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Tag: ornamental plants

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Fusarium wilt caused by the fungus Fusarium oxysporum f.sp. chrysanthemi is a vascular

wilt disease of chrysanthemum, and one I worked on for my Master's thesis. The fungus is soil-borne or spread through vegetative cuttings, and invades the stem. The fungus plugs water conducting tissue (xylem) with mycelium and spores. Fusarium wilt symptoms are often confused with root rot but plants infected with Fusarium may show wilt only on one side and roots often appear healthy. Early symptoms of Fusarium wilt are wilting leaves on one side of the plant followed by yellowing and browning of the leaves. Infected plants are stunted, fail to produce flowers, and vascular browning can be seen on cut stems. Symptom development is favored by temperatures above 24 C (75 F) and high humidity. Although specific to chrysanthemum, the fungus can survive in soil or debris for years and is difficult to control if established in a field or bed.


Managing Fusarium wilt includes use of disease-free (culture-indexed) cuttings and pathogen-free media and materials. Avoid highly susceptible cultivars such as 'Bravo', 'Cirbronze', 'Illini Trophy', 'Orange Bowl', 'Royal Trophy', Allegra and 'Yellow Delaware'. Other management practices include maintaining soil pH between 6.5 and 7.0, utilizing the nitrate form of nitrogen in fertilizers and drenching with fungicides. Effective fungicides include azoxystrobin (Heritage), pyraclostrobin plus boscalid (Pageant) and Trichoderma harzianum (PlantShield). Fungicides containing thiophanate methyl (Cleary's 3336) and fludioxonil (Medallion) have been reported to suppress Fusarium.
In studies at the Long Island Horticultural Research and Extension Center, Cornell University, yellow-flowered mums were evaluated for susceptibility to Fusarium wilt. Wilt developed three weeks after inoculation in ‘Allegra’ (susceptible check), and the cultivars ‘Conaco’, ‘Florina’, ‘Elena’, ‘Malmo’ and ‘Golden Helga’ developed wilt. Symptoms did not develop and the fungus was not re-isolated from cultivars ‘Bernadette’, ‘Bethany’, ‘Diana’, ‘Mary’, ‘Mildred’, ‘Mouria’, ‘Novare’, ‘Castor’ or ‘Sundance’.
NFG, 10/2017

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Photo Credit: Michele Walfred
Hydrangea Frost Damage Photo Credit: Michele Walfred

Cloudy, wet, damp, cool and dreary are words that have been heard over and over recently, regarding the weather in Delaware. Cloudy and damp weather is conducive to plant pathogens that infect in the spring. Fungi and bacteria overwinter in twigs and buds of trees and shrubs. Spring rains and humidity will prompt new growth and spore production, and then winds and rains carry spores to newly emerging flowers and leaves. Recent weather has favored plant disease, but we have also had injury from freezing weather that occurred in April.  Hydrangea has been reported with browning and dieback, and samples have come into the Plant Diagnostic Clinic. New growth came out early due to warm weather, and growth of buds and leaves has been affected by the freezes that we had in the area April 5, 6, and 10th. Plants will put out new growth when the weather warms again. Affected growth could be pruned back, depending on the type of
Boxwood Frost Damage 2016 Image, N. Gregory
Boxwood Frost Damage 2016 Image, N. Gregory

hydrangea, and whether it blooms on new wood or old. Frost or freeze damage has also been observed on new growth of boxwood, and other shrubs. These plants should put out new growth when the weather warms. Fruit trees that were affected by frost and freeze will have fewer fruits this season. Keep up fruit tree sprays. Fungicide sprays should also be going on Douglas fir and spruce that are affected by needlecast fungi. Fungicide applications should be made when new needles are ¼ inch long, followed by a second application ten days later. Check annuals carefully for Botrytis blight or grey mold, and prune or discard plants. Sanitation is a big part of plant disease management.
N. Gregory 5/6/16