PDC Fact Sheet Leaf Spot Diseases of Shade Trees and Ornamentals

Cause:	Leaf spot is a common descriptive term applied to a number of diseases affecting the foliage of ornamentals and shade trees. The majority of the leaf spots are caused by a variety of fungal pathogens but some are caused by bacteria. Anthracnose is a term for a group of loosely related fungal diseases that often cause irregular blotches on leaves. For more specific information about anthracnose, see the separate disease profile on anthracnose.
Primary Hosts In Missouri:	All species of trees of shrub can potentially develop leaf spots, but some species are more susceptible than others.
Symptoms / Diagnosis:	The primary symptom of a leaf spot disease is spots on foliage (figure 1). The spots will vary in size and color depending on the plant affected the specific organism involved, and the stage of development. Spots are most often brownish, but may be tan or black. Concentric rings or a dark margin around the spot may be present. Fungal bodies may appear as black dots in the center of the spots (figure 2). Over time the spots may combine to enlarge to form blotches. Spots or blotches that are angular and located around the veins are generally referred to as anthracnose (see disease profile on anthracnose). Leaves may yellow and drop prematurely.
Life Cycle:	The organisms that cause leaf spots survive in fallen infected leaves and twigs. Some may remain in dead twigs on the tree. During wet weather, spores are released which may splashed or be windblown onto newly emerging tender leaves where they germinate in the moisture and infect the leaf. Overhead watering late in the day or during the night, heavy dews and close spacing of plants prolong wetting of the leaf surface and provide more opportunities for fungal or bacterial infections.
Integrated Management Strategies:	Live with the disease. Leaf spots are largely an aesthetic problem as few leaf spots seriously damage the host. Also control is seldom achieved after the infection has started. Remove infected leaves and dead twigs. Raking up and disposing of infected leaves as they drop and pruning out dead twigs can help control the disease by removing spores that can reinfect the new leaves. This will not cure the problem but it can help minimize infections. Keep foliage dry. Avoid overhead watering. Use soaker hoses or water early in the day so the foliage can dry before night. Watering can also spread the disease by splashing. Prune plants and space plants to allow for good air circulation that promotes rapid drying of foliage. Keep plants healthy. Since most plants can tolerate some defoliation, keep them in good health so they can rebound quickly. Avoid over fertilization as it promotes a flush of young leaves that are more susceptible to attack by insects and disease. Use fungicides wisely. In rare cases of severe infection where the size and value of plants make it practical, applications of fungicides may be helpful. Generally fungicidal control is warranted if: 1) repeated defoliations occur in one year or subsequent years, 2) the plant is under stress, 3) the plant is in decline, 4) the plant is a needled evergreen or 5) the disease is black spot of roses. Sprays will not cure the infection but protect leaves from becoming infected. To be effective fungicidal sprays must be begun at bud break before symptoms are noted and be continued at intervals specified by the label (usually 10-14 days) through the period of spring rains. Spraying after infection is present will provide little benefit. Recommendations will vary with the disease and fungicide used. It is always good practice to have the disease identified before purchasing a control product. See table 1 for a general listing of active ingredients listed for control of various leaf spotting fungi. Replace the plant. For plants that chronically are plagued by leaf spots, gardeners find it more convenient to replace a plant with a different species or a variety that is more resistant or tolerant of disease. A nursery can help you in your selection.

Figure 1. A fungal leafspot (Cercopsora sp.) of redbud	Figure 2. A closeup of the fruiting structures of the Cercospora sp. fungus sporulating in the center of the leaf spot.
Figure 3. Crabapple leaf infected with apple scab.

Table 1. A general listing of active ingredients labeled for use for control of leaf spotting diseases on woody ornamentals and trees. Always consult the label to make sure both the host and disease are listed.

Active Ingredient	Examples of Tradenames	Remarks
azoxystrobin	Heritage	Certain varieties of apple, cherry and crabapples are susceptible to injury by sprays. See label for details.
Bordeaux mixture	Bordeaux Mixture (various manufacturers)	Some fungicides containing copper may cause plant injury. Damage is most likely to occur in cool, humid weather.
captan	Captan
chlorothalonil	Bravo, Daconil, Manicure, Thalonil Homeowner: many trade name including Daconil
fenarimol	Rubigan	commercial use only
fixed coppers	Kocide, Phyton 27 Homeowner: many trade names	Some fungicides containing copper may cause plant injury. Damage is most likely to occur in cool, humid weather.
iprodione	Chipco 26019	commerical use only
maneb	Pentathlon	Not intended for use on fruit trees by homeowners. Do not use treated plants for food or feed.
mancozeb	Mancozeb, Dithane, Protect Homeowner: many trade names including Mancozeb	Not intended for use on fruit trees by homeowners. Do not use treated plants for food or feed.
mancozeb + copper hydroxide	Junction	Not intended for use on fruit trees by homeowners. Do not use treated plants for food or feed.
myclobutanil	Eagle, Systhane Homeowner: Immunox
propiconizole	Banner Maxx
quaternary ammonium compounds	Physan 20 and Triathlon	For greenhouse and plant propagation areas.
Thiophanate-methy	Cleary's 3336, Fungo 50 Homeowner: GreenLight Systemic Fungicide, Fertilome Halt
triforine	funginex
University Outreach and Extension does not endorse commercial products. Follow the label on all pesticides.

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