Cornell University researchers are seeking input from growers as they embark on an investigation into the chronic decline or rapid collapse of apple trees in young, high-density plantings.
“Symptoms of chronic decline can include poor growth, off-color foliage, and a generally ‘unthrifty’ appearance that worsens over several years,” writes Dan Donahue, Cornell Cooperative Extension Associate Tree Fruit Specialist and Tess Grasswitz, Cornell Cooperative Extension Integrated Pest Management Specialist. “In contrast, the death of a previously healthy tree over the course of just a few weeks has been termed Sudden Apple Decline (SAD) or Rapid Apple Decline (RAD).”
Although some of the tree deaths are due to fire blight or crown/root rot, sometimes the cause is unclear.
“Over the last year, the decline and demise of apple trees in orchards up to the eighth leaf has become a hotly debated topic among producers, researchers, Extension specialists and industry consultants in several states across the Mid-Atlantic/New England regions, as well as parts of Canada,” Donahue and Grasswitz state.
Researchers have begun to compile a list of potential causes, including winter injury, herbicide injury, ambrosia beetles, dogwood borer, and latent viruses.
“We cannot discount the possibility that the observed declines are due to interactions between multiple stressors, or that we are facing the possibility of a previously unrecognized problem,” they write.
Kari Peter of Penn State University has developed a comprehensive list of symptoms found in declining orchards. From this list, Extension professionals in Pennsylvania and New York have developed an online survey on apple tree decline in order to identify commonalities among affected blocks and to facilitate consistency in the collection of orchard data.
Growers who have apple blocks showing decline symptoms are encouraged to fill out the survey as the team seeks to identify potential causes and search for answers to the problem. In order to accurately complete the survey, it will be necessary to have the following information at hand: cultivar/rootstock combinations, site history (e.g. previous crops), and herbicides used. Apple decline may be due to the interaction between multiple factors. Accurate and detailed information is necessary to properly diagnose the problem.