What is it? What to do about it? ♣ Download fact-sheet
Botryosphaeria Canker and Dieback of Juniper
by Paige Thrush, Nancy J. Taylor & Francesca Peduto Hand
Species of the fungus Botryosphaeria are stem and branch pathogens, causing cankers and dieback on many species of woody trees and shrubs. The species Botryosphaeria stevensii is responsible for canker and dieback of juniper. Junipers, or Juniperus species, are extensively planted landscape ornamentals with a wide range of susceptibility and resistance to this disease. The disease reduces the vigor and aesthetic quality of ornamental trees and shrubs in the landscape and may cause significant damage to young seedlings, grafts, and transplants in nurseries.
The species Botryosphaeria stevensii is responsible for canker and dieback of juniper. Symptoms of Botryosphaeria canker and dieback are most evident in late spring and summer. Typically, the first symptom to be observed is a sudden wilting and yellowing of foliage, which gradually turns brown and dies. Cankers, or lesions, will form at the base of dead shoot tips, marking the site of stem infection and the abrupt transition between heathy and infected tissue. Cankers first appear as discolored, sunken areas on the bark, growing to be elongate in shape and resinous. Cankers are capable of girdling, or encircling, small stems. Once a stem is girdled by a canker, all foliage and woody tissue above the lesion site will become blighted and dieback (Figure 1). Cankers may be difficult to observe until diseased bark has fallen from the tree. To examine the canker, remove a diseased branch from the host and scrape away the outer bark to reveal the dead wood underneath (Figure 2). On some junipers, cankers may also form on the trunk, which results in complete branch dieback. If a branch has died back to the trunk, examine the area where the branch attaches to the trunk for a sunken area or enfolded bark.
Small black fruiting bodies called pycnidia (Figure 3), the reproductive structures of the pathogen, develop in cankers and diseased plant tissue weeks to or months after the initial infection, depending on the rate of disease development. These fruiting bodies, which may be observed with the aid of a hand lens, hold the spores of the pathogen, which allow it to survive, spread, and cause new infections (Figure 4).
Botryosphaeria results in branch dieback and gradual tree decline. Repeated infections may result in dieback of a large portion of the tree canopy and may reduce the ornamental value and overall health of the plant. In severe cases, the disease may kill entire plants.
Dieback symptoms similar to those caused by Botryosphaeria can be caused by insects, environmental stresses, or other fungal diseases, such as Phomopsis and Kabatina tip blight. It is important to identify the cause of disease in order to make proper management and control decisions. If disease is suspected, samples can be sent to a diagnostic laboratory for confirmation. Information on The Ohio State University laboratory can be found on the C. Wayne Ellett Plant and Pest Diagnostic Clinic website.
Botryosphaeria stevensii is an opportunistic pathogen, most often damaging plants that are weakened by environmental stress or poor management. Common stressors that predispose hosts to this disease include freezing, heat, drought, compacted soil, and transplant shock. Disease symptoms often develop more rapidly on stressed plants than healthy plants, and cankers grow to be much larger on stressed hosts.
Botryosphaeria stevensii may overwinter as an endophyte, residing in apparently healthy plant tissue until signals from the environment or host trigger growth and reproduction of the fungus. This adaptation allows the species to remain dormant in a host without causing disease symptoms. On a diseased host, the pathogen will overwinter as fruiting bodies in plant tissue that was infected during the previous growing season.
Stromata (singular=stroma), which are compact masses of fungal tissue that hold fruiting bodies, develop in diseased cankers and tissue of the host. In the beginning stages of the pathogen’s life cycle, pycnidia will be produced, which are fruiting bodies that hold asexual spores, called conidia. In the beginning, the outer bark may need to be removed to observe the fruiting structures underneath. Once mature, stromata will protrude through the bark surface, appearing as small black dots to the naked eye.
Spores are released from fruiting bodies in response to moisture. The spores are dispersed to healthy plant tissues and new hosts through rain, irrigation, wind, and sometimes through cultural activities, such as pruning. Infection is initiated through natural openings in the plant, such as growth cracks or lenticels, which are pores on woody tissues that allow for gas exchange to occur within the plant. Infection can also occur through manmade wounds, such as those caused by pruners, hedge trimmers, or lawn mowers. Most new infections occur primarily in late May and June and repeat infections may occur throughout the growing season. The fungus requires about 4-6 hours of free water with optimal temperatures around 20-25°C (68-77°F) for infection to occur. Once infection has occurred, the fungus grows in the xylem and phloem, which are the vascular tissues that transport water and nutrients throughout the host plant. Death of the vascular tissues results in the production of canker and dieback symptoms.
