Pine Wilt

This issue is a major problem for a variety of mature pine trees across the state of Kansas. Pine Wilt is caused by the pinewood nematode (a microscopic worm) and affects Scotts, Austrian, white and mugo pines in the eastern 2/3 of the state of Kansas. The nematode is carried from one tree to another by the pine sawyer beetle. Female beetles lay their eggs under the bark of pine trees usually during the summer and the eggs hatch then the larvae tunnel deep into the wood. While the larvae are maturing, the nematodes are also maturing. Just after the adult sawyer beetle breaks out of its pupal shell, large numbers of pinewood nematode larvae move into the tracheae (breathing tubes) of the new adult beetle. These nematodes are then carried to new host plants by the beetles.

While we call this “Pine Wilt” it is truly not a disease because, the damage is caused by the nematode feeding and multiplying in the trees resin canals which ultimately blocks the movement of food and water throughout the tree leading to the wilting a death of the plant. In Kansas the wilt infestations are most apparent starting in August through December and infected trees can die over a period of weeks or months depending on the tree. In the first stages the needles turn gray-green then yellow then brown. The change can happen branch by branch or the damage may show up all at once over the entire plant. During the early stages Pine wilt can be confused with tip blight (a fungal disease of pines that causes damage to the new growth of the pine tree. Damage shows up in late May or early June) however tip blight has different symptoms and causes slow die back of the tree over years rather than months. If you are concerned you have pine wilt one way to check is cutting a live or recently turned brown branch off the tree. For pines impacted by Pine wilt there will be a decrease in amount of resin since the nematodes feed on the resin canals. Once a tree has died the needles will remain on the tree for up to a year. The unfortunate part of this issue is that it only impacts mature trees that we have had for years.

The most important step to prevent the spread of Pine wilt is sanitation. If a tree is suspected of having Pine wilt or has died try to get it cut down and removed by May 1^st at the latest, preferably April 1^st, to prevent the beetles from emerging and flying away. Be sure to cut the tree all the way to the ground and do not leave a stump. The wood from the tree should be chipped or burned immediately. Don’t save the wood for firewood as the beetles will hatch from the wood. If possible, avoid stress on the tree as much as you can. During periods of drought be sure to water the tree periodically to keep it healthy as the beetles are attracted to trees that are stressed. If the tree hasn’t been infested by the nematodes there are injections that can be done to help prevent death from Pine wilt. I should note that none of the treatments are 100% effective and they must be done by a professional. There is research being done on possible cultivars of resistant pines at the John C. Pair center near Haysville so I hope that in the future we will have some new evergreen options for windbreaks and landscape trees. At this time I would not recommend planting Scotts or Austrian pines in the state of Kansas. Hopefully in the future we can plant pines again but for now other evergreens are our only option.

Have questions? Contact our office where our Horticulture Extension Agent will assist you with questions.

Phone: (316) 321-9660

Email: callae@ksu.edu