Botryosphaeria Canker

  • Symptoms

    • Rough, sunken, dark-brown areas form around wounds or natural openings in the bark. The wood of a recently killed branch is lighter brown than the pith. Dead bark falls off the cankered area. Leaves on affected branches wilt as affected branches die. Chocolate-brown cankers enlarge along the branch more quickly than around its circumference. Tiny black fungal fruiting structures that pepper the dead bark are most easily seen on the light tan bark.
  • Management

    • Irrigate plants to prevent drought stress, which predisposes the plants to this canker. Prune infected branches, cutting back to where growth will resume. Do not leave large stubs of non-growing tissue. Disinfect the pruning shears frequently. No chemicals adequately control this disease.

Botrytis Blight

  • Symptoms

    • Small, water-soaked lesions develop on petals. Gray fungal growth covers petals
  • Management

    • Remove fading flowers and yellowing leaves. Apply chlorothalonil, copper, copper sulfate, cupric or hydroxide

Botrytis Blight


Cercospora Leaf Spot

  • Symptoms

    • Circular to irregular brown spots up to 1/2 inch in diameter form on leaves, especially lower leaves. Spots may become tan in the center and may have a yellow halo. Dark-brown, pimple-like fungal fruiting structures form within the spots. Infected leaves may fall.
  • Management

    • Inspect new plants and do not use if found to be infected. Rake and destroy fallen leaves. Avoid overhead irrigation. Apply chlorothalonil, myclobutanil, cupric hydroxide, mancozeb + thiophanate methyl, or triadimefon to protect leaves before infection in the spring.

Leaf Spot on an Azalea


Cylindrocladium Blight

  • Symptoms

    • Leaves turn brown to black and fall in 3 to 4 days. Stems have brown spots on which white masses of spores later form. Or roots die and plants wilt without having leaf spots form. Plants die rapidly.
  • Management

    • Rake and destroy fallen leaves. Use clean, disinfested tools. Remove severely infected plants. Apply thiophanate methyl as a soil drench

Cylindrocladium Blight


Leaf & Flower Gall

  • Symptoms

    • Young leaves and flowers become swollen, fleshy, and pale green. These become white due to the formation of spores by the fungus on the surface. Later, the galls become hard and brown. Infection occurs in the spring. The new spores formed on the surface of the galls are dispersed but do not cause more galls to form during that same season. They remain dormant until the following spring.
  • Management

    • Remove and destroy all galls before they become white with new spores. If many plants had the disease in previous years and galls were too numerous to pick, apply mancozeb to protect new foliage and flowers as they emerge. Applications can cease when the leaves reach their full size.

Leaf Gall


Ovulinia Petal Blight

  • Symptoms

    • Pale-white to rust-colored spots form on petals. Spots enlarge rapidly. Petals become slimy and fall apart easily.
  • Management

    • Remove crop debris. Water in a manner that keeps plant surfaces dry. Space plants to ensure good air circulation. Apply thiophanate methyl, chlorothalonil, mancozeb, mancozeb + thiophanate methyl, triadimefon, triforine, or myclobutanil as blossoms open. Chlorothalonil is phytotoxic to some cultivars.

Ovulinia Petal Blight


Phytophthora Root Rot & Top Dieback

  • Symptoms

    • Plants are stunted and wilted. Leaves yellow, and the entire plant eventually dies. Roots with few feeder roots die. Stem wood at the soil level has red-brown discoloration. In the top dieback phase, leaves have dark-brown spots. Shoots die from the tips back as dark-brown cankers form.
  • Management

    • To protect healthy plants, apply mefenoxam, etridiazole, etridiazole + thiophanate methyl, fosetyl-Al, potassium salts of phosphorus acid, fluopicolide, or propamocarb.

Rhododendron Root Rot


Powdery Mildew

  • Symptoms

    • Faint yellow areas form on expanded leaves. White fungal growth forms on the yellow areas of some cultivars while only small dead spots with no fungal growth occur on other cultivars
  • Management

    • PureSpray Green is a very effective way to control powdery mildew (buy now)

Powdery Mildew


Rhizoctonia Web Blight

  • Symptoms

    • Small tan to black spots form on leaves and expand to engulf the entire leaf. Leaves fall. Webbing may develop. Small plants may die.
  • Management

    • Maintain good air circulation. Avoid late afternoon watering. Apply triflumizole, thiophanate methyl, chlorothalonil, fludioxonil, or iprodione.

Azalea Web Blight