While summer hasn’t officially packed its bags, some trees across Central Ontario are already shedding leaves and painting lawns with the colours of fall. Reports of yellowing leaves and thinning branches are appearing weeks earlier than the typical autumn shift. If your maple tree is already dropping, it doesn’t necessarily mean fall is starting early. Simcoe County forester Graeme Davis said the issue isn’t widespread and could be linked to a fungal disease affecting some urban maples. Native maples appear healthy Davis said conditions in the county’s forests have been relatively normal this season. “Overall we have had a pretty average growing season locally with more than adequate precipitation,” Davis said to CTV News. He added the county has not seen anything significant affecting its natural hardwood forests, like widespread stress or early leaf loss among native sugar and red maples. Instead, Davis said some of the more noticeable problems may be transpiring on Norway maples, a non-native species commonly found along streets and on residential properties. Fungus could be behind the early drop For some of those trees, the culprit could be fungal disease. Davis pointed to the tar spot and anthracnose, which can cause leaves to develop dark spots, turn yellow and drop prematurely. The Ministry of Natural Resources also identifies tar spot as a possible cause of early leaf loss. Wet and rainy conditions can encourage the fungus, with affected trees sometimes beginning to shed their leaves as early as August. While a lawn covered in leaves this early may look concerning, Davis said these fungal diseases are generally cosmetic and typically do not cause long-term damage to the tree. Weather can put trees under stress Fungus isn’t the only reason a maple might give up its leaves early. Danijela Puric-Mladenovic, a forestry expert and graduate of the University of Toronto, said heat combined with limited moisture in the soil can put trees under stress. When a tree is losing water through its leaves faster than its roots can replace it, shedding some leaves can help it conserve water, Puric-Mladenovic said. The Ministry of Natural Resources also told CTV News that it identifies prolonged warm and dry conditions as a possible cause of early colour change and premature leaf drop. In other words, a maple turning yellow ahead of schedule may not be getting an early start to fall. It could be responding to the conditions around it. When should homeowners be concerned? Puric-Mladenovic said one season of premature leaf loss does not mean a tree is dying. Repeated stress over several years is more concerning. It can reduce a tree’s growth and energy reserves, potentially making it more vulnerable to insects, disease and other pressures. Puric-Mladenovic added that she has seen this pattern before. “I remember the summer of 2016 being fairly dry. We were sampling in the Lake Simcoe watershed, and by early August, many ground-layer plants in the forest had wilted. It was also a bumper crop year for oaks, but because of the dry conditions, many trees dropped their acorns by late August,” she said. For homeowners dealing with fungal disease, Davis recommends raking up fallen leaves and putting them out with compost. Removing infected leaves can reduce the amount of fungal material left behind to return the following year. Autumn officially arrives in the Northern Hemisphere on Sept. 22 at 8:04 p.m., according to The Old Farmer’s Almanac. So for the region’s native maples, the best of the fall colour show is still to come.
