Anthracnose Crown Rot in Strawberry Plug Plants

Plasticulture strawberry growers in Maryland should be aware that North Carolina and Virginia growers have reported an unusual number of problems this season with anthracnose crown rot in plug plants. The infected plants were apparently shipped by nurseries in NC and VA. The varieties affected are ‘Chandler’, ‘Camarosa’, and ‘Festival’.

The pathogen responsible for the outbreak is Colletotrichumgloeosporioides (glee-o-spor-ee-OY-dees), one of three species of Colletotrichum that can cause crown rot on strawberry. The key symptom is a general wilting of the plant, followed by plant collapse. This collapse may occur quickly in warm weather or over several weeks under cooler conditions. When an infected crown is cut open lengthwise, the inside surfaces will be reddish-brown and firm, or show reddish-brown streaks (see photo).

Anthracnose crown rot is a latent infection that progresses under warm, moist conditions. Most cases in NC and VA appeared during establishment, before covers were applied. It is possible, however, that additional infections could have developed under the covers during warm periods in the late fall and winter. We did have some plant losses reported in Maryland last fall, but they appeared to be due to a combination of plugs in poor condition and hot, dry weather during establishment. The Plant Diagnostic Clinic did not find any pathogens in strawberry plant samples submitted to them.

As a precaution, Maryland plasticulture growers may want to check the health of their plants by looking under the covers on a mild day. If you find wilted or collapsed plants:

• Remove the entire plant, including roots, from the bed. Wrap plants in dry newspaper and put them in sealed plastic bags in the refrigerator. Those who are curious may cut open a crown to see whether it displays the symptoms of crown rot, but keep at least one plant intact for the Plant Clinic. Crowns discolor once they are cut and cannot be used for diagnostic purposes.
• Call your county Extension office promptly to arrange for the plants to be sent to the Plant Diagnostic Clinic in College Park for diagnostic testing. It is very important to have plants tested to determine the cause of death before beginning any preventive treatment in the field. Do not rely on the visual appearance of the crown alone, as organisms other than C. gloeosporioides can cause similar symptoms.

If your plant samples are found to be infected with C. gloeosporioides, you may wish to apply a single early fungicidal spray to prevent the spread of infection when covers are removed in the spring and active plant growth resumes. Research in Florida has shown that a tank mix of Topsin-M (thiophanate-methyl) at 1 lb/ac and captan at 2 lb of active ingredient/ac (for example, 4 lb/ac of Captan 50WP or 2.5 lb/ac of Captan 80WDG) can reduce the spread and severity of anthracnose crown rot caused by C. gloeosporioides. This fungicidal spray may not be effective against other Colletotrichum species or other pathogens.