Leading Producers of Strawberries State Harvested Acres* California 25,000 Oregon 6,200 Florida 5,100 New York 3,800 North Carolina 2,400 Pennsylvania 1,500 Washington 1,500 LOUISIANA 1,100 1st in taste *USDA 1995
Morphology a, crown and leaf bases; b, stolon (runner); c, first (blind) runner node; d, daughter plant; e, secondary runner
Production Strategies Matted Row System Consists of rows 12 to 24 inches wide that are allowed to fill in or be renewed with runner plants. Fields are renewed or renovated each year. Fields planted in the matted row system generally produce three to four profitable crops. If disease, insects, or weeds heavily infest a planting, renovation may not be economically justified. Annual Hill Plasticulture The annual hill system is a high-density system that grows strawberries as annuals. This system consists of closely spaced plants in double rows planted on raised beds covered with black plastic. Plasticulture is an annual system of planting freshly plants in the fall. Plants and plastic are removed after spring harvest and the process begins again the next fall.
Important Diseases • Red Stele • Anthracnose and Black Leaf Spot • Botrytis Grey Mold • Mycosphaerella Leaf Spot • Many viruses, insects and regional nematodes and numerous abiotic constraints that will not be covered
Red Stele Pathogen: Phytophthora fragariae Distribution: Serious disease of strawberry in the northern 2/3 of the United States. Many desirable commercial cultivars are highly susceptible. Thrives in poorly drained, cool, wet soils.
Symptoms Aboveground: Symptoms of red stele rarely occur in the first year of strawberry growth unless plants are infected before planting or if conditions are suitable for rapid fungal growth. The disease is first noticed during bloom of the second year. The symptoms will be most noticeable in low or soil compacted areas of a field where water drainage is poor. Strawberry plants will show a general lack of vigor with poor runner growth and small berries. New leaves may appear bluish-green, while older leaves sometimes turn red, orange or yellow. The leaves tend to wilt during warm weather or drought stress. Severely diseased plants may collapse prior to fruiting. Although these aboveground symptoms are typical for red stele, they may resemble symptoms caused by other types of root disorders; therefore, roots also need to be examined.
Symptoms Belowground: To correctly diagnose, roots should be sampled during early spring and summer up until harvest. Samples taken after harvest are not reliable because infected roots may have already begun to decay. If red stele is present, the roots will appear unbranched and will be lacking feeder roots. This "rat-tail" appearance of the root is a diagnostic trait of red stele. Infected roots will have a reddish-brown core, but the outer tissue will be white. The discoloration will begin at the root tip and move upwards, but usually will not move into the crown. This is in contrast to another root disease, black root rot, in which outer root tissues are affected earlier than the inner (stele) root area. Normal roots have both a white center and outer root surface
Symptoms Red Stele, & Rat tail appearance
Disease Cycle The fungus is spread from one field, or area to another by the distribution of nursery infected plants. Infection is then spread within the field by moving water and by soil movement. Once in the field, oospores in roots produce zoospores when soil moisture is high, infecting the tips of the young, fleshy roots and destroying water- and food-conducting tissues. Infection and growth of the fungus in roots reduces the flow of water and nutrients to the developing leaves and fruit causing drought-like symptoms in the plant.
Disease Cycle The optimum temp. for growth and infection is 57 F. When soil moisture is high and the temperature is cool, plants show symptoms within 10 days after infection. The fungus is inactive at 40 F and above 86 F. The critical periods for development and spread are in the spring and the fall. As summer, soil temperatures rise, the fungus forms oospores in the stele of infected roots. The fungus survives periods of hot, dry, or cold weather primarily as these oospores
Disease Management Pre-Plant Soil drainage: the pathogen requires free water in order to develop. Avoid low-lying areas, and, raised beds 10 inches or more. Can persist in the soil for at feast 17 years, even in the absence of strawberry plants = no crop rotation benefits. Site Preparation: Cover crops can build organic matter in the soil (heavy, compacted soils favor red stele). Sanitation: Clean cultivators or equipment. Planting: Exclusion and prevention. The pathogen is introduced most frequently on infected-plants; therefore, mother plants should be purchased from a reputable nursery. Host Resistance: “Resistant varieties" are not resistant to all strains of P. fragariae
Disease Management Post - Plant Use cultural practices which favor good plant growth and development. Avoid over irrigation. Chemical: Soil fumigation with soil sterilants and/or pesticide applications may be helpful in situations where resistant varieties are not available or are not adapted.
