In western Colorado, home to the treasured Palisade peach, cytospora canker is one of the most economically consequential fungal diseases faced by growers.
A recent survey conducted by Colorado State University in Orchard Mesa found that 100% of the orchards have trees infected with cytospora canker. In some orchards, you can smell the sweetness of gummosis, the sweet oozing of sap from a tree that occurs from injury, stress, pathogen infection or insect damage.
We are part of a team of fruit tree growers, extension personnel and researchers who are developing tools for mitigating cytospora canker in fruit tree orchards in Colorado and Utah.
In a study we published, we estimate this disease results in at least US$3 million in annual economic losses for growers in Colorado. In infected large branches, which are called scaffolds, the damage can result in a 50% loss of peaches per tree.
Peaches were first planted in Palisade and Grand Junction in 1882 by one of the first white settlers to the area, John Harlow. Peaches and other fruit trees have been Colorado staples ever since. In 2024, Colorado farmers produced roughly 15,000 tons of peaches valued at $34 million.
However, fruit tree production in the Intermountain West, which covers Colorado, Utah and Idaho, is threatened by diminishing water supplies, spring frosts, variable winter temperatures and soils that are above the ideal pH range for peach trees. Further exacerbating the environmental stresses are pest problems and the persistent cytospora canker disease.
What is cytospora canker?
Cytospora canker is caused by fungi within the genus Cytospora. These pathogens are found globally and affect more than 70 species of woody shrubs and trees. These fungi have been present on fruit trees in the U.S. since at least 1892 when cytospora canker was first discovered on peach, plum and almond trees in Pennsylvania and New Jersey. Cytospora canker was first described as only a disease of stressed trees, but now it is recognized as a destructive disease in tree fruit across the U.S.
Plant Talk Colorado: What is cytospora canker? A video from Colorado State University Extension.
Growers expect peach trees to live for 20 years. The first five of those years are initial growth. The next 10 years are full production. Then, the tree’s productivity tapers off in the last five years of its life. The disease has halved the life of an orchard in Colorado from 20 years to 10 years or fewer. Trees that get infected during the first or second year are typically dead by year four or five before they reach peak production.
Cytopora canker typically enters through wounded and woody branches or twigs. Wounding occurs when branches are pruned to maintain tree vigor or through severe freezing or hail events. Freeze events are common in Colorado and are particularly harmful in the fall if temperatures drop abruptly without…
