Phomopsis twig blight of juniper, also known as nursery blight, cedar, juniper, or needle blight, is caused by the fungus Phomopsis juniperovora. Economic damage to landscape plantings and nursery stock is largely restricted to species and cultivars of juniper (Juniperus). Other evergreens that are attacked include arborvitae (Thuja), species of true cedar (Cupressus), and false cedar (Chamaecyparis), European larch (Larix decidua), jack pine (Pinus banksiana), English yew (Taxus baccata), Japanese plum yew (Cephalotaxus drupacea), Douglas fir (Pseudotsuga taxifolia), species of fir (Abies), and Cryptomeria japonica. The disease is mainly a leaf and shoot infection found in young plants and on the new growth of older plants.
Juniper seedlings and transplants in nurseries are highly susceptible and are commonly killed by the blight. Overhead irrigation in a nursery is conducive to infection, and a large number of seedlings, transplants, or grafts can be blighted and killed in a very short time. The value of older nursery stock diminishes markedly from infection and the survival of this stock is poor after planting. The disease be-comes progressively less serious as trees and shrubs grow older, even though the new growth of older plants is very susceptible, death or severe damage to a plant over five years old is much less likely.
During prolonged wet, warm periods in spring and summer (April through early June) and again in late August and September, the fungus becomes particularly infectious. Phomopsis twig blight to juniper is found in most of the United States–from the Pacific Northwest, throughout the Great Plains from South Dakota to Texas, and eastward through the entire Midwest to the East Coast–as well as in Canada, however, it is not common on plants growing in the wild.
on image for larger version
Figure 2. Phomopsis juniperovora,
the cause of Phomopsis blight
of junipers - seen under microscope.
(drawing L. Gray).
Yellow spots at the shoot tips of young needles are the first symptoms to appear, although older needles may also show the spotting. As the infection progresses from the needles into the stems, a gradual dieback of the new shoot growth occurs changing from light yellow to red brown to ash gray, eventually killing the entire branch.
Lesions occur on the stems and frequently develop into cankers at the junction of healthy and diseased tissues. Small stems (less than 1/3 inch in diameter) are usually girdled by these cankers, causing the stem tissue beyond the cankers to die. Older branches (more than 1/3 inch in diameter) are more resistant to infection, and cankers that form on them usually heal. In advanced stages of infection, small black spots (the fungus fruiting bodies or pycnidia) can be seen with the unaided eye or with a magnifying glass on the dried, ash gray parts of stems and needles (Figure 1). The central part of a plant is often more affected than its outer portion, with the new growth showing almost continuous infection. Under certain conditions favorable for fungal development, the entire shrub or tree (especially a young plant) may be affected, and all its needles and stems will die and turn brown.
Phomopsis twig blight is easily confused with four other problems of junipers:
Under drought conditions, the -tips of branches may be killed, but the line of demar-cation between green and dead tissues is gradual, while in Phomopsis blight, this line is sharp;
Damage from the lesser cornstalk borer (Elasmopalpus lignosellus) can be distinguished from Phomopsis blight by the straw color of the dead tops and by the feeding wounds on the lower stem and taproot;
Another fungus, Cercospora sequoiae, causes a blight in junipers and related species, but in this disease only the needles, not the stems (as in Phomopsis blight), are infected. Also, infection by Cercospora starts on the oldest needles of the lower branches, spreading upward and outward, whereas infection by Phomopsis starts in newly developed needles and progresses inward; and,
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The most common sources of infection each spring are spores (conidia) produced in fungal fruiting bodies (pycnidia) that appear as black spots on the needles and stems infected the previous year (Figure 2). New pycnidia formed in the current growing season are also a source of infective spores. The microscopic spread by the wind, insects, and during pruning and other handling operations. Under moderate temperatures (60 ° to 82° F or 15 ° to 27 ° C) and high humidity, the spores germinate within seven hours after coming in contact with young needles, especially those still in the yellowish green stage. After the needles mature (develop a normal, deep green color), they are not susceptible to infection.
Germinated spores of Phomopsis are not killed by drying, like many other fungi, but begin growing again when moist conditions return. Within three to five days after infection, the fungus permeates the young needles and quickly invades young stem tissue. After colonizing a side shoot, the fungus mycelium progresses into the main stem, growing rapidly along the inner bark, killing the cambium and staining the wood a brownish color.
Within three to four weeks after infection, pycnidia develop on the needles and stems that have died and turned ash gray. At first, the pycnidia are embedded in the tissue, but later, after the infected tissue has dried considerably, they partially erupt through the epidermis. During wet, warm weather, spores ooze from the pycnidia and are easily and quickly dispersed. The fungus can persist as mycelium in dead parts of infected plants for as long as two years.
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Contact Nancy R. Pataky, Extension Specialist and Director of the Plant Disease Clinic, Department of Crop Sciences, University of Illinois at Urbana, for further information on diseases of ornamental plants.
University of Illinois Extension provides equal opportunities in programs and employment.
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