on the latest data. Specific vineyards can be moved up the replant schedule or pushed back.

Issues considered include overall vineyard performance, pest and disease challenges, grape quality and yield performance, and if the vineyard has a low net operating income or NOI.

At the end of the day, Smith does not want to remove a vineyard which still makes money or has a customer who really wants the fruit.

Smith concluded, “If you don’t know if the vineyard is profitable or if the variety is profitable, it’s difficult to pull the trigger on redevelopment decisions.”