Common Diseases of Conifers in Oklahoma - OSU Fact Sheets ...

Figure 1. Dothistroma needle blight on Austrian pine.ControlSeedlings and young trees that are infected with the stemrot phase cannot be treated successfully. When Diplodia TipBlight has been a problem in seedling production, the use ofsteam-pasteurized soil or soil fumigants will help in controllingroot and stem infection.Diplodia Tip Blight on older trees can be controlled bypruning and sanitation. As soon as blighted terminals andcones are noticed, the needles, twigs and cones should bepruned to healthy tissue and destroyed. Do not prune whenthe branches are wet because the conidia of the fungus caneasily be spread when moisture is present. Where infectionhas been severe, the use of Bordeaux mixture or CopperFungicide 4E will control this disease. It should be appliedearly in the spring, when the buds open, and twice more atweekly intervals until the needles break through the needlesheaths. An application of fungicide in the fall may also aidin slowing the spread of the disease; however, fertilizationand watering in the fall may be more beneficial. Homeownerswho maintain vigorous trees through good tree health carewill have fewer problems with Diplodia Tip Blight.Needle CastsSymptomsThe first indication of this tree disease is the scorchedbrown or yellowish appearance of most of the needles. Manypines are affected by this disease and it can become a severeproblem in Christmas tree plantings. The initial discoloration ofthe needles is followed by needle fall or casting. Few trees areactually killed by this defoliation but sustained needle kill willeventually reduce the overall growth rate and make the treemore susceptible to other diseases and insect attack. Over40 different species of fungi are capable of causing needlecase. The more important ones are Lophodermium pinastri,Hypoderma lethale, and Hypoderma hedgcockii.Disease CycleSmall black elliptical fruiting bodies of the fungus areproduced on the needles. These structures break open in thelate spring or early summer during periods of wet weather andrelease great numbers of spores. The spores can be spreadby splashing rain or wind to infect other needles or trees.Figure 2. Stunted terminal branch of pine infected withDiplodia pinea.Infected needles begin to turn brown during the late fall andearly spring and will have a mottled appearance due to thedeath of needle tissue at the infection sites. Temperature andhumidity are very important in determining the severity of theinfection.ControlIn nurseries this disease can be controlled by the applicationof the fungicide after the needles are half grown followedby a second application when the needles are fully developed.No chemical control measures are normally recommendedfor homeowners even though the tree may appear unsightly.Collection of infected needles and their destruction will greatlyreduce this disease. However, if a homeowner wishes tocontrol this disease, the proper application of a fungicide willprovide excellent control.Phomopsis Blight of JunipersThis is the most common disease of cedar, juniper, andarborvitae in Oklahoma. Phomopsis Blight can be a severeproblem in nursery plantings and can cause the death of manyseedlings. Older trees are less affected by Phomopsis Blightand unless these trees are environmentally stressed or inpoor health they are usually not affected enough to warrantchemical sprays.Symptoms and Disease CycleInfected trees will exhibit browning of the foliage and dyingof twigs and branches (Figure 4). Small black fruiting bodies ofthe fungus, Phomopsis juniperovora, are formed on this deadtissue. Conidia are produced in these structures and whenmoisture is present masses of conidia will ooze out to formtendrils or horns. The conidia are spread by rain and variousother means such as mechanical disruption and insects. Thefungus enters the plant through wounds as well as unbrokentissue. The browning of the needles and twigs begins at thetips and progresses downward toward the stem. Moisture isan important factor in disease spread and severity. Nurseriesand Christmas tree plantations that utilize overhead irrigation7618-2