Maple Motion Sickness

Submitted by Paul Hetzler, ISA Certified Arborist

No one wants to be told they have a weathered complexion, but many trees this summer, especially maples, are looking a bit worse for the wear as a result of conditions earlier in the season. “Leaf tatter” is a term used to describe foliage which may be torn and bedraggled-looking, distorted, sometimes with blackened spots or zones. It can easily look like a disease or mysterious pest is ravaging the tree.

As tree buds open and young leaves begin to unfurl, they can get damaged by a couple of different situations. One of the main causes of leaf tatter is a late frost that is just cold enough to freeze the folded edges of the baby leaves, yet not kill the whole thing. When it finally opens all the way and hardens off, there are slits or holes along the lines where the leaf was folded. Sometimes the leaf cannot open fully, and may remain partly cupped.

The other case is when we get strong wind events while tender young leaves are still expanding. Depending on wind strength, this physical abrasion can result in leaves that are a little beat-up, to ones that are utterly shredded. Usually this damage is not as neat or uniform as compared to that caused by frost injury. Leaf tatter may be alarming to see, but generally does no real harm.

No one needs to be reminded that this year set all-time records for total rainfall as well as for consecutive days of rain. As a result, the “tenderized” margins of tattered leaves became waterlogged. Normally, foliage does not become water-soaked because of a natural wax on the upper and lower leaf surface of all leaves. But torn edges have no such barrier. Moisture seeped in, the soggy tissues died, and opportunistic decay fungi started to break down the dead areas. To add insult to injury, tiny insects called pear thrips may have colonized some damaged leaves as well (they are not specific to pears).

Another thing adding to unruly tree complexions this year is the proliferation of seeds. In the case of maples, these are in the form of “helicopters,” winged seeds known to tree-nerds as samaras. As crazy-wet as this season is, 2018 was dry to the far opposite extreme. Woody plants determine the number of flowers, and therefore seeds, it will make in any given spring during the previous summer. If things are peachy, it will set a modest number of flower buds for the next year. If life is hard, it will make few or none.

However, if conditions are so dire that the life of the tree is at risk, it will use much of its stored energy reserves to produce an exorbitant amount of flowers. This paradoxical response seems to be an evolutionary mechanism to preserve the species even if it kills the parent tree. The plethora of seeds, many of which are turning brown as they dry and prepare to fall, gives maples an even more “weathered” appearance.

There is a something called anthracnose, which is unrelated to anthrax, and is not as bad as it sounds. Caused by a number of different fungal pathogens, anthracnose is worse in very wet years, and affects many deciduous trees and shrubs, mostly ones already in a weakened state. Anthracnose causes dead or necrotic zones bounded by major veins, and usually leads to early leaf drop. Simply rake up and destroy affected leaves, which is how the disease overwinters.

Otherwise, relax if you think you have a sick tree. It is just having a bad-complexion year.

Paul Hetzler is a member of ISA-Ontario, the Canadian Institute of Forestry, and the Society of American Foresters.