Identifying Fungal Diseases

The hot and humid conditions of summer make it an ideal time for various fungal problems in your trees and shrubs. Two of the most common diseases are Septoria Leaf Spot and Cedar Apple Rust.

Septoria Leaf Spot

Appearing as spots on the leaves of both variegated and green leafed varieties of red twig dogwood, this fungal disease is mostly cosmetic but can weaken a plant if left untreated for many years in a row. Although Septoria Leaf Spot most commonly appears during damp and cool springs or humid summers, there are precautions you can take to limit your dogwood's chance of contracting it.

  • Rake leaves as they fall and discard them into the trash. By putting them into compost or leaf piles, the fungus can often overwinter and survive, only to reinfect your tree the next year.
  • Apply a 2-4" layer of mulch and make sure to water thoroughly during the hottest months. Just make sure to keep all your mulch away from any stems and to water only the base of the tree. Watering the leaves may spread the fungus.
  • Feed with a mild fertilizer such as Plant-tone, Holly-tone or diluted Miracle-Gro.

Cedar Apple Rust

This fungus affects several kinds of plants, but the most notable are cedar and apple trees. Other forms have been known to infect hawthorne and junipers, but cedar apple is the most common fungus found here. The first signs of infection include brown to orange spots appearing on leaves and spores developing in more humid weather.

To control the spread of these spores, we recommend one of two approaches:

  • The application of a fungicide. We carry many different brands so if you've noticed possible signs of this fungus on your plants, please consult with one of our nursery professionals and we'll tailor a solution to your needs.
  • Removal of the host plant. This in effect quarantines the issue and limits the possibility of the fungus spreading. However, this extreme measure should only be used if the fungicide proves to be ineffective in solving your needs.