Ganoderma adspersum, the Cause of Extensive Wood Decay of Almond Trees in California Orchards

Ganoderma adspersum, previously unreported in North America, was identified as the primary causal agent of root and butt rot-related failure in almond trees in California's Central Valley. This disease has been observed over approximately 340 km in California and in orchards spanning 5 to more than 20 years old. The most common sign is reddish-brown basidiomata that develop at the base of the trees in the later stages of the disease. Ganoderma adspersum was isolated from the decayed wood of failed trees with the peach rootstock cultivar Nemaguard. Rootstocks were inoculated with G. adspersum in a greenhouse setting, and decay similar to naturally infected trees developed. The pathogen was reisolated from the inoculated plants, confirming pathogenicity.