Sunday, May 17, 2009

Landscape - Hawthorn Leaf Spot

The following is information on Hawthorn leaf spot, a disease now present in the landscape.

Hawthorn leaf spot is present on susceptible hawthorns. Look for small round to angular spots. They can become numerous and can cause leaf loss on susceptible English hawthorn. This disease is caused by the fungus Entomosporium mespili, which causes Photinia leafspot.

Cause: Diplocarpon mespili (asexual: Entomosporium mespili), a fungus. Other names include Fabraea scald, leaf blight, or fruit spot. Host range is wide. 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 at 10- to 14-day intervals until dry weather arrives.

a. Daconil Weather Stik at 1.4 pints/100 gal water. Daconil (12.5%) can be used in home gardens. 12-hr reentry.
b. Eagle 20 EW at 6 to 12 fl oz/100 gal water. 24-hr reentry.
c. Bonide Fung-onil Multi-purpose Fungicide at 2.25 teaspoons/gal water.
d. Spectracide Immunox at 1 fl oz/gal water.
e. Mancozeb-based products. 24-hr reentry.
-Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
-Pentathlon DF at 1 to 2 lb/A or per 100 gal water.
-Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
f. Spectro 90 WDG (chlorothalonil plus thiophanate methyl) at 1 to 2 lb/100 gal water. 12-hr reentry.
g. Thiophanate-methyl-based products. 12-hr reentry.
-AllBan Flo at 10 to 14.5 fl oz/100 gal water.
-Cleary’s 3336 WP at 12 to 16 oz/100 gal water.
-Ferti-Lome Halt at 2.5 tsp/gal water is registered for home use.
-OHP 6672 4.5 F at 10 to 14.5 fl oz/100 gal water.

Tebuject is registered for tree injection. Trees are to be injected as a preventative treatment. Do not inject trees less than 2 inches in diameter or those that are suffering from various stresses.

Hawthorn leafspot. Photo from the Oregon State University Online Guide to Plant Disease Control.

Information from Bob Mulrooney, Extension Plant Pathologist, UD and the Oregon State University Online Guide to Plant Disease Control. For more information go to:

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