Anthracnose and Black Leaf Spot Pathogens: Colletotrichumacutatum, C. fragariae, Distribution: Throughout the United States The fungus may cause petiole and runner infections, flower blight, and anthracnose crown rot. Flowers and ripening fruit are very susceptible to anthracnose fruit rot.
Symptoms Lesions on stolons and petioles are sunken, firm, dark, and dry with a sharp line separating healthy from diseased tissue. When a runner is girdled by a lesion, the daughter plants beyond the lesion wilt and die. Lesions on petioles also result in the death of leaves.
Symptoms Crown rot occurs when the fungus grows into crowns from infected runners or petioles. Plants with crown rot may die in the nursery or after being transferred to production fields. Wilting plants with crown rot have a reddish brown, firm rot in the interior of the crown. Crown rot is sometimes difficult to identify just on the basis of crown discoloration because crowns of dying strawberry plants turn brown regardless of what kills them.
Symptoms and Signs Fruit rot can occur on both ripe and unripe fruit. Infected tissue on ripening fruit appears as round, firm, sunken, tan to brown spots that turn into sunken black lesions with age. The spots may remain a light tan color for a few days, especially during wet weather. The entire fruit may become infected, dried, and mummified. Dark brown to black, firm lesions can occur on the green fruit. Under humid conditions, salmon colored sporulation may be visible on the lesions.
Symptoms Leaves: Lesions on leaves are small (<1/4"), round, and black (sometimes light gray) often resembling ink spots. Spots may become numerous on leaflets without causing leaf death and often appear first on expanding leaves of runner plants. The presence of leaf spot may be a warning signal that abundant inoculum is present on other plant parts and fungicide applications are needed.
Disease Development Infected transplants and soil from infected transplants appear to be the primary source of inoculum in most instances, especially in annual production systems. This may be especially true for C. fragariae, which has a limited host range and does not survive in soil over the summer. In perennial systems, the fungi may overseason in infected plants and debris, providing inoculum for the following fruiting season. Conidia may be dispersed in the field by wind-driven rain, splashing water, insects, movement of workers, equipment or animals.
Disease Development Disease development and spread is minimal in most cases under cool, dry conditions. Crown infections often occur in the nursery but do not appear until after planting. The fungus continues to develop in newly planted nursery infected plants, which may suddenly die during warm weather in the fall or early spring of the following year. Infected berries eventually dry up and mummify and can become a source of inoculum for the following season. C. acutatum is known to survive in infected plant material for up to nine months
Management Difficult to control when conditions are favorable for infection during harvest. Control measures must begin early in the season. Disease-free planting material, however it is difficult to detect the fungus in planting material because it causes latent infections. Follow a protective fungicide program from transplanting through harvest. Avoid overhead irrigation if possible. If fruit rot occurs, remove all infected fruit at each harvest. To prevent the spread of the disease, never move pickers from an infected to a non-infested field. When they are available, plant strawberry varieties resistant to anthracnose (Resistant varieties are currently being developed).
Botrytis Grey Mold One of the most common and serious diseases, in wet seasons on unsprayed plants 80-90% losses of flowers and fruit can occur Causal agent – Botrytis cinerea
Symptoms and Signs Young blossoms are very susceptible to infections. One or several blossoms in a cluster may show blasting. Soft, light brown lesion form at calyx end of fruit with lesions without distinct borders Produces light grey spores that are easily airborne. Berries resting on soil or touching other decaying fruit often infected Good berries become a rotted mass within 48 hours Berries soon dry out leaving dark brown, mummies covered with grey-white fungal growth.
