Site Selection and Plant Disease Management

It was a landscape catastrophe, the novice Kentucky gardenerís worst nightmare. The saga of establishing this landscape was a chronicle of earnest gardening labors all gone wrong. There they were, a trio of drab, wilted dogwoods, a whole bed of cankered rhododendrons, an alignment of fading, brown-tipped white pines, a denuded rose bush, and an expensive sickly specimen yellow-leaved red oak. These were perfectly good trees and shrubs when they were first planted - all purchased from the very best nurseries, and set in an arrangement that would please the most tasteful garden connoisseur. What happened? Why is this garden deteriorating?

The plants in this sad scenario are suffering from diseases that are only active because perfectly good plants have been located in sites that favor disease outbreaks. One of the essentials for creating healthy landscapes is to use principles of Integrated Pest Management, or IPM. An important IPM idea is to choose plants that will grow well in a particular landscape site, or to modify the site so that the plants will grow at their best. For it is plants that must struggle to overcome the effects of a poor growing location that are most vulnerable to diseases.

For example, Rhododendrons and azaleas require well-drained acid soil. If the soil is poorly drained, they are vulnerable to Phytophthora root rot, and if the soil is too sweet, they will turn yellow. If you want to plant those nice azaleas and rhododendrons and your soil is poorly drained and not at all acid, are you out of luck? Not entirely, for one can create well-drained beds with acid soil in which to place those plants with special needs. What about the fading white pines? They can grow well in some Kentucky locations, but they, too need acid soil. Furthermore, white pines need sandy soils, not clay soils to be at their best. If the roots are not provided with these good conditions, expect white pine decline to gradually take out the trees.

Rhododendron

Are defoliating leaf spot diseases ruining the landscape? Where were they planted? If plants such as crabapples, dogwoods, roses, and other plants prone to leaf diseases such as scab, black spot or powdery mildew are planted in shady locations or if they are planted too densely so that good air movement and ventilation is not possible, the planting site has been poorly selected.

The gardener who wishes to create a healthy landscape will remember some landscape IPM principles and choose the right plant for the right site or modify the site before choosing the desired plant. Plants placed in a location that does not suit them will be stressed, vulnerable to attack from diseases and may require more care.

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