Favorable Environmental Conditions
- The optimum time period for infection and disease development is in late May and June.
- Wet periods of 4-6 hours with optimal temperatures around 20-25°C (68-77°F) promote infection.
Integrated pest management (IPM) is an approach to plant health care and disease and pest control. IPM incorporates a wide range of strategies to prevent, minimize, and/or control abiotic and biotic diseases and pests. These strategies involve monitoring and scouting, learning behavior and life cycle of pests and pathogens, accurately identifying the source of disease, developing threshold levels, employing preventive measures and integrating cultural, mechanical, biological and chemical controls. All management decisions should be carried out based upon the specific requirements of the plant. Analysis of each strategy involves considering the impact on host plants, pests/pathogens, microbial interactions, the environment and society. The costs and benefits of each strategy should be evaluated before making management decisions.
- Plant selection:
- Purchase pest and pathogen-free stock from reputable sources.
- When purchasing plants from a nursery, inspect for signs and symptoms of disease. Avoid purchasing plants that look defoliated, discolored or wilted.
- Select plants with an appropriate hardiness zone, based upon your geographic location.
- Consider planting resistant species/cultivars if disease pressure is high in the landscape.
- Quarantine incoming plants and inspect for signs and symptoms of disease. Remove and dispose of, or return, all infected plants to the original source.
- Proper site selection:
- Avoid planting susceptible species in compacted and/or poorly drained soils.
- Proper planting practices:
- Proper plant spacing will minimize moisture retention on the plant surface and will decrease the likelihood of disease development. When planting new trees in the landscape, space them to allow for optimum air circulation and sunlight penetration into the tree’s interior. Plan for the mature size of the tree(s) when spacing plants, or plan to remove trees as they begin to intermingle lower branches.
- Use proper transplanting techniques to prevent damage to roots.
- Set plants at a proper depth in the soil, according to the specific needs of the species.
- Prevent and minimize stress to plant:
- Conduct regular soil and plant tissue analysis tests to determine if plants require supplemental nutrients. Otherwise, do not fertilize woody plants. Excessive fertilization results in succulent plant growth, which may be highly susceptible to pest and disease problems.
- Water plant(s) during periods of drought.
- Keep weeds and other vegetation from encroaching around the base of trees or shrubs to encourage air circulation among and light penetration to the lower branches.
- Apply a 1-2” layer of mulch around the base of trees and shrubs for weed control. Do not let mulch touch the bark of woody plants, as this may reduce aeration in the soil.
- Avoid wounding plants during cultivation.
- Proper irrigation techniques:
- Provide plants with adequate water during establishment. If weekly precipitation does not reach 1 inch, provide supplemental water to bring the total number to 1 inch/week.
- If possible, do not water newly planted trees or shrubs with sprinklers or overhead irrigation, which will keep foliage wet for long periods. Drip irrigation or hand watering is preferable.
- Irrigate during morning hours so that plants will have sufficient time to dry.
- Inspect junipers for symptoms of dieback in late spring and throughout the growing season.
- Look for cankers near the base of dead twigs and branches.
- If a canker is suspected or found gently remove diseased bark to see the dead wood underneath the surface and to identify the area of transition from diseased and dead to healthy.
- Look for resin exudation around and near the canker site.
- Use a hand lens to observe fruiting structures on dead tissue.
Cultural control practices:
- Avoid pruning, shearing, and/or other operations that would facilitate spore dispersal and infection during wet periods.
- If disease has been observed, remove infected limbs using proper pruning techniques:
- Prune diseased junipers during dry weather in winter. Avoid pruning plants in May and June when Botryosphaeria is releasing spores most abundantly.
- Remove infected branches by cutting several inches below the visibly dead wood to remove all the diseased tissues but do not leave stubs.
- Disinfect tools in between cuts.
- Pruned branches should be discarded or burned.
- Once the pathogen has become well established in/on the host, the specimen may need to be removed from the landscape.
- Fungicides are not recommended for Botryosphaeria canker and dieback.