The Minnesota Department of Agriculture (MDA) announced on Thursday, Aug. 6, that emerald ash borer (EAB) was confirmed in Chisago County by the Washington County border near Manning Trail.

Two adults were discovered on a purple EAB trap. When a follow up visit was conducted, an ash tree with tunneling consistent with EAB was found adjacent to the trap.

The specimens were sent to the USDA for confirmation (standard procedure when EAB is found in a county for the first time). Assuming the beetles are verified as EAB, Chisago County is likely to be put under quarantine sometime next week. A quarantine helps prevent EAB from spreading outside of a known infested area. It is designed to limit the movement of any items, including ash trees and ash tree limbs, as well as all hardwood firewood, to help reduce the spread of EAB Chisago County becomes the ninth county in Minnesota to confirm EAB, joining Anoka, Dakota, Fillmore, Hennepin, Olmstead, Ramsey, and Winona counties. For more information about EAB, see Emerald ash borer in Minnesota. See also the MDA news release, MDA identifies emerald ash borer find in Chisago County.

Also making headlines in the gardening world is that several rust fungi are now showing up in brilliant colors on hawthorn, apple, crabapple and other trees and shrubs in the Rosaceae family. Infected leaves have bright orange, yellow or red spots. Infected fruit are covered with small tube like fungal structures, that pour out large quantities of powdery orange fungal spores. Cedar apple rust, hawthorn rust and quince rust are all caused by fungi in the genus Gymnosporangium. The Gymnosporangium rust fungi infect juniper for half of their life cycle. On cool wet spring days gelatinous bright orange spores can be found on galls or cankers on juniper trees.

Those spores cause the infections on trees and shrubs in the Rosaceae family. In turn spores produced by the Rosaceae trees and shrubs will infect junipers. As a result of this unique life cycle, leaf spots may grow slightly bigger, but no new leaf spots or fruit infections will form this year on the Rosaceae trees and shrubs.

The Gymnosporangium rust fungi rarely cause damage to the health of trees and shrubs in Minnesota.

So enjoy the colors and unique biology of these interesting fungi. No management is needed.

There are also Maple leaves that look like they have been peppered with black paint spots. This, too, is something that may look like it will kill your maple trees but it is usually harmless to the trees and it is called Tar spot. Since tar spot fungi overwinter in fallen leaves, the most effective management technique is to rake and destroy leaves in the fall. This will reduce the number of overwintering “spots” (containing the fungal reproductive structures) that can infect new leaves the following spring. Neighbors should also rake and destroy infected leaves to be effective.

Mulching leaves will destroy many of the spots before they mature, but the mulch pile should be covered or turned before new leaves begin to emerge in the spring.

Applications of fungicides are possible when high levels of infection become unacceptable, but control of tar spot is challenging, especially on mature maples.

In addition, if others in a neighborhood setting are not managing the disease on their trees with fungicides or proper sanitation, the act of spraying may be a waste of time and money.

For more information regarding gardening, you can reach me at s.dejaeghere@me.com