7/2/2013 - By Matthew Shultz

For the month of January I wanted to talk about a disease that often goes unnoticed until the summer when it is often too late to keep crops aesthetically salable. This month I want to discuss Entomosporium leafspot.

In the nursery and landscape setting this disease will usually show up on plants from the Rose family, most commonly on Photinia and Hawthorn trees. This disease overwinters as dormant spore bodies in fallen leaf debris and on dormant buds and twigs. As the weather warms in the early spring these spore bodies swell and start to release their spores into the air and onto the newly flushing leaf material.

Spores are also spread via splashing water, so drip irrigation is recommended for susceptible crops. When the new infection occurs it often goes unnoticed for several weeks or months, until someone recognizes the newly forming leafspot. The infection often goes unnoticed because it first shows up as a couple of plant specks, often on the underside of the leaves. As the fungus grows and reproduces small red halos start to form around the infection site, this is often what most people recognize as a problem.

In Hawthorn species the leafspot will be bright red in color, and in Photinia the leaf turns more maroon or purple. As the disease progresses the necrotic center of the infection will continue to consume the leaf material leaving entire sections of the leaf dead or defoliated. Spraying susceptible crops during bud break and thru early spring will pay huge dividends in the summer and fall plant sales. Rotations of a copper fungicide, Daconil, Dithane or Protect DF, thiophanate methyl and Bayleton work well on 14 day rotations from bud break thru the middle of summer.

Early infection of Entomosporium on Red Tipped  Photinia – Photo by Matthew Shultz

Severe necrosis caused by Entomosporium pathogen on upper leaf surface of Photinia
Photo by Matthew Shultz

Necrotic Entomosporium leafspot on underside of Photinia leaf – Photo by Matthew Shultz