Disease Cycle Fungus overwinters as minute, irregular, black fungal bodies (sclerotia) and as dormant mycelium on dead leaves, stems, fruit and on annual weeds. In spring, sclerotia produces conidia, wind, splashing water, human activity spread throughout the patch depositing on blossoms, stems young fruit and leaves. Some plant parts may be infected in 3 hours. Temp 70-80, free moisture (rain, dew, fog, irrigation) are ideal for germination and infection. Fungus can penetrate unbroken skin of fruit. Single berry may contaminate many others in field or after harvesting.
Factors Favoring Disease Moderate temperatures and long wetting periods or periods of humidity during bloom. Prolonged rainy and cloudy periods just before and during harvest. Dense foliage and wide rows keep plant wet longer, all varieties are susceptible but some are much more than others.
Disease Management Avoid narrow rows Encourage air flow Apply fungicides Mulching with clean straw Black polyethylene sheeting Limiting cultivation from early bloom until after harvest Avoid wounding plants Care in handling berries Refrigeration of berries
Mycosphaerella Leaf Spot One of the most common and widespread diseases of strawberry. Mycosphaerella fragariae is also the cause of black seed disease of strawberry fruit, which occurs occasionally in North America where Mycosphaerella leaf spot is present. Prior to the development of resistant cultivars and improved control programs, leaf spot was the most economically important strawberry disease.
Symptoms Leaves: Leaf symptoms vary with strawberry cultivar, strain of the fungus, and environmental conditions. Leaf lesions or "spots" are small and round (3-8 mm diameter), dark purple to reddish, and are found on the upper leaf surfaces. The center of the spots becomes tan to gray to almost white, while the broad margins remain dark purple. Lesion centers on younger leaves stay light brown, with a definite reddish purple to rusty brown margin. Numerous spots may coalesce and cause death of the leaf. In warm humid weather, atypical solid rusty brown lesions without purple borders or light colored centers may form on young leaves. Lesions are evident on the undersurface of the leaf but are less intense in color, appearing as indistinct tan or bluish areas.
Symptoms Leaf stems (petioles), runners, fruit stalks (pedicels), berry caps (calyxes): Almost identical to those on leaves. pathogen. Fruit: Superficial black spots (6 mm in diameter) form on ripe berries under moist conditions. These spots surround groups of seeds (achenes) on the fruit surface. The surrounding tissue becomes brownish black, hard and leathery, however, no general decay of the infected berry occurs. Usually only 1-2 spots occur on a berry but some may have as many as 8-10 "black-seed". Symptoms are most conspicuous on white, unripe fruit and on ripe fruit of light colored cultivars. Economic losses in this case are due to unattractiveness of "black seed" spots on fruit, rather than fruit rot.
Signs of the pathogen Late in the season, dark specks (sclerotia and/or perithecia) may be seen in older lesions.
Disease Cycle - North In northern growing regions, the life cycle is somewhat different. Three sources of primary inoculum may be present: conidia overwintering on living leaves, conidia from overwintering sclerotia, and ascospores. Abundant conidia, produced in early summer on lesions on both upper and lower leaf surfaces and lesions on other plant parts, are spread primarily by water splash. Sclerotia are produced during the winter on dead infected leaves. These may also produce abundant conidia in the spring.
Disease Cycle - North Conidia also develop on occasion from the bases of perithecia. Perithecia are produced on upper surfaces of overwintered leaves. Forcibly discharged ascospores from these perithecia are wind disseminated. It is not known if these ascospores serve as an important source of primary inoculum, but they are most probably a means by which genetically different strains of the fungus may travel long distances. M. fragariae establishes in the stigma at the time of flowering and then grows to the achene. From there it infects surrounding berry (receptacle) tissue. Conidia produced in leaf infections are probably the primary inoculum source for fruit infections.
Disease Management Plant in well drained soil with good circulation and exposure. Choose disease resistant cultivars suitable for the region. Plant only disease free plants purchased from reliable nurseries. Apply nitrogen fertilizers only at renovation to reduce succulent new leaf tissue which is more susceptible. Remove older or infected leaves before setting runners in new plantings. Removing and burning all debris at renovation (after harvest) helps to reduce overwintering inoculum Fungicide spray schedule - Thoroughly cover all above ground plant parts with spray, especially undersides of leaves