Disease name: Diplodia tip blight (formerly known as Sphaeropsis tip blight)
Pathogen name: Diplodia pinea (syn. Sphaeropsis sapinea) (fungus)
Hosts: Diplodia tip blight is a common fungal disease of pines with needles in bunches of 2’s and 3’s. Austrian pine (Pinus nigra) is the most susceptible host, although the following pines are also susceptible: Scots pine (Pinus sylvestris), red pine (Pinus resinosa), Mugo pine (Pinus mugo), and Ponderosa pine (Pinus ponderosa). Pines with needles in bunches of 5 are highly resistant. The disease can attack other conifers such fir, spruce and juniper, but generally does very little harm to these species.
The disease is more common on trees older than 15 years of age (trees that are more stressed), and most severely damages trees that are older than 30 years. It is seldom seen in forests but is common in landscape trees stressed by poor sites, drought, hail or snow damage, over shading, compacted soils, root restrictions, insect activity, or other mechanical wounding. The fungus affects current year shoots and sometimes branches, and can disfigure or even kill them under severe conditions.
Symptoms
Diplodia tip blight kills needles at the tips of branches. Symptoms often start on the lower half of the tree and progress upwards. When the new needles (candles) are expanding, they become stunted, turn yellow, and then turn tan or brown. Generally all needles on the current season’s shoot are killed.
Often resin droplets from cankers are seen on the dead shoots. During summer and fall, black fungal fruiting bodies will appear at the very base of the needle under the fascicle (sheath). The fruiting bodies may also be seen on the scales of second year seed cones and on infected bark. As lateral shoots are killed, whole branches may die back to the trunk and the tree becomes disfigured. This disease can also form perennial cankers that can cause branch death.
Disease Cycle
The diplodia fungus overwinters as fruiting bodies in infected shoots, bark, and seed cones. Tiny spores erupt from them in wet weather. Although they are produced from spring to early fall, they are especially abundant in spring and early summer, when the new shoots (candles) are expanding. Candles can only be infected by the fungus while they are elongating in the spring. After the needles have fully expanded, the shoot can no longer be infected by the fungus. Wind and rain disseminate the spores. When the spores land on a susceptible plant part, they infect it by penetrating the plant through wounds or stomates (breathing pores). Once the fungus penetrates the plant, it quickly spreads throughout the needles, then to the stem and into nearby needles. The needles begin to die several weeks after infection. Later in fall after the needles have died, the fruiting bodies appear on the base of the needles or on second year seed cones.
Management
Cultural Management
To help prevent infection from diplodia tip blight, maintain tree health, as the disease is more severe on trees that are under stress. Keep the tree watered during dry periods. Maintain a layer of mulch under the tree to conserve moisture. Because the fungus can also infect wounded tissues, avoid pruning trees from late spring to early summer when they are most susceptible. Since cones and dead tips contain the fruiting bodies, when feasible, remove and destroy all infected cones and dead and dying branches during dry weather. Pruning tools should be disinfected between cuts.
Chemical Management
There are fungicides available to treat diplodia tip blight. The first treatment should be done at budbreak. Additional treatment should be applied according to label directions.
The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.
For current pesticide recommendations, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).