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Kabatina Tip Blight of Juniper

by Paige Thrush, Nancy J. Taylor & Francesca Peduto Hand

Introduction

Junipers are generally considered low maintenance plants because they are relatively resistant to many major pests and diseases, although there are some fungal diseases that can cause significant damage to the crop. The fungal pathogen, Kabatina juniperi, is the causal agent of tip blight of juniper and can also cause tip and shoot blights, cankers, and dieback on a wide range of other conifer species. The disease is especially common in nursery plantings where it has been detrimental to young juniper seedlings, grafts, and transplants and, in epidemic years, has caused total loss of first year seedlings. It is also found in landscape plantings of junipers in central and eastern America where it reduces the vigor and aesthetic quality of ornamental trees and shrubs in the landscape. Susceptible species growing in natural stands do not sustain significant damage.

Commonly affected species include the eastern red cedar (Juniperus virginiana), Rocky Mountain juniper (J. scopulorum), creeping juniper (J. horizontalis), and savin juniper (J. sabina). Other susceptible hosts include species of false cypress, arborvitae, Japanese cedar, true fir, Douglas fir, and yew.

Identification

Kabatina tip blight causes foliar discoloration, cankers and dieback. Young plants less than 5 years old are more severely damaged than older plants, although older specimens, especially those in crowded and stressed conditions are also capable of becoming infected. The disease often begins in the lower branches of the canopy on twigs that are 1 year or older.

Symptoms usually appear on the terminal 2-6” of branch tips in late winter or early spring the year following initial infection and before new growth has been initiated. Diseased foliage will turn a dull green, gradually becoming a red (Figure 1) to yellow (Figure 2) color, before turning brown and dying (Figure 3). Dead foliage will be prematurely cast, most often in late May through June.

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 appear as gray, sunken areas on the bark that correspond to necrotic wood tissue underneath. 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. Blighting is restricted to branch tips, therefore extensive branch dieback is uncommon in larger plants.

Small fungal fruiting bodies, or reproductive structures, can be seen within lesions on dead shoot tips and stems (Figure 4). These fruiting bodies hold the spores of the pathogen, which allow it to survive, spread, and cause infection. The fruiting bodies may appear black, dark brown, or gray and may be observed with the aid of a hand lens.

Dieback symptoms similar to those caused by Kabatina tip blight can be caused by insects, environmental stresses, or other fungal diseases, such as Phomopsis tip blight and Botryosphaeria canker and dieback. It is important to identify the cause of disease in order to make proper management and control decisions. Fungal diseases can be distinguished by microscopic examination of fruiting bodies and spores. 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.

From top left to bottom right: Figure 1. Kabatina tip blight symptoms on Thuja occidentalis (Cheryl Kaiser, University of Kentucky, Bugwood.org); Figure 2.  Kabatina tip blight symptoms on Juniperus virginiana (Cheryl Kaiser, University of Kentucky, Bugwood.org); Figure 3. Blighted juniper shoots as a result of Kabatina tip blight (Bruce Watt, University of Maine, Bugwood.org); Figure 4. Canker with fruiting bodies of Kabatina juniperi (Bruce Watt, University of Maine, Bugwood.org)

Pathogen Biology

Kabatina juniperi is an opportunistic pathogen, infecting plants that have been previously stressed. The pathogen enters the host’ foliage or stems through wounds which may be caused by insects, winter injury, or mechanical damage and it overwinters in plant tissue and debris that was infected during the previous growing season, usually in the fall. Under environmental conditions that are favorable to disease development, the pathogen will progress from foliage to succulent shoot stems and eventually toward woody tissues. Repeated infections do not occur throughout the growing season, therefore disease severity is usually low and tree death is uncommon.

Disc-shaped fruiting bodies, called acervuli, are produced within diseased tissue of the host, and once mature, rupture the epidermal tissue. Acervuli produce asexual spores, called conidia, which are released in response to moisture. The spores are then dispersed to healthy plant tissues and additional hosts through rain, irrigation, wind, and sometimes through cultural activities, such as pruning.

Favorable Environmental Conditions

  • Cool weather, high humidity and abundant moisture

Management Guidelines

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.

Prevention:

  • 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.
    • Consider planting resistant species/cultivars if disease pressure is high in the landscape. There are many species and cultivars of juniper with a wide range of susceptibility and resistance to this disease. For more information refer to Table. 1 ‘Disease Resistance of Juniper Cultivars’.
  • Nurseries:
    • 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 poorly drained soils or shaded areas of the landscape.
  • 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 within and between plants 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.
  • 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.
    • Water tree(s) during periods of drought.
  • 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.
  • 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 is highly susceptible to many 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.
  • Avoid activities that will encourage succulent new growth of highly susceptible hosts:
    • Maintain adequate fertility, but do not over-fertilize.
    • Avoid excessive pruning or shearing, especially during spring and fall.
    • Avoid excessive watering.

Scouting:

  • Inspect trees and shrubs, especially those less than 5 years old, for symptoms of tip blight and dieback from February through May.
  • Look for red to yellow shoot tips, which gradually become brown and necrotic throughout spring. Dead foliage is typically cast in May and June.
  • Look for small lesions near the base of dead shoots and branches, which marks the transition between healthy and dead tissue. Use a hand lens to observe fruiting bodies on the surface of lesions.

Cultural control practices:

  • During wet periods, avoid shearing and other operations that could facilitate spore dispersal and infection.
  • If disease has been observed, remove infected limbs using proper pruning techniques:
    • Prune plants during dry weather in summer after primary infection has occurred or in winter before new growth is produced in spring.
    • Infected shoots and branches should be pruned back to live wood.
    • 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.

Chemical control:

  • Fungicides are ineffective for Kabatina tip blight.