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Strawberry Leaf Diseases
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Leaf ScorchInfected leaves have many irregular purplish blotches. Centres of blotches become brownish, and blotches run together. Later, edges of the leaves dry up and look burned or scorched. Youngest leaves are initially immune to the disease. Disease may also develop on leaf stems and fruit calyx. Spores travel in air currents and the disease is also spread by splashing rain.
Figure 1. Purple blotching on strawberry leaves are symptoms of leaf scorch. Plants affected by leaf scorch do not overwinter well, and yields the following year may be reduced. Conditions which favour the disease are susceptible cultivars (e.g. Kent), perennial plantings, repeated leaf wetness periods of 5-9 hours or longer, and temperatures of 20-25 °C. Recommendations to control leaf scorch and leaf spot are very
similar. Use resistant cultivars where practical. On susceptible
cultivars, fungicides are recommended in early spring, and again
in late summer and early fall. See Publication 360, Fruit Production
Recommendations | Top of Page | Phomopsis Leaf BlightThis disease begins as one to six nearly circular, reddish purple spots on a leaflet. The spots expand and develop zones: purple, red or yellow outer zone, light brown inner zone, with a dark brown central zone. Characteristic zones are v-shaped and include a leaf edge. The fungus overwinters in old leaves, and the disease is spread by splashing rain. Little is known about this disease, and losses caused by Phomopsis leaf blight have not been measured.
Figure 2. Lesions caused by Phompsis leaf blight are charachteristic v-shaped and include a leaf edge. There are no fungicides labelled for leaf blight control. Control
measures for leaf spot and leaf scorch (as recommended in Publication
360, Fruit Production Recommendations) will probably control
leaf blight indirectly. | Top of Page | Leaf SpotInfected leaves have small round purple spots which eventually develop grey or light brown centres (bird's eye). Leaves less than 10 days old are most susceptible. Spores are produced on living and dead leaves, and are spread by splashing rain. Spores germinate and enter the leaf through stomata on the lower leaf surface. Young leaves are particularly susceptible.
Figure 3. Small round purple spots with grey or light brown centres are found on strawberry leaves infected with leaf spot. Conditions which favour disease include susceptible cultivars (e.g. Jewel, Startyme), 15-25oC and long wetting periods. Recommendations to control leaf scorch and leaf spot are very similar. Use resistant cultivars where practical. On susceptible cultivars, fungicides are recommended in early spring, and again in late summer and early fall. Sprays should be applied to protect plants during periods of rapid leaf growth. Good spray coverage of both upper and lower leaf surfaces is required. See Publication 360, Fruit Production Recommendations. | Top of Page | Powdery MildewWhite patches of fungus develop on the lower leaf surface, causing the leaf edges to roll up. Reddish or purple blotches on the underside of the leaf may also develop. The disease can cause economic losses if flowers or fruit become infected. A white powdery substance formed on fruit may spoil its appearance. Infection of leaves after harvest probably has little, if any, effect the following year.
Figure 4. Powdery mildew causes leaf edges to curl upwards and turn pinkish in colour. Conditions which favour powdery mildew include, susceptible cultivars (e.g. Annapolis, Governor Simcoe), sheltered plantings, and warm humid weather. Angular Leaf SpotThis bacterial disease causes small, water-soaked angular spots on lower leaf surface, and dark, wet looking blotches on the calyx. In the Northeast, infection on leaves may not harm plants, but can lead to infection of calyx and fruit when conditions are ideal for disease.
Figure 5. Small angular leaf spots appear water-soaked on lower leaf surface. The calyx on this berry also has a small dark water-soaked spot. Bacteria can travel within the plant from leaves to crowns and roots, and can be spread to new fields on symptomless propagation material. Within the field, the disease is spread by irrigation water, splashing rain, wet equipment, etc. Conditions which favour the disease are moderated to cool daytime temperatures, low nighttime temperatures, and high humidity. There are no pesticides labelled for control of angular
leaf spot. Research has not shown copper sprays to be very effective
in controlling this disease. Avoid over use of nitrogen. Cultivars
vary in their susceptibility. Cavendish, Annapolis, Allstar, Honeoye
and Kent are very susceptible. Overhead irrigation, especially for
frost protection, should be used judiciously in problem fields.
| Top of Page | Slime MouldsSlime moulds are a very primitive form of fungus. During warm wet weather in spring and fall, they can be many colours, grey, white, purple, yellow, and look like jelly-like masses, or crusty structures. Slime moulds survive on decaying organic matter (straw) and by ingesting bacteria and other microorganisms. Slime moulds do not actually infect strawberry plants, but they do grow on leaves and fruit and do not have an attractive appearance.
Figure 6. This purple crusty substance is a slime mould on strawberry leaf.
Slime moulds appear on low lying vegetation when weather is warm and wet, and generally disappear when hot dry weather returns. They do not generally require control, but many fungicides ordinarily applied to strawberries will also control slime moulds. Related Links| Top of Page | Toll Free: 1-877-424-1300 Local: (519) 826-4047 E-mail: ag.info.omafra@ontario.ca |
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