Nebraskans, as the keepers of the Arbor Day tradition, are fond of our trees. For a prairie state, we have been known as tree planters. But there are signs across the state that the health of our forest resource is not always perfect.
Mark Harrell, forest health program leader with the Nebraska Forest Service, told a group of tree enthusiasts at a tree care workshop in Norfolk recently that chlorosis is a distinct problem around the state. Symptoms of iron chlorosis or manganese deficiency include yellow leaves with green veins, browning on the edges and between veins on the leaves and branches that dieback. Both iron and manganese are involved in the production of chlorophyll.
Chlorosis can be caused by insects, mites and diseases, according to Harrell. But nutrient deficiencies, like planting in soils that do not have enough iron available to the tree, generally cause the condition. Commonly, herbicides and other chemicals can cause problems, too.
Chlorosis-type conditions affect silver maple, one of the most popular trees growing on farmsteads and in rural communities, as well as pin oak, red maple, hybrid red maple, birch, crabapple, cottonwood, amur maple and swamp white oak. Evergreens like ornamental juniper and eastern white pine can also be affected.
"If the tree doesn't leaf out and stays dormant, it doesn't have enough energy to put on leaves in the spring," Harrell says. "If you correct the problem, it will leaf out again."
Soil conditions are the main cause of chlorosis, Harrell says. High pH soils cause micronutrients to be tied up and not available to the tree. Wet and compacted soils and places where the soil has been over-fertilized cause problems. Poor planting practices when the roots are damaged or when the tree is planted too deep can lead to chlorosis as the tree matures.
Treatments of sulfur, either broadcast or dug into evenly-distributed holes in the ground, applied below the tree's canopy in the spring or fall have been found to help alleviate chlorosis in some cases. Harrell says that improving conditions around the tree by mulching with woodchips, avoiding excess watering or fertilization, and protecting the roots from damage can correct the problems. Some trunk injections and implants have been useful, especially in pin oak trees, Harrell says.
"A better bet is to not have the problem," he says. Harrell suggests planting trees that are unlikely to suffer from chlorosis problems, like most white oaks, northern red oak, linden, hackberry, honeylocust, redbud, Ohio buckeye and Kentucky coffeetree. Instead of planting the popular silver maple around the farm or rural residence, Harrell suggests other maples like Norway. Evergreens on his suggestion list include spruce and fir.
For more information on chlorosis and other tree problems around the farm, contact Mark Harrell at the Nebraska Forest Service at 402-472-6635 or email Harrell at [email protected].