June 23, 1995

Apple Scab Resistant Crabapple Varieties

The cool, wet weather this spring has created ideal conditions for the development of apple scab on susceptible crabapple varieties. Scab is caused by the fungus Venturia inaequalis. Initial symptoms are small olive-green to black spots on the foliage. Eventually the leaves turn yellow and fall from the tree. Highly susceptible crabapple varieties may lose most of their foliage by midsummer. The heavy defoliation will weaken the trees somewhat, but will usually not kill them. The damage is mainly aesthetic. Heavily defoliated trees are unattractive.

Ash Rust

Ash rust is an easy disease to diagnose. The causal rust fungus, Puccinia sparganioides, produces bright yellow-orange spores on infected leaves, petioles, or stems. Diseased tissues are also often swollen and distorted.

The spores produced on ash infect marsh and cord grasses, the alternate hosts of this rust fungus. The fungus overwinters on these grasses.

The disease is rarely destructive enough to warrant control measures. Severe rust in successive years can weaken trees, especially young trees, and make them more susceptible to winter injury.

Cottony Maple Scale, Again

Cottony maple scale was discussed this time a year ago when a localized outbreak occurred in northwest Iowa (between Kossuth and Green Counties). Another very localized outbreak has been reported this year in Black Hawk, Polk, Jasper, Marshall and Poweshiek Counties.

NOTE TO COUNTY EXTENSION OFFICES: Detailed information on cottony maple scale has been sent to the counties named. Other county offices that have reports of scale outbreak are encouraged to contact Extension Entomology for a copy of the electronic file on this insect.

Hackberry Witches'-Broom

A number of hackberry samples showing symptoms of witches'- broom have been arriving in the Plant Disease Clinic. As the common names implies, witches'-broom is characterized by a dense clustering of twigs. Each "broom" consists of numerous short twigs that arise close together. The cause of witches'-broom is not known with certainty, but it is thought that it caused the interaction of an eriophyid mite and a powdery mildew fungus.

Installing Interlocking Concrete Pavers, Part One

Interlocking concrete pavers are versatile sections of compacted concrete that are used to pave paths, patios, driveways and steps. They are available in numerous colors and shapes and simulate bricks, tiles, cobblestones and granite blocks. Pavers are available from garden centers and nurseries, lumber yards, hardware stores and discount stores. Because of their uniformity, pavers fit together easily and their installation is a common do-it-yourself project.