May 28, 1999
The frequent rains this spring have created ideal conditions for the development of apple scab on crabapples. Apple scab is caused by the fungus Venturia inaequalis and is a serious problem on susceptible crabapple varieties. Scab appears on leaves as roughly circular, velvety, olive-green spots on both the upper and lower leaf surfaces. The spots eventually turn dark green to brown. Margins of these spots are feathery rather than distinct. Heavily infected leaves may curl up, become distorted in shape, turn yellow and fall off.
The ISU Crabapple Symposium
July 17, 1999
118 Horticulture Hall
Iowa State University
Presented by the
Department of Horticulture , ISU
Ah, springtime in Iowa. The crabapples have just finished regaling us with a bonanza of blooms, pagoda dogwoods and late-flowering lilacs are ready to take center stage, liquid precipitation is an every other day occurrence, and green ash in many parts of the state are raining leaflets as if it were October. So, what's new. Springtime defoliation on green ash happens every year. And the reason? Experience tells us the most likely culprit is ash anthracnose, a common disease of green ash caused by a fungal pathogen in the genus Discula. You've all seen the symptoms.
One of the best aspects of spring is the colorful floral display produced by several ornamental trees and shrubs. We wait so patiently for this spectacular spring show, that it can be a huge disappointment when it fails to occur. So why do woody plants fail to bloom? There are several factors that can contribute to a plant not blooming. The most common include