2003 Season Review: Ornamental Plant Disease Problems

Paul Pecknold, Professor, Botany & Plant Pathology, Purdue University

Wet, cool weather during the time of early leaf development resulted in a high incidence of shade tree anthracnose on ash, sycamore, oak and maple. Ash and sycamore showed moderate defoliation, however affected trees recovered without significant problems. As usual, apple scab was also evident during the spring period, but did not reach the epidemic levels that it has over the past few years. However, scab-susceptible crabapples showed extensive leaf yellowing and drop by the middle of June. Other prominent leaf diseases included Guignardia leaf blotch of horse chestnut and buckeye; powdery mildew of lilac, rose and susceptible shade trees; and cedar hawthorn rust. Of interest was the lack of blister leaf of oak and cedar quince rust, two diseases that have been fairly prominent over the past few years. Sphaeropsis tip blight continues to devastate pine plantings throughout the state; especially Austrian and Scotch pines. A less obvious effect of the early wet conditions was poor root growth, especially for trees and shrubs in poorly drained locations. The resulting plant stress caused scorch, dieback/decline, and chlorosis to be common occurrences on many ornamentals. From this, it is anticipated that we will see an increase in Phytophthora and Pythium problems over the next few years.