Home & Garden: Sycamores still suffering from fungus in Colorado’s Grand Valley | PostIndependent.com

Home & Garden: Sycamores still suffering from fungus in Colorado’s Grand Valley

Curt Swift
Free Press Gardening Columnist
Sycamores around the valley are blighted with fungal infections.
Curt Swift |

This year we have experienced major problems with sycamore anthracnose and coryneum blight of peach and apricot due to this spring’s extended wet cool conditions. The causal agents of these diseases are fungal and require extended periods of wet leaf surfaces to invade and increase in severity. The initial infections require the proper conditions to produce more spores; this results in more infection and more injury.

Sycamore anthracnose, while common in this area annually, was much more severe this year due to the extended cool wet spring. This year many sycamore trees in this area have clusters of dead twigs and branches and sparse vegetation due to the causal disease organism. You will notice some sycamores are not showing these symptoms. This is because these uninfected trees are hybrids.

The Oriental Sycamore Platanus orientalis grew up with the causal agent of anthracnose. The American sycamore Platanus occidentalis did not. Consequently the American species of the genus Platanus is susceptible to Plane Anthracnose. The American/Oriental hybrid, known as the London Plane tree, Platanus x acerifolia has the anthracnose resistance of its Oriental parent. The “x” in the scientific name indicates this tree is a hybrid.

Replacing all the American sycamores in the Grand Valley with London Plane trees would be a very costly solution to this disease problem.

Removing them without planting replacements would mean a major loss to our urban forest. Paying attention to spring weather conditions and treating with the appropriate fungicide at the appropriate time is a more logical solution. Following through on the latter approach means the arborist or pesticide applicator needs to understand how weather conditions affect this disease and what spray schedule is necessary to reduce the amount of damage the American Plane trees in this valley suffer when wet cold spring weather occurs. Having the resources to follow through on multiple applications of a fungicide is also critical to prevention.

Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.

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