July 2008

Ask Us About Diseases By Colleen Warfield

Q I've been hearing more about anthracnose diseases recently, particularly in regards to cyclamen. What exactly is it?

A Anthracnose is a catch-all name for various plant diseases caused by a group of closely related fungi. Some anthracnose-causing fungi are capable of infecting only one or a few plant species. However, the most common anthracnose-causing fungus on greenhouse ornamentals, Glomerella cingulata, can infect hundreds of annuals and perennials. Glomerella cingulata produces different spore types during its life cycle. This can be confusing because the same fungus can also be called Colletotrichum gloeosporioides, depending on what spore type is found in the infected plant tissue at the time of diagnosis.

Symptoms of anthracnose diseases are somewhat dependent upon the host, but generally small, dark, sunken lesions develop on the leaves, petioles and sometimes flowers. Lesions may coalesce, resulting in larger patches of dead tissue. Under humid conditions, masses of fungal spores erupt from black structures called fruiting bodies that develop within the infected plant tissue. Look for these pinkish-orange spore masses on the upper surface of the lesions.

Cyclamen is the host that I most commonly see infected with anthracnose diseases in the greenhouse, but begonia, gardenia, gloxinia and kalanchoe are also on the long list of susceptible hosts. A combination of early detection, good air circulation to reduce humidity and leaf wetness, careful sanitation and fungicide application can be used to manage anthracnose diseases in the greenhouse. Chemical fungicides that have shown good efficacy in preventing anthracnose disease include strobilurins (Heritage and Cygnus), fludioxinil (Medallion), mancozeb (Dithane, Protect, Pentathlon), myclobutanil (Systhane, Clevis) and iprodione (Chipco 26019, OHP 26 GT-O). Two new products to look for later this year include Palladium (combination of fludioxinil and cyprodinil) and Pageant (combination of pyraclostrobin and boscalid).

Q Is there a resource where I can find out how newer, reduced-risk fungicides are performing in research trials?

A The IR-4 Ornamentals Program develops efficacy and plant safety data on disease, insect and weed management tools for use in greenhouses, nurseries and landscapes. The Ornamentals Program is one of several under the umbrella of the IR-4 Project, a cooperative program of the USDA and the state agriculture experiment stations of the nation's land grant universities. The principal goal of the IR-4 Project is to generate data to support and speed up the process of bringing newer, reduced-risk pest-control products to specialty crop growers, which includes ornamental crops.

The results of research trials conducted through this program are available online via a searchable database. Go to ir4.rutgers.edu/Ornamental/Ornamentals.cfm, where you have several options in which to access trial data. Let's say, for example, that you are interested in the fungicide Pageant. Select "Search All Projects," and if you choose the arrow after "Product," a long list of products in the database will appear. Select Pageant 38WG, and a list of more than 20 planned or completed research trials will appear.

If the project has been completed, you will find a PDF link to the research report. If you take time to explore the database, you'll quickly discover that you have a wealth of information at your fingertips. But do keep in mind that many of the products under trial may not yet be commercially available.