Gray mold, caused by the fungus Botrytis cinerea, is the most important disease on strawberry fruit. The fungus infects strawberry and almost all other plants. It is literally everywhere. On strawberry, this disease primarily affects fruit, but can also infect leaves, petioles, stems, and the flower as well. It is favored by cool (59° to 77° F), wet weather. It first establishes itself on a plant part that is weakened, damaged, dying, or older vegetation, especially on the dying petals of older flowers. It then can grow into the healthy parts of the plant, such as the fruit being produced from the flower with the dying petals. This disease can destroy green fruit immediately, but it usually remains dormant in the fruit until the fruit ripens. The many spores produced can infect the fruit directly as well. A healthy fruit that is touching an infected fruit can become infected by the fungus growing directly from one to the other. Often spores that are on the plants are distributed over the planting by the activity of harvest, and can cause serious storage rots, especially if the fruit is wet.
Symptoms. On green fruit, firm brown spots can appear. On ripe fruit, light brown spots are formed, which remain firm. Spots usually begin at the cap end, but can also start at the point where an infected berry touches a healthy berry. Affected areas become covered by a powdery gray fungal growth, and thousands to millions of gray spores are produced during wet or foggy weather. In high humidity, berries can be covered with cottony white fungal growth. Berries that are entirely rotted can retain their general shape but become tough and dry.
Prevention. The most important prevention for this disease is to keep the air circulating between plants and to keep the leaves, flowers, and fruit dry. Select a well-drained site. Space plants widely in the rows, and avoid planting in excessively wide rows. Control weeds, as extra plants in the area will inhibit drying. Proper nitrogen balance is important in order for plants to be healthy but not too lush. Avoid excessive nitrogen application. Avoid overhead irrigation, which leaves foliage and fruit damp. Some varieties are less susceptible, but none are completely resistant. See current recommendations for chemical control of this disease.
Leather Rot is caused by the fungus, Phytophthora cactorum. It can infect the crowns, runners, and fruit of strawberry, and many other plants as well and losses can be quite high. This disease is favored by wet weather, and temperatures of approximately 60° to 80° F. It can progress quickly when conditions are favorable (as little as one hour of wetting), causing huge losses in just a few days.
Symptoms. On immature fruit, brown to dark brown spots that remain firm appear. The spots expand quickly until they cover the entire fruit. The fruit appears dark and leathery in texture, inside and out. Mature fruit may become soft and be dull pink to lilac, or may remain a normal color. When the fruit is split open, it usually has a sharp, pungent smell. The fruit tastes quite bitter. A white fuzzy growth may appear on the fruit if conditions are moist or if it is placed in a plastic bag with a moist paper towel for a few days.
Prevention. The fungus, Phytophthora cactorum, is in the soil, and can infect fruit after being splashed onto it by rain or by the fruit being in direct contact with the soil. A thick layer of straw mulch is important to keep the fruit off the ground and to prevent the soil from splashing onto the fruit. Mulching with straw rather than plastic prevents the berries from sitting in water. This disease is worse in wet situations, so plant in well-drained soil and avoid compacting the soil around the plants. Plant narrow rows and space plants widely within the row to keep the canopy dry. Plant in an area with good air circulation and control weeds to improve air circulation. Irrigate in the morning so that leaves can dry quickly. See current recommendations for chemical control of this disease. Resistant varieties are available.
Anthracnose is caused by the fungus Colletotrichum acutatum. This is generally thought to be a Southeastern fruit problem, but can be found in New England if the weather in spring is very warm. It has been of increasing significance since the mid-1980s in this area. It is favored by warm, humid, or wet weather. It is more severe in day-neutral or late bearing varieties.
Symptoms. Circular, slightly sunken, water-soaked spots can appear anywhere on both green and ripe fruit. The spots become tan to dark brown, and can reach 1/8″ to 1/2″ in diameter. Several spots can be found on one fruit. Creamy pink to salmon-colored ooze containing millions of spores can be seen in the centers of the spots in wet or humid weather. Although this disease causes spots that remain firm, the fruit will often become soft and rot from other organisms. If this does not happen or if the weather is dry, the fruit may become mummified and black. On runners, long black sunken spots appear that may grow completely around the runner and kill it.
Prevention. A crop rotation of two to three years can be helpful in controlling this disease, as the fungus overwinters in plants and debris in the soil. Plant disease free plants. Keep the leaves as dry as possible to help prevent this disease from spreading. Avoid overhead irrigation. Avoid working in the field when the plants are wet. A straw mulch will help prevent the fungus from splashing onto fruit from the soil. Plastic mulches promote disease spread, as they act as ‘trampolines’, causing raindrops full of spores to bounce higher into the plants. Plant resistant varieties or, at least, those that are less susceptible. See current recommendations for chemical control of this disease.
Cooley, D., D. Handley, S. Schloemann, and W. Wilcox. 1998. Disease Management and Physiological Disorders. Chapter 9 in Strawberry Production Guide for the Northeast, Midwest, and Eastern Canada. Cooperative Extension, Ithaca, NY.
Maas, J.L., ed. 1984. Compendium of Strawberry Diseases. APS Press, St. Paul, MN
New England Small Fruit Pest Management Guide, 1996-1997. S. Schloemann, ed. University of Massachusetts Cooperative Extension System.
By: Pamela S. Mercure, IPM Program Assistant, University of Connecticut
Updated by: Mary Concklin, UConn IPM. 2012
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