Species of Fungus in Ornamentals Now in Harvestable Crops

Top photo: Spruce Decline by Phomopsis sp. Lower: Tip Blight by Phomopsis juniperovora

by Bryce Axelrod – Sustainable Plant Systems – Horticulture

Phomopsis (Phomopsis sp.) fungal disease has many different species that negatively impact multiple plant species. Most are ornamentals or large landscape trees or shrubs with the rest being a few important harvestable crops.

Susceptible plants include: spruces (Colorado Blue, White & Norway), junipers (Eastern Red Cedar, Creeping Juniper, Rocky Mountain Juniper, Savin Juniper and other Cypresses), arborvitae, Japanese cedar, Douglasfir, true firs, yews, forsythia, viburnum, American Elm, hickory, maple, oak, privet, highbush blueberries, grapes, and soybeans.

The species infecting spruces leads to development of cankers and dieback of more mature limbs whereas the species infecting junipers and other cypresses (P. juniperovora) is known to only have impact on new growth (this includes arborvitae, Japanese cedar, Douglasfir, true firs and yews).

Highbush blueberries adopt characteristics of each in that the infecting species (P. vaccinii) effects new growth as well as forms cankers, although the blight is an overall tip blight, including flowers and fruit.

Phomopsis sp. is believed to cause gall formation on forsythia, viburnum, American elm, hickory, maple, oak and privet.

  • viticola infects grapes and creates lesions on new leaves and stems, eventually moving to mature leaves as well as small, black spots at base of developing shoots and shriveling fruit.
  • longicolla infects seeds of soybean plants, making them shriveled and elongated, cracking the coat and making them white and chalky. Each of these species of Phomopsis result in twig & blossom blight, the formation of cankers, leaf spots and fruit spots/rot.

Across the spectrum of Phomopsis species, means of overwintering and spreading is identical.

Eventually, fruiting bodies called pycnidia are produced and release spores called conidia.

The spores overwinter and spread further by rain/splashing or wind in spring and even if the spores do not necessarily spread, they can remain viable within diseased tissue for as long as two years, which is why it may not seem to be as prevalent as a previous season.

While Phomopsis does not pose a huge threat to too many plants, it does effect some valuable, ornamental and crop species.

Methods of control focus primarily on physical/biological management and include:

  • Pruning infected branches
  • Disposal of infected cuts
  • Resistant species/cultivars
  • Avoid planting in poorly drained, poorly circulated and shaded areas
  • Avoid wounding/injuring while planting
  • Sterilize pruning tools

These are all examples of basic horticultural practices. With the correct planning, if the landscape is monitored and correct action is taken, there is some chance of no issues with the fungus (and others) in our valued crop and ornamental species.

About Me:

Before transferring to Ohio State, my focus in horticulture was in Landscape Design & Management. While I enjoy the designing aspect of landscaping very much and would like to keep expanding in that area, I also really enjoy the care & management aspect of it as well. One of my favorite trees is the Colorado Blue Spruce and my parents have one on their property. I figured taking the time to learn a little more about exactly what Phomopsis is and what other plants it has an effect on would be nothing but beneficial. Obtaining knowledge of how to get the most longevity out of my landscape is a very important factor to me and I cannot wait to eventually have a landscape of my own.