Author: HAGAN PubID: ANR-0941

Title:

SPOT ANTHRACNOSE ON FLOWERING DOGWOOD

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ANR-941, New Sept 1995. Austin Hagan, Extension Plant Pathologist, Professor, Plant Pathology, and Jacqueline Mullen, Extension Plant Pathologist and Diagnostician, Auburn University

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Plant Disease Notes Spot Anthracnose on Flowering Dogwood

Spot anthracnose, which is caused by the fungus Elsinoe corni, is a common disease of flowering dogwood (Cornus florida). This disease is usually seen on dogwoods growing in partial to full sun; it is rarely a problem on trees in heavy shade. Dogwoods that flower first in the spring often suffer the heaviest spotting of the leaves and bracts. Generally, spot anthracnose is most damaging when the weather is cloudy and wet starting at bud-break through bloom.

Symptoms. Numerous small reddish purple spots on the white bracts and brown spots on the unfurling pink or red bracts are the earliest symptoms of spot anthracnose in the spring on flowering dogwood. Through the remainder of spring, a similar spotting on the new, expanding leaves, shoots, petioles, and fruit of dogwood occurs. Bracts and new leaves with numerous spots are often twisted or deformed. Heavily spotted bracts are often shed early. Although severe outbreaks of spot anthracnose will ruin the floral display of dogwood, this disease rarely reduces tree vigor.

Persistence And Transmission. As dogwoods begin to bloom, fungal spores are spread from tiny fruiting bodies on diseased shoots to flower and leaf buds by a combination of splashing water and wind. Extended periods of mild, wet, humid weather favor pathogen spread and colonization of bracts and juvenile leaves. In the landscape, disease spread generally is limited to early to mid-spring when the trees are putting on new leaves. Once the leaves mature, little development of spot anthracnose occurs.

Control. Spot anthracnose on flowering dogwood can be controlled by the following strategies:

• Plant early-flowering dogwood selections in partial to full shade to avoid disease outbreaks. You can plant later-flowering dogwoods in full sun because they have moderate to good resistance to spot anthracnose.
• Plant resistant cultivars. Nearly all native flowering dogwoods are susceptible to this disease. Some common cultivars of the flowering dogwood and their susceptibility to spot anthracnose are:
  • Very Sensitive Plants. Barton White, Cloud 9.
  • Somewhat Resistant Plants. Rubra, Welch's Junior Miss.
  • Resistant. Cherokee Princess, First Lady, Fragrant Cloud, Plena, Purple Glory, Spring Time.
• In late fall, collect and discard the leaves from around the base of spot anthracnose-damaged trees.
• For specimen or valuable flowering dogwoods in the landscape, apply a protective fungicide. Make the first application as the flower buds begin to swell. Make two to three additional applications every 7 to 14 days to fully protect the bracts and leaves from attack by the spot anthracnose fungus. Stop applying fungicides once the bracts fall.
• Fungicides labeled for use on flowering dogwood for the control of spot anthracnose are:

Fungicide	Rate per gal.	Rate per 100 gal.	Comments
chlorothalonil Daconil 2787 4.17F	2 t.	2 pt.	Start sprays at bud break; repeat every 7 to 14 days until bracts fall. On badly diseased trees, begin sprays again in late summer at flower bud set.
chlorothalonil Twosome 4.4F	2 t.	2 pt.
thiophanate-methyl Cleary's 3336 50W Cleary's 3336 4F Domain 4F	1 T. -- --	12 oz. 20 fl. oz. 20 fl. oz.
mancozeb Dithane T/O 80W Fore 80W Dithane WF	2-1/4 t. 2-1/4 t. --	1-1/2 lb. 1-1/2 lb. 1.2 qt.
thiophanate-methyl + mancozeb Zyban/Duosan 75W	2-1/2 t.	1-1/2 lb.

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Use chemicals only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed.

Trade names are used only to give specific information. The Alabama Cooperative Extension Service does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.

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For more information, contact your county Extension office. Look in your telephone directory under your county's name to find the number.

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For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information.

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