CU-developed apple rootstocks survive extreme winter

By Aaron Goldweber

GENEVA, N.Y. -- Last winter a "perfect freeze" in New York's Champlain Valley destroyed nearly 25,000 apple trees, resulting in losses projected to be as high as $2.5 million. Out of this devastation comes the encouraging report that two new Cornell-developed rootstocks show strong resistance to unusually harsh conditions.

"The new rootstocks in our trial tolerated this cold snap and survived extremely well compared to those in growers' orchards on standard rootstocks," said Terence Robinson, associate professor in the department of horticultural sciences at the New York State Agricultural Experiment Station (NYSAES) in Geneva. Among five rootstocks showing the most hardiness were Geneva 30 and Geneva 16, which exhibited 96 and 92 percent survivability, respectively.

In commercial orchards, apple varieties are grafted onto rootstocks that help growers control tree size and productivity, and manage pests, diseases and environmental stress. During a 20-year period from the mid-1970s through the mid-1990s, two Cornell researchers working at the NYSAES, James Cummins and Herb Aldwinckle, developed the apple rootstocks for tolerance to fire blight, a devastating bacterial disease.

"Their survival this past winter demonstrates another important characteristic -- extreme-cold-hardiness," said Robinson, who specializes in tree fruit systems. He and Kevin Iungerman, extension associate with Cornell Cooperative Extension's Northeast New York Commercial Fruit Program, have a five-acre, 3,200-tree rootstock trial comparing 16 rootstocks at Chazy Orchards in the Champlain Region.

Planted in 2001, trees in the trial were in a unique location to show the effects of the 2003-04 winter, which was one of the harshest of the past 50 years. The stress of bearing the large apple crop of 2003 coupled with mild temperatures in the fall and early winter made the apple trees extremely vulnerable to conditions that followed. A late-December and early-January thaw was followed by rains that saturated the ground and eliminated the snow cover that usually insulates tree roots. In the space of 24 hours, the mercury plunged to extreme subzero temperatures and stayed there. The freeze penetrated the soil and damaged root systems, especially those of trees that were 3 to 5 years old.

According to a survey taken in June by Iungerman, 24,632 trees were lost coming out of the 2003-04 dormant season. This number is on the rise now that the consequences of summer stress and cropload are showing. Trees that appeared to survive are now seen as lost. The survey showed the freeze hit younger and more productive trees hardest.

The 25,000 trees lost represent only about 5 percent of Clinton County's apple trees, but they were predominantly young orchards representing the recent investments by growers and the future production of the area. Growers will have to make considerable new investments to replant the lost orchards.

The economic impact of the loss will not be clear for some time, but Robinson has some numbers that can be used as a starting point. "Each tree that is 3 to 5 years old and is killed represents a $50 loss if it was McIntosh and a $100 loss if it was Honeycrisp," he said. "Even working with the assumption that all of the lost trees were McIntosh, the current losses represent $1.23 million. And that doesn't include the cost of replanting." This monetary loss includes the original tree cost and the lost production time.

To avoid the same level of damage in the future, growers are advised to choose wisely among commercially available rootstocks when replanting.

Three Canadian rootstocks in the trials also showed strong survival rates. These included Ottawa 3, Vineland 1 and Vineland 3.

"Growers may have to leave their plots open while they wait for commercial stock to become available, but that small amount of time will be a big help in the future of the farm," said Robinson.