Colorado's prized Palisade peaches are under threat from a fungal disease, exacerbated by climate change. Cytospora canker, a destructive fungal disease, has been found in 100% of orchards surveyed in Orchard Mesa, Colorado. This disease, caused by fungi within the genus Cytospora, affects over 70 species of woody shrubs and trees globally. It was first discovered in the U.S. in 1892 and has since become a significant threat to fruit trees across the country.
The economic impact of cytospora canker is substantial, resulting in at least $3 million in annual losses for growers in Colorado. In infected large branches, known as scaffolds, the damage can lead to a 50% loss of peaches per tree. The disease has halved the life of an orchard from 20 years to 10 years or fewer, with trees typically dying before reaching peak production.
Cytospora canker enters through wounded and woody branches or twigs, which can occur due to pruning, severe freezing, or hail events. In Colorado, freeze events are common and particularly harmful in the fall if temperatures drop abruptly without giving trees enough time to acclimate. Ice formation within plants causes swelling and cracking in woody tissues, making them vulnerable to infection.
The correlation between cytospora infection and cold damage is a significant factor in the disease's prevalence in Colorado. In 2020, a major freeze event damaged many trees, leading to the death of tens of thousands of peach trees and the proliferation of new cytospora canker infections. The surviving trees were often more vulnerable due to cracked skin and bark, making them susceptible to fungal infection.
Managing cytospora canker is challenging due to the ideal peach-growing microclimate in Palisade, Colorado. Growers can remove infected trees, protect wounds with chemicals, and ensure trees are free of stress. However, these strategies have limited efficacy due to the environmental conditions. Researchers from Colorado State University are working on developing chemical options for conventional and organic growers to slow the spread of the disease.
The pathogen can be spread through air, insects, irrigation, and the movement of new peach trees into orchards. Understanding the population biology of cytospora and determining peach cultivar tolerance to the pathogens are ongoing areas of research. The establishment of the cytospora working group aims to collectively develop solutions for managing the disease and keeping the Colorado peach industry vibrant.
In conclusion, the threat of cytospora canker to Colorado's peach industry is a complex issue, requiring a multifaceted approach. By understanding the disease's biology and implementing effective management strategies, growers can work towards preserving the state's prized Palisade peaches and ensuring the industry's long-term sustainability.
