Fusarium wilt of chrysanthemum was diagnosed this week in the UMass Extension Plant Diagnostic Lab. Chrysanthemums infected with Fusarium show symptoms of wilting and dieback, often on one side of the plant. Discoloration of the vascular system is often observed when the base of the stem is cut open.
Fusarium wilt can cause serious losses year after year because of the presence of the fungus in infected propagation stock, its persistence in the soil, and the difficulty of controlling the fungus once it becomes established in the soil. Symptoms can vary by cultivars; the occurrence and severity of specific symptoms depends on the interaction of cultivar with the soil and air temperature. High temperatures are conducive to disease development.
Control measures include starting with disease-free cuttings and pasteurized potting media. Sanitation is crucial for disease management. Remove and destroy infected plants, plant debris, and soil. Greenhouse structures, crates, benches, and tools should be cleaned regularly. Avoid over-watering and provide good drainage. Maintaining growing media pH at 6.5- 7.0 will help control this disease. Use nitrate rather than ammonium fertilizer and maintain adequate fertility levels. Preventive fungicide drenches along with growing on a high-lime, all nitrate nitrogen regime have been demonstrated to manage Fusarium wilt effectively. See http://ag.umass.edu/greenhouse-floriculture/publications-resources/new-england-greenhouse-floriculture-guide for a full listing of registered fungicides.
Angela Madeiras, Extension Educator & Diagnostician, UMass Extension Plant Diagnostic Lab