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Ash anthracnose recently observed.

Ash anthracnose is a recurring problem. This year (2014), it was a little later than normal, but has finally arrived.

Some ash trees have recently lost their leaves because of a problem called ash anthracnose.  We see this in spring, especially following wet weather, as we’ve experienced lately.  Additional symptoms can include black blotches on leaf margins, causing leaf distortion, and small purple-to-brown spots in the middle of leaves. The leaf symptoms may not necessarily be visible on fallen leaves, since the infection that triggered leaf drop is likely on a petiole or other inconspicuous location.ash anthracnose.  Notice the dead leaflet margins, and the curved growth of the leaflet(s).

Treatment with fungicides is usually not warranted. Fungicides are only effective as a preventative treatment, usually as leaves are expanding.  Treating trees now can prevent mid-season infections, but infection is more common in the wet spring, rather than the drier summer.  For most large trees, fungicide applications aren’t very practical.  However, there are cultural practices you can implement now, such as a light fertilization, to help reduce recurring stress on ash. “Light” fertilization would be 1-3 pounds of nitrogen per 1,000 square feet of soil surface around the tree.  If you already fertilize your lawn, then there should be more than enough to meet the tree’s nutritional needs.

The fungus that causes ash anthracnose overwinters in the upper parts of trees on seeds, on twig cankers, and on any other plant part that remains attached to twigs, so raking and destroying fallen leaves and twigs may only help reduce inoculum rather than completely eliminate it. As a result, ash anthracnose is a recurring problem on ash as long as we have wet, cool weather in the spring. Disease severity varies from one year to the next, and among individual trees.

-Joe Zeleznik

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