Although limited surveys have been conducted to determine the incidence of Macrophylla decline in lemons, research has not been conducted to determine if Coniophora is an important component in lemon decline in California. Results from this project will help to elucidate the role of Coniophora in lemon decline. Symptoms produced by Coniophora are a brown heartwood rot on woody host plants. When the heartwood of a selected branch is decayed the branch dies rapidly, leaving the dry leaves on the dead branch. The fungus generally enters a host through injuries such as broken branches.
Additional decay weakens the branches causing more breakage.
Heavy fruit load can cause branches to split resulting in injuries that are prone to infection by the fungus. In Yuma, there is a high incidence of Coniophora in older orchards. Coniophora is not known to produce spores on citrus but can sporulate on native hosts such as desert willow. New infections must come from spores produced on native hosts and thus lemon tree to lemon tree spread is not known to occur. We will be surveying orchards in the desert this fall and winter.