Brown needles on pine trees could be sign of diplodia tip blight
Do you have a mature pine tree with bunches of brown needles? It may be suffering from a fungal disease called diplodia tip blight.
“Diplodia has become more common due to environmental stress and overplanting of some pine species,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “Since our suburbs and city neighborhoods don’t offer very good conditions for pine trees, most pines in Chicago-area yards are likely to be stressed.”
The obvious sign of diplodia tip blight is seen in spring, when new needles at the tips of branches quickly die and turn brown. The new needles are often much shorter than normal. The disease usually starts low on the tree and moves upward. As a result, by late summer, most branches on an afflicted pine tree will have dead brown needles at their tips.
“It’s a disfiguring disease, and in the long run badly affected trees may die,” Yiesla said.
If you look closely at the dead needles, you may see tiny drops of sticky resin. In late summer and fall, tiny dots like black pepper start to be visible at the very base of the dead needles and sometimes on the scales of cones and on bark. They are called pycnidia and are the fruiting bodies of the fungus Diplodia pinea.
Spores, the reproductive bodies of the fungus, overwinter in the pycnidia and are released in spring to affect the “candles,” the shoots of new growth at the branch tips. Eventually, the blight can kill whole branches.
Not every pine that has dead needles is infected with diplodia tip blight. “It’s normal for pine trees and other evergreens to lose some of their oldest needles every fall,” Yiesla said. “But those needles are lost from the oldest part of the branches, close to the trunk. Diplodia kills new growth at the ends of branches.”
The disease commonly affects pine species that have their needles in bundles of two or three. Austrian pine (Pinus nigra) is the most susceptible host, which is one reason the Arboretum does not recommend planting Austrian pines in the Chicago area. Diplodia can also infect other kinds of pine, such as Scots pine (Pinus sylvestris), red pine (Pinus resinosa), mugo pine (Pinus mugo) and ponderosa pine (Pinus ponderosa).
In rare cases, the fungus may attack other conifers such as Douglas fir (Pseudotsuga menziesii), Norway spruce (Picea abies), Colorado blue spruce (Picea pungens), American larch (Larix laricina), noble fir (Abies procera), silver fir (Abies alba), cedars (Cedrus), cypress (Cupressus), arborvitae (Thuja), and juniper (Juniperus).
Diplodia usually affects pine trees older than 15 years and is most severe on trees older than 30. In urban areas where they are planted for ornamental purposes, these trees are often weakened by poor sites, drought, hail or snow damage, shade, compacted soils, limited space for their roots, insect activity, or wounds from lawn mowers and string trimmers.
The Plant Clinic can help you determine whether your unhealthy pine or other evergreen tree is afflicted with diplodia tip blight. If so, you should prune out all affected branches, needles and cones and remove them from your garden. Do this pruning in winter or in a dry part of late summer or fall; don’t prune in spring or early summer, when the new growth is most susceptible to infection by the spores.
Certain fungicides may help if they are applied to the whole tree at specific times, starting when new growth emerges in spring. Get expert advice before choosing or applying a fungicide. “If a tree is severely infected, it may be too damaged to save,” Yiesla said.
The best way to avoid diplodia tip blight is to not plant a susceptible kind of tree. Get expert help to choose an evergreen tree that is most likely to be able to withstand the stresses of life in your yard. “Then help it stay healthy by keeping a layer of mulch over its roots and watering it during dry spells,” she said.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
