Lavender Leaf Fungus

Wilt Viruses

• Wilt viruses such as fusarium solani or phytophthora spp. can affect lavender plants, causing leaves and shoots to wilt, turn brown and die. Gardeners will find English lavender more susceptible to wilt diseases than other varieties, according to Dr. Joe-Ann McCoy of the North Carolina State University Cooperative Extension. Wilt viruses tend to affect lavender plants in August in areas where temperatures reach 90 degrees or higher and humidity levels remain high. To offset the potential for wilt or protect nonaffected plants from the virus, gardeners may remove the infected plants and destroy any leaves or shoots that have fallen to prevent spread.

Verticillium Wilt

• Soil-borne, verticillium wilt fungi attack "more than three hundred woody and herbaceous plant species," according to James Schuster, a horticulture educator with the University of Illinois Extension. Stressed lavender roots become susceptible to attack. The disease typically begins at the roots and moves upward. Once infected, verticillium symptoms include wilting and curling leaves that may turn red or yellow, as well as falling foilage. Eventually, the plant will die.

Lavender Leaf Spot

• When lavender leaf spot, or septoria lavandulae, affects the plant, leaves have a yellowish shade, spots and eventually die, according to an article published on the Washington State University Extension website. Lavender grown in humid climates or environments such as greenhouses may experience leaf spot disease more often. Frequent spring rainfall may cause the disease, even if the area has low humidity. A change in climate conditions, reducing the humidity and/or moisture, usually allows lavender to recover from leaf spot.

Root Rot

• Root rot, caused by phytophthora cinnamoni or the armillariella mellea, affects a variety of ornamental plants and herbs, including lavender. Fungi causing root rot occur in the soil and particularly affect plants growing in soil with poor drainage. Symptoms of infected lavender include smaller foliage and/or wilting. If left untreated, part of a lavender plant may die one season with the rest of the plant dying the following season, according to Curtis Beus, author of the WSU Extension website article. Poorly drained soil increases the likelihood of root rot. Gardeners may remove affected the plants to a new location, assuring the new site has adequately drained soils.

Shab

• Shab, another fungal disease that attacks lavender, has affected European crops, Beus writes. Symptoms of shab include yellowing and wilting of leaves and dying shoots. If severe, the entire lavender plant infected with shab will die. However, not all lavender varieties succumb to disease. Shab does not affect the L. angustifolia variety, and if the L. x intermedia lavender grows in a soil with adequate drainage and ventilation in a sunny area, the disease will not affect it. Gardeners can help prevent the disease or lessen its severity by planting lavender in well-drained soils in arid, sunny sites.