Cause Leaf spots may be caused by a wide variety of fungi including Cercospora, Elsinoe corni (cause of spot anthracnose), Phyllosticta, Ramularia, Septoria, Sphaceloma, Phlyctema vagabunda and others. Botrytis cinerea often comes in as a secondary pathogen once these other fungi have killed the tissue. Botrytis will also cause spotting and blight on leaves injured by cold temperatures. Leaf spots are more prevalent during and following very wet spring weather. Occasionally severe enough to cause defoliation, these fungi are sporadic and usually do not significantly impact the tree's overall health.
Symptoms Leaves develop small (less than 0.25 inch) round or angular spots, often with a purplish or brown border. Some lesions may have a whitish bloom in their centers. Elsinoe corni also affect the flower bracts, young shoots, and fruit. Stem and fruit spots are often dark and slightly raised. Septoria causes angular brown leaf spots up to 0.25 inch, often with a purple border. Tiny round fruiting bodies, pycnidia, can be seen with a hand lens on the upper surfaces. Cercospora leaf spots are similar but do not have the fruiting bodies. Phyllosticta can produce numerous small, round to irregular spots with tan-to-gray centers and brown to reddish-brown borders.
Cultural control
- Choose to grow resistant cultivars.
- Rake and destroy leaves in the fall.
- Avoid overhead irrigation or apply such that trees are not wet for extended periods of time.
Chemical control Fungicides usually are not warranted in yards or landscapes because these fungi usually do not significantly damage the tree. Fungicides may be used if leaf spots were severe the previous year and the weather is very wet. Apply fungicides at regular intervals from bud swell through bloom.
- 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.
- Avelyo at 3 to 5 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
- Banner MAXX at 2 to 4 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
- BioAdvanced Disease Control at 0.75 fl oz/gal water. H
- Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. Group M5 fungicide. H
- Broadform at 4 to 8 fl oz/100 gal water. Group 7 + 11 fungicide. 12-hr reentry.
- Chipco 26019 FLO at 1 to 2.5 quarts/100 gal water. Group 2 fungicide. 12-hr reentry.
- Cleary's 3336 EG at 12 to 16 oz/100 gal water. Group 1 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 Weather Stik at 1.38 pints/100 gal water. 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.
- Fame SC at 1 to 4 fl oz/100 gal water. Group 11 fungicide. 12-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Mancozeb-based products. Group M3 fungicides. 24-hr reentry.
- Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
- 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.
- Nu-Cop 50 DF at 1 lb/100 gal water. 48-hr reentry.
- Ortho MAX Garden Disease Control at 2 teaspoons/gal water. H
- Pageant at 8 to 12 oz/100 gal water. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. 12-hr reentry.
- Postiva at 10 to 28 fl oz/100 gal water. Group 3 + 7 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- 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 EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Mmbaga, M.T., and Sauve, R.J. 2004. Multiple disease resistance in dogwoods (Cornus spp.) to foliar pathogens. Journal of Arboriculture 30:101-107.