Warm and humid with combined with plentiful rainfall is sure to put fungus in the spotlight…… Leaf spot that is with all sorts of these problems afflicting gardeners from Septoria leaf spot on tomato foliage to Blackspot on Roses to Tar spot on Maple trees. Fungi hang around until weather conditions are right….and when they are the spread of disease can be rapid. Defoliation from blackspot on roses can be swift when the fungus becomes active in wet warm environments. If left unchecked black spot can quickly blanket an entire rose bed until the plants are standing “naked” outdoors. Fall Winter and Spring cleanup is very important with roses. Irrigate plants at the base if possible, have plants spaced for air movement and have roses in a sunny spot with preferably east exposure to quickly dry the foliage in the morning. There is an all-in-one drench available from Bayer that can help roses if used throughout the season systemically taken up through the roots.
Another fungi in the spotlight right now is Tar spot on Maple trees. Yellowish green spots on tree foliage become raised black spots which eventually become “wet tar” called a stroma. Released spores from fruiting bodies of the disease travel in the air to tender developing maple leaves in spring. Within a month or two light green spots develop on the foliage. Later the green spots become yellow to black with the “tar-spots” visible in late summer and into the fall. Again just like with the roses good cleanup in fall and spring makes a big difference. Some winter pruning to open up the canopy of the tree for better air movement is good idea too. In many cases a fungicide for the homeowner is not practical because A) the tree is too large to reach and B) once the tar spot is there and visible it’s too late anyhow. Keep trees healthy with supplemental watering in hot dry periods and feed the trees annually. Tar spot won’t kill the tree but repeated episodes can weaken the tree over time. Here’s a great picture of maple leaf tar spot courtesy of Michigan State University.