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Juniper Tip Blight in Wet Areas of Illinois

May 16, 2001

No, we have not yet seen any cases of Phomopsis blight on junipers this year. The fungus infects new growth as it emerges. Those of you who had problems with this in the past and want to protect plants this year need to take action now.

Phomopsis infection occurs on the youngest needles, starting as yellow spots. Shoot tips then turn light green before becoming brown. Growers may dismiss early symptoms as winter burn and may not be concerned until the appearance of brown shoot tips. One diagnostic feature to help identify this disease and distinguish it from weather scorch, salt injury, or other stress is the presence of a grayish band at the base of the dead shoot. In this band are pinhead-sized, black fruiting bodies (pycnidia) of the fungus. The pycnidia are visible with the naked eye or with the aid of a hand lens, and they are embedded in the plant tissue. If the tissue is very dry, place it in a plastic bag with wet paper toweling overnight. The fruiting bodies will be easy to see the next day.

Infection by Phomopsis occurs when succulent new growth is present in wet weather. Parts of central Illinois may not see the disease this year, but it will be common in wetter areas of the state. Spores germinate under moderate temperatures (60° to 82°F) and high humidity within 7 hours after coming into contact with the new foliage. If the foliage dries before infection occurs, the spores are not killed; they begin growth again with wet weather. Pycnidia form 3 to 4 weeks after infection. This means you won’t see the symptoms for a few more weeks on this year’s growth. That is too late to take action with fungicides. If you had this problem in the past, consider using a fungicide to help protect growth this year.

Commercial growers can use azoxystrobin (Heritage), propiconazole (Banner), copper hydroxide (Kocide), thiophanate-methyl (Cavalier, Cleary 3336), or mancozeb (Protect T/O, Dithane, Fore, Junction, Lesco Mancozeb, Pentathalon). Homeowner products available for this use include thiophanatemethyl (Bonide Bonomyl, Dragon 3336, Ferti-lome Halt), mancozeb (Bonide Mancozeb), potassium bicarbonate (Bonide Remedy), and copper sulfate (Hi-Yield Bordeaux). Sprays must start when new flushes of growth appear and continue through maturity. Prune out the dead and infected twigs when they are dry. See Report on Plant Disease no. 622, “Phomopsis Twig Blight of Juniper,” for more details. You can get a copy at your local Extension office or view it on the Web at http://www.ag.uiuc.edu/~vista/horticul.htm.

If you have tried using fungicides in years past and still have the disease, you may have Kabatina blight and not Phomopsis blight. Kabatina infects only wounded tissue and infects later in the season. You see it on old growth from last year. Kabatina blight is not clearly understood, and fungicide timing has not been effective in disease control. It is important to remove and destroy infected twigs in dry weather. Reports indicate that disease-resistant varieties are in development, so ask for these at your nursery. Some information about Kabatina blight can be found in Sinclair, Lyon, and Johnson’s book, Diseases of Trees and Shrubs.

Resistant varieties are available for Phomopsis blight. If you are starting a new planting, by all means find a resistant variety. A good Web site that discusses both diseases and lists relative resistance to disease is http://www.ag.ohio-state.edu/~ohioline/hyg-fact/3000/3056.html.

Author: Nancy Pataky


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