Carnation

Dianthus spp.

Fusarium Wilt (fungus – Fusarium oxysporum f. spp. dianthi): First symptoms are a slow wilting of shoots, often on only one side of the plant. Wilting is accompanied by a discoloration of leaves, at first a light gray-green and finally a pale yellow color. When stems of diseased plants are split, a brown discoloration or streaks are evident in the vascular tissues. Symptoms develop rapidly and are more severe during periods of high temperatures. Most effective methods of control are propagation of disease-free cuttings and complete sterilization of potting soil, tools and benches.

Rhizoctonia Stem Rot (fungus – Rhizoctonia solani): Foliage gradually becomes pale and wilted. A wet rot of the bark occurs at the soil line. Rot in the cortex is dry and corky with formations of sclerotia in the center of the stem. Soil sterilization and soil drenches with fungicides are effective methods of control.

Leaf Spot (fungus – Septoria dianthi): Small circular light-brown spots with purplish brown border. Occurs on leaves and stems especially on lower portions of the plant. Small black specks (fruiting bodies) develop in the center of the spots. Tips of the leaves may die. Regular applications of a foliar fungicide spray in the greenhouse will control the disease.

Storage Rot or Botrytis Blight (fungus – Botrytis cinerea): Primarily a disease of cut flowers. Petals of infected flowers turn brown. May also cause a watersoaked flecking of the outer petals. Will also cause a soft rot of stem ends. Disease usually prevalent under high humidity. Spray or dips will effectively control this disease.

Other Diseases: See the appropriate sections on Curly Top (virus), Root Knot Nematode Meloidogyne spp, and see the section on Nematodes other than Root Knot.

Streak (bacterium – Erwinia spp.): This bacterial disease usually starts at flowering time causing purplish-brown streaks on the stems, beginning from the base and extending upwards. The petioles, flowers, flower stalks, and pods are also streaked. Small round spots appear on the leaves running together gradually until the whole leaf is affected. Leaves may become dark brown or be entirely destroyed. Since this bacteria may be carried on the seed, chemical seed treatments and clean seed are advisable.

Other Bacterial Diseases: This host is also subject to crown gall caused by (bacterium – Agrobacterium tumefaciens) and leaf spot caused by (bacterium – Pseudomonas syringae pv. pisi).

Mosaic (Pea Mosaic Virus): Leaves are mottled, curled and yellowish. Flower stalks are short and flowers are streaked with white. Remove and burn infected plants. Control aphids which spread the disease.

Spotted Wilt (Tomato Spotted Wilt Virus – TSWV): Purplish spots on the stems and leaves develop after the leaves are mottled. Discolored or bleached spots may appear on the blossoms. Since the disease is carried by thrips, control the thrips and destroy all infected plants. Bud Drop Disease: This disease is due entirely to faulty culture; it results in the production of soft succulent growth and a lowered carbohydrate accumulation. A deficiency of phosphorus and potassium in the soil, coupled with low light intensity, are believed to aggravate the condition. If possible, provide extra light in the greenhouse during cloudy weather. Avoid overwatering and overfeeding with high nitrogenous fertilizers.

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