Disease name: Pine wilt disease
Name of causal agent: Bursaphelenchus xylophilus (nematode)
Hosts: Pine wilt is a fatal disease. The most common hosts are Scots pine (Pinus sylvestris), Austrian pine (Pinus nigra), mugo pine (Pinus mugo), red pine (Pinus resinosa), and Japanese red pine (Pinus densiflora). The disease is uncommon on white pine (Pinus strobus).
Pine wilt disease is widespread in much of the United States, especially in the Midwest.
Symptoms
On pines infested with the pinewood nematode, the needles appear as an off-color grayish-green, turning yellow and, finally, brown. The tree dies rapidly after the needles turn color, usually within a few weeks or months.
The dry, brown needles remain on the dead tree, rather than falling off. They are held on by the resin produced by the tree.
Most deaths occur in late summer or fall. A tree that declines slowly is usually not suffering from pine wilt.
Disease Cycle
Pinewood nematodes cannot move from tree to tree on their own. They are carried from dying trees to living trees during the growing season by the pine sawyer beetle.
This beetle will visit dying trees to feed, mate, and lay eggs. The beetle will conduct most of its life cycle in the dying tree, and during that time, the tiny nematodes will move into the spiracles (breathing pores) of the beetle’s body. When the beetles emerge as adults, they will fly to healthy trees to feed on the bark.
As the beetle feeds on a healthy tree, the nematodes leave the beetle and enter the tree through the feeding wounds. The nematodes will then infest the resin canals of the pine, multiply rapidly, and clog the water transport system of the tree.
The life cycle of the nematode can be completed in three to five days, so the population increases quickly.
The clogging of the water transport system of the tree by this large population of nematodes leads to the rapid death of the tree.
Management
A laboratory test to check for the presence of the nematode is necessary to confirm the diagnosis. The University of Illinois Plant Clinic will confirm pine wilt for a nominal charge. Some arborist companies have their own labs, or have access to other labs, and can assist with obtaining a proper diagnosis.
Cultural Management
Once a pine has started to die from pine wilt disease, it needs to be removed from the site immediately or burned where burning is permitted. The stump should be ground or buried. The wood should not be kept for firewood but can be chipped for use as mulch.
Chemical Management
Insecticide treatments to control the beetles that carry the nematodes are impractical because the beetle has a long period of activity. There are nematicides registered for management of the nematode. These products are for prevention, not cure, of pine wilt. They must be injected into the tree by a licensed professional before the tree is infested by the nematodes.
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 at 630-719-2424 or plantclinic@mortonarb.org.