The arrival of the “high risk period” for above ground transmission of oak wilt disease will be arriving soon. Oak trees are at high risk when the oak wilt fungal mats are present on trees killed the previous year by the disease and when nitidulids (sap-feeding beetles) are active. The onset of high risk season occurs earlier as you go farther south and varies with weather conditions. In 2012, spring (and the high risk period) arrived earlier than usual, and in 2013 it arrived later. This is why phenological indicators are better for timing the high risk time, which are when, Viburnum dentatum (arrowwood) begins to bloom, Spiraea nipponica ‘snowmound’ is in early bloom or cornus alternafolia is in late bloom. The “rule of thumb” for the Upper Midwest is to avoid pruning or wounding oaks during the months of April, May, and June. Nitidulids, carrying spores of the fungus, can be attracted to fresh wounds on oak trees. When nitidulids visit these wounds spores can be transferred to the oaks, initiating oak wilt disease infections. To avoid infection, all necessary wounds to an oak in the spring should be treated immediately with wound dressing or paint. (this is the ONLY time I will recommend wound dressing, normally a no-no!!) New symptoms of oak wilt disease usually are apparent in July and August.
If you want to know more about Oak Wilt or think your tree may be infected, check out Ilex VS Oak Wilt for more information. Feel free to post in comments or email me photos of your tree for positive ID.