This spring we are seeing a large number of evergreen trees and shrubs with winter injury. Winter injury usually results from the interaction of low temperatures, frequent freeze/thaw cycles and rapid cooling and thawing rates. (For more information see the article by Jeff Iles, HHPN, March 15, 1996.) Tress with winter injury will usually recover provided that the new buds aren't damaged.
While many of the brown trees can be attributed to winter injury, we need to be careful not to lump every brown evergreen into the winter injury group. For example, winter injury on junipers produces identical symptoms to two common fungal tip blights (Phomopsis and Kabatina tip blights). Winter injury and Kabatina tip blight both show up as the weather warms in the spring (February or March). Last year's growth starts to brown and die just as everything else greens up. If twig blight symptoms are evident in the spring on junipers that appeared healthy in the fall, Kabatina is probably the culprit.
Phomopsis tip blight also attacks new growth, but it is able to spread anytime during the growing season when new growth occurs. Tip browning due to Phomopsis tip blight usually appears mid- to late-May and continues through the summer months.
How can you tell what is wrong with your junipers? To check your junipers for tip blight, inspect dead or dying shoots for symptoms. Affected foliage is initially red or brown but turns ash gray and drops from the plant. Look for small gray lesions at the base of the discolored tissue. Small black specks should be evident in the gray areas. These specks may be viewed easier with a hand lens. Alternatively, the Plant Disease Clinic can check for tip blights for you.
For appropriate control, it is important to identify which tip blight you have. Kabatina infects shoots in the fall while Phomopsis infects new growth throughout the growing season. Time of infection determines which control measures are most effective.
- Prune out and destroy infected twig tips. Prune when the foliage is dry to minimize spread of the fungus.
- Avoid overhead sprinkler irrigation, or water early in the day so foliage has time to dry.
- Plant junipers in well drained soils and space them adequately to promote good air circulation.
- Avoid planting highly susceptible cultivars.
- Scout for insect pests which may be creating wounds necessary for Kabatina infection.
- Chemical control of Phomopsis and Kabatina are usually not necessary in landscape or windbreak plantings unless the damage is severe or the plantings have a history of the disease.
- Kabatina The fungicides Cleary's 3336, 3336F and Protect T/O are labeled for control of Kabatina tip blight. Apply fungicides in late summer or fall. One or two applications of Bordeaux mixture in late September or October may also reduce the severity of the disease. Spraying in the spring after symptoms have appeared is too late for that infection period.
- Phomopsis Bordeaux mixture, Protect T/O, 3336F, Duosan and Domain are fungicides which can be used to protect new flushes of growth. Fungicide applications for Phomopsis are applied in the spring and repeated every 7-10 days during the disease period and while new growth is still emerging. In general, these fungicides are protectants and need to be applied whenever new growth appears.
This article originally appeared in the May 24, 1996 issue, p. 87.