STRAWBERRIES

ANTHRACNOSE OF STRAWBERRY:

Symptoms:  The fungus can attack fruit, runners, petioles, and the crown of the plant. Dark elongated lesions develop on   petioles and runner stems. Affected petioles and stems are sometimes girdled by le­sions causing individual leaves or entire daughter plants to wilt and die. Under warm, humid conditions, salmon-colored masses of spores may form on the lesion surface. If the crown tissue is infected, crown rot may develop and the entire plant may wilt and die. When infected crowns are sectioned, internal tissue is firm and reddish-brown to dark-brown in color (Figure 1). Crown tissue may be uniformly discolored or streaked with brown.  Whitish, tan, or light-brown water-soaked lesions up to 3 mm in diameter initially develop on fruit. The lesions eventually turn brown or dark-brown, are sunken, and enlarge within two to three days to cover most of the fruit (Figure 2). Lesions are covered with pale-orange or salmon-colored spore masses. Under moist conditions, the fungus may grow out around the edge of the lesion or through the lesion, giving a fuzzy appearance. Infected fruit eventually dry down to form hard, black, shriveled mummies. Fruit can be infected at any stage of development.

The disease is probably introduced into new plant­ings on infected plants. Recent research indicates that the fungus can grow and produce spores on the surface of apparently healthy leaves.  Once the disease is established in the field, the fungus can overwinter on infected plants and plant debris, such as old dead leaves and mummified fruit. Spore production, spore germination, and infection of strawberry fruits are favored by warm, humid weather and rainfall. In spring and early summer, spores are produced in abundance on previously infected plant debris. The spores are spread by splashing rain, wind-driven rain, and by people or equip­ment moving through the field. They are not airborne so they do not spread over long distances in the wind. Spores require free water on the plant surface in order to germinate and infect.

The optimum temperature for infection on both im­mature and mature fruit is between 77 and 86 degrees F. Under favorable conditions, the fungus produces second­ary spores on infected fruit. These spores are spread by rain and result in new infections throughout the growing season. Disease development can occur very rapidly. Up to 90 percent of the fruit can be infected within a week or less. Both immature and mature fruit are susceptible to infection; however, the disease is most common on ripening or mature fruit.

Control:  Use disease-free planting material as the disease is introduced to the field with infected plant material.  Although there are no nurseries that can certify plants to be free of fungal and bacterial plant pathogens, inspection of plants for the disease before planting is recommended.  If the field was previously infected, or the disease is present in the field, minimize the amount of overhead irrigation used. The fungus is spread by splashing water. Avoid the use of overhead irrigation and use drip irrigation if possible. Plastic mulch increases the level of splash dispersal of the pathogen. Mulching with straw is recommended in perennial matted row plantings to reduce water splash and disease spread.

Treatment:  Remove infected plant parts. Infected plant parts serve as a source of inoculum for the disease. Remove as much old, infected plant debris as possible. Try to remove infected berries from the planting during harvest.  Fungicide use. Once anthracnose fruit rot is established in a planting, it is difficult to control with fungicides. Fungicides for control of anthracnose fruit rot should be used in a protectant or preventative program. In order to obtain effective disease control, fungicides should be applied before the disease develops.

BOTRYTIS CROWN ROT OF STRAWBEERRIES:

 

Symptoms:  Usually begin in the upper part of the crown and spread downward. The youngest leaves wilt suddenly and often turn a bluish green. Wilting spreads quickly throughout the plant, and complete collapse occurs within days.   Collapse may be one sided, depending on the number of crowns infected. Infected plants will often break at the upper part of the crown when lifted from the soil. When cut lengthwise, the crown appears brown or sometimes rose pink throughout. Crown tissue will disintegrate with time.  Rot symptoms are most common between flowering and harvest when the plants are under stress. Warm, wet conditions and poorly drained soils favor infection. Symptom development is favored by high temperatures and low moisture conditions, factors that apparently stress the plant before harvest

Control:  Always plant healthy certified plant stock. Make sure growing site is well drained. If strawberry crown rot has set in remove infected plants. Apply a good layer of straw or other protective material to keep fruit off soil surface. Plant new crop far from the previous growing site. Provide adequate soil drainage (plant strawberries in raised beds)reducing the risk of plants developing strawberry crown rot.

PHYTOPHTHORA CROWN ROT:

 

Symptoms:  Initially, symptoms typically include plant stunting and small leaves. As the season progresses, plant collapse may occur rapidly or slowly. When infected plants are cut open, a brown discoloration can be seen in the crown vascular tissue or throughout the crown tissue. The same Phytophthora species also attack roots, causing a brown to black root rot.

Control:  Soil fumigation and good cultural practices provide adequate control of Phytophthora in production fields. Good cultural practices include the use of certified transplants, avoiding poorly drained soils, and preparing fields to provide good soil drainage during wet weather. Phytophthora can be moved in water that has drained from infested fields, so avoid using runoff water for irrigation or for wetting down field roads for dust control. In fields that are prone to Phytophthora problems, you may want to plant less susceptible cultivars. Even with tolerant cultivars, however, it is important to follow good cultural practices. As cultural controls, use raised beds and carefully managed drip irrigation; plant in noninfested soils that have good drainage. Also, use clean plant stock and consult your farm advisor about cultivar susceptibility. Soil solarization can also provide control.