Wilt in redbay during initial disease stages
Stephen Fraedrich, USDA Forest Service
Laurel wilt is a deadly disease of redbay (Persea borbonia) and other tree species in the Laurel family (Lauraceae). The disease is caused by a fungus (Raffaelea lauricola) that is introduced into host trees by a non-native insect, the redbay ambrosia beetle (Xyleborus glabratus).
Keywords: redbay, Persea borbonia, Lauraceae, fungus, Raffaelea lauricola, redbay ambrosia beetle, Xyleborus glabratus, drooping foliage, foliage discoloration
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Laurel wilt distribution
The fungus resides in specialized pouches (mycangia) within the heads of beetles. It is thought to ooze out of the mycangia and enter the water conducting tissues (xylem) of susceptible hosts as beetles bore into trees. Fungal spores reproduce and spread within the xylem. The xylem becomes plugged, resulting in drooping foliage with a reddish or purplish discoloration. Discoloration may occur in a portion of the crown at first, but gradually the entire crown wilts and reddens. Foliage eventually turns brown and may remain on branches for up to a year or more. As trees die, they are increasingly attacked by the redbay ambrosia beetle as well as other beetles. Beetles live in tunnels excavated into dead and dying trees and produce significant numbers of offspring. As trees are colonized by more ambrosia beetles, toothpick-like tubes or piles of fine sawdust may be observed on the bark. Redbay ambrosia beetles that emerge from dead and dying trees carry the laurel wilt fungus, and can spread it to healthy trees. The rate of spread of the beetle is estimated at about 20 miles per year (without help from humans, who may inadvertently transport it in firewood or infested plants).