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Disease Briefs, 5/13/98

We discussed peach leaf curl and oak leaf blisters in the previous issue of this newsletter. Another Taphrina species was reported May 2 at The Morton Arboretum in Lisle: Taphrina leaf curl was discovered there on river birch. We continue to see very severe cases of leaf curl on peach.

Anthracnose has become quite intense on sycamores in Illinois, as expected. The conditions from the time of budbreak to two weeks later were cool and wet—ideal for the anthracnose fungi. Reports of anthracnose on ash have been widespread, including cases at The Morton Arboretum on Korean ash, Texas ash, and some white and green ash. Leaf drop of ash in central Illinois is often traced back to anthracnose. Fungicide sprays are not recommended. Trees will continue to form new leaves. Help the tree by watering in periods of drought and fertilizing in the fall.

Cankers of various types are showing up on many tree and shrub species. These fungal pathogens invade stressed plants or wounded sites. Canker fungi tend to grow all winter long when plant growth is minimal. The cankers we see now may have occurred on recently winter-injured wood but are more likely to be older cankers. They are more visible now because sap is flowing and cankers often ooze sap, or because sporulation of causal fungi may be more prevalent or foliage has not yet covered up stem abnormalities. Prune cankers (in dry weather) from the tree where possible. Remember, the primary cause of cankers is generally stress; the fungus is usually secondary.

Author: Nancy Pataky


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