Dogwood (Cornus spp.)-Powdery Mildew

Cause Erysiphe pulchra (formerly Microsphaera penicillata) and Phyllactinia guttata can produce white mycelial growth on leaves, buds, flowers, and new stems of dogwood. Powdery mildew on dogwood has been an increasing problem in Southeastern States since 1995, was reported from Washington during 1999 and found in Oregon in 2002. The predominant pathogen in Tennessee, Erysiphe, overwinters as black spherical spore structures (chasmothecia) on leaf debris. Chasmothecia release ascospores in spring. New growth is particularly susceptible to infection. Conidia are produced on mycelia that colonize new plant growth and are the spore type that caused new infections through the growing season. Under favorable conditions, this fungus can go from spore to spore in as little as 7 days. Buds may become infected but do not appear to be an important overwintering site. However, surveys reported in 2019 from the southeast USA found that asexual reproduction was more common noting a shift in this exotic population.

Disease-resistant species, hybrids and flowering cultivars are available including Cornus alba, C. alternifolia, C. controversa, C. kousa, C. mas, and C. sericea. Many red-flower cultivars of Cornus florida are susceptible while only a few white flowering types are resistant.

Symptoms The disease is on foliage, current-year twigs, blossoms, fruit, and buds. The first symptom is often yellow patchy areas on a leaf that become necrotic. A white, very thin, dry growth (mycelium) that is somewhat similar in appearance to a very dense covering of plant hair develops on the lower leaf surface directly below affected leaf spots. All plant parts can become covered with mycelia and spores (conidia). If newly expanding tissue is affected, the growth of that part is restricted or distorted. During late summer and early fall, a peppered speckling (chasmothecia) may develop on the white to light gray growth on leaf surfaces.

Cultural control

  • Disease-resistant cultivars of C. florida include Karen's Appalachian Blush, Jean's Appalachian Snow, Kay's Appalachian Mist, and Appalachian Joy. The C. kousa x florida hybrids 'Aurora', 'Constellation', 'Galaxy', 'Stardust', and 'Stellar Pink' are highly resistant.
  • Improve air circulation to reduce relative humidity and accelerate drying of foliage. Space plants well and plant in more exposed areas; especially avoid planting in heavily shaded areas.
  • Irrigate with microjet sprinklers or soaker hoses to avoid wetting foliage.
  • If practical, prune out and destroy infected tissue as it appears early in the year. If disease continues to build up, stop removing leaves; removing too many leaves is damaging.
  • In the fall, rake up and destroy fallen leaves.

Chemical control With an active scouting program, fungicides can be started at the first sign of disease. Fungicides will do best when used before symptoms develop. Few materials have good eradicant activity. Use at 7- to 14-day intervals; using shorter intervals when environmental conditions favor disease development. Alternate or tank-mix products from different groups that have different modes of action. Limit the use of any one group during the growing season.

  • Armada 50 WDG at 3 to 9 oz/100 gal water. Do not use a silicone-based surfactant. Not for nursery or greenhouse use. Group 3 + 11 fungicide. 12-hr reentry.
  • Bayer Advanced Disease Control at 0.75 fl oz/gal water. H
  • Bayleton 50 T&O at 5.5 oz/275 to 550 gal water. Landscape only, not for use on plants for sale. Group 3 fungicide. 12-hr reentry.
  • Bicarbonates have protectant activity only. Complete coverage is important. It is easily washed off with no residual capability, thus requiring 7- to 10-day intervals during periods favorable to infection. O
    • Kaligreen at 1 to 3 lb/100 gal water. 4-hr reentry.
    • MilStop (85% potassium bicarbonate) at 2.5 to 5 lb/A. Oregon and Washington only. 1-hr reentry.
    • Monterey Bi-Carb Old Fashioned Fungicide at 4 teaspoons/2 gal water. H
  • Broadform at 2 to 4 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Concert at 22 to 35 fl oz/100 gal water. May cause injury to buds, blooms or tender new growth. Landscape use only. Group 3 + M5 fungicide. 12-hr reentry.
  • Daconil Zn at 2 pints/100 gal water (leaves a whitish residue), at 7- to 14-day intervals. Group M5 fungicide. 12-hr reentry.
  • Disarm 480 SC at 1 to 4 fl oz/100 gal water. Group 11 fungicide. 12-hr reentry.
  • Eagle 20 EW at 6 to 12 fl oz/100 gal water. Group 3 fungicide. 24-hr reentry.
  • Mural at 4 to 7 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Myclobutanil 20 EW T&O at 6 to 12 fl oz/100 gal water plus spreading agent. May observe a PGR effect. Group 3 fungicide. 24-hr reentry.
  • Pageant at 6 to 12 oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
  • Propiconazole-based products. Group 3 fungicides.
    • Banner MAXX at 8 fl oz/100 gal water. 12-hr reentry.
    • ProCon-Z at 5 to 8 oz/100 gal water. 24-hr reentry.
  • Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
  • Strobilurin-based products may require 14-day intervals to achieve the best control. Preventive applications only. Group 11 fungicide.
    • Compass 50 WDG at 1 to 2 oz/100 gal water. Do not mix with a silicone-based surfactant. 12-hr reentry.
    • Fame SC at 1 to 4 fl oz/100 gal water. 12-hr reentry.
    • Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. 4-hr reentry.
    • Insignia SC at 3 to 6 fl oz/100 gal water. Do not use with organosilicate-based adjuvants. Use preventively only. Group 11 fungicide. 12-hr reentry.
  • Tebuject 16 is registered for tree injections. The number of capsules used is based on tree size. Group 3 fungicide.
  • Tebuzol 3.6F at 4 to 10 fl oz/100 gal water. Group 3 fungicide. No reentry interval listed.
  • Terraguard SC at 8 fl oz/100 gal water at 7- to 14-day intervals. Group 3 fungicide. 12-hr reentry.
  • Torque at 4 to 10 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Tourney 50 WDG at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
  • Trigo at 3 to 9 oz/100 gal water. Group 3 + 11 fungicide. 12-hr reentry.

Biological control

  • Bayer Advanced Natria Disease Control RTS (Bacillus subtilis strain QST 713) is registered for the home garden. Active ingredient is a small protein. H O
  • Cease or Rhapsody (Bacillus subtilis strain QST 713) at 2 to 8 quarts/100 gal water. Active ingredient is a small protein. Efficacy in the Pacific Northwest is unknown. 4-hr reentry. O

Reference Wyman, C.R., Hadziabdic, D., Boggess, S.L., Rinehart, T.A., Windham, A., Wadl, P., and Trigiano, R.N. 2019. Low genetic diversity suggests the recent introduction of dogwood powdery mildew to North America. Plant Disease, 103:2903-2912.