Anthracnose of Shade Trees
Sherman V. Thomson/Extension Plant Pathologist
Scott C. Ockey/Plant Disease Diagnostician
|Characteristic tissue chlorosis and brown necrotic lesions along the veins of Sycamore leaves.|
Dark colored fungal reproductive bodies (Pycnidia) forms on woody tissue of trees infected with Anthracnose causing fungi. Pycnidia can often be found on affected twigs and branches.
|Mature sycamore trees with severe anthracnose. Trees may be defoliated by mid to late summer depending on severity of infection.|
Anthracnose of Shade Trees
Anthracnose is a fungal disease common throughout Utah on Maple, Sycamore, Oak and Ash. Although in most years it does not cause significant damage, it can be very destructive during years when extended cool wet spring conditions occur. Consecutive years with conditions conducive to disease can seriously weaken trees and may cause death if the conditions persist and control measures are not implemented.
The group of fungi that cause anthracnose produce spore bearing structures called acervuli. The acervuli erupt through the plant tissue and are evident as small black dots on twigs. The fungi that cause anthracnose are Kabatiella apocrypta in Maple, Apiognomonia veneta in Sycamore, A. quercina in Oak and A. errabunda in Ash.
The first symptoms occur on leaves as small water soaked lesions. They are usually found along main veins of leaves, but can also occur between the veins. The spots enlarge and eventually turn tan, reddish-brown or black, depending on the species and cultivar of tree affected. Acervuli are then produced by the fungus in the necrotic tissue. Sycamore leaves can become infected as they emerge from buds resulting in blighting of the entire leaf cluster.
Infections on twigs and branches initially appear as discolored depressed areas in the bark followed by splitting bark. Severe infections may even result in death of small branches. Cankers usually develop raised margins resulting from the healing process in the tree. Sycamore branch infections result in multiple lateral shoots called witches brooms.
The fungi overwinter in fallen leaves, petioles, twigs or branches. Under cool moist spring conditions the fungi mature and produce spores that are dispersed by wind and rain. Spores that contact susceptible host tissue infect and grow throughout the adjacent tissue leading to the characteristic leaf spot symptoms.
Cultural controls are only marginally effective for anthracnose and are mostly aimed at sanitation by reducing overwintering sites of the fungi. The effectiveness of sanitation is often minimal because there are many external sources of spores that are blown into the area. Cultural controls should be considered if the tree or adjacent trees have a history of anthracnose. Recommended cultural controls include:
1. Rake and destroy fallen leaves.
2. Prune out and destroy infected twigs and branches.
3. Maintain tree vigor with adequate water and fertilization.
4. Plant resistant cultivars. Sycamore cultivars Bloodgood, Columbia and Liberty are reported to be resistant. Check with your local nursery for resistance information regarding other tree species.
It is usually not necessary to use chemicals to control anthracnose because the fungus only infects when wet conditions persist. Most trees can withstand occasional infections without any serious damage. However Chemical controls should be implemented in addition to the cultural controls when cool, wet spring weather occurs year after year. Chemical applications should begin at bud swell and continue at labeled rates and intervals during wet weather. Table 1 lists registered chemicals for control of anthracnose on Maple, Sycamore, Oak and Ash. Be sure to check the label for specific information about labeled uses and rates.
Table 1 Registered products as of January 2000.
|Banner MAXX||Maple||5 to 8 fl oz/100gal water||24 hour re-entry|
|Sycamore||6 to 8 fl oz/100gal water||24 hour re-entry|
|Oak||16 oz/100gal water||Test on small portion of tree before complete application. 24 hour re-entry.|
|Champ Formula 2||Sycamore||1.3 to 2 pints/Acre||24 hour re-entry|
|Cleary's 3336 WP||Maple||12 to 16 oz/100 gal water||12 hour re-entry|
|Sycamore||12 to 16 oz/100 gal water||Apply resistance management strategies. Alternate fungicides. 12 hour re-entry|
|Oak||12 to 16 oz/100 gal water||12 hour re-entry|
|Ash||12 to 16 oz/100 gal water||12 hour re-entry|
|Daconil Weather Stik||Maple||1.4 pints/100 gal water||Daconil 12.5% can be used on Sycamore and Ash in home gardens. 48 hour re-entry.|
|Fore (80%mancozeb)||Maple||1.5 lb/100 gal water||24 hour re-entry|
|Kocide DF||Sycamore||2 to 3 lb/Acre||24 hour re-entry|
|Nu-Cop 50DF||Sycamore||2 to 3 lb/100 gal water||24 hour re-entry|
|Bayleton||Consult current label for this fungicide before use.|
Precautionary Statement: All pesticides have benefits and risks, however following the label will maximize the benefits and reduce risks. Pay attention to the directions for use and follow precautionary statements. Pesticide labels are considered legal documents containing instructions and limitations. Inconsistent use of the product or disregarding the label is a violation of both federal and state laws. The pesticide applicator is legally responsible for proper use. This publication is issued in furtherance of Cooperative Extension work. Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Vice President for Extension and Agriculture, Utah State University.