I live in Toronto, Ontario (Zone 6) and have a river birch tree planted in a corner of my small yard. It faces south and east, and is directly beside a fence on the north side and the house on the west. For the past couple of years it has emerged with yellow leaves with green veining. They eventually develop brown spots come mid-summer, and as of now they’re also browning along the edges. I’m thinking the browning is due to insufficient moisture, so I will do a deep watering today. In an attempt to try and correct what I’m guessing is an iron deficiency, I applied Milorganite to the soil in early summer, but it doesn’t appear to be helping. Do you have any suggestions?
River birch (Betula nigra) it is susceptible the fungus leaf blight. The first symptoms of birch leaf blight include small (barely visible) brown to black spots on young leaves. The spots appear in early summer and increase in size and number. A distinctive symptom is a yellow “halo” which surround each of the spots. By mid-summer to late-summer, infected leaves turn pale yellow and fall from the tree. While unsightly ( and sad) this fungus will not kill your birch. A healthy tree is the answer. Going forward making sure the tree is receiving proper air circulation and promptly rake and remove all fallen leaves from the site in order to help eliminate the fungal spores. Follow these good cultural steps and give your tree a better chance for next year.
Are you sure you have a river birch? Other birch (Betula papyrifera- white birch; Betula pendula-European birch) are susceptible to a borer pest. Have a look at our Toronto Master Gardener Guide Bronze Birch Borer.
Good Luck with your birch!