2003 Season Review: Ornamentals - Noninfectious Problems

Bruno Moser, Professor, Horticulture and Landscape Architecture, Purdue University

Numerous samples of both evergreen and deciduous species showing dieback and foliar browning in late summer and early fall were sent in this year. In most cases, damage was due to flooding conditions and soil waterlogging brought on by extensive summer rains and high temperatures. Foliar damage was secondary to root damage due to exclusion of soil oxygen and death of young roots, which made it difficult for them to take up sufficient water and nutrients to sustain the foliage. In many cases, these plants will continue to decline over the coming months. Many of these samples were from mature "established" plants in the landscape that had not experienced this extent of summer waterlogged soil in the past.

A large number of samples also demonstrated dieback of the shoots and death of the plants due to girdling roots and root flares being too deep in the soil. These problems occurred on both recently transplanted as well as established trees. An effort to educate both nursery growers and landscape contractors to be aware of these problems and adapt practices to minimize them in the future is underway on a national level.

Problems due to mulch being applied too deep and "volcano" mulching around tree trunks were also numerous this year. Symptoms of chlorosis and dieback due to damage to the root system and transport tissues were evident.

A number of tree and conifer samples displaying dieback and death were diagnosed as due to waterlogged soil and accompanying root system damage from automated turf irrigation systems. Although shallow rooted turf can withstand frequent irrigation, deeper rooted shade trees and conifers growing in the same landscape cannot thrive under these conditions. Dieback and death occurs from exclusion of oxygen in the root zone with damage to the root system. The maximum of one inch of irrigation one time per week and then only during dry spells needs to be encouraged to minimize this growing problem.

This past year was dominated of root system damage from waterlogged soils due to several causes, both natural and man made. Unfortunately, the effects often showed up on older "established" landscape plants.