| General Recommendations: Anthracnose is the name given to a group of fungal diseases that infect a wide variety of herbaceous and woody plants. The infections of anthracnose diseases are distinctive and appear as limited lesions on the leaves, stem and/or fruit. In leaves and in some fruit, the lesions are often angular and follow the vein pattern. Secondary pathogens that then invade the dead tissue typically cause some stem dieback, premature leaf fall, and/or fruit rot. Multiple infections in small areas where the lesions coalesce may result in stem and leaf blight.
Anthracnose is common on ash, maple, oak and walnut. On these trees it mainly causes leaf drop late in the season, and is thus not serious. When present on dogwood and sycamore, however, stem death, which causes malformation, is common. Dogwood anthracnose, which is a serious disease in the eastern US, can kill dogwoods. Raspberry is the fruit most commonly infected by anthracnose. The disease is a common, significant disease of beans, cucurbits, tomato, eggplant and peppers where disease control is generally advised.
A typical disease cycle starts with primary infection of the host in spring or early summer from spores that have overwintered in debris from the previous year or from cankers that have formed on the host in the previous season. Lesions form and produce secondary spores that repeat the infection cycle. In some cases, leaf infections lead to stem and bud infections where the fungal pathogen continues to grow and cause dieback. Stem and branch dieback is commonly the result of active cankers that grow over several seasons and eventually restrict the vascular flow of nutrients and water to the leaves.
Anthracnose diseases typically do not kill the host directly, however, repeated infections on woody plants over a period of years may lead to a general decline and dieback. Control of anthracnose diseases becomes important when the host is economically important and the goal is production for fruit or lumber. Otherwise, anthracnose diseases generally go unattended and raise concern only when premature leaf drop calls attention to the situation.
Control of Anthracnose:
1. Clean up diseased debris. Since leaf litter is commonly the prime source of infection, a thorough cleanup of this material helps reduce the inoculum and thus the potential for infection.
2. Improve air circulation by pruning to open up the leaf canopy. This will increase the air flow which lowers the relative humidity and reduces free moisture on the plant. Also, avoid overhead irrigation or getting the plant wet directly. Since spores require free moisture to germinate and penetrate host tissue, this reduces the probability of infection.
3. Promote good cultural conditions. Balancing soil fertility by applying only what nutrients are needed (according to a soil test report) and rotating crops from one area to another in the garden, reduces the success of inoculum overwintering and initiating new infections in the spring. Cleaning garden tools by dipping them in a solution of a diluted bleach solution of 1 part bleach to 4 parts water or rubbing alcohol helps keep the disease from spreading to healthy plant parts.
4. Use preventive fungicides. Keep in mind that these materials are commonly preventive, which means that they should be on the plant before any inoculum is generated. Fungicides are subject to being washed off the plant by rainfall and should be reapplied at 7- to 10- day intervals (sooner when rainfall above 1 inch has fallen since the last application). Continue to apply until daytime temperatures are above 85 degrees F. Some common fungicides used to control anthracnose include: sulfur, copper sulfate, cuprous oxide and fixed copper. These materials are sold under various trade names and should be used in accordance with the label. Fixed copper fungicides should not be applied during cool, wet weather because they may damage the plants. |
