Thursday, September 12, 2013
Rust fungi infect fall blooming perennials
M.Grabowski, UMN Extension Educator
As the summer winds down, Minnesota gardeners look to fall blooming asters like goldenrod and New England aster to bring color to the garden. In addition to colorful blossoms, less desirable colorful rust fungi can commonly be found infecting the leaves of these perennials. Many gardeners first notice rust infection when the lower leaves of an aster plant turn brown and die. In severe cases, over 50% of the leaves can be killed, often from the bottom up. Upon closer examination, a gardener will notice bright orange or chocolate brown bumps on the lower surface of green leaves and along green stems. These rust pustules are filled with hundreds of fungal spores.
If leaf death is not severe, rust can be tolerated on asters. Infection by rust fungi often results in little to no affect on plant growth or blossom production. To reduce the severity of the disease, gardeners should take steps to reduce moisture on the foliage. Dense beds should be thinned and overgrown plants divided. Water with drip irrigation or use sprinklers early on a sunny day so that leaves dry quickly. Mulch the soil with woods chips or other organic matter to keep soil moisture from evaporating and increasing humidity in the plant canopy. Plants with a history of infection can be scouted regularly throughout the summer. As rust infection develops on a few leaves, theses leaves can be pinched off and buried to reduce spread of the pathogen.