Chestnut anthracnose is a disease of culinary chestnut that is found in orchards throughout the eastern United States. The disease, caused by the fungus Colletotrichum henanense, has progressively become a major economic detriment to chestnut producers. Anthracnose lesions render the nuts unsaleable. If nuts with anthracnose symptoms are not culled, they exhibit increased post-harvest molds in cold storage compared to healthy nuts. In addition, anthracnose can ruin a chestnut’s ability to germinate and grow because the lesions typically form over the growing tip of the kernel, killing it. This can impact seedling production for commercial chestnut nurseries. Disease severity cannot be assessed until harvest time because burs conceal the nuts throughout the growing season, so growers cannot predict crop loss until after harvest begins.
Disease Development and Symptoms
Anthracnose affects all layers of a ripe chestnut (Figure 1), and chestnut tree twigs but little is currently known about the life cycle of the fungus and the environmental conditions that favor disease development.
Anthracnose appears as a blackening of the kernels that may or may not be visible on the stylar end of the chestnut shell (Figure 2, top photo). The most common location for the lesion is on the tip of the kernel (Figure 2, bottom photo); however, lesions are occasionally found on other parts of the kernel. Each kernel will have only one lesion, but the lesion can occupy anywhere from 1–100% of the kernel area. Lesions are light brown to black, appear dry, have a dehydrated texture compared to healthy kernel tissue, and do not have an odor or flavor that is different from healthy kernel tissue. While rare, orange spore masses can form on the shell lesions during prolonged periods of high humidity.
Typically, kernel lesions that occupy more than 10% of the kernel area also exhibit a black lesion on the shell (Figure 2).
Often when the lesion on the kernel covers less than 10% of the area, black lesions are not apparent on the shell. This can make it difficult to identify an infected kernel. Because of the dry nature of the lesions, disease can be confirmed in fresh chestnuts by pressing on the tip with a finger. If the tip or suspected lesion area is soft, disease is present. If the tip is firm and turgid, the tissue is healthy. The squeeze test works only on fresh chestnuts that are fully hydrated.
On 1-yr twigs of chestnut seedlings, cankers are brown with a purplish and/or orangish hue, sunken, and approximately 0.4 in (1 cm) in length (Figure 3).
In some seedlings, the distal portions of infected twigs may die. In other seedlings, only shoots and leaves within the cankered areas die. Black acervuli (spore-bearing structures) have been observed erupting from canker tissues and may serve as a source of inoculum. However, how and where the fungus overwinters in mature orchards is not yet known.
Plant disease management recommendations are developed based on the disease cycle and focus on the exclusion of the pathogen into the plant production system. Given our limited knowledge of the anthracnose disease cycle, management recommendations for chestnuts are still being developed and validated.
Host resistance is the most effective and economical practice for controlling plant diseases. In Ohio, variation in disease incidence among commercially important chestnut cultivars has been observed (Table 1). Qing, Liu, and AU Homestead cultivars are the least susceptible to anthracnose. Offspring of these cultivars are being evaluated to assess the heritability of disease resistance and usefulness of these parents in seedling orchards.
|*Low: less than 2% incidence. Moderate: two to 10% incidence. High: >10% incidence. Based on data from field trials conducted in Ohio from 2019 to 2021 (Miller and Lewis Ivey 2022).|
Practices that promote healthy tree growth or reduce tree stress are recommended, including planting trees at wide spacing in well drained, slightly acidic soils (pH 5– 6.5). Balanced soil fertility, minimal soil compaction, irrigation, and other practices that maximize tree carbohydrate reserves can optimize tree health. Insect pests should be minimized, especially those that cause twig damage and defoliation, such as the Asian chestnut gall wasp.
Chemical and Biological Control
There are no fungicides that are registered for anthracnose control in culinary chestnuts. Until more is known about the disease cycle and the best time to apply fungicides or biocontrol products, they are not recommended.
Post-harvest Storage Practices
Anthracnose develops on chestnuts on the tree, and producers should not expect to see anthracnose lesions develop or expand in cold storage. However, chestnuts with anthracnose are more susceptible to storage molds and should be separated from healthy chestnuts. Healthy chestnut kernels at full moisture may exhibit shell surface molds from adjacent unhealthy chestnuts, but kernel quality is not affected by these shell surface molds. Healthy chestnuts at full moisture can be maintained in good condition in high humidity (>90%) cold storage (32–38 degrees Fahrenheit) until kernels start to sprout in February–April of the year following harvest.
For Further Reading
Miller, Amy, Diane D. Miller,, and Paula M. Pijut. 2013. “How a Flower Becomes a Chestnut: Morphological Development of Chinese Chestnuts (Castanea mollissima).” 103rd Annual Report of the Northern Nut Growers Association (Sept.): 27–33.
For information about chestnuts, growing chestnuts, and eating chestnuts visit route9cooperative.com or the chestnut resource page of the Northern Nut Growers Association at nutgrowing.org/chestnut-resources.
View more Ohio State University Extension facts sheets about common diseases of Ohio fruits and hops at:
For more information, contact your Ohio State University Extension office or educator.
Watch "Chestnut Anthracnose - The Squeeze Test."
Miller, Amy, and Lewis Ivey, Melanie. 2022. “Biology of Chestnut Anthracnose (formerly blossom end rot) in Culinary Chestnut.” The NutShell (Northern Nut Growers Association), 76(3): 10–13.