Anthracnose

Family: N/A (The family is different depending on host plant)

About Anthracnose

Life Cycle

These fungi have the ability to overwinter among plant and leaf litter or on twigs of deciduous trees. When the spring comes, the fungi produce spores that are spread through water. They will find new growth, either leaves or twigs of host plants, and soon germinate. During spring seasons that are very moist, a second spore generation will develop and spread to more host plants, which is why damage to deciduous trees is often much more critical during lengthy rain periods in the springtime. The blight caused by these fungi can severely affect tree types such as ash, evergreen elms, sycamore, and oak. These fungi are unable to spread under dry weather conditions; in this situation, spore development will cease and damage will not be near as fatal.

Anthracnose Identification and Habitat

Identification

Symptoms caused by this group of diseases vary depending on the specific type of plant infected, weather conditions, and when infection occurs. With trees such as oak, the leaves that have been infected will typically have dark spots that appear. Sycamore symptoms are differentiated by the browning of leaf veins. Trees like ash hardly show any symptoms at all. Leaves that become distorted in shape usually indicate that infection had occurred early in development. Mature leaves are often unaffected unless weather conditions are favorable for the fungus. Leaves that have bad infection will die completely and fall from the tree prematurely. In some cases a tree can be entirely defoliated. Infection can also occur in tree branches or twigs, which will appear as cankers or swollen edging, and can occasionally girdle the plant. If buds have regrowth after, branches may appear crooked or knotted. Unless a plant is completely defoliated each year and experiences cankering, long term damage to the plant is unlikely.

Habitat

Anthracnose prefers wet, cool weather as this is how the spores spread to new host plants, especially when temperatures vary between 50 and 68 degrees Fahrenheit. Anthracnose fungi are considered a group of diseases that can develop on several different plant types. It may affect shrubs, evergreen and deciduous trees, although it has also been known to affect vegetables, fruit, and turfgrass. This disease will create lesions on stems, leaves, fruits, and flowers. Anthracnose is caused by a few different fungi, some of which include Colletotrichum gloeosporioides, Apiognomonia errabunda, Discula fraxinea, amd the Glomerella and Gnomonia species, dependent on what the host plant is. Anthracnose usually infects the lower branches of a tree due to how the spores spread, but in severe cases, the infection can travel to the inner and upper parts of the tree.

Anthracnose Management and Control Methods

Cultural Control

To manage anthracnose, avoid watering methods that wet the bottom of the tree canopy. That being said, ensure the plant is receiving the appropriate level of water to encourage growth and plant health. Also, whenever possible, select a tree type that is more resistant to this disease. Other management methods include raking up leaves in the fall that had been infected and dispose of them accordingly, prune and remove infected branches or twigs, and thin the tree’s crown to promote better air movement as this helps the leaves dry faster. Only fertilize as needed. If this is the case, promote its effectiveness by applying the fertilizer about a month after the first frost in the fall, or a month before the last frost in the spring.

Chemical Control

If a fungicide is used, apply as a preventative measure rather than to eradicate an already present infection. However, unless the conditions are advantageous for anthracnose and the area is highly susceptible to this disease, it can be impractical to spray large trees, especially during springs with warm and dry weather conditions. These large trees require a specific type of spray equipment and so typically a professional should be hired for effective results. If, however, anthracnose has been present in the past few years and has caused major defoliation, this would be a valid time to consider fungicide application. When fungicides are needed, ones that include mancozeb can be applied during bud swelling and then 2 more times when the leaves expand (intervals of approximately 10 to 14 days). Sycamore trees can be injected every 3 years with thiabendazole hypophosphite, if they are of high-value. Other fungicides with active ingredients such as chlorothalonil, thiophanate methyl, propiconazole, or those with copper have shown to have effective preventative effects. That being said, always carefully read the fungicide’s label for cautions and proper application before use.

Alternative Anthracnose Names

• • Colletotrichum leaf spot
• • Leaf blight
• • Shoot blight
• • Twig blight

Sources