Plant Pathogens


Cayuga Nature Center   Smith Woods   Total species found
    0     1 9     1 9


A plant pathogen is any organism that causes disease on a plant. They are highly diverse and found in all five taxonomic kingdoms. 

Although fungi cause eighty percent of all plant diseases, other organisms that cause plant diseases include bacteria, oomycetes (water molds related to algae), phytoplasmas, nematodes, parasitic plants and viruses. At least one of each of these was represented in the BioBlitz survey.

Unless damage or symptoms are serious, most individuals will not notice signs of pathogens because only a small percentage of plant pathogens cause economically and environmentally devastating diseases.

Introduced plant pathogens, like chestnut blight and Dutch elm disease, caused significant economic loss as they killed billions of trees (American chestnuts and American elms respectively) and significantly altered our forests and landscapes. Similarly plant diseases may affect the quantity and quality of our food; the same pathogen which caused the potato famine, Phytophthora infestans, can wipe-out garden tomatoes in any given year. 

Plant Pathogen diversity is strongly correlated with plant community & species diversity. The Cayuga Basin, like many forest ecosystems of the Northeast, represents an interesting intersection for plant pathogens where pathogens found traditionally in old-to-mature forests are conspecific with those found in early-successional systems and urban landscapes. 

Smith Woods, is considered one of the lone remnant pockets of old-growth forests in the Finger Lakes, and hence, possesses an open understory with large-diameter oaks, beech, and hemlock dominating the overstory. Forested portions of the Cayuga Nature Center, are consistent with a secondary (post-settlement) forest and possess a greater diversity of trees and shrubs. Forest-covered drainages, as well as a wetland and abandoned field at the CNC, further enhanced the plant communities present on site. The differences in forest structure and composition greatly influenced the diversity of plant pathogens present. 


Rusts were the most prevalent diseases found. 20% at Smith Woods and 17% at CNC. Rust diseases are caused by fungi with certain morphological and/or developmental features in common, and they are collectively known as "rust fungi." 

Some rust Fungi have complicated life cycles, wherein they can produce as many as five different kinds of spores and host-switch between taxonomically diverse host plants. Other rust fungi have relatively simple life cycles with just one or two spore stages and/or infect only the same or closely-related host plants. Typical signs on leaves usually include bright orange pustules containing dry, powdery spores that are either borne exposed on the leaf surface or are contained within a delicate membrane that stretches as it fills with spores until it finally breaks and the spores are liberated. 

Most rust infections of leaves intensify so late in the season that any defoliation they might cause does not impair the vigor of host plants, and chemical control to preserve plant health is not necessary. However, some can be sufficiently unsightly that efforts to prevent infection by reducing over-wintering inoculum or by fungicide sprays may be necessary. 

Many rusts require two hosts to carry out their life cycle, which can take up to two years to complete. Past management strategies for economically important plants focused on removing one of the hosts in hope of disrupting the life cycle of the pathogen. This method was implemented for White Pine Blister Rust with the two hosts being White Pine and Ribes (currants or gooseberries). Some states still ban the sale and cultivation of Ribes spp in an effort to control this disease.


Team Plant Pathology had nine participants from the Section of Plant Pathology and Plant-Microbe Biology (one faculty member and eight staff members). Most of the team had a strong background in tree and shrub pathology as well as diseases of herbaceous perennials.

Dawn Daily O'Brian, Shawn Kenaley, Maryann Karp,surveyed Smith Woods and part of CNC on Friday. On Saturday they were joined by Mary McKellar, Gary Bergstrom, Rachel McCarthy and Molly Towne. Karen Snover-Clift staffed the CNC booth Sandra Jensen helped with identifications back at the diagnostic lab.