Spring 2010 - A Chink in the Armor

by Anthony C. Arnoldi, Board-Certified Master Arborist WI-0102B

Spring 2010 Newsletter in Adobe PDF format Beautiful crabapple trees, adorning prominent viewing points for all to see and handsome evergreens of pine and spruce to show off against the pure white snow are some of the best features of a glowing landscape, a landscape with interest and health.

Such landscapes can be challenged by adversarial fungi, however. Fungal lesions of apple scab ruin the looks of susceptible ornamental crabapples.

Tip blight and needlecast fungi can slowly turn evergreens brown and cause thinning that diminishes their beauty and their ability to screen out undesirable views.

At Wachtel, we are able to protect these trees from the fungi through the use of very carefully timed sprays that place specific materials on the newly forming foliage. When the foliage is soft and new, it is vulnerable. It is also at a time of year when frequent rains will enable infection. Fungi “know” this and send out their infecting spores at this time of year. The infection time “window” varies with the disease and the year, but generally, lasts from the spring through mid-summer. Fungicide products form a protective coating that can stop the infecting spores. Because of added waterproofing agents known as spreader-stickers, the coating can last up to three weeks. Usually, two or three of these sprays are applied approximately three weeks apart. Taken together, these sprays form a continuous barrier to the spores during the entire infection window. Effectiveness is quite good if this “armor” is in place for the entire siege.

Sometimes the armor is not in place as long as it should be. If only one of the prescribed sprays are ordered to be done, it is done at the beginning of the infection window – the most important part of the program. Once the coating has worn down however, infection can breach the armor and damage can begin. Unless a single spray (“round”) was prescribed by your arborist (because of significant disease resistance contributed by certain cultivars), one spray should not be relied upon for sufficient disease control. In view of recent budgeting considerations, many have ordered only one spray round. This may actually prove to be counter-productive as disease control could be lost.

If the disease is allowed to re-infect many new leaves, needles or branch tips, this resurgence could undo previous efforts. Worse, it could allow damage that threatens its health enough to question the tree’s ability to function well in the landscape, or even its ability to stay in the landscape.

We encourage discussion with your Certified Arborist about how to best prioritize treatments and thus use your tree care dollars in the most cost-effective way.

© Copyright 2009 – Wachtel Tree Science & Service, Inc.

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