In the fertile orchards of western Colorado, a quiet crisis is unfolding among the rows of trees that produce the state’s celebrated Palisade peaches. A persistent and aggressive fungal disease, cytospora canker, is significantly shortening the lifespan of orchards and creating a mounting economic burden for local growers. Compounded by the volatile weather patterns associated with climate change, this pathogen has become one of the most serious threats to the region’s long-standing fruit industry.
A recent survey conducted by Colorado State University researchers in Orchard Mesa revealed that 100% of the orchards surveyed were infected with the fungus. The disease is often signaled by the presence of gummosis—a sweet-smelling, amber-colored sap oozing from the bark—which serves as a visible indicator of the tree’s struggle against the pathogen, environmental stress, or physical damage. For farmers who have cultivated these lands for generations, the rapid decline of their trees is not just an agricultural challenge. it is an existential threat to a tradition that dates back to the late 19th century.
The economic impact is stark. Researchers estimate that cytospora canker leads to at least $3 million in annual losses for Colorado growers. In orchards where the fungus infiltrates the major structural branches, known as scaffolds, fruit production per tree can plummet by as much as 50%. With Colorado’s 2024 peach production valued at approximately $34 million, the cumulative effect of these losses is forcing a hard reevaluation of orchard management strategies across the Western Slope.
Understanding the Pathogen
Cytospora canker is caused by fungi within the genus Cytospora, which affect more than 70 species of woody plants globally. While the disease has been documented in the United States since at least 1892, its behavior has evolved. Once considered a secondary issue that only plagued already stressed trees, it is now recognized as a primary, destructive force in modern fruit orchards.
The fungus typically gains entry through wounds in the bark. These openings can be caused by routine maintenance like pruning, but they are increasingly created by extreme weather events—specifically, the severe freezes and hail that have become more common in the Intermountain West. When a tree suffers a freeze injury, the resulting cracks in the wood provide an ideal gateway for fungal spores to colonize the plant’s vascular system.
The impact on orchard longevity is profound. Ideally, a peach tree provides full production for about 10 years after its initial five-year growth phase. However, in Colorado, cytospora canker has effectively halved that lifespan. Many trees now succumb to the disease by their fourth or fifth year, often dying before they ever reach their peak productive capacity.
Plant Talk Colorado: What is cytospora canker? A video from Colorado State University Extension.
The Intersection of Climate and Disease
The vulnerability of these trees is inextricably linked to the region’s shifting climate. Peach trees require a period of cold to transition into dormancy, but they rely on a gradual acclimation process. Abrupt temperature swings—such as the 2020 event where temperatures plummeted from 65 degrees Fahrenheit to below 10 degrees Fahrenheit in just 48 hours—can be catastrophic.
When trees remain active and sap is still flowing during an unseasonable warm spell, a sudden freeze causes ice crystals to form within the plant’s cells. This internal freezing causes the woody tissues to swell and crack, leaving the trees defenseless against infection. The 2020 freeze, which killed tens of thousands of trees, demonstrated how environmental instability acts as an accelerant for the spread of cytospora canker.
the Intermountain West is grappling with a broader set of environmental stressors, including diminishing water supplies and soil pH levels that often fall outside the ideal range for optimal peach tree health. These factors combined create a state of chronic stress that leaves orchards perpetually susceptible to the fungus.
Mitigation and Future Research
Managing cytospora canker is a complex, ongoing process. Current best practices involve the rigorous removal of infected wood, the application of protective chemicals to seal pruning wounds and the implementation of stress-reduction techniques to keep trees as healthy as possible. However, given that the Palisade microclimate sits at the very edge of what peach trees can tolerate, these interventions have limited success.
Researchers at Colorado State University are currently leading a collaborative effort to find more durable solutions. This includes evaluating different peach cultivars for natural tolerance to the pathogen and investigating the population biology of the fungus itself. By understanding how the spores travel—whether through air currents, irrigation water, or insect activity—the research team hopes to develop more effective management strategies.
The formation of the Cytospora Working Group represents a significant step forward, bringing together extension personnel, fruit tree growers, and academic researchers. Their mission is to establish sustainable, science-backed management practices that can help stabilize the industry. While there is no immediate “cure” for the fungus, the focus remains on slowing its spread and protecting the long-term viability of Colorado’s agricultural heritage.
Growers and stakeholders are encouraged to monitor updates from Colorado State University Extension for the latest findings on disease prevention and orchard management. As the industry approaches the 2027 growing season, the focus will remain on developing resilient planting cycles that can withstand both the persistent threat of cytospora and the unpredictable nature of the regional climate.
This report is intended for informational purposes based on current agricultural research. Please consult with local extension offices for specific guidance on orchard health and disease management. We welcome your thoughts on how climate shifts are impacting your local agriculture; please feel free to share your experiences in the comments below.
