The Homeowners Column

The Homeowners Column

Be on the look out for pine wilt disease

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator

Over the past few years many evergreens are more everbrown than evergreen. From needle blights to bagworms pines and spruces have succumbed to numerous problems. In addition most of our landscape evergreens are not native here; therefore, they tragically suffer from our heat and drought.

Not all evergreens have the same problems even though brown needles and even tree death is the outcome. Accurate identification of tree problems is always a good idea before any treatments or management programs are started. Nothing replaces good tree care of proper mulching and watering.

So much for the disclaimers. If you happen to have Scotch pines in rapid decline, a good bet as to the cause is pine wilt. Most pine fatalities due to pine wilt occur from now to late fall and in spring. The disease has been severe enough over the last decade that Scotch pines are no longer recommended as landscape trees. The disease can also be found in Austrian and Jack pines and less common in red and mugho pines. Pine wilt is rare in white pines; however white pines are having other problems with Illinois soils and temperatures.

Pine wilt is not caused by a fungus as with many wilt diseases, but by pine wilt nematodes which are threadlike microscopic round worms. They ride from pine to pine inside the breathing tubes of different varieties of sawyer beetles. The nematodes enter the tree through the feeding wounds made by the beetle. Once inside the tree, the nematodes reproduce rapidly. The tree's water conducting vessels become clogged and the tree quickly dies within a few weeks or months after the initial symptoms appear. Adult beetles emerge from dead trees in June and July with their nematode cargo then feed on twigs of healthy pines to repeat the disease cycle. The only method of infection from pine wilt nematode is via the sawyer beetles.

The first indication of Scotch pine problems is a change in needle color as it changes from a light grayish green, to yellowish green, yellowish brown and finally completely brown. The color change may appear first on a single branch in the top of the tree or perhaps the entire tree. The brown needles will often stay on the tree for long periods. In Scotch pines this disease affects the entire branch. You will not see green needles on the stem tips or on older growth. Occasionally a section of the tree is infected, but it always infests entire branches. There is no recovery once a tree has pine wilt.

Quickly removing dead Scotch pines is the most effective control for this disease. Allowing dead trees to stand increases the risk that the beetles will spread nematodes to other trees. There are no known effective chemical controls for the disease, the nematode or the beetle.

Trees should be removed to the ground line or deeper. Wood should be burned or buried immediately and not saved for firewood. It can be chipped for mulch, although it should be composted for a few months or spread out to dry before using around pines.

To determine if a pine tree has pine wilt, send samples to the University of Illinois Plant Clinic at 1401 West St. Mary's Road in Urbana, IL 61801 (location after September 30: 1102 S. Goodwin, S-417 Turner Hall Urbana, IL 61801.) PH: 217-333-0519. Fee is $20.00. Send in recently dead branches with brown needles still attached. Samples should be 1 to 2 inches in diameter and at least 6 to 8 inches long. Wrap in aluminum foil and be sure to include information such as age of tree, what kind of pine, when symptoms were first noticed, date of sampling, name and address of owner and any information on the planting site such as type of soil, low area, etc.

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