Causal Agent

The fungus Diplodia pinea

 

Hosts

Pine.

 

Symptoms

This fungal disease can seriously attack pine seedlings in nurseries, causing a rot that starts below the soil line in the collar area of the stem and extends upward into the main stem. The scales of young cones are also attacked. This disease also causes a dieback of the branches of older pine trees. Growth from these blighted terminals is usually stunted, the needles turn brown, and the terminal buds exude an excessive amount of resin. Diplodia can also infect the cones of these older pines and the minute black fruiting bodies can easily be seen on the scales of the cones.

 

This disease can be easily confused with Pine Tip Moth injury. One of the differences between these two problems is that with Diplodia Tip Blight the dead portion of the plant is soaked with sap or has sap on the outside; Pine Tip Moth damage does not.

 

Control

Seedlings and young trees that are infected with the stem rot phase cannot be treated successfully. When Diplodia Tip Blight has been a problem in seedling production, the use of steam-pasteurized soil or soil fumigants will help in controlling root and stem infection. Diplodia Tip Blight in older trees can be controlled by pruning and sanitation. As soon as blighted terminals and cones are noticed, the needles, twigs, and cones should be pruned to healthy tissue and destroyed. Do not prune when the branches are wet because the conidia of the fungus can easily be spread when moisture is present. Where infection has been severe the use of Bordeaux mixture or Copper Fungicide 4E will control this disease. It should be applied early in the spring, when the buds open, and twice more at weekly intervals until the needles break through the needle sheaths. An application of fungicide in the fall may also aid in slowing the spread of the disease; however, fertilization and watering in the fall may be more beneficial. Homeowners who maintain vigorous trees through good tree health care will have fewer problems with Diplodia Tip Blight. Please contact your local county extension office for current information.