Dianthus Diseases

Anthracnose

• Caused by the fungus colletotrichum, anthracnose manifests itself as irregular spots on lower leaves that enlarge in size until they cover the entire surface. The infected leaves gradually turn brown and the disease spreads upward to the stem, causing the plant to collapse. Fungal spores spread through rain and irrigation water, wind or insects. Adopt good cultural practices to reduce chances of the fungal disease. Use sterilized pruning scissors and remove dead plant matter from the base of the dianthus plant. Treat dianthus anthracnose with a registered fungicide.

Stem Rots

• Dianthus plants are susceptible to a variety of stem rots, including rhizoctonia stem rot, phytophthora stem rot and fusarium stem rot. Favored by warm, humid and moist conditions, rhizoctonia and phytophthora stem rots cause the entire stem to rot at soil level, causing the plant to wilt and die. Fusarium stem rot damages the stem at soil level and higher up on the plant and the roots. Because no chemical cures exist for stem rots, destroy damaged plants immediately and fumigate or steam the soil. Always use disease-free cuttings and sterilized rooting medium.

Leaf Spots

• Septoria, alternaria and fairy ring are fungal diseases that exhibit similar symptoms on dianthus plants, such as light brown to tan spots with purple margins on petals and leaves. Fairy ring leaf spot manifests itself as deep brown spots with concentric rings. Left untreated, masses of black spores form in the spots that are carried to the same or surrounding plants by wind, water and pests. Adopt good cultural practices to limit the chances of leaf spots. Snip damaged leaves with sterilized pruning scissors, and treat foliage with chlorothalonil or mancozeb.

Fusarium Wilt

• Commonly occurring in moist, humid conditions and temperatures above 75 degrees Fahrenheit, fusarium wilt in dianthus causes the branches on one side of the plant to turn yellow and wilt. While some infected plants may appear healthy in the morning, only to wilt suddenly by evening, others show no signs of infection until they suddenly collapse during bloom. Left untreated, the stems rot and roots decay, although they remain intact. Dianthus plants infected with fusarium wilt gradually die. Control the soil pathogens so your dianthus plants remain healthy. Plant disease-resistant varieties of the plant in treated soil. Adjust the soil pH to 6.5 to 7.2 and solarize it with methyl bromide.