Look close — is it Anthracnose?

1. Cyclamen is host to a Fusarium wilt disease as well as to at least two anthracnose fungi, Colletotrichum gloeosporioides and Cryptocline cyclaminis. It’s important to recognize these fungal diseases and to be able to tell them apart from virus-induced symptoms of Tomato spotted wilt (TSWV) or Impatiens necrotic spot (INSV).
2. Fusarium wilt and Cryptocline anthracnose affect only cyclamen, while the Colletotrichum anthracnose has many hosts worldwide, including apple, pear and pecan. Development is best favored by warm to high growing temperatures typical of summer production in the northern United States.
3. For Fusarium wilt, organic debris mixed with seed has been a source of contamination in the past. Because disease symptoms develop over months, the fungus may be moved from one greenhouse to another on symptomless plants. Fusarium also survives well as a saprophyte on the floor of a greenhouse. It is likely that both anthracnose fungi are also capable of surviving in plant debris between crops. C. gloeosporioides might originate in landscape plants just outside the greenhouse. Its sticky spores could be moved into the greenhouse by insects or people.



4. Both anthracnose diseases cause round brown leaf spots. The Cryptocline anthracnose is also known to attack the immature flower stems below the canopy, stunting and killing them. Leaf spots should not be automatically attributed to one of these fungi. The tospoviruses TSWV and INSV also cause round brown spots on mature cyclamen leaves. There is a possibility of Botrytis leaf spots as well.

Monitoring

• On young plants, watch for stunted, yellowed seedlings and check their roots for root rot: this may be the first sign of the presence of Fusarium oxysporum f. sp. cyclaminis, which causes Fusarium wilt.
• Watch for round brown spots on foliage and, if found, use immunostrips or another diagnostic assay to check for thrips-borne TSWV or INSV.
• Look closely: tiny dots of orange ooze suggest that one of the anthracnose fungi is present.
• Check the tiny new flowers and, if they are crippled, seek the help of a diagnostic laboratory to determine the cause.
• If yellowing or wilting is seen on older plants, cut across the corm. A brown, reddish or purple discoloration in the vascular system is a strong indicator of Fusarium wilt.

Prevention

• Avoid extended periods of leaf wetness.
• Practice exemplary sanitation methods in a house where cyclamen is grown.
• Space plants adequately.
• Use fans to circulate air.
• Keep calcium and pH up and ammonium levels down to suppress Fusarium, but stay within the crop’s cultural demands.
• Monitor for symptoms on leaves, tiny developing flowers, roots and corms.

Treatment

• Start a fungicide management program in advance of symptoms if diseases have occurred before in the same greenhouse.
• Rotate fungicides among different Fungicide Resistance Action Committee (FRAC) groups to switch modes of action.
• Utilize biofungicides to get some Fusarium wilt suppression.
• Discard diseased plants; use appropriate fungicides to guard the rest.
• Utilize systemic materials according to label directions. Strobilurin (FRAC 11) and DMI (FRAC 3) materials are two of the most effective groups for cyclamen fungal diseases. Some fungicide combination pre-mixes are now available as well. Contact fungicides will also assist with anthracnose management.

Margery is a plant pathologist specializing in ornamentals at Cornell’s Long Island Horticultural Research & Extension Center. She aims to help growers outwit diseases.