Fungus on Lavender Plants

Cause

• High humidity and overcrowding are one of the main causes of the growth of fungus on your lavender plant. Many soil-borne fungi will attack this plant as well. Overly moist or poorly draining soils will also cause fungus to grow on lavender.

Types of Fungus

• Root rot is caused by a soil-borne virus that thrives in poorly drained soils. Shab is a fungus that is common in Europe, but not in the United States. This fungus attacks lavender plants that have poor air circulation. Lavender leaf spot will cause the leaves of the plant to yellow and eventually fall from the branch.

Symptoms

• Discolored leaves, either yellow or brown to black, are one of the first symptoms your lavender plant is infected with a fungus. With some fungal diseases, parts or all of the plant will wilt suddenly. Your lavender plant may also defoliate, or lose all its leaves.

Treatment

• Fungicides can be used on lavender plants but they do not often work with soil-borne fungi. Removing the plant and the soil where the plant was growing may work, but according to Washington State University, it's better not to attempt to grow lavender in the area again. Plants with leaf fungus may recover on their own without additional treatment if proper care is taken of the plant. Do not compost infected plants. These plants should be removed from the area.

Prevention

• Leave plenty of room around your lavender plant to allow air circulation. Space plants so, when full grown, there will still be at least 9 inches between each plant. Avoid watering the leaves of your lavender plant, for instance, by overhead sprinkler. Instead, water at ground level using drip irrigation or a soaker hose. When mulching the plant, use sand or small pebbles instead of moisture retaining organic mulch. This will reflect the sun and dry out the areas of your plant not reached by the sun’s rays. Cut back any sign of fungal growth immediately to avoid spread.