Anthracnose is an important disease of strawberries and has started to show up in our organic day-neutral strawberries at the West Madison Ag. Research Station. I noticed more anthracnose on fruits near the grass line on the edge of the mulches (Figure 1). The grass and weeds can create a wet and humid microclimate that is conducive to the spread of the pathogen. Anthracnose, caused by Colletotrichum species (namely, C. acutatum) can infect the fruits, petioles, leaves, runners, and crown. The anthracnose fruit rot stage can appear as brown to black water-soaked spots on green (immature) and ripe fruits. The lesions become sunken over time, and under humid conditions orange-colored spores form on the lesions (Figure 2). The orange spores can be diagnostic for this disease. Under dry conditions the lesions can cause the fruits to shrivel and become mummified. Spores can spread via splashing water (i.e., rain, overhead irrigation), and some plastic mulches can exacerbate the spread by encouraging splashing off the surface; this is not normally an issue with straw mulches. Control should be preventative and often starts during bloom when the fungus can first infect the plant. Once anthracnose fruit rot symptoms show up, management can be difficult but removing infected fruits (i.e., sanitation) and applying effective fungicide sprays ahead of any rain events can help suppress the disease. When harvesting fruits, infected berries should be removed last to minimize spread. Visit the Midwest Fruit Pest Management Guide for fungicide recommendations and efficacy ratings.
Botrytis fruit rot (gray mold) is a serious disease of strawberry. Rarely has it been observed in our organic day-neutral strawberries. When fruits are infected a gray, velvet-textured mold appears on fruits; dead petioles and leaves can also harbor the pathogen. High humidity favors disease development. Water splash and wind can spread the pathogen to leaves and flowers. The pathogen can remain dormant on green tissue but as fruit ripens lesions develop and mold grows. Strawberry varieties with dense canopies are more prone to Botrytis infections. Over fertilization (i.e., too much nitrogen) can also increase susceptibility. Sanitation is most helpful in the spring before bloom to reduce inoculum levels, however at this point in the season, removal of infected fruits can help reduce disease, but this is not always feasible or economical especially when fungicides are being used. Fungicides to prevent Botrytis infections should be made during bloom to minimize flower infections that lead to fruit rot. Applications to protect fruit through harvest are more costly than preventative bloom sprays.
Leather Rot can be a devasting disease of strawberry fruits under conducive conditions (i.e., excessive rainfall, poorly drained areas, or berries touching the soil). Leather rot is caused by Phytophthora cactorum which is a “water mold” that can survive in mummified fruit. Leather rot can impact developing fruits at all stages. Symptoms on green fruit look brown and leathery, while ripe fruit infections display light colored lesions. Infected fruits have a distinct odor and bitter taste. To manage leather rot, ensure good soil drainage and avoid shaded areas that may hold moisture longer than areas exposed to the sun. Avoiding direct contact with the soil (where the pathogen overwinters) can be achieved by using mulches. We have not observed leather rot in our mulched day-neutral strawberries.
Neopestalotiopsis fruit rot is a new disease of strawberry. The fruit rot phase of this disease has not been reported in Wisconsin; however, the crown and root rot stage has been reported in the state; it is not widespread. Symptoms of the disease can appear on most tissue types. On leaves, small spots with light brown centers and dark borders appear first. As the infection advances, these spots expand and merge forming irregular-shaped, necrotic lesions. Stunting and dieback of the entire plant may occur. Fruit infections begin as small, tan lesions that eventually turn orange before they are covered in black fungal spores. Symptoms of Neopestalotiopsis leaf spot and fruit rot are very similar to other strawberry diseases, making field diagnosis difficult. Fruit symptoms of Neopestalotiopsis are very similar to Anthracnose infections, the major difference is the development of black spores in the fruit lesions; the fungus that causes Anthracnose has salmon- or orange-colored spores. To manage this disease, minimize working with the plants when they are wet to avoid spreading the fungus. If practical, removal of infected fruits can help reduce inoculum, but this should not be done in wet conditions. Some fungicides registered for the control of other fruit rot diseases can be effective against Neopestalotiopsis fruit rot, but there is an increased risk for fungicide resistance develop with repeated use.This article was posted in Berries, Disease and tagged Anthracnose, disease, Fruit Rot, leather rot, Leslie Holland, Neopestalotiopsis, Strawberries, strawberry fruit rot.