Black root rot
Caused by soil fungi, nematodes, winter injury, fertilizer burn, drought, too much water or any combination of these. Plants show poor vigor, produce few runner plants and may die in patches. Roots may be spotted with black zones or lack feeder roots, or the entire root system may be killed. Infected roots are black when cut in a cross section. There is no way to control black root rot. However, proper cultural practices that minimize plant stress should limit this disease. If a bed becomes infected with black root rot, plant a new bed in different location, and use only healthy, white-rooted plants.

Red stele root rot
Caused by a soil-borne fungus and occurs most frequently on poorly drained sites with clay soils. The fungus is most active in the spring and fall when soils are cold and wet. Small feeder roots are killed, giving a "rat tail" appearance. Main roots that are infected have rusty-red color in the core or stele. Plants may wilt and die during hot, dry conditions. To avoid this disease, plant only red-stele-resistant varieties and plant in a well-drained site in a loamy soil.

Leaf spot and leaf scorch
Two common foliage diseases. Leaf spot produces spots 1/8 to 1/4 inch in diameter with purple borders and light gray centers. Leaf scorch produces small solid purple spots with rather undefined borders. When numerous they almost cover the entire leaf. Cultivars vary considerably in tolerance to these diseases. Foliage fungicides aid in the control of these diseases.

Verticillium wilt (fungus)
Caused by a soil-borne fungus. In new strawberry plantings, symptoms appear about the time runners start to grow. In established plantings, symptoms appear when the berries ripen. Older outer leaves of infected plants wilt, turn brown around the edges and between the veins and eventually die. Petioles of the leaves may also turn red. Few new leaves develop and new roots that grow from the crown are short and have blackened tips. To avoid this disease, select resistant strawberry cultivars and avoid sites that were previously planted with wilt-susceptible crops.

Gray mold
Caused by the fungus Botrytis, which overwinters on plant debris on the ground. During bloom the fungus may be spread to blossoms during rainy weather, and the infection then spreads to the developing fruit. This disease often occurs where a dead petal or leaf adheres to the fruit or where a berry touches the soil. The disease appears as a gray, fuzzy mass of fungal spores on berries. To prevent this disease, thin plants to improve air circulation within the bed and use straw mulch. Fungicides may also be applied.

Leather rot
Caused by a fungus that infects the berries when ripening fruit clusters are in contact with the soil or standing in water after a period of warm, rainy weather. Infected immature fruit turns brown. On ripening fruit, the color becomes bleached out and infected areas are tough and dry. Berries taste bitter and smell rotten. A single infected berry can ruin the flavor of a whole jar of jam. To prevent this disease, use a mulch to minimize rain splash onto the fruit, or fungicides may be applied.

Viruses
May stunt plant growth or cause mottling or curling of leaves. They are introduced by insects such as aphids or leafhoppers. To prevent viruses, use certified plants and control these insects.

Insects and other pests

Tarnished plant bugs
Cause deformed or "nubbin" berries with a concentration of seeds at the tip of the fruit. Nymphs puncture individual seeds and inject a toxin so that the fleshy part of the berry stops developing where the seed was injured. Damaged seeds are hollow and turn a straw-brown color. Plant bugs are often in alfalfa; to prevent the bugs from feeding on strawberries, avoid mowing alfalfa when strawberry plants are in bloom.

Leafrollers
Small worms that roll the leaves together and feed on the leaves. They must be controlled if they become numerous.

Mites
Tiny, spiderlike creatures that are typically found on the underside of leaves. Mites tend to be the most damaging during hot, dry periods, when they suck plant juices from the leaves.

Strawberry weevils or clippers
Puncture fruit buds with their snouts to feed on immature pollen. Later, females deposit an egg inside a floral bud and girdle the petiole of the bud so that it falls to the ground or is left hanging by a small bit of tissue.

Slugs
Eat holes in ripe fruit and are worse during rainy weather or near rotting foliage. Shiny slime trails are evidence of slugs.

Nematodes
Found in the soil and are too small to be seen with the naked eye. Most nematodes feed on roots. Symptoms of nematode damage include galls on the roots or stubby, stunted roots. To avoid a buildup of nematodes, rotate plantings to a different site when establishing new beds.

Causes of malformed fruit

"Nubbins" or "button berries" may be caused by feeding tarnished plant bugs (see above), heavy infestations of cyclamen mites, frost injury, nutrient deficiencies (boron, calcium), inadequate pollination, abnormally high temperatures that make pollen nonviable, or by the application of 2,4-D from August 1 to November 1, when fruit buds are differentiating.

Fasciated berries, those that have a cockscomb shape as if several berries have grown together with multiple tips, are caused by short day-lengths in the fall or by cold, dry weather during this time. Fasciated fruit often occurs when cultivars adapted to northern conditions are grown in the south.