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Phomopsis Tip Blight of Juniper

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

Introduction

Phomopsis tip blight is a disease that causes tip and shoot blights, cankers, and dieback on a wide range of conifer species and is especially destructive to nursery and landscape plantings of junipers in central and eastern America. Commonly affected species include creeping juniper (Juniperus horizontalis), savin juniper (J. sabina), Rocky Mountain juniper (J. scopulorum), and the eastern red cedar (J. virginiana). Other susceptible hosts include cypress, false cypress, arborvitae, English yew, Japanese plum yew, true cedar, Japanese cedar, hemlock, European larch, jack pine, true fir, Douglas fir, and giant sequoia.

Junipers, or Juniperus species, are extensively planted landscape ornamentals with many desirable characteristics such as being low maintenance, relatively resistant to most major pests and diseases, and tolerant of most soil types and extreme weather conditions. However, some fungal diseases can cause significant damage to juniper.

The fungal pathogen, Phomopsis juniperovora, is responsible for tip blight of juniper. In nurseries, young juniper seedlings, grafts, and transplants are commonly killed by the disease. In epidemic years, total loss of first year seedlings may occur. In the landscape, the disease greatly reduces the vigor and aesthetic quality of ornamental trees and shrubs. Susceptible host species growing in natural stands do not sustain significant damage.

Identification

Phomopsis tip blight causes foliar discoloration, cankers and dieback on juniper and other coniferous trees and shrubs. Foliage is most susceptible when it is immature and becomes resistant to infection by Phomopsis once fully mature. As a result, most disease symptoms occur on the terminal 4-6” of branch tips. Young plants less than 5 years old are more severely damaged than older plants, although older specimens, especially those in crowded and stressed conditions can be infected. The disease often begins in the lower branches of the canopy. Infection usually occurs in late spring or fall, although it can occur anytime throughout the growing season when new, succulent foliage and shoot tips are present. Most infections occur in April through early June, and again in late August through September if young tissues develop following pruning.

Initially, small yellow spots will appear on the foliage 3-5 days after infection. Under favorable environmental conditions, the pathogen will rapidly progress from new foliage into succulent shoot stems and eventually toward woody mainstems. Young, diseased foliage will turn a dull red to brown (Figure 1). Infected shoots will remain on the host for many months, gradually fading to an ash gray color (Figure 2).

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 (Figure 3). 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 less than 1 cm in diameter. Stems that are larger than 1cm are usually able to resist infection by Phomopsis. Once a stem is girdled by a canker, all foliage and woody tissue above the lesion site will become blighted and dieback.

Small fruiting bodies can be seen within lesions on dead shoot tips and stems, usually within 3-4 weeks after the initial infection. These fruiting bodies hold the spores, or reproductive structures, of the pathogen, which allow it to survive, spread, and cause infection. The fruiting bodies may appear black or gray (Figure 4). During wet periods, pale yellow to cream colored masses of spores may be seen exuding from the fruiting bodies (Figure 4). A hand lens can be used to view the fruiting bodies and spores of the fungus.

Repeated blighting in early summer can result in abnormal bunching and dense clusters of shoots and stems, a symptom often referred to as witch’s broom. In severe cases, the disease can cause stunting of young plants and can even kill entire trees or shrubs.

Similar dieback symptoms can be caused by insects, environmental stresses, or other fungal diseases, such as Kabatina tip blight and Botryosphaeria canker and dieback. It is important to properly identify the cause of disease in order to make proper management 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. Phomopsis tip blight symptoms on J. virginiana in a nursery bed (Robert L. Anderson, USDA Forest Service, Bugwood.org); Figure 2. Ash gray J. virginiana shoot infected with Phomopsis (Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org); Figure 3. Canker on eastern hemlock branch (Lorraine Graney, Bartlett Tree Experts, Bugwood.org); Figure 4. Close up of fruiting bodies (pycnidia) with cirrhi of Phomopsis juniperovora (Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org)

Pathogen Biology

Phomopsis juniperovora is capable of surviving as a saprobe, decomposing dead tissue and producing viable spores for up to 2 years. On a diseased host, the pathogen overwinters in plant tissue and debris that were infected during the previous growing season. Flask-shaped fruiting bodies, called pycnidia, are produced within diseased tissue of the host and once mature, rupture the epidermal tissue. Pycnidia produce asexual spores, called conidia, which are released in response to moisture. The spores may be exuded in a sticky matrix, or under drier conditions, as tendrils, called cirrhi. The spores are then dispersed to healthy plant tissues and new hosts through rain, irrigation, wind, and sometimes through cultural activities, such as pruning. Infection is initiated in succulent young tissue, or sometimes through wounds. Once the fungus enters the host, it can spread to stem tissue, resulting in canker formation and stem dieback.

During cool, wet periods, fruiting bodies and spores will be produced, resulting in repeated infections throughout the growing season as long as new growth is present. Late season infections are common in nurseries, where plant growth is prolonged using watering and shearing techniques and through providing plants with optimal fertility. These cultural practices result in the production of new growth in the fall, which is then susceptible to infection by Phomopsis.

The fungus requires about 7 hours of free water on foliage with optimal temperatures around 20-24°C (68-75°F) for infection to occur but germination can occur at temperatures as low as 8°C (46°F). These spores are able to tolerate temporary drying. After infection is initiated, high temperatures around 26-32°C (79-90°F) result in increased disease development and severity. Abundant moisture and high humidity also promote disease severity.

Favorable Environmental Conditions

  • The optimum time period for infection and disease development is in spring and fall.
  • Wet periods of 7 hours with optimal temperatures around 20-24°C (68-75°F) promote infection.
  • High temperatures around 26-32°C (79-90°F), abundant moisture, and high humidity promote disease development and severity.

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 variety of growth habits, sizes, and colors. Within these cultivars, there is a wide range of susceptibility and resistance to this disease.
  • 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 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.
  • Proper irrigation practices:
    • 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 foliage and stems will have sufficient time to dry.
  • Prevent and minimize stress to plants:
    • 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 April through September. Optimum infection periods occur from April through early June and again from late August through September.
  • Look for dull red to brown foliage on new shoots in spring, which gradually turn an ash gray throughout the growing season.
  • 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 and spores on the surface of lesions.

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 plants during dry weather in summer after primary infection has occurred or in winter before new growth is produced.
    • Infected shoots and branches should be pruned back about 2-3” into live wood to ensure removal of all diseased tissue; but be careful not to prune in a way that leaves bare branch 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.

Chemical control:

  • Fungicide treatment for prevention and control of Phomopsis tip blight is recommended in nurseries, where the value of the crop is high and the risk of financial loss is significant. Highly valued landscape trees and shrubs can also be treated.
  • Timely applications of fungicides containing active ingredients such as mancozeb, thiophanate methyl, chlorothalonil, potassium bicarbonate, propiconazole, benomyl, and copper based products are effective for prevention of Phomopsis tip blight.
    • The first application should occur right before or soon after new growth begins in spring.
    • Additional applications must be made every 7-21 days, until new growth has fully matured in summer. If trees or shrubs produce new growth in fall, additional applications must be made until maturation.
    • The interval rate will be dependent upon which product is used and seasonal weather patterns.
  • Read each fungicide label thoroughly for safety precautions and information on how to prepare, apply, store, and dispose of the product.
  • To minimize the risk of fungicide resistance, alternate products based on modes of action (FRAC codes). Check with your county or state extension specialist for an updated list of registered fungicides that are available.