Good Practices for Insect and Disease Control
Good Air/Water Drainage
Good air drainage and circulation within the strawberry planting speeds the drying off of plants and reduces the potential for infection. Botrytis (gray mold) requires wet foliage or fruit for infection to take place. Similarly, it is important that the soil dries out quickly after rain. Waterlogged soil increases the likelihood of disease infection in the root system. Red stele and verticillium are two soil fungi that can infect strawberry root systems more easily in wet soil.
Plants need full sunlight to grow and produce fruit, but sunlight also helps the foliage and fruit to dry off quickly after a rain or heavy dew. Rapid drying will reduce fruit and leaf diseases.
No Infested Runoff
Disease organisms (e.g., red stele, verticillium, black root rot) can be carried in runoff water from a diseased planting to a healthy planting. Do not plant new fruit plantings below older, diseased plantings.
Some crops can build disease organisms in the soil, which can devastate the next crop if it is susceptible to the disease. Strawberries should not follow tomatoes, potatoes, eggplant, peppers, strawberries, raspberries or stone fruits for 5 years since these crops might harbor the Verticillium fungus. Avoid an area with a history of verticillium or red stele problems.
Some plants are not susceptible to certain diseases or are less susceptible than other varieties. Resistance or tolerance to diseases will eliminate or greatly reduce the need for disease control. Refer to Table 8.1 for specific examples.
Disease-Free Planting Stock
Plant only disease-free planting material. Since viruses cannot be seen at the time of planting, the grower must rely on good propagation and cultural practice methods used by the nursery in producing the plants. Virus-infected plants are infected for life, and plants infected with soil-inhabiting fungi can contaminate the site for many years. Buy only healthy plants from reputable nurseries.
Adequate Plant and Row Spacing
Most disease organisms that cause foliage or fruit diseases require wet surface areas for infection to take place. By speeding the drying time after rain or heavy dew, the grower can greatly reduce the potential for disease development. Two important methods for accomplishing this in a strawberry planting are to maintain narrow rows and a low plant density within each row.
No Cultivation from Infested Soil
Cultivating in a diseased planting and then moving that equipment to a healthy planting without washing the soil from the equipment can transport disease organisms between plantings.
Mulch to Prevent Winter Injury
Mulch will protect a strawberry plant from winter injury. In some cases, strawberry plants may be injured but not killed by cold temperatures. Those plants are often susceptible to black root rot.
Avoid Frosted Blossoms
Strawberry flowers that have been injured by frost are more susceptible to botrytis (gray mold). Avoid frost injury to blossoms to reduce gray mold incidence in a planting.
Fungicide applications should be used only if other control strategies are not adequate to control the disease. Fungicide sprays will help in the control of powdery mildew and fruit rots.
Harvest before Overripe
The fruit rots will spread more quickly on overripe fruit. Overripe fruit also will allow a disease to build up in the planting, therefore making control more difficult.
Fruit Storage Conditions
Fruit rots will develop more slowly or not at all if the fruit is cooled rapidly (to 40°F) after picking.
Weeds can be a big problem in strawberry beds. Hand weeding and using a generous layer of straw mulch are the best options for control.