Different types of fungal pathogens in your home garden threaten to infect and damage your prized azalea plants. Azaleas are susceptible to both soil-borne fungi as well as mold that develops as a result of a pest infestation. Promote vigorous growth with careful care as a means of prevention of azalea stem mold.
Vigorous azalea plants have a much greater chance of avoiding and healing from mold infections when compared to azaleas in decline or stressed conditions. Grow your azaleas in areas that offer partial shade, according to the Clemson University Extension. Azaleas thrive in well-drained acid soil high in organic content with a pH of 4.5 to 6.0.
Phytophthora root rot is a fungal infection of azaleas caused by the fungi species Phytophthora parasitica and Phytophthora cinnamomi, according to the Virginia Cooperative Extension. Sooty mold is another fungus problem that arises due to pest infestations like azalea bark scale (Eriococcus azaleas), according to the N.C. State University Cooperative Extension Service.
Phytopthora root rot results in mold problems on stems of azaleas when soil-borne pathogens invade through azalea root systems. Look for diminished health and discoloration of foliage, leaf wilt, stunted growth and browning of entire plants. Stems experience this mold problem along with roots when plant tissue decays and changes to a reddish brown hue, according to the Virginia Cooperative Extension. When sooty mold appears on azalea stems, it is a response to the presence of the pest azalea bark scale. These scales are tiny bugs that suck the sap from the plant. The scales produce honeydew, a sugary substance that attracts fungal pathogens that develop into sooty mold, which is is black and resembles soot. It may lead to twig dieback, according to the N.C. State University Cooperative Extension Service.
For natural control of phytophthora rot rot, provide well-drained soil to your azaleas. If your site is soggy, consider planting azaleas in a raised bed, according to the Virginia Cooperative Extension. For natural control of sooty mold, control the insect causing the problem. Remove affected plant parts and dislodge bugs with a strong stream of water. You can also release predatory bugs to kill the insect pests. Predatory insects are available in garden supply stores and catalogs.
For chemical control of phytophthora root rot mold on azalea stems, apply a fungicide with metalaxyl or fosetyl-A. Saturate the soil surrounding your azalea with the fungicide for control, according to the Virginia Cooperative Extension. For sooty mold on azalea stems, clear up a pest infestation of azalea bark scale with chemical controls at the end of spring and the end of fall. Apply dormant oil to plants to kill overwintering insects, according to the University of Connecticut IPM.