Symptoms of Dogwood Anthracnose

Dogwood anthracnose affects leaves, bracts, current-year shoots, localized areas of bark and cambium of trunk or branches, fruits, and seeds of C. florida (Brittonand others1993; Daughtrey and Hibben 1983). C. kousa also is considered a host, but leaf infection is generally minimal(Daughtreyand others1996)BROKEN-LINK .

Leaf symptoms on C. florida generally occur within 4 weeks after flowering (Britton 1993, Hibben and Daughtrey 1988). Symptomsand include: (1) necrotic lesions surrounded by a reddish or brown-purple zone (some with chlorotic halo), (2) shot holes, (3) necrotic blotches at the leaf tip or along the blade periphery, or (4) blight of the entire blade (Hibben and Daughtrey 1988). Leaf spots vary according to light exposure. Purple-rimmed lesions (BROKEN-LINK Parham and Windham 1992) or shot holes predominate on leaves exposed to sunlight, while necrotic blotches predominate on shaded leaves (BROKEN-LINK Parham and Windham 1992). Blighting commonly occurs throughout the canopy of understory C. Florida, or within the interior canopy or on epicormic branches of exposed trees. Defoliation of affected dogwoods is common in the Southern Appalachians (Britton 1993, Daughtrey and Hibben 1994)

Twig dieback is caused by infection, which may occur directly through bark or indirectly through spread from the petioles of affected leaves (Daughtreyand others1996). Epicormic shoots often form along the entire length of the main stem and on major branches of infected C. florida (Hibben and Daughtrey 1988). Infection of epicormic branches via petioles of blighted leaves is very common. Infections then spread from infected shoots into the main stem, forming annual cankers that can kill the entire tree (Hibben and Daughtrey 1988,Daughtrey and Hibben 1994, Daughtreyand others1996).

The disease kills dogwoods of all sizes, but it is most severe on young seedlings. Regeneration can be eliminated in some areas. Large C. florida often die 2 to 3 years after the first symptoms are found in the leaves (Andersonand others1994). Overall, vigorous trees tend to be less damaged than weak trees. Trees that survive one or more seasons of severe anthracnose usually have swollen areas on trunks and branches where cankers were enveloped by new tissue(Daughtrey and Hibben 1994).

Environmental factors influence dogwoods susceptibility to the disease. Understory forest dogwoods are more prone to infection than trees growing in full sunlight. For this reason, ornamentals grown in open, sunny sites are often disfigured without being killed. In the Southern Appalachians, mortality is most likely at elevations above 3,000 feet. Below 3,000 feet, damage is most severe on moist, cool sites such as northeast-facing slopes (Chellemiand others1992, Hoffardand others1995).

Infection of dogwoods is most likely to occur during cool, wet weather in spring and fall, but can occur at any time during the growing season. Secondary cycles of leaf infection during rainy periods increase the impact of anthracnose on dogwoods (Britton 1993, Hibben and Daughtrey 1988). Drought and winter injury appear to increase susceptibility(Daughtrey and Hibben 1994).

Diseases with similar symptoms

The symptoms of dogwood anthracnose (D. destructiva) are often similar to symptoms of less serious diseases. Anderson and others (1994) point out the following:

• Spot anthracnose, caused by Elsin orni, infects leaves in the spring, causing numerous round lesions (1 to 2 mm diameter) that can coalesce into large spots.
• Leaf spots, caused by Septoria cornicola, appear in late summer or fall. Spots, about 1/4 inch in diameter with square margins, may merge to form large blotches.
• Bracts infected by B. cinerea have irregular brown patches, and can be easily confused with bracts infected by D. destructiva.
• The dogwood twig borer (Oberea tripunctata) kills shoots in clumped areas of the crown. The emerging borer causes a hole in the affected shoot.
• Mechanical injuries and drought can also cause symptoms in foliage and branches that mimic dogwood anthracnose.

Due to the difficulty of distinguishing these similar diseases and pests, researchers recommend that the presence of D. destructiva should beconfirmed by directly examining fungal sporulation in tissue lesions (Andersonand others1994).