Last year I planted some trees to provide some privacy for my “fishbowl” backyard. I decided on amur maple, Acer tatariucum subsp ginnala ‘Flame.’ It was a low maintenance, hardy and pest-free tree. The three graceful trees, strategically lined up, beautifully blocked the neighbours’ prying windows.
But the second hot dry summer revealed a problem with one of the trees: Verticillium wilt. And I blame my bleeding heart attitude towards ailing plants.
When I first bought the tree trees, I noticed that one of the three trees was very root-bound. I should have returned the tree then. But no, Dr. Cristina felt she could nurse the tree back to health. I gently teased the roots apart and planted it in a hole three times the root ball, and it thrived the first year.
This last drought-prone summer I carefully watered the trees, watering slowly to allow the water to percolate deep down to the trees roots.
I was making sure the top 12 inches of the soil was moist because 90 percent of the roots are located there. I kept moving the hose every 20 minutes to water right around each tree along the dripline.
Two of the trees sailed through the drought without much problem. But the third maple started to exhibit symptoms. Whole branches started dying out. Rapidly. But it couldn’t be drought…the other two trees right next to it were thriving.
It was Verticillium wilt: a fungal disease that affects over 300 broad-leaved species of plants.
The tree must have it when I bought it. The hot, challenging summer comprised the tree’s health and the wilt started to take over.
I had to replace the tree to maintain the privacy screen, but I couldn’t replace it with another maple. Why?
Verticillium wilt persists in the soil indefinitely. I couldn’t plant a verticillium susceptible tree. But I couldn’t use dogwood, plum, redbud, serviceberry, maple or magnolia.
I needed a small tree to sort of match what I already had as screen. Trees resistant or immune to Verticillium wilt that could work include apple, hawthorn, pear, poplar and mountain ash. I decided on a crabapple, Malus ‘Sugar Tyme,’ a hardy strong tree with a similar form to the amur maple.
Well, my garden doesn’t look so well designed with this third different tree, but it will thrive. Fingers crossed.
University of Guelph’s Pest Diagnositic Clinic. Verticillium Wilt of Maple.
University of Minnesota Extension. Verticillium Wilt of Trees and Shrubs
Missouri Botanical Garden: Amur Maple, Acer tatariucum subsp ginnala ‘Flame.’
Missouri Botanical Garden: Crabapple, Malus ‘Sugar Tyme’