Organic Disease Control of Strawberry Plants
Stop Powdery Mildew, Plant Viruses, Fruit Rot, and Leaf Spot
Jun 28, 2009
As if there weren’t enough insects and animals clamoring for the first juicy berries in the strawberry patch, strawberry plants are subject to several diseases as well. It’s no wonder, then, that conventionally grown strawberries are considered one of the “dirty dozen,” as they carry a large amount of toxic chemical residue from the field to our homes. Learn the methods for controlling strawberry diseases without chemicals in the organic garden.
Alkaline Soil Problems
Strawberry plants require a soil that is slightly acidic, with a pH of 6.2 being ideal. If the soil is too alkaline, strawberries can exhibit a problem called alkali yellows. This causes the plant to be unable to absorb iron or manganese from the soil, which affects chlorophyll production. The diseased plants will have yellow or variegated yellow and green leaves. Over time, this reduces the vigor of the strawberry patch.
Gardeners who observe symptoms of alkali yellows should test the soil pH. If the soil is too alkaline, acidify it naturally by adding organic matter like compost or well-rotted manure whenever possible. Plant the strawberry patch away from concrete patios, as concrete releases lime into the soil, increasing its alkalinity.
Strawberry Leaf Spot
Common leaf spot is a fungal disease encouraged by moist conditions and warm temperatures. Affected plants have grey or white speckles across the leaves, and fruit can be afflicted with leathery dark spots. Cultural control methods for preventing leaf spot include adequate spacing of plants in an open, breezy area that receives eight hours of full sun. Gardeners should also irrigate strawberry plants in the morning, using drip irrigation to allow leaves to stay dry. ‘Earlibelle’ and ‘Titan’ strawberry varities are very resistant to leaf spot.
Powdery Mildew
Powdery mildew on strawberries has the same effect as it does on other flowering plants and vegetables, causing a gray fuzzy growth on leaves that stunts the plant. Gardeners can use Safer Garden Fungicide on plants, which is a sulfur-based product. However, this spray can burn plants if applied to plants when temperatures exceed 85 degrees F. Gardeners can also look for a potassium bicarbonate based spray, such as GreenCure.
Gray Mold, or Botrytis Fruit Rot
Gray mold in strawberries is insidious, because the plant may look fine until berries are mature, when a gray fuzzy growth rapidly ruins the fruit. Prevent this fungus by giving plants adequate spacing in the garden, which allows plants to dry quickly after rain. Pick ripe strawberries daily, especially during periods of damp weather.
Strawberry Viruses
More than 30 viruses affect strawberry plants, so identification of the particular virus isn’t as important as prevention. Generally, strawberries affected with a virus appear stunted, and plant death eventually occurs. Gardeners can get the strawberry patch off to a healthy start by planting virus-resistant varieties, such as ‘Sumas’ and ‘Northwest.’ Controlling aphids is critical to preventing strawberry viruses, as these sucking insects act as a vector for these diseases. Release ladybugs in the spring when aphids are most problematic, and encourage the lacewing population in the garden with nectar-rich flowers.
Sources:
Oregon State University Extension
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