Key Features
- Browning of branches
- Pine sawyer beetles present
Symptoms
All needles on the affected branches die and turn brown at about the same time. Eventually the tree will succumb to the disease and all of the needles will turn brown. Pine sawyer beetles may be observed feeding or laying eggs on the pine trees. If a dead branch is pruned away, bluish staining may be observed in the wood. This is caused by a fungus, also transmitted by the pine sawyer beetle, that the nematodes feed on. These symptoms resemble those of fungal diseases or may be confused with winter or freeze injury. Send samples to a plant disease diagnostic lab for confirmation.
Biology
Pine wilt is a complex disease caused by nematodes that are transmitted to the trunk and branches by pine sawyer beetles. A fungus associated with wilting may also be involved in this disease. The nematodes make their way to the vascular tissue through feeding wounds or by following tunnels formed by pine sawyer beetle larvae. Destruction caused by the feeding nematodes kills the associated branch. Pine sawyer beetles also lay their eggs on dead wood. While this will not cause immediate harm to the landscape, more beetles and nematodes will emerge the following year which increases the risk to living pines.
Management Recommendations
Avoid wounding or stressing susceptible pines, which include non-native species like Japanese black pine, Austrian pine, and Scotch pine. Prune pines in late winter or early spring so the trees have time to heal before pine sawyer beetles begin laying their eggs. Consider native pine trees, fir, or hemlock for new plantings or to replace already damaged trees. Trees severely suffering from drought, winter injury, or other ailments can be removed and either de-barked or destroyed to prevent pine sawyer beetle survival. Chipping and debarking will not kill the nematodes, but will prevent the pine sawyer beetle from spreading them.
Effective Pesticides
Pesticides are neither available nor recommended for managing this disease.
Resources
- Pine Wilt
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
