By Janelle Daberkow,
Horticulturalist
High temperatures, accompanied by sunny or partly cloudy conditions between March 13 and March 20, will be conducive to emergence of Colopterus truncatus. This is one of the two principal nitidulid beetle species that transmits the oak wilt fungus. The lack of snow cover during the winter of 2011-12 and higher than average temperatures for the month of March, are the basis for the earliest calendar date shifting the risk status of spreading oak wilt from “safe” to “high” risk in Minnesota. This means that pruning of all oak trees should cease for 2012.
This updated status for the oak wilt risk season will begin 10 days earlier than ever before: Based on recent weather and the flight activity of the beetles that transmit the fungal pathogen, the high risk period begins Sunday, March 18.
There are three risk season timeframes for oak wilt in Minnesota: High Risk, Low Risk and Safe. They refer to the probability that oak wilt will infect a tree. High Risk months in Minnesota are April, May and June. Low Risk months are July, August, September and October. Safe months are November, December, January, February and March. Avoid any wounding during the High Risk (and as much as possible during the Low Risk) period. No pruning and no construction activities should take place near the oaks. If a tree is wounded during the High and Low Risk months, seal the wound quickly (within 15 minutes) with one coat of shellac (preferable) or a water-based paint. If oak wilt is in the area, it’s the High Risk season, and the wounding is unattended for more than 15 minutes, the probability of infection rises dramatically. If oak wilt is established in an oak woodland, it is especially important to prevent the spread of the pathogen through root grafts. This is done by cutting through the connecting roots using a vibratory plow. This will need to be done by a professional, preferably a Certified Arborist and if done correctly is a very reliable technique to reduce the amount of oak wilt spread.
For more on oak wilt and oak wilt risk status in Minnesota please visit: www.myminnesotawoods.umn.edu/2010/03/oak-wilt-risk-status-in-minnesota/.
Oak wilt risk status updated to high, stop pruning oak trees now
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