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Pestalotiopsis Tip Blight and Dieback of Conifers

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

Introduction

Pestalotiopsis is a very common pathogen found on many trees and shrubs in North America. Pestalotiopsis funerea, is responsible for tip blight, dieback and stem canker of conifers, most often associated with previously stressed plants. Susceptible hosts of P. funerea include arborvitae, juniper, cypress, false cypress, true cedar, Japanese cedar, incense cedar, pine, spruce, hemlock, yew, redwood, and Douglas fir. Thuja occidentalis, the Eastern/American arborvitae or the Northern/Eastern white cedar is widely planted in landscapes and is very susceptible to Pestalotiopsis. Although the pathogen rarely kills its host, it greatly reduces the vigor and aesthetic quality of affected plants.

Identification

Pestalotiopsis causes a wide range of symptoms on arborvitae and other conifers. Infection typically begins during wet periods in spring and summer, often developing in the lower canopy of the tree where foliage is denser and shaded, and receives less air flow, thus trapping moisture for longer periods of time compared to higher branches. If conditions are conducive in the following years, the disease will begin to spread up the tree. Infection usually starts on the tips of immature or newly expanding foliage and progresses toward the base. Diseased foliage will initially turn yellow, but will gradually turn brown to black, and will be cast prematurely (Figure 1).

The pathogen can also enter plants at the base of succulent new shoots, although this is less common. After it has entered a stem, a canker, a discolored, sunken area of bark corresponding to dead wood underneath, may form. Cankers may eventually girdle, or encircle, stems, leading to death of the stem and foliage above the lesion.

When the environment is favorable, fungal fruiting bodies called acervuli will develop in diseased foliar and stem tissue, and once mature, will rupture the epidermal tissue (Figure 2). A hand lens can be used to observe the fruiting bodies, which will appear as tiny black specks on the surface of diseased tissue (Figure 3). Under wet conditions, masses of black spores may be observed exuding from the fruiting bodies (Figure 4).

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. Pestalotiopsis symptoms spreading from the tip to the base of arborvitae foliage (Bruce Watt, University of Maine, Bugwood.org); Figure 2. Close up of infected Japanese cedar foliage with signs of fruiting bodies of Pestalotiopsis (Lorraine Graney, Bartlett Tree Experts, Bugwood.org); Figure 3. Yew needle with many black, spore-producing bodies called acervuli (Bruce Watt, University of Maine, Bugwood.org); Figure 4. Close up of tendrils of conidia (cirrhi) extruding from Japanese cedar foliage infected with Pestalotiopsis(Lorraine Graney, Bartlett Tree Experts, Bugwood.org).

Pathogen Biology

Pestalotiopsis funerea can behave either as an endophyte (=not causing disease) or as a pathogen. As an endophyte, the fungus resides in apparently healthy plant tissue until signals from the environment or host trigger further growth and reproduction. This adaptation allows the fungus to remain dormant and overwinter in a host without causing disease symptoms. As a pathogen, P. funerea often infects and colonizes plant tissues that have previously been stressed (i.e. secondary or opportunistic pathogen). Stressors that predispose coniferous hosts to this disease include senescence, freezing, sunscald, drought, waterlogging, winter injury, wind damage, transplant shock, mechanical damage caused by pruning or hedge trimming, and damage by other pathogens and insects. Once it has infected and colonized a host, the pathogen is capable of causing extensive damage if the environment is favorable to disease development.

Once environmental conditions are conducive for reproduction, the fungus will produce fruiting bodies, called acervuli (singular=acervulus) in diseased tissue of the host. Fruiting bodies often mature during spring when humidity is high and produce asexual spores, called conidia. When diseased plant tissue containing acervuli becomes sufficiently moist, the fruiting bodies will rupture the epidermal tissue and a black mass of conidia will exude in a sticky matrix, or under drier conditions, as black tendrils, called cirrhi (Figure 4). These spores are then dispersed to healthy plant tissues or to new hosts through splashing and running water, and possibly through insect activity. Infection can occur anytime throughout the growing season when adequate moisture is present. Disease incidence and severity increases as precipitation increases.

Favorable Environmental Conditions

  • High humidity
  • High precipitation
  • Host under stress

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.
  • 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:
    • Arborvitae, along with most conifers, prefers full sun. Avoid planting trees in low lying or shady areas.
  • 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:
    • If possible, do not water newly planted trees 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 a sufficient amount of 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.
    • Water trees and shrubs during periods of drought.

Scouting:

  • Inspect trees for dead foliage and/or branches in spring and summer.
  • Use a hand lens to observe small, black fruiting bodies and spore tendrils on the surface of diseased 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:
    • When removing branches, make a smooth cut at the base of the limb, as near to the trunk as possible, without damaging the branch collar. Jagged and rough cuts promote infection.
    • Prune plants during dry weather.
    • Disinfect tools in between cuts.
    • Pruned branches should be discarded or burned.
  • For high value trees, dislodge and destroy fallen needles that collect in branch crotches and on the ground. These needles may harbor large amounts of pathogen inoculum.
  • 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 not effective for control of Pestalotiopsis tip blight.