Here’s Leif’s Yard & Garden Notes for June 3rd. Check out Leif’s articles every weekend in the Saturday Northfield News in the Home and Garden Section (Sec. C) of the paper.
This spring at the nursery we have received quite a few calls about leaf blemishes and falling leaves on ash, oak and maple trees. Back in early to mid-May we experienced a long stretch of wet and cloudy weather that allowed anthracnose fungus to grow in the leaves of many trees.
The brown and blackened portions of leaves and curling leaves result from this common fungus which usually does not kill the tree. They main problem is unsightly leaves, and a little less growth potential due to less leaf surface creating food for the tree. In another year you might see little or no anthracnose fungus damage if weather conditions are different. If you want to prevent or stop the spread to newly emerging leaf surfaces, you can spray the tree with a broad spectrum fungicide. This is usually practical only on small and medium sized trees.
I’ve also noticed some tar spot fungus on maple leaves. Again, while unsightly, these dark black spots 1/8″ to ½” in size are not a threat to the life of the tree, but a mostly cosmetic problem. Where practical, a fungicide treatment right after the tree leafs out may help prevent the problem, or you may decide to just accept some blemishes.
On ash trees, both ash plant bug and anthracnose have been active. Ash plant bugs suck juice out of the leaves, causing pin prick sized light brown spots, and leaf curling, and sometimes leaf drop. An insecticide spray right after leaves emerge may help reduce populations of this pest. Again, the problem lies in spraying large trees, and the unappealing prospect of chemical applications. If both ash plant bug and anthracnose affect a tree for many years in a row, the tree may lose vigor gradually, and eventually die. Sometimes the owner decides that enough is enough and chooses removal and planting of a less susceptible variety of tree.
One way to reduce problems with trees in the urban landscape is to diversify. By planting a wide variety of trees, there is less tendency for pest infestations. Plant diversity also protects against catastrophic and almost complete loss of the urban tree canopy should a tree disease as devastating as Dutch Elm disease work it’s way through our forests and towns. A balanced mix of Maple, Ash, Oak, disease resistant Elms, Hackberry, Linden, Thornless Honeylocust and ornamental trees will preserve much of the look and feel of a neighborhood even if a really bad tree disease hits us someday.
Plant Spotlight: Briotii Red Horsechestnut.
Largely unknown, but deserving of consideration for us in Minnesota landscape, the Briotii Red Horsechestnut is among the flowering trees that are possible to grow in our challenging climate. The huge 10″ tall red blossoms of the Briotii would certainly draw lots of attention – possibly even stopping traffic!
Producing large leaves, it creates a bit of a tropical atmosphere. The tropical theme is accentuated by the large red flowers that stand erect on sparse and coarse branches. This offers the viewer an exceptionally open and direct visual feast. Height 30′ – Width – 40′. Zone 3.
Labels: Yard and Garden Notes by Leif
