How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

The most obvious symptoms of anthracnose in the field are stem 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 rare in California annual plantings. Stem lesions or characteristic crown symptoms usually precede the collapse of affected plants. Stem lesions appear as dark brown or black, lens-shaped, sunken spots on petioles and runners. Under warm, humid conditions, salmon-colored masses of spores may form on lesions.

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, stem and foliage lesions are not produced by Phytophthora spp.

Fruit decay caused by anthracnose is common in production areas. 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 commonly occur on the lesions. Decayed tissue is firm and dry.

COMMENTS ON THE DISEASE

The pathogen that causes anthracnose 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 that were planted to strawberry. In addition, inoculum can come from contaminated soil on field equipment or be blown in from nearby weeds.

MANAGEMENT

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 eliminates most inoculum from infested transplants. Follow good cultural 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.

Cultural Control
Using drip irrigation and clean planting stock are important components of managing this disease. Thoroughly washing all soil from plants before planting will reduce disease in crowns and fruit. It may be worthwhile to dip trays of long-term cold storage (28°F) transplants into a hot water bath for 7 minutes right before planting to reduce occurrence of this disease. Prepare plants for this treatment by thoroughly washing them to remove all dirt; then place them in a circulating water bath that is held at a constant temperature of 120°F. Afterwards, submerge them in very cold water and then plant them as soon as possible. (This treatment is not recommended for fresh-dug transplants that have only been stored at 33°F.)

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 part of the field to a noninfested section. Crop rotation with a nonhost crop can also help in reducing levels of this pathogen in the soil. Also important is 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.

Soil Solarization
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.

Organically Acceptable Methods
Cultural controls, including soil solarization, washing soil from crowns before planting, and crop rotation, are acceptable for use in an organically grown crop. 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.

Monitoring and Treatment Decisions
Good results in managing anthracnose have been obtained with a sequential application of chloropicrin (200 lb/acre) or 1,3-dichloropropene/chloropicrin (300 lb/acre) followed 7 days later with metam sodium (45 gal/acre) or metam potassium (37 gal/acre).

At planting, fungicide dips can be used on transplants before planting in 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 be present with rainfall or sprinkler irrigation, they shouldn't be problems when the weather is dry. If moisture occurs, pay close attention to developing fruit on day-neutral cultivars. 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.

PUBLICATION

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468
Diseases
S. T. Koike, UC Cooperative Extension, Monterey Co.
W. D. Gubler, Plant Pathology, UC Davis
G. T. Browne, USDA Crops Pathology and Genetics, UC Davis

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