Diplodia Blight in Conifers

Diplodia Tip Blight in Conifers | Atlanta, Georgia

red oak tree leaf covered with brown blotches on leaves

Diplodia Blight | Signs and Symptoms

A few brown needles at the tip of the current season's growth are the first evidence of tip blight. These blighted needles are usually located on the lower branches of the tree. Needles that are in the early stages of development stop growing after infection and therefore appear stunted when compared to healthy needles. The number of blighted needles increases until the new growth for that year has been killed. This stunted and dead new growth on lower branches draws attention to the disease. With a hand lens you may see minute black fruiting bodies (pycnidia) at the base of diseased needles, especially under the papery leaf sheath. These are sure signs of this disease. Symptoms of tip blight are not restricted to the needles. Future tree growth is often reduced by damage to or death of terminal buds during infection. Twigs may be infected and become stunted or deformed. Stunted twigs may exude resin which traps blighted needles before they fall to the ground. Close examination of these twigs reveals cankers at the first branch whorl and often near the leaf scars of blighted needles. Enlargement of these cankers results in the girdling of the twig and rapid death of the branch tip. In most cases, these symptoms are not observed beyond the current season's growth.

Management Strategies

The damage caused by this disease is most severe on old or weakened trees. Old trees or trees exposed to unsuitable growing conditions, mechanical injury, or damage by insects may eventually be killed. Thorough weekly watering during extended dry periods of the growing season and spring broadcast fertilization will result in a tree that is more vigorous and more resistant to tip blight.

When only a few branches of a tree show symptoms of tip blight, a program of pruning and sanitation should help minimize disease. Prune off blighted twigs and destroy or discard them. Since fungal spores can be transported to healthy twigs during the pruning operation, prune when the tree is dry. Disinfect pruning tools before each cut by swabbing the cutting blades with a solution of 70% rubbing alcohol between each cut. Rake up all blighted needles, twigs, and especially cones which harbor the fungus and destroy or discard them.

Where disease is severe on smaller landscape trees, homeowners in the state of Georgia may apply some fungicides containing either potassium bicarbonate or propiconazole to try to minimize new infections. Follow label directions. Homeowners are discouraged from trying to apply pesticides to large landscape specimens, and should consider hiring a professional applicator if good cultural practices and fertilization do not sufficiently improve the overall health of such trees. Additional fungicides may be available for use by professional pesticide applicators.

Infected needles, cones and twigs should be collected and destroyed to minimize the spread of the disease. Removal of some branches to increase air movement will also help minimize incidences of Diplodia Tip Blight in Conifers. Trees that are severely defoliated by this fungus should be fertilized slightly more than normal to stimulate new growth. For more information see Cornell University factsheet

Arborist Evaluations