Fragaria chiloensis and Fragaria ananassa
Anthracnose complex (fungi – Colletotrichum spp.): All plant parts are susceptible to one of the three major fungal species. Crown rot, caused by C. fragariae, is primarily a plant production problem in annual systems. Plants become infected in nurseries but show no symptoms until transplanted to production fields. High temperatures trigger symptom development. Plants die quickly. It is essential to acquire disease free transplants. The other Colletotrichum species cause fruit rot, flower blight or leaf spots. Stolons and petioles can also be infected. Rigorous fungicide programs are necessary to minimize losses to anthracnose diseases. Under favorable conditions for disease development, chemical control may give disappointing results. Varieties vary in susceptibility.
Black Root Rot (various fungi): The exact cause of black root rot is unknown. It has been associated with several different organisms or conditions. The symptoms of black root rot are a black and woody root system. On healthy plants, the roots will appear white and pliable; however, diseased plants will have stiff roots. The feeder roots are partially or completely destroyed. The tip of the main roots will be destroyed. Fumigation has helped with this problem.
Cercospora Leaf Spot (fungus – Cercospora spp.): This is one of the more common, but usually minor, leaf spots of strawberry. It occurs in all areas of Texas. At first, small round purple spots are seen on the upper side of the leaves. As the leaf matures, the center of the spot becomes tan or gray then almost white while the edges of the spot remain purple. On the underside of the leaf, the spots are bluish or tan in color. Varieties vary in their resistance to Cercospora leaf spot.
Fruit Rots (fungi – Botrytis cinerea, Rhizoctonia spp. plus others): Fruit rots destroy a large percentage of the fruit each year in Texas. There are several organisms involved in this complex and symptoms are somewhat different for each fungus. Gray mold rot (Botrytis) is the most damaging. It attacks green fruit as well as ripe fruit. The first sign of infection is a small, brown, soft spot. Ripe fruit rapidly rots, becoming covered with a gray moldy growth. Rhizoctonia attacks ripe fruit that in most cases contacted soil. The disease is called hard rot. Affected berries are usually one sided. Fruit rot control is achieved with chemical applications and cultural practices. Maintain good air circulation by not crowding plants. Avoid excessive fertility rates.
Leaf Scorch (fungus – Marssonina fragariae): The disease is similar to Cercospora leaf spot. At first, small dark purple spots up to one-fourth of an inch in diameter appear on the upper side of the leaves. These spots never have light centers as do those of Cercospora leaf spot and they have a more irregular outline. The fungus can also attack other parts of the plant. Some varieties have resistance to leaf scorch. Fungicide applications at repeated intervals should give adequate control.
Red Stele (fungus – Phytophthora fragariae): Red stele is the most serious root disease of strawberries. It occurs during the late winter and spring. The fungus attacks only strawberries and is spread from one area to another primarily through diseased plants. In a healthy plant, the roots are a yellowish-white and in a diseased plant, the center is a distinctive brownish-red. Infected plants are stunted and wilt in dry weather. The root systems have a rattail appearance with few lateral roots produced. The disease is more disastrous in low, poorly drained fields during cool weather. There are no chemical or cultural methods for reducing disease losses, except to replant resistant varieties. The fungus does not persist in well drained soils.
Verticillium Wilt (fungus – Verticillium albo-atrum): This is a widespread soil-borne disease of strawberries growing in cool, poorly drained soils. Symptoms show up as a burning of the outer margins of the leaves. Young roots turn black at the tips and die back. If Verticillium has been a problem in your area, consider a variety which has resistance to the wilt organism. Soil fumigation with a chloropicrin-containing fumigant is recommended when resistant varieties are not available. When using soil fumigants, follow manufacturer’s directions and use caution in handling the material.
|Table 1: Strawberry Varieties* and their reaction to disease|
|Variety||Leaf Spot||Leaf Scorch||Red Stele||Verticillium Wilt||Anthracnose||Virus Diseases|
|Sequoia||Resistant||Tolerant||Susceptible||Susceptible – Intermediate||Resistant||Tolerant|
|Fort Laramie||Intermediate||Intermediate||Susceptible||Intermediate – Resistant||Susceptible||–|
|Dover||Susceptible – Tolerant||Tolerant||–||Intermediate||Resistant||–|
|Florida 90||Susceptible||Susceptible||Susceptible||Susceptible||Intermediate – Resistant||–|
|* These varieties are not necessarily recommended in Texas.|