Juniper trees and shrubs are a popular choice in the ornamental home garden. These slow growing plants require little maintenance, are fairly drought tolerant, take full sun and are able to grow in a variety of soil types. They are fairly salt tolerant and make good roadside plantings. In addition to this they are evergreens and provide year-round beauty and interest to the landscape. With over 170 cultivated varieties to choose from there is one for almost any landscape situation. The biggest threat to these junipers is blight. Particularly Phomopsis blight and Kabatina blight. These 2 fungal blights first kill the growing tips then produce a canker on the stem that girdles the twig shutting down the transportation of water and nutrients to that area and the twig dies. The disease is most serious on young or newly transplanted junipers. Learning to recognize these diseases will help to empower home gardeners who care for these trees and shrubs.
Phomopsis Blight
Phomopsis blight is caused by the fungus Phomopsis juniperovora. Infection predominantly affects the healthy new growth that is still yellow green in colour. Primary infection time is spring when the juniper is putting on a big flush of new growth, but repeated infections can occur throughout the season when conditions for it’s spread and growth are ideal. Those ideal conditions are when temperatures are between 21-27 degrees C (70 – 80 degrees F), during periods of high humidity, and when foliage is wet (Morton Arboretum n.d.).
Life Cycle of Phomopsis Blight
Phomopsis overwinters on needles and stems of young trees that were infected the previous year. The fungus is most abundant on dead tissue that has become ash gray in color (Missouri Botanical Garden n.d). These diseased tissues produce black fruiting bodies that are released and splashed onto the new young growth during wet rainy weather. Wind, insects, or mechanical means can also spread the fungus. Infection can take place in as short as 7 hours, under ideal conditions. About 3 days later yellow spots begin appearing on infected tissue. This is followed by dieback of the new shoot tips (predominantly occurring in early summer). Affected foliage first turns a dull green, then changes to turns dull red, then brown and finally to ash gray. As the disease progresses, small lesions (cankers) form on the stems where infected and healthy tissue meet. Progressive dieback follows, eventually killing an entire branch by girdling the stem. The fungus will progress to the main stem and can infect and girdle stems less than 1/2 inch in diameter (Missouri Botanical Garden n.d). The fungus can persist in dead parts of infected plants for as long as two years.
Species Susceptible to Phomopsis Blight (OMAFRA rev. 2020)
- Abies spp., fir;
- Chamaecyparis spp., false cypress
- Cupressus, spp., cypress
- Juniperus spp., junipers
- Larix spp., larch
- Metasequoia spp., redwood
- Taxus spp., yew
- Thuja spp.,white cedar
- Tsuga spp., hemlock
Kabatina Blight
Kabatina blight is caused by the fungus Kabatina juniperi. Unlike Phomopsis, infection predominantly affects juniper twigs one year or older and a wound is necessary for infection to take place. Again unlike phomopsis, the infection period is autumn, but the damage is not apparent until Feb./Mar. when they begin turning brown, this is well before symptoms of Phomopsis tip blight appear. Greatest infection occurs when temperatures are 16 to 21 °C. There is only one infection period and kabatina does not cause extensive branch die back, like with phomopsis. Other than these differences Kabatina causes symptoms very similar to Phomopsis,
Life Cycle of Kabatina Blight
During wet fall weather, fungal spores are released and enter new tissues through wounds. The disease survives on infected plant debris as grayish lessions at the base of blighted portions of shoots (Missouri Botanical Garden n.d.). The first symptoms, dull green then red or yellow discoloration of branch tips, appears in February and March. The dead foliage eventually drops from the plant in late May or June. In fall, when the temperatures are just beginning to drop, fungal spores are once again released and the cycle continues.
Species Susceptible to Kabatina Blight (OMAFRA rev. 2020)
- Cupressus spp.; Cypress;
- Junipers spp., Junipers
- Thuja, white cedar.
Cercospora Twig Blight
Cercospora Twig Blight is caused by the fungus Cercospora sequoiae var. juniperi. This disease differs from Phomopsis and Kabatina blight in that the disease begins in the oldest growth. The needles brown from inside to out usually beginning at the bottom of the tree and work its way up. The disease spreads best during warm, wet or humid weather. Initial infection occurs during late June and early July. Symptoms may be visible between two to three weeks after infection. Fussy brown/black fruiting bodies can be seen with a hand lens on affected foliage.
Species Susceptible to Cercospora Twig Blight (For a more complete list of susceptible species)
- Junipers spp., Junipers
- Rocky Mountain juniper (Juniperus scopulorum)….the most susceptible
- Oriental Arborvitae (Platycladus orientalis)
- Eastern redcedar (Juniperus virginiana)
Management
Cultural
- Plant resistant cultivars when possible. For a list of cultivars that are reportedly resistant to Phomopsis blight. For a list of cultivars resistant to Kabatina blight. Note however that there are very few cultivars that are resistant to both diseases.
- Prune out dead and diseased plant material during dry summer weather and destroy. Disinfect your pruning shear between cuts.
- When planting, avoid heavily shaded areas and space plants to allow for good air circulation.
- Avoid wounding plants, especially in spring and fall.
- Water plants in early morning so the foliage will dry as quickly as possible.
- Remove heavily infected junipers entirely.
Chemical
- Phomopsis blight can be controlled with registered fungicides if applications are made before new growth starts in the spring and continued as long as new growth is produced.
- However, at present, there are no fungicides effective for Kabatina blight.
- Cercospora Twig Blight can be controlled with applications of Bordeaux mixture or a liquid copper fungicide. At least two applications are needed for good control. The first application should be made during the first half of June, just prior to initial infection. The second treatment should be made during the last half of July. The second application normally gives good protection against infection for the remainder of the season. However, additional applications may be necessary during periods of frequent rains.
Photo Credits: all photos taken by the author.
Updated: on Oct. 22, 2021
References:
Missouri Botanical Garden n.d., Phomopsis Blight of Juniper, Retieved on Feb. 12, 2021 from: Phomopsis Blight of Juniper (missouribotanicalgarden.org)
Missouri Botanical Garden n.d., Kabatina Blight, Retrieved on Feb. 12, 2021 from: Kabatina Blight (missouribotanicalgarden.org)
Morton Arboretum n.d., Juniper tip blight, Retrieved on Feb. 12, 2021 from: Juniper tip blight | The Morton Arboretum
OMAFRA rev. 2020, Juniper Dieback, Retrieved on Feb. 12, 2021 from: Juniper Dieback (gov.on.ca)
University of Maryland Extension rev. 2020, Juniper Twig Blights, Retrieved on Feb 12, 2021 from: Juniper Twig Blights | University of Maryland Extension (umd.edu)
Other reading resources:
Cercospora Blight | Backyard Farmer | Nebraska (unl.edu)
Cercospora Blight | Focus on Plant Problems | U of I Extension (illinois.edu)
Plant Pathology Circular No. 397 – January/February 2000 (fdacs.gov)
Blue Rug Juniper Diseases (sfgate.com)
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