As the disease progresses, a gray mold develops. In the spring, spores form and spread to dying, wounded, or extremely soft plant tissues. The spore-producing structures of the fungus develop along the base of the rotting stalks and survive in debris left in the garden over the winter. Open flowers are affected occasionally, and they also turn brown and later develop a covering of gray mold.īotrytis fungi are both saprophytic and parasitic. During a severe outbreak of the disease, 90% of the buds fail to develop. Small buds that are affected turn black and wither. The spores are carried by wind and insects to young leaves and flower buds and cause a leaf blight and bud rot. Just above the ground level, the stalk will be covered with a gray mold which sheds large numbers of spores. The rotted portion of the plant will become covered with a soft brown or blackish mass of spores. The leafy shoots wilt suddenly and fall over. The stems often have a water-soaked, cankerous appearance. On peonies afflicted with botrytis, the young shoots rot off at ground level when they are 5 to 8 inches tall. This destructive disease is very prevalent during damp, rainy seasons. It is the most common disease of garden peonies. Gray mold or botrytis blight is caused by the fungus, Botrytis paeoniae. Infected plants are not killed but should be discarded because they may serve as a possible source of infection for other plants.Botrytis blight on peony foliage ( Paeonia) Viruses (virus – several): Infected plants have distorted leaves that are mottled in color. Natural infection seems to be slight but infected tissue is perpetuated by some who sell this unusual looking plant under the name of “Witchcraft”. Do not use infected plants for propagation.Ĭrown Gall (bacterium – Agrobacterium tumefaciens): Fleshy galls form around the base of the plant with a profusion of leaves being produced at that point. The nematode may also be transmitted by petiole cuttings from infected plants. This condition can be prevented by using nematode free propagating stock and a sterilized potting medium. Root Knot (nematode – Meloidogyne spp.): Galls form on roots of plants causing the root system to be inefficient in absorbing and translocating water and nutrients. Such a possibility exists when a breeze blows across the wet area and produces an evaporative effect. In some cases, damage may occur even if warm water is used. This condition is caused by cold water coming in contact with the leaves. Ring Spot (Physiogenic): Light brown rings form on leaves with some running together to form irregularly shaped spots. Construct a collar from aluminum foil to be fitted around the rim of the pot. Use rain water or another salt-free source of water and avoid over fertilization. This damage results from salt accumulation on the rim of the pot and the soil surface. Petiole Rot (Physiogenic): An orange to brown, rust colored spot appears where the petiole touches the pot. If the systemic fungicide is used, one may have to spray blossoms since the fungicide is not translocated to floral parts when the pot drench method is employed. Control with fungicides is very effective. Spores of the fungus are air-borne from one plant to another. It is more easily seen on dark blossoms than white ones even though the white varieties may be slightly more susceptible. Powdery Mildew (fungus – Oidium spp.): A white powdery type substance may be observed on leaves, petioles, petals or flower stems. Surface sterilize the area surrounding the plants with a household cleaner or bleach. All disease tissue should be removed as this serves as a source for new spores. The disease is more severe when atmospheric conditions are cool and damp, poor air circulation exists and when light intensity is low. A grayish fungal growth may be seen upon close examination of diseased tissue. Preventive measures include using sterilized soil and avoiding plant introductions that may harbor crown rot organisms.īotrytis Blight (fungus – Botrytis cinerea): Leaves, flowers and petioles develop small water-soaked spots that enlarge rapidly. Caution should be used in getting the right dosage levels since excessive levels of some chemicals may damage plants. Drenches should be administered when the first evidence of disease occurs. Two alternatives are available for infected plants: One is to discard all affected and exposed plants and the other is to use fungicide drenches. Unless treatment is administered before massive root death, the plant will have to grow an entirely new root system before recovery occurs. Roots are killed rapidly and appear brown. Older leaves droop and younger leaves showing stunting. Crown Rot (fungi – Pythium spp., Phytophthora spp., Fusarium spp.): Crown rot is probably the most serious disease of African violets and may cause loss of entire groups of plants.
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