Monday, May 19, 2008

Landscape and Nursery - Juniper Tip Blights

Twig and branch tip dieback is a common sight in many juniper plantings in Delaware this spring. While other factors can cause these general symptoms, two fungal diseases are frequently responsible for the dieback. These fungi (Phomopsis juniperovora and Kabatina juniperi) attack several species of Juniperus, including red cedar, common juniper and creeping juniper. Arborvitae is also susceptible. In the spring, Kabatina twig blight is most noticeable. The following is information on these diseases.

Kabatina Twig Blight.

Brown shoots scattered within the healthy green foliage are being seen now. The disease is especially noticeable in beds of creeping juniper. These shoots, green all winter, have only recently turned brown. In early spring, as junipers begin to green up, infected twigs from the previous season's growth begin to fade to a pale green and then turn brown in contrast to healthy green tissues nearby. Grayish lesions with numerous gray-black fruiting bodies appear at the bases of blighted shoots. Kabatina twig blight infections begin through a wound caused by insects or mechanical injury and are thought to begin the previous fall.

Disease Management: 1) Prune out and destroy infected twig tips. Pruning should be done when the foliage is dry in order to minimize fungal spread. 2) Use an approved insecticide to control insect pests. It is possible that insects, such as the juniper midge, create the wounds necessary for Kabatina infections. 3) Avoid planting highly susceptible cultivars. Instead, select varieties that are known to be tolerant to Kabatina.

Phomopsis Twig Blight.

In late spring and in summer, as new shoots are developing, they can become infected with this pathogen during periods of moist weather. This disease begins as an infection of newly developing needles which then spreads to and kills stem tissues. As with Kabatina tip blight, a tan lesion with fungal fruiting bodies (pycnidia) develop after infection.

Disease Management: 1) Fungicides can be used in spring and summer to prevent infections of new growth. Applications of fungicides containing thiophanate-methyl, azoxystrobin, propiconazole, mancozeb, or fixed copper can protect twigs from infection. 2) Prune out and destroy infected twig tips when foliage is dry. 3) Avoid overhead irrigation, especially late in the evening.

Because these two diseases are so similar in appearance, the time of symptom development can be helpful in distinguishing between the two. Kabatina twig blight symptoms generally develop early in the spring before new growth begins. Phomopsis twig blight symptoms, on the other hand, are more likely to develop any time during the growing season. If twig blight symptoms are evident now on junipers that appeared healthy in the fall, Kabatina is likely responsible.
Most junipers are not immune to tip blight diseases.

Kabatina tolerant juniper (that are not known to be susceptible to Phomopsis) cultivars across several species include: Aurea Gold Coast, Blue Mountain, Burkii, Cologreen, Emerald Sentinal, Expansa, Henryii, Hetzii, Hetzii glauca, Hibernica, Hornbrooki, Keteleeri, Manhattan Blue, Marcellus, Mas, McFarland, Mint Julep, Mountbatten, Nana, Perfecta, Prostrata glauca, Robusta Green, Saybrook Gold, Sargentii viridis, Sargentii glauca, Silver Globe, Sutherland, Variegata.

Phomopsis tolerant juniper (that are not known to be susceptible to Kabatina) cultivars across several species include Arcadia, Ashfordii, Aureo-Globosa, Aureo-spica, Buffalo, Calgary Carpet, Campbellii, Cinerascens, Depressa, Douglassii, Expansa, Fargesii, Fastigiata, Femina, Globosa, Hetzii, Hibernica, Hillii, Iowa, Keteleeri, Knap Hill, Meyeri, Mint Julep, Mountbatten, Oblonga Pendula, Pfitzeriana, Pfitzeriana aurea, Prostrata aurea, Pumila, Pyramidalis, Repanda, Reptans, Robusta Green, Sargentii, Sargentii glauca, Saxatilis, Saybrook Gold, Shoosmith, Silver King, Skandia, Suecia, Tripartita,

Avoid the cultivars Adpressa, Albospica, Alpina, Argentea, Bar Harbor, Blue Chip, Blue Haven, Blue Horizon, Blue Mat, Blue Pacific, Broadmoor, Columnaris, Emerald Sea, Emerson Creeper, Eximius, Horizontalis, Japonica, Pendula, Platinum, Plumosa Compacta, Prince of Wales, Procumbens, Sky Rocket, Spartan, Torulosa Hollywood, Variegata, Welchii, Wiltonii, and Wichita Blue.

Information from the May 23, 2008 edition of the Kentucky Pest News from the University of Kentucky, College of Agriculture.

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