Powdery Mildew and Holes in Trees

You may have seen the silvery white coating on many of the big leaf maples in the local landscape this summer- you can thank one or more fungi for this blight. Warm, moist air favors the growth of fungus on the upper surface of the leaves. While not usually important to the tree species, this year marks the second year in a row where a strong infection will lead to partial to full loss of leaves in some trees. Thankfully, maples will naturally lose leaves in response to extreme stress (in order to conserve resources), but early leaf loss can weaken the tree’s ability to fight off other pathogens and handle climatic stress. While online forums say this pathogen is not important to tree health, looking at any new maple growth near infected trees will show otherwise as opportunistic seedlings and new sprouts will mostly die for the second year in a row. Additionally, this second year of leaf loss may be too much to handle for some trees, even more so if this happens yet again within the next couple of years. The least one might expect is the reduction of canopy growth/ size in many trees due to continued leaf loss and connected decrease of chlorophyll-based energy production. A fun fact is that western red cedar will connect to big leaf maples underground due to use of the same supporting fungus- having both trees planted near each other will cause to pair to gain resiliency (and leave those lower limbs on!). Supporting health of the trees is something a tree manager can do- make sure affected trees have enough water and good soil or cross your fingers and look for changes in canopy health.

Both holes in trees and “tree holes” are important parts of the local treed ecosystem. Individual, smaller holes in bark of the lower tree can come from one of many beetles that like to eat trees when in larval form- these range from 1 mm to 1 cm in size but just seeing them does not mean that tree decline is occurring- the number of beetles, tree production of resin, and degree of tree stress are the more important factors. Holes further up the stem are analyzed by spacing- if laid out in general lines, a sapsucker is at work; if in random profusion, a woodpecker is likely nearby. The meaning for your tree is vastly different. Sapsuckers (a subgroup of woodpeckers) often attack healthy trees in their hunt for tree sap- they like to flitter back and forth along a newly pecked line of holes, licking up the sap as it exudes out.Intense use of the tree for food will often cause decline, although serious, aerial pathogens can get in after the first hole is made and some trees may sustain multiple thousands of holes before going into severe decline. There is not much you can do except keep the birds away with a net. Random holes from a woodpecker means a degree of heartwood decay and/or boring beetles are infecting your tree. This is often a more important indicator of decreasing tree health. An effective tree owner/manager should have a Certified Arborist out to help make a tree health and hazard potential analysis if this tree is particularly loved or is of a size and/or with a proximity-to-infrastructure to make it a possible hazard.

“Tree holes” are most often found in big leaf maples who have the ability to compartmentalize a decaying portion of tree with response wood which can be water-tight and resistant to decay. Frogs, salamanders, ferns, and other creatures can be found using these often water-filled holes for a habitat which is often found high in the canopy out of reach of land animals.My favorite “tree hole” is a maple in the woods behind my house who had lost its stem near the base, regrowing upwards with a whorl of sprouts which have now healed remnants of the original stem, allowing it to hold water for about half of the year. Be careful when you find these sometimes water-filled tree aquariums. Soft creatures may be about. We may not have much in the area of water resources in the summer months but mulching properly and possibly watering your loved trees during hot droughts will often be the least you can do to prolong/ create a good life. Let me know if I can help.

Yours in Trees, Sal

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