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Fungal foes in your garden
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FUNGAL FOES IN YOUR GARDEN 16. TULIP FIRE
The Disease: Tulip fire, specific to Tulips, causes severe damage wherever tulips are grown and has even been responsible for the total loss of tulip crops in some seasons. Fire is first seen when a few plants with malformed leaves or shoots emerge above ground, scattered among the healthy ones. Frequently the whole shoot is reduced to a shrivelled, stunted shaft that is soon covered with conidiophores and sclerotia especially in wet weather or under humid conditions. Slightly infected leaves and stems may continue to grow and also produce conidia from the grey or greenish-grey diseased areas which enlarge rapidly to cover the whole leaf under moist conditions. Spread of the disease is hindered or completely checked by dry weather as the infected leaves often dry up, becoming split and torn. Some conidia are dispersed by air currents to the leaves, flower stalks or flowers of Fig. 1. Tulip plant showing extensive black healthy plants where they give rise to leaf spots. lesions. on the leaves and bulb scales where Each yellowish spot is roughly circular, or sclerotia may be found. somewhat elongated, slightly sunken and surrounded by a dark-green, water-soaked area. These spots are readily seen when the leaf is held up to the light. Most spots remain minute and are incapable of forming conidia as the fungus rarely survives for long but occasionally comparatively large spots or blotches merge and spores are produced. Nevertheless tulips that are grown for cut flowers are spoilt by the small spots or blisters on the petals. Flower buds that fail to open may become covered with mould. Dark brown patches that extend along the flower stalks, sometimes bear black sclerotia. After the external papery scale of the bulb has been removed, the outermost fleshy scale may reveal depressed circular lesions which also often bear sclerotia. Sometimes bulbs may become encased by masses of sclerotia after they have rotted. Newly planted tulip bulbs usually become infected through contamination of the parent bulb by conidia that are borne on its surface or mycelium that survives in the lesions on the outer scales. Although infection is often blamed on sclerotia in soil or on the bulbs, especially at the base of the old flower stalk, few sclerotia over two years old can still germinate. The Pathogen: The conidiophores of Botrytis tulipae Lind. emerge through the stomata singly or in pairs are olivaceous-brown above then hyaline below; the basal cell of each is somewhat swollen and the upper part has 3-5 short lateral branches. After producing one head of conidia, growth of the main axis of the conidiophore may continue to produce further whorls of conidia borne on a short sterigma. The clear grey hyaline conidia are variable in size (16-20 x 10-13 Mm). The sclerotia, usually 1 mm in diameter, are readily detached. Control: Inspect any bulbs that are to be purchased for sclerotia and reject any with blackened fleshy bulb scales. As a further safeguard, dip all bulbs before planting for 15-30 minutes in a suspension of a general garden fungicide that contains a benzimidazole fungicide, such as carbendazim, benomyl or thiophanate-methyl. This will also give some protection against some other important bulb diseases. Tulips should not be planted on land where infected bulbs have grown for at least three years, during this time avoid spreading soil to clean beds. The spread of disease to neighbouring plants is fast, so any infected tulips should be destroyed without delay. Spray the remaining healthy plants with a general garden fungicide that conR T V Fox tains a dithiocarbamate.
FUNGAL FOES IN YOUR GARDEN 16. TULIP FIRE
The Disease: Tulip fire, specific to Tulips, causes severe damage wherever tulips are grown and has even been responsible for the total loss of tulip crops in some seasons. Fire is first seen when a few plants with malformed leaves or shoots emerge above ground, scattered among the healthy ones. Frequently the whole shoot is reduced to a shrivelled, stunted shaft that is soon covered with conidiophores and sclerotia especially in wet weather or under humid conditions. Slightly infected leaves and stems may continue to grow and also produce conidia from the grey or greenish-grey diseased areas which enlarge rapidly to cover the whole leaf under moist conditions. Spread of the disease is hindered or completely checked by dry weather as the infected leaves often dry up, becoming split and torn. Some conidia are dispersed by air currents to the leaves, flower stalks or flowers of Fig. 1. Tulip plant showing extensive black healthy plants where they give rise to leaf spots. lesions. on the leaves and bulb scales where Each yellowish spot is roughly circular, or sclerotia may be found. somewhat elongated, slightly sunken and surrounded by a dark-green, water-soaked area. These spots are readily seen when the leaf is held up to the light. Most spots remain minute and are incapable of forming conidia as the fungus rarely survives for long but occasionally comparatively large spots or blotches merge and spores are produced. Nevertheless tulips that are grown for cut flowers are spoilt by the small spots or blisters on the petals. Flower buds that fail to open may become covered with mould. Dark brown patches that extend along the flower stalks, sometimes bear black sclerotia. After the external papery scale of the bulb has been removed, the outermost fleshy scale may reveal depressed circular lesions which also often bear sclerotia. Sometimes bulbs may become encased by masses of sclerotia after they have rotted. Newly planted tulip bulbs usually become infected through contamination of the parent bulb by conidia that are borne on its surface or mycelium that survives in the lesions on the outer scales. Although infection is often blamed on sclerotia in soil or on the bulbs, especially at the base of the old flower stalk, few sclerotia over two years old can still germinate. The Pathogen: The conidiophores of Botrytis tulipae Lind. emerge through the stomata singly or in pairs are olivaceous-brown above then hyaline below; the basal cell of each is somewhat swollen and the upper part has 3-5 short lateral branches. After producing one head of conidia, growth of the main axis of the conidiophore may continue to produce further whorls of conidia borne on a short sterigma. The clear grey hyaline conidia are variable in size (16-20 x 10-13 Mm). The sclerotia, usually 1 mm in diameter, are readily detached. Control: Inspect any bulbs that are to be purchased for sclerotia and reject any with blackened fleshy bulb scales. As a further safeguard, dip all bulbs before planting for 15-30 minutes in a suspension of a general garden fungicide that contains a benzimidazole fungicide, such as carbendazim, benomyl or thiophanate-methyl. This will also give some protection against some other important bulb diseases. Tulips should not be planted on land where infected bulbs have grown for at least three years, during this time avoid spreading soil to clean beds. The spread of disease to neighbouring plants is fast, so any infected tulips should be destroyed without delay. Spray the remaining healthy plants with a general garden fungicide that conR T V Fox tains a dithiocarbamate.