Anthracnose

The most obvious symptoms of anthracnose in the field are petiole, runner, and fruit lesions. In some fields after planting, stunting and yellowing of plants may occur. Wilting and collapse of plants may occur, but this is less common in California annual plantings. Petiole and runner lesions or characteristic crown symptoms usually precede the collapse of affected plants. Diseased petioles and runners develop lesions that appear as dark brown or black, lens-shaped, sunken spots.

When crown tissue is infected and becomes decayed, the entire plant may wilt and die. Like Phytophthora crown rot, the internal crown tissue is discolored, but with anthracnose the discolored tissue is cinnamon to red in color whereas Phytophthora-rotted tissue is more of a chocolate brown; in addition, petiole and runner lesions are not produced by Phytophthora spp.

Fruit decay caused by anthracnose may be common in production areas depending on environmental conditions. If infected plants are present, decay can develop following periods of warm, rainy weather. Fruit at any stage of ripeness can be affected. Small, sunken, oval-to-round brown spots (on green fruit) or black spots (red fruit) develop and may expand to cover most or all of the fruit surface. Under high humidity, salmon or orange-colored spores can form on the lesions of the fruit, petioles, and runners. Decayed fruit tissue is firm and dry.

Colletotrichum acutatum can survive in soil for at least 9 months without host plants. In addition to strawberry, several weeds are known to host this pathogen including chickweed, fiddleneck, and vetch. If strawberries are planted in infested soil, they become infected when soil containing spores is splashed onto crowns or stems by rain or irrigation water. In fields that have been fumigated, the disease usually originates on infected nursery stock or from volunteer strawberry plants in adjacent fields. In addition, inoculum can come from contaminated soil on field equipment or be introduced from nearby weeds.

Soil fumigation destroys most residual inoculum of Colletotrichum in the soil. In warm, inland fields soil solarization can be effective in destroying soil inoculum. Running water treatments can be used to wash soil from transplants. This reduces inoculum from infested transplants. Follow good sanitation procedures to prevent disease inoculum from entering the field, and rotate to nonhost crops where fumigation and solarization are not feasible. Fungicide dips can be used on transplants before planting in production fields. Foliar fungicides are available for use on plants when the disease is present and conditions are ideal for foliar and fruit disease development.

• Thoroughly wash all soil from plants before planting to reduce disease in crowns and fruit.
• Heat treatment of plants has been shown to reduce the amount of disease but can reduce the viability of some cultivars.

• Use drip irrigation.
• Clean field equipment before using it in a field to ensure that contaminated soil and plant parts are not transported into a field or from an infested section of the field to a noninfested section.
• Clean equipment before leaving a contaminated field.
• Rotate with a nonhost crop to reduce levels of this pathogen in the soil.
• Practice good weed management in and around the field to destroy any weeds that may harbor the pathogen. Recent research has demonstrated the importance of removing the weeds from the fields after they are destroyed because the pathogen can still produce spores even though the weeds are dead.

In warmer areas of the state, solarization has been shown to be effective for the control of soilborne pathogens and weeds. Solarization is carried out after the beds are formed and can be effective if weather conditions are ideal (30–45 days of hot weather that promotes soil temperatures of at least 122°F down to about 14 inches). The effectiveness of solarization can be increased by solarizing after incorporating the residue of a cruciferous crop, in particular broccoli or mustards, into the soil or following an application of metam sodium (40 gal/acre). For more details on how to effectively solarize soil, see Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds, UC ANR Publication 21377.

Use cultural controls, including soil solarization, and crop rotation, and wash soil from crowns before planting. Use annual plantings, as inoculum tends to readily build up in multi-year plantings; this disease tends to be much more severe in California in second-year fields.

Good results in managing anthracnose have been obtained with a sequential application of chloropicrin or 1,3-dichloropropene plus chloropicrin followed 7 days later with metam sodium or metam potassium.

At planting, fungicide dips can be used on transplants before planting in fruit production fields.

During the growing season, watch for anthracnose symptoms during routine monitoring for spider mites and other pests. Because anthracnose and Botrytis should only occur following rainfall or sprinkler irrigation, they shouldn't be problems when the weather is dry. If moisture occurs, pay close attention to developing fruit. If fruit disease appears in a small area of the field or before the plant canopy is well developed, foliar fungicides may help prevent further spread of the disease and reduce crown infections. Thorough coverage of the fruit is important.

Be aware of developing fungicide resistance issues in some areas. Consult your local extension advisor . for more information.

For more information on the symptoms and management of anthracnose, see the Anthracnose of Strawberry Production Guideline. (PDF)