Japanese Weeping Maple Tree

(Question)

Toronto Master Gardeners

Re: Japanese weeping maple tree
On Thursday July 14th l brought to your office, cuttings of a red and a green Japanese weeping maple trees.
The red maple is about 15 years old. It is about 7 feet high with a foliage spread of 8 feet diameter. It receives about 2 hours of mid-morning sun. There are a large birch tree and a blue spruce tree to the south.
It is in full sun from noon.
Until 3 summers ago, it boasted healthy, luxuriant foliage not unlike the green maple in the photo. The green maple is 25 feet north. It was planted 2 1/2 years ago. The red maple foliage was sparse, anemic, dull wine for the past 2 years. Around mid-July the leaves began to shrivel and curl up like a cocoon. In October these leaf cocoon turned orange. However not the brilliant orange of past years.
Past week the leaves started to shrivel again.
What is the cause? Is there a remedy?
I have attached photos of the trees.

Your advice would be most appreciated.
Thank you.

leaf 2

(Answer)

According to the Toronto Master Gardeners Gardening Guide on Growing Japanese Maples (link to guide below), a common problem with Japanese maples is leaf scorch and twig burn. “There may be many causes: wind burn, exposure to extremely hot sun, late spring frost, salt runoff from roadways or excessively alkaline soils, short intense drought periods, container plants in full sun.” Elsewhere in the guide it says Japanese maples need a uniform supply of moisture and that proper water management is far more important than fertilizer or soil types. Given the very dry hot summer we are having,  I originally thought insufficient watering was the main problem.

However, after reading and thinking about the question in more detail, I now think the problem is verticillium wilt. You mention that this is the third summer in a row that you have had this problem (the previous 2 summers were not particularly dry), your green Japanese maple 25′ north of the red one is fine (presumably you water them both the same amount) eventually the leaves dry and shrivel up like a cocoon and then stay on the tree into the fall (diagnostic of verticillium wilt). For these reasons I have changed my mind about the problem.

Verticillium wilt is a fungal disease caused by soil-borne pathogens Verticillium dahliae and V. albo-atrum. This fungus enters the cambium layer of the plant through the roots or injured areas on the trunk and blocks the flow of nutrients within the tissues. This leads to dryness and wilting in affected twigs. There will be brown streaking in the sapwood under the bark and in cross section, an infected branch will show a dark ring or pin-point dark spots. There is no cure for this disease – spraying anti-fungal chemicals will not work. Integrated pest management strategies to try are: 1) prune damaged areas. Maybe this pruning in addition to increasing the vigor of the tree through consistent watering and mulching to maintain soil moisture and moderate soil temperatures will  help to keep symptoms in check. Be sure to sterilize pruners with a 10% solution of household bleach between cuts and avoid moving soil or debris from an area of known infection 2) plant resistant or tolerant species in this location. The link below from the Missouri Botanical Garden has lists of plants that are vulnerable to this fungus and lists of plants that are immune to verticillium wilt.

I have included a third link for a pdf with good information on the disease and pictures of vascular iscoloration in maples.

Growing Japanese Maples: A Toronto Master Gardeners Guide

https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/cankers/verticillium-wilt.aspx