Researchers find crown gall may signal almond orchard longevity risks
A survey of more than 23,000 California almond trees found orchards with crown gall were six times more likely to also have butt rot disease.
Almond orchards affected by crown gall were six times more likely to have butt rot, according to research conducted from 2024 through 2026 by University of California Cooperative Extension (UCCE) and California State University, Bakersfield scientists.
Researchers surveyed more than 23,000 almond trees in Kern and Tulare counties, documenting crown gall and butt rot prevalence. Scientists at CSU Bakersfield conducted molecular identification of the butt rot pathogen in each surveyed orchard.
Ganoderma adspersum was the only Ganoderma species isolated from the surveyed orchards. The introduced fungal pathogen, which causes butt rot, was first reported in California in 2016.
Trees with historic or active signs of butt rot also had 1.5 times the mortality rate of healthy trees during the 26-month survey period.
Crown gall, caused by a soilborne pathogen, is common in almond and walnut orchards and produces tumors on tree roots and crowns. Although the disease generally does not kill trees unless severe, it can restrict tree size and affect yield.
The findings suggest crown gall could be an important indicator of long-term orchard longevity where G. adspersum is present. Planting crown gall-free rootstocks during orchard establishment may help reduce future risk from the butt rot pathogen, the researchers reported.
Related UCCE work also associated crown gall with increased incidence of thousand cankers disease and greater root predation by ten-lined June beetle in walnuts.
The almond study was supported by the Almond Board of California and involved UCCE and CSU Bakersfield researchers. Read the full article here.