Managing leaf spot diseases

Leaf spot diseases will not seriously harm your plants, but there are things you can do that, when done together, can reduce the disease on the tree in following years.

• Rake up and destroy fallen leaves before the first snowfall to eliminate locations where diseases can survive to re-infect the plant the following growing season.
• Do not overcrowd plants — use size at maturity as a spacing guide when planting.
• Prune trees or shrubs to increase light penetration and improve air circulation throughout the canopy.
• Wet conditions promote disease, so water trees at the base and be careful not to splash water on leaves. A drip or soaker hose works best for this. Avoid sprinklers.
• Reduce stress to your tree:
  • Water your tree throughout the growing season so that the top 6 to 8 inches of the soil is moist, especially during dry summer periods.
    • Soil should be allowed to dry before watering again.
  • Maintain a 3- to 4-inch-deep layer of mulch around your tree.
    • Do not mound the mulch around the trunk of the tree but lay a flat layer with at least a 2-inch space between the mulch and stem to allow for air movement.
    • Annually reapply mulch and inspect to ensure levels are maintained.
• Do not fertilize trees and shrubs suffering from leaf spot diseases, unless it is recommended by a soil test to correct a nutrient deficiency.
• Fungicides are not necessary unless a tree has lost all of its leaves several years in a row.
• Fungicides are protective and need to be applied before symptoms appear on the leaves.
  • Proper timing of fungicide applications can vary depending on the biology of the disease.
  • High-pressure spraying equipment is needed in order to get complete coverage of the canopy of large trees.