June 13, 2003 at 10:29 a.m.
The day after I received these calls, there was an article in the St. Paul Pioneer Press on ash anthracnose. The article stated that ash anthracnose has made its regularly scheduled appearance in Minnesota.
In Minnesota, this occurs most commonly and severely on ash, sycamore, white oak, maple and walnut, all of which can be severely defoliated.
It is believed that the fungi are producing hormones that cause the leaves to fall off prematurely. As the fungus grows, lesions expand and grow together, creating a more characteristic anthracnose lesion. It works its way down the midvein of the leaf, into the leaf stem and eventually into the branch. Lesion color is variable from tan to dark brown on leaves. Branch cankers are small and somewhat elliptical or football shaped. This may cause the trees to lose their leaves. Since it takes about one week for the symptoms to develop, fallen leaves may appear to be perfectly healthy.
To manage ash anthracnose, dispose of the infected foliage and cankered branches by raking and pruning. Although fungicides are labeled for control, they aren't recommended unless defoliation has occurred in three of the last five years. Anthracnose will rarely kill a tree, but it will weaken it. It is very important to maintain tree vigor and prevent the tree from declining. Fertilize, water and mulch trees to protect and encourage solid growth and keep the nuisance problem of anthracnose from developing into a tree killer.
Anthracnose is a generic name for a group of diseases caused by several different fungi that cause similar symptoms. The bad news is that repeated loss of leaves over several successive years weakens the tree and makes it vulnerable to borer attack and winter injury. The good news is that each fungus has a different host, which means the anthracnose on your ash isn't going to infect your maple or oak trees nor vice versa.
More good news is that the defoliated branches will produce new shoots in midsummer, another symptom of the disease. Keep in mind that there are other tree diseases that can be mistaken for anthracnose, but if the leaves come back, it probably was anthracnose.
Do you have a problem with insects or pests invading your home or other gardening questions? Please call the Yard and Garden Line at (612) 624-4771, option #5. Leave your name and phone number and the nature of your problem and a Master Gardener will return your call. You can also access many other publications on our web site at www.extension.umn.edu.
Samples can still be dropped off at the Extension Office during regular business hours or Monday evenings from 4:30 to 8 p.m. May 5 through September.
The Chisago County Master Gardeners are working on plans to construct several gardens at the fairgrounds in Rush City. This year we will be working on the area of the Historical Society building. We are looking for donations of items to be used in these gardens such as large planters, birdbaths, trellises, statuary, benches and materials for building raised beds. Used items in good condition will be accepted. If you have anything to donate, please call the Extension Office at (888) 234-1229 and leave a message. A master gardener will contact you to determine if we can use the item.