Colletotrichum is a common disease

Quick Control Tips 1. The first step in solving any disease problem is a good diagnosis. Take the time to send in a plant sample to a diagnostic lab to make sure your control strategy is the best one available for your situation. Guessing costs time and money. 2. Change the environment to reduce disease severity. While this can be exceptionally effective in a greenhouse or sometimes in a nursery. For landscapes this is not as easy to manage. 3. Choose the best program for your needs. Read the control product labels carefully and ask for assistance if something is not clear. 4. If you cannot spray weekly, then choose the best product you can afford and spray it at the higher end of the labeled rates. 5. Be sure to alternate products from different chemical classes. Anthracnose diseases have repeatedly been shown to develop resistance when a single mode of action was used without rotation. 6. Obtain an accurate diagnosis. Yes, I am repeating myself since this is usually the last step chosen and not the first.

Aglaonema colletotrichum

Colletotrichum anthracnose is one of the most common diseases on many ornamentals. It can occur at anytime during the year and is often confused for other leaf spot and dieback diseases.
 

1. What are the symptoms of Colletotrichum?
Anthracnose diseases are usually characterized by leaf spots and blight. Diagnosing anthracnose can be challenging since many people do not recognize that the leaf spots and cutting rot found in propagation are due to the same pathogen as shoot dieback later in the production cycle.

If you do not achieve control this disease during the propagation phase, you will be fighting a generally losing battle a year or more later when the dieback phase becomes obvious. Sometimes there are black specks in the leaf spots. They can form in concentric rings and look like a pin cushion under magnification.
 

2. How do anthracnose diseases spread?
These diseases spread by spores that are easy to splash with irrigation water or rainfall. However, since they are somewhat sticky they do not easily spread by simple air movement by the wind or fans. Wounding of the plants can increase disease severity, but it is not necessary for infection.

Usually the pathogen starts on infected cuttings and the disease may be apparent in propagation where the mist can easily spread spores and provide ideal conditions for infection. If you start with infected cuttings, you will be applying fungicides the entire life of the crop.
 

3. What plants are most commonly affected by Colletotrichum?
Many plants can be attacked by anthracnose fungi especially those grown outside of greenhouses like woody ornamentals and tropical foliage plants. There are far fewer examples of disease infection in greenhouse potted crops and the bedding plants. Some of the most commonly affected ornamental plants are camellia, cyclamen, euonymus, ficus (many species), hydrangea, hosta, Vinca minor, lupine, azalea, aglaonema, cordyline, dieffenbachia, palms, yucca, cacti and succulents.

Research published in the 1960s showed that the Glomerella cingulata (Colletotrichum spp.) present in the greenhouse and nursery trade at the time were not host specific. That is, an isolate from a plant like ficus was capable of infecting the other plants tested and visa versa. This is important in deciding which plants might need protecting.
 

Hosta colletotrichum

4. How can fungicides help prevent anthracnose?
Experience at Chase Horticultural Research with fungicide control of anthracnose diseases indicates that those caused by Colletotrichum spp. are somewhat faster to develop than those pathogens (i.e., Phyllosticta or Phoma) that cause other anthracnose diseases. Control in our trials was nearly always better when fungicides were applied on a seven or 10 day interval compared to a 14 day interval. Preventive control is always better than curative.

The best control products were Daconil Ultrex (chlorothalonil), Pageant (pyraclostrobin and boscalid) and Spectro 90WDG (chlorothalonil and thiophanate methyl). In addition, mancozeb (i.e., Dithane and Pentathlon) or copper (Phyton 27) were also very effective when used preventively.

Have a Question? You can write Ann at archase@chaseresearch.net.