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Once the disease is established, asexual fruiting bodies called acervuli form on diseased areas. Heavy rainfall and warm temperatures are ideal for disease development and spread. Disease symptoms start to develop approximately 13 days after infection occurs at 36 degrees F and at four days after infection occurs at 90 degrees F. The higher the temperature, the faster disease develops. Conidia germinate and infect at temperatures ranging from 36 to 90 degrees F.
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In early spring, when free moisture from rain or dew is present, conidia germinate and infect succulent tissue. Note the lesion resembles a bird’s eye.Ĭonidia are by far the most important source of primary inoculum in the spring. Typical symptoms of anthracnose on grape berry. The importance of ascospores in disease development is not clearly understood.įigure 3. Conidia are spread by splashing rain to new growing tissues and are not carried by wind alone.Īnother type of spore, called an ascospore, is produced within sexual fruiting bodies and may also form on infected canes and berries left on the ground or in the trellis from the previous year. In the spring, sclerotia on infected shoots germinate to produce abundant spores (conidia) when they are wet for 24 hours or more and the temperature is above 36 degrees F. The fungus overwinters in the vineyards as sclerotia (fungal survival structures) on infected shoots. Causal OrganismĪnthracnose of grape is caused by the fungus Elsinoe ampelina. Clusters are susceptible to infection before flowering and until Véraison. Lesions on the rachis and pedicels appear similar to those on shoots. Lesions may extend into the pulp and cause the fruit to crack. A pinkish mass of fungal spores (conidia) exudes from these structures during prolonged wet weather. Acervuli (fungal fruiting structures) eventually develop in the lesions. This typical symptom on fruit often resembles a bird’s eye, and the disease has been called bird’s eye rot. The centers of the spots turn whitish gray and are surrounded by narrow reddish-brown to black margins (Figure 3). The spots then enlarge to an average diameter of ¼ inch and may become slightly sunken. On berries, small, reddish circular spots initially develop. Note the shot holes where infected tissues drop out. Lesions may cover the entire leaf blade or appear mainly along the veins.įigure 2.
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When veins are affected, especially on young leaves, the lesions prevent normal development, resulting in malformation or complete drying or burning of the leaf. Young leaves are more susceptible to infection than older leaves. The necrotic center of the lesion often drops out, creating a shot-hole appearance (Figure 2). Eventually, they become circular with gray centers and brown to black margins with round or angular edges. Leaf spots are often numerous and develop in a similar manner to those on shoots. Anthracnose on petioles appears similar to that on the shoots. In addition, hail damage generally appears on only one side of the shoot, whereas anthracnose is more generally distributed.
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Anthracnose lesions on shoots may be confused with hail injury however, unlike hail damage, the edges of the wounds caused by the anthracnose fungus are raised and black. Infected areas may crack, causing shoots to become brittle. A slightly raised area may form around the edge of the lesion. Lesions may coalesce, causing a blighting or killing of the shoot. Dark reddish-brown to violet-black margins eventually surround the lesions. Spots then enlarge, become sunken, and produce lesions with gray centers and round or angular edges (Figure 1). Symptoms on young, succulent shoots first appear as numerous small, circular, and reddish spots. Anthracnose symptoms on grape cane.Īll succulent parts of the plant, including fruit stems, leaves, petioles, tendrils, young shoots, and berries, can be attacked, but lesions on shoots and berries are most common and distinctive. Once the disease is established in a vineyard, it can be very destructive.įigure 1. Anthracnose reduces the quality and quantity of fruit and weakens the vine. The disease is not common in Ohio however, it caused severe damage in a central Ohio vineyard on the cultivar ‘Vidal’ in 1993 and in a southern Ohio vineyard on the cultivars ‘Vidal’ and ‘Reliance’ in 1998. It quickly established in American vineyards and became a significant disease of grape in rainy, humid, and warm regions of the United States. The disease was probably introduced into this country by grape plant material imported from Europe. Anthracnose of grape was first detected in the United States in the mid-1800s.