Q: Why are my green ash trees dropping leaves?
The leaf drop is probably due to anthracnose. Anthracnose is a common fungal disease of trees in Iowa. Anthracnose may occur on ash, sycamore, maple, oak, walnut and other deciduous trees. Cool, rainy weather in spring favors anthracnose development. Symptoms of anthracnose vary with the tree species. On ash, brown or black blotches typically appear on the leaflets. Affected leaflets often become distorted (they tend to curl toward the blighted areas) and fall from the trees.
Fortunately, anthracnose does not cause serious harm to healthy, well established trees. The affected trees will continue to leaf out. Leaves that develop later in spring are usually not affected as weather conditions are less favorable for anthracnose development. There is no need to apply a fungicide to affected trees.
Q: What visual symptoms are associated with an emerald ash borer infestation?
Noticeable symptoms of emerald ash borer usually appear in the second or third year of the infestation or later. Emerald ash borer infested trees exhibit thinning of the leaf canopy and dieback in the crown. Also, infested ash trees may produce epicormic ("water") sprouts on or at the base of the trunk. When the adult beetles emerge, they create small, 1/8 inch, D-shaped exit holes in the bark. Extensive woodpecker activity/damage is another symptom of an emerald ash borer infestation. (Several woodpecker species feed on the emerald ash borer larvae.) Infested trees often exhibit vertical cracks in the bark due to callus tissue forming around larval galleries. Ash trees exhibiting two or more of the aforementioned symptoms should be examined closely to determine if the ash tree's problems are due to the emerald ash borer.
Should I treat my ash trees now that the emerald ash borer has been found in Iowa?
Treatments to protect ash trees from the emerald ash borer are available, but careful and thoughtful analysis is needed to prevent the spread of false information and excessive and needless use of insecticides.
Insecticide control measures against emerald ash borer should not be used unless you have healthy ash trees and live within 15 miles of a confirmed emerald ash borer infestation. As of May 2010, the only confirmed infestation of emerald ash borer in Iowa was located along the banks of the Mississippi River in Allamakee County.
Q: It's mid-May, but my rose-of-sharon hasn't leafed out yet. Is it dead?
The rose-of-sharon (Hibiscus syriacus) can be successfully grown in the southern half of Iowa. (It's hardy in USDA Hardiness Zones 5 to 9.) The rose-of-sharon leafs out late in spring. In Iowa, plants may not leaf out until late May or early June. Give the plant a few more weeks. If it hasn't leafed out by mid-June, it's probably dead. Winter temperatures of -20 F or lower can injure or destroy the plant.
Got gardening questions? Call the Hortline at 515-294-3108, Monday-Friday from 10 a.m. to noon and 1 to 4:30 p.m., or send an e-mail to firstname.lastname@example.org. For more gardening information, visit us at Yard and Garden Online, www.yardandgarden.extension.iastate.edu.