Q&A
A: There is a good chance that your tree has Guignardia leaf blotch, which gives the appearance of a tree with leaf scorch from a distance.
Guignardia leaf blotch is caused by a fungus and is primarily a cosmetic issue on mature trees, since the leaves remain until late summer and next year’s buds remain viable. This disease is more of an issue in young nursery stock, for which controls are often applied.
Guignardia leaf blotch can be distinguished from environmental scorch by the presence of small, black specks, which are the fruiting bodies of the fungus in the lesions on the leaves. This fungal disease affects most leaves on the tree, while scorch typically affects new leaves on the side of the tree with more sun or wind exposure.
Once a tree is infected, you have to live with the unsightly leaf blotch until leaves drop in the fall.
You are seeing the symptoms of the leaf blotch now on your tree, but the infection began in spring. Lots of wet weather in spring this year promoted the growth of this disease.
In early spring, Guignardia fruiting bodies mature, and during wet weather, they release spores into the air. An infection can result if any spores land on young, developing, susceptible leaves that remain wet for several hours. Blotches then develop in 10 to 20 days. New fruiting bodies develop in early June, and in wet weather, more infections may continue throughout the summer.
Guignardia blotch first appears as water-soaked irregular areas on the leaves that are easy to miss. These areas enlarge quickly, and in a few days, will be reddish-brown to brown leaf spots with clear, bright yellow margins. These blotches will enlarge over time and may cover the entire leaf surface by late summer. Leaves then become dry and brittle and may drop off the tree early. You may already be seeing this happen with your tree.
A chemical treatment is not recommended at this time. Garden conditions are dry currently, so the tree will benefit from supplemental water with an occasional deep soaking of the root zone at this time and throughout the fall season, if the weather remains dry.
The Guignardia fungus overwinters on fallen leaves, so removing and discarding all the fallen leaves will reduce the source of inoculum next spring. Proper pruning will improve air circulation throughout the tree’s canopy and speed up the drying of the leaves.
If a tree has been defoliated for several years in a row, then gardeners may want to consider applying a fungicide in the spring to protect the tree and give it a chance to recover. This will require applying a fungicide, starting when the buds begin to open up, every 10 to 14 days, as long as the wet conditions continue in spring.
PREVIOUS ARTICLE
