Spots on My Leaves: Phyllosticta Species in the Landscape

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Gardeners and farmers are some of the most astute folks. They pay close attention to the health of their plants and anything out of place raises warnings in their mind. One of the most common and obvious issues plants have are spots on their leaves. A once-pristine leaf changing to anything but green, or whatever color it should be, usually ends up on the desk of the horticulture agent or the Extension Master Gardeners. I had an old, familiar foe arrive this week: Phyllosticta on a paw paw leaf (Asimina triloba).

Phyllosticta’s effect on Plant Health

Phyllosticta species are wide-spread fungal plant pathogens. They cause brown spotting or splotching with a black and/or yellow rim (called necrosis) as they grow. There is usually additional discoloration, depending on the species and the patterning of these blotches can vary across the plant and how bad the infestation is.

Phyllosticta on pawpaw_landscape_Photo by Amanda Wilkins

Species occur around the world and infect a wide variety of plants. The species of Phyllosticta can be host-specific, like in the case of the Phyllosticta hamamelidis is specific to witchhazel, but also general and cross between species. Even Cacti can become susceptible to them!

Fungi in the Landscape

Fungi are all around us all the time and most are not pathogenic, or cause health issues, to our plants. Fungi are important decomposers in the landscape (you like compost and healthy soil right?), are a food source for many types of organisms, and help move the circle of life along.

Most fungi are opportunists. Cut hay while the sunshines, right? Phyllosticta is most evident after cool, wet winter and spring periods. According to UMass Extension, “The fungus produces tiny, black fruiting bodies within the necrotic tissue and spores are easily disseminated to healthy foliage during wet weather.” If you suspect you have Phyllosticta in your landscape and are concerned for your plant’s health, please contact your local Cooperative Extension Office for a confirmed diagnosis, as there are lots of leaf spot-causing pathogens out there!

What’s to Do

Phyllosticta is taking advantage of cool, wet weather! It only shows up when the weather is ideal for it to grow, so it can be bad one year and not be seen the next year. If you do have Phyllosticta, it is best to remove the leaf litter from beneath the infected plants as the leaves fall. If it is in a large section of the plant, you can cut out the infected area. Do not compost these leaves and debris. If it is a small infestation you can pick the leaves off, and sterilize your tools and hands between treatments. There are chemical options available for treatment of the pathogen. Please contact your local Cooperative Extension Office for a list of control options.

It is important to always remain diligent in your landscape and observe changes in the weather and the health of your plants. Plant health and weather are inextricably linked, and even the most attentive gardeners and farmers doing all the right maintenance practices can be stumped by a change in the weather!

References:

Phyllosticta Leaf Blotch

A phylogenetic re-evaluation of Phyllosticta

PHYLLOSTICTA LEAF SPOT – University of Florida

Phyllosticta leaf spot on ornamental plants

Phyllosticta leaf spot and dieback

Phyllosticta leaf spots Phyllosticta spp. Pers.

Disease Control for Trees, Shrubs and Flowers, 2018

Problems and Pests of Agave, Aloe, Cactus and Yucca