DRAFT September 14, 2012
Birch skeletonizer and septoria leaf spot affecting birch trees across northern Ontario
August-September 2012
Symptoms:
Leaves of white birch trees have been turning yellow, orange, or brown in mid- to late August and early September. The leaves then dry and fall from the trees. Surrounding hardwoods remain green and fully foliated until normal fall colouration begins.
Area affected:
This event is occurring in 2012 across a wide swath of northern Ontario, from the western portion of Northwest Region east to Sudbury and south to Killarney.
This is the third year in a row for this event. In 2010 and 2011 it was heavily concentrated in north western Ontario, becoming more scattered in the eastern parts of the region in Wawa District. In 2012 it has moved south of Wawa with heavy amounts now occurring in Lake Superior Park and further east to Sudbury and south along Georgian Bay.
Causes:
In some areas, most of the damage is being caused by a native insect, birch skeletonizer (Bucculatrix canadensisella). In other locations the primary agent is a native fungal disease, septoria leaf spot (Septoria betulae). Often both agents are occurring together on the same leaves.
Birch skeletonizer tends to turn the leaves brown as the insect eats the green tissues between the veins of the leaf, with only the translucent skeleton of the leaf remaining.
Septoria leaf spot starts out as black spots on the leaves. The fungus kills surrounding tissues, and tends to turn the leaves yellow to orange. Over a few weeks the fungus kills sections of the leaf, and in severe cases the entire leaf is discoloured and killed.
Similar symptoms:
Drought is sometimes confused with the skeletonizer or the leaf spot disease. Drought however turns the leaves reddish brown to brown. It does not cause skeletonizing of the leaf or result in numerous black spots.
Fall colouration typically occurs later in September and October, and like drought doesn't cause skeletonizing or black spots. Also, other hardwoods will be turning colour in the fall at the same time as the birches.
Impact:
Although the trees appear unsightly and unhealthy, the impact on the tree is minor. The event occurs late in the growing season, allowing enough time for the tree manufacture enough food from the leaves before they are affected by the insect or the fungus.
Control:
Generally no control action is needed for either the fungus or the skeletonizer. For ornamentals, the fallen leaves can be raked up and disposed of off-site or burned, but re-infection by the fungus or re-infestation by the insect can occur from surrounding areas.
For more information:
For specifics on what is occurring in your area, or for questions regarding other aspects of forest health, please contact your local Ministry of Natural Resources forest health technical specialist, or:
Dan Rowlinson (Forest Health Field Program Coordinator (705) 946-7445 dan.rowlinson@ontario.ca )
Taylor Scarr (Provincial Forest Entomologist (705) 945-5723, taylor.scarr@ontario.ca ), or
Richard Wilson (Forest Program Pathologist (705) 541-5106 richard.wilson@ontario.ca ).
Prepared by:
Taylor Scarr, with the assistance and information from the forest health monitoring program, Inventory Monitoring and Assessment Section, Ministry of Natural Resources.
