Diseases of lemon (
Lemon heartwood rot
Three different wood rot fungi are associated with heartwood rot in lemon in Arizona: Coniophora eremophila, Antrodia sinuosa and a Nodulisporium species. Coniophora eremophila has been isolated from many other desert shrubs, trees and cacti. Antrodia sinuosa rot is usually associated with conifer forest trees, but is not considered problematic on conifers in Arizona. Coniophora eremophila and Antrodia sinuosa both cause a brown heartwood rot in older lemon trees. They occur in large branches and progress through the trunk. Nodulisporium sp. differs in that it is isolated from younger, smaller branches of lemon and produces a white wood rot (photo 1).
Coniophora eremophila, Antrodia sinuosa and Nodulisporium sp. invade the heartwood through wounds or open exposed areas caused by breaking from heavy fruit load, pruning, and wind or equipment damage. Infections are probably initiated in lemon trees in commercial orchards that undergo extreme pruning (photo 2) annually and in landscape trees at pruning sites or other mechanical wounds. Once established, these fungi grow throughout the heartwood. In the cases of Antrodia sinuosa or Coniophora eremophila infections, the tree’s structure is eventually weakened and branches break (photo 3). In the case of Nodulisporium sp. infection, portions of relatively young citrus branches die, and trees suffer crown dieback.
All of these fungi can produce windborne spores, but reproductive structures of Coniophora and Nodulisporium have not been found in lemon orchards to date. Coniophora spores are probably blown in from desert plants, but the source of Nodulisporium spores is still unknown. Antrodia produces flat, off-white to beige (photo 4) reproductive structures on lemon wood that have been found in Yuma in every season of the year and are a source of inoculum to infest nearby trees.
Controlling the spread of fungal heartwood rots by sanitation and by
keeping the sources of spores at a minimum is the best treatment for lemons.
Home growers should cut out infected areas from the tree. Removing broken
infected branches and disposing of them from the site will help to prevent
further infections. Adequate irrigation and proper fertilization should
promote wound healing and minimize the development of wood rot. Fungicide
treatment for the disease is not recommended, and in a commercial setting,
it would not be cost effective.
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February 11, 2008