Fallen infected leaves shelter the fungus until the next year's disease cycle. Disease Management Tree resistance is the best way to prevent foliar diseases. Several poplar hybrids or species are resistant to one or more of these diseases. Ask your local nursery for a resistant variety. Some aspens are resistant to leaf spots, but aspen production methods make it difficult to select trees for resistance.
Sanitation is an effective control for some foliar diseases.
Fall removal of infected leaves, twigs and branches can reduce the amount of disease the next spring. Raking and destroying infected leaves can reduce Marssonina leaf spot, ink spot and leaf rust. Water in early morning so leaves can dry out. Keep sprinkler patterns adjusted so leaves don't stay wet. Space trees apart to reduce humidity to help prevent leaf diseases.