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Cause Diplocarpon mespili (asexual: Entomosporium mespili), a fungus. Reported from Washington and found numerous times by the OSU Plant Clinic. Reported to be the most serious disease of hawthorn in coastal BC. Other names include Fabraea scald, leaf blight, or fruit spot. Host range is wide including Indian hawthorn, photinia, and quince. The fungus overwinters on dead leaves and young twigs. Cool, wet weather favors disease development. English hawthorn (Crataegus laevigata) is very susceptible including the cultivars 'Paulii' and 'Crimson Cloud'. Most other commercial hawthorns appear resistant.
Symptoms Small reddish-brown spots on upper and lower leaf surfaces, numerous and severe after a wet spring. Later, the tissue between leaf spots turns yellow. The area bordering the leaf lesions may remain green, creating a green island effect. Raised bumps (acervuli) appear in the centers of lesions. When spots are numerous, defoliation often occurs. Repeated annual defoliation can reduce growth and weaken trees.
Cultural control
- Rake and destroy leaves in fall.
- Grow other, more resistant species of Crataegus.
Chemical control Begin foliar applications at budbreak and repeat on 10- to 14-day intervals (if label allows) until dry weather arrives.
- 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.Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water. H
- Daconil Weather Stik at 1.38 pints/100 gal water. Group M5 fungicide. 12-hr reentry.
- Eagle 20 EW at 6 to 12 fl oz/100 gal water. Group 3 fungicide. 24-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. Do not apply to certain crabapple or drift onto apples trees. 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.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 1 fl oz/gal water. Group 3 fungicide. H
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Group 1 + M5 fungicide. 12-hr reentry.
- Tebuject is registered for tree injection as a preventive treatment. Do not inject trees less than 2 inches in diameter or those that are suffering from various stresses.
- Thiophanate-methyl-based products. Group 1 fungicide. 12-hr reentry.
- Cleary's 3336 EG at 12 to 16 oz/100 gal water.
- OHP 6672 4.5 F at 10 to 14.5 fl oz/100 gal water.
- Tourney EZ at 1 to 4 oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Chen, H., White, J.F., Malik, K., Qi, F. and Li, C. 2022. Diplocarpon mespilicola sp. nov. associated with Entomosporium leaf spot on Hawthorn in China. Plant Disease. 106:2884-2891.