COLUMBUS, Ohio — Nursery tree stock throughout Ohio is suffering from bark splitting, a common injury sustained under cold conditions. But the severity and scope of the damage is costing nursery growers millions in lost revenue, and is driving Ohio State University researchers to investigate other potential causes behind the problem.
Hannah Mathers, an Ohio State University Extension nursery and landscape specialist, said that the problem was first reported to Ohio State's C. Wayne Ellett Plant and Pest Diagnostic Clinic in 2003 and has since increased in severity, causing major stock losses for nurseries, and a conundrum for researchers.
"Some growers have reported losses exceeding 5 percent of their inventory of 3,000 to 4,000 trees per nursery. At an average cost of $125 per tree and the number of nurseries reporting problems, the stock losses in the state have been staggering," said Mathers, a researcher with the Ohio Agricultural Research and Development Center. "I always felt that bark splitting was something that was easy to diagnose. But what is happening here is unusual."
Bark splitting, or cracking, occurs on thin-barked trees and most commonly on the southwest side of the trunk, where a combination of bright sun and snow cover causes rapid freezing and thawing and subsequent cracking on exposed bark. The problem, however, is that the injuries are also occurring on other areas of the bark. In addition, the injuries are happening throughout the year, not just winter, possibly indicating that there are other causal agents.
"Although very cold temperatures on sunny days are thought to be the cause of bark splitting, other researchers believe that improper pruning may be a factor," said Mathers. "The improper pruning creates a wound that can lead to trunk cracking, especially when herbicides or systemic postemergents are used shortly after any pruning or the removal of tree suckers has occurred," said Mathers.
She added that researchers are no longer recommending the practice of tree sucker removal with glyphosate-containing producets for that very reason. Mathers and her colleagues have received a one-year $14,000 Horticultural Research Institute grant to study the effects of pre-emergent herbicides on root and shoot hardiness and whether those chemicals are a contributing factor to tree injury.
Speculation abounds that the use of tree guards may also contribute to the bark splitting problem. Mathers said that research has shown that the use of plastic trunk guards — designed to reduce injury — may actually be intensifying the problem.
"The guards inhibit the cold acclimation process in the fall if put on too early in the growing season, and can result in an increased incidence of cold injury in the spring," said Mathers. "Not only do the plastic guards reduce cold hardiness in the guarded region, but they also increase the moisture content in that region, resulting in increased susceptibility to mechanical injury and thus splitting caused by ice formation under the guard."
Mathers said that another problem that looks similar to bark splitting could be Internal Bark Necrosis (IBN), a condition that occurs when soil conditions are acidic or is related to manganese toxicity.
Mathers will be presenting information on bark splitting during an Abiotic Workshop at the Ohio State University Extension Short Course and the Ohio Nursery and Landscape Association "CENTS" show on Jan. 23, 2006, from 1 p.m. to 3 p.m. For more information on CENTS, log on to http://www.onla.org/cents.html.