Anthracnose Diseases

From From BASF: The Chemical Company Website

By Paul Pilon

There are a number of fungal pathogens that collectively cause what growers refer to as anthracnose diseases.  Some of the most common pathogens are Colletotrichum, Phoma, and Phyllosticta; however, there are additional pathogens including Coniothyrium, Cryptocline, Diplodia, Gloeosporium, Glomerella, Macrophoma, and Phyllostictina that cause anthracnose diseases.

Numerous perennials, tropical foliage plants, and woody ornamentals are commonly afflicted by anthracnose diseases. Some of the most common plants affected by these diseases include Anthurium, Azalea, cacti and succulents, Camellia, Cyclamen, Euonymus, Ficus, Hosta, Hydrangea, Lupine, Mandevilla, Nandina, palms, Spathiphyllum, and Vinca minor to name a few.  Anthracnose can be problematic for growers because the presence of leaf spots may greatly reduce the appearance and marketability of crops and plant losses often occur with more severe symptoms expressed by some of these pathogens.

Anthracnose symptoms take on numerous appearances and varies with the fungal pathogen causing the infection and by the plant species being attacked. The primary symptoms observed are leaf spots and blights, but they are also commonly observed as dieback, cutting rot, and stem rot.  These diseases can sometimes be difficult to diagnose.  For example, in many cases they appear in propagation as leaf spots or cutting rot diseases; however, they usually carry through and cause symptoms and crop losses later in the production cycle. In some cases, symptoms may not arise until two or three years after the plants were propagated.

Needless to say, Anthracnose symptoms take on numerous forms and appearances and can easily be confused with other fungal pathogens or plant disorders. It is beneficial to submit samples to a diagnostic clinic for proper identification. 

Anthracnose diseases are most prevalent under moist growing conditions, particularly following exposure to rainfall or where overhead irrigation is used.  They spread from plant to plant with splashing water.  The occurrence of anthracnose can often be traced back to infected starting materials.  Wounding can also contribute to disease severity, but is not necessary for infections to occur. 

Depending on the type of anthracnose disease and its severity, they can be slightly difficult to control.  The first step is to obtain proper identification of the disease you are dealing with.  If an anthracnose disease has been identified, the next step is to modify the environment if possible.  Although it is not usually an option, changing from overhead irrigation to drip irrigation will greatly reduce the conditions necessary for disease development as well as prevent spreading from plant to plant with splashing irrigation water.

If the method of irrigation cannot be modified, at least use the following guidelines.  Avoid overhead irrigation late in the day or during overcast conditions to help reduce the time the leaves remain wet after watering.  Where possible, provide good air circulation by placing crops at wide plant spacing, minimize contact from plant to plant, and water early in the day to allow the foliage to dry quickly.  If these methods are not providing adequate disease prevention, then the application of fungicides is necessary.

Fungicide applications work best when they are applied preventatively or just as infections are beginning to occur. The most effective fungicides for controlling anthracnose diseases are chlorothalonil + thiophanate methyl, copper sulphate pentahydrate, and pyraclostrobin + boscalid. It is particularly important with anthracnose diseases to rotate the chemical families of the fungicides being applied to prevent resistance to these chemistries. 

As with most diseases, good cultural practices along with early detection and implementation of control strategies will greatly alleviate the severity of Anthracnose diseases.

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