To overcome rootstock-scion incompatibility, two Chelan trees on Mazzard rootstock were planted next to the original tree on a Mahaleb rootstock and entwined to grow into what is now in effect a Mazzard-rooted tree.
California cherry growers must contend with variable production, says a California orchardist.
Yields can range from ten tons one year to two-and-a-half tons the next, depending on the weather and fruit set, said Jeff Colombini, president of Lodi Farming Company. "We struggle to get three to four tons per acre a year."
Lodi Farming has grown cherries since the late 1960s, but also grows walnuts, apples, and olives.
Inconsistent cherry yields are due to a variety of factors, Colombini said. In some years, low chilling hours in the San Joaquin Valley result in erratic and light bloom. Another factor is poor weather during pollination, he said. But probably the most common reason for the inconsistent crop volume is rain during harvest that reduces the marketability of fruit.
Fluctuating crop size makes long-term planning difficult. After a light crop year, some growers may prune less the following year so they can hang a larger crop to make up for the small crop the year before, he added. Lighter pruning can adversely affect fruit size.
The predominant rootstock used in the state for cherries is Mahaleb, a precocious rootstock that produces good-sized fruit, he said. "But the disadvantage is that Mahaleb likes to die, especially if you get a good, wet spring."
Years ago, Mazzard was the rootstock of choice, Colombini remarked. He remembers 20-foot tall cherry trees grown by his grandfather and father that required ladders with extensions so workers could reach the fruit. "The workers even used hooks to pull the limbs lower for picking," he said.
But in recent years, Mazzard has fallen out of favor in California because growers found more precocious rootstocks. Also, they are trying to grow shorter trees.
While Colt rootstock is resistant to the stem pitting virus (tomato ringspot virus) and does well on sandy soils, it is too vigorous for most growers, Colombini explained.
They learned the hard way about rootstock/scion incompatibility. In 1999, they planted a relatively new variety Chelan on Mahaleb. A year after planting, they visited a new Chelan/Mahaleb block in Washington State owned by Bob Harris and were alarmed to see his trees dying because of scion/rootstock incompatibility.
To rectify their situation in Lodi, instead of replanting they chose to plant two Mazzard/Chelan trees six inches apart on either side of the Mahaleb tree, and entwine the three trees together. A few trees didn’t take, but very few died and the experiment worked, Colombini said.
"Now, they are literally Mazzard trees," he said. "It was a nurseryman’s dream because he actually sold us three trees instead of one for one block."
Their cherry pruning strategies include mechanically topping trees in late summer, making thinning cuts to the top of the tree only, and keeping the centers cleaned of suckers. Hydraulic chain saws are used when they make big cuts. In some years, they’ve had to back off pruning in some blocks to get "fruit set back in there," he explained. All pruning is done from self-propelled pruning towers.