Pines grow in most every state of the U.S., and are planted for many reasons. They offer year-round color, protect homes from wind and snow, subtle fragrance, harborage for wildlife and a great backdrop to help show off ornamentals planted in front of them. Unfortunately, they are susceptible to several maladies.
It’s important to keep pines viable by providing good tree care for your customers, especially in two areas, separating trees from turf and proper planting procedures. These basic, but foundational factors are all-important and should always be a reference point when diagnosing tree maladies such as ones on pines.
Separation & Planting
Why are separation and planting so important? There are many reasons, but perhaps the most influential is that these are implementations that get a tree off to the best start possible if done correctly and mistakes that can’t be corrected if not.
Separation – This means designing or re-designing the landscape so that the trees are here and the turf is over there. Think about it. Trees are woody, while turf is herbaceous. Turf usually receives moderate to high volumes of water and fertilizer, and requires mowing. When trees are growing in a co-located landscape setting, they are usually over fertilized and over watered, and constantly run into with lawn mowing equipment; not a healthy environment.
Planting – Good planting practices include: digging a wide but shallow hole, pulling tangled roots apart, placing the root mass such that the uppermost lateral root is even with or slightly above grade, using existing/native soil instead of amended soil to backfill around roots, watering thoroughly to settle the roots, placing wood chip or pine needle mulch over the roots but not the bole and checking the soil moisture weekly to make sure that it’s moist but not soggy or dry. These are all important parts of the process. Way, way too many times trees are planted too deeply, in heavily amended soils, watered once and forgotten, covered with rock mulch and planter boxes built over the roots and more — these practices prevent tree success.
Diseases are not just biological — it’s both — pathogenic and abiotic causes that challenge the overall health of pines. Regular scouting, often referred to as monitoring will help identify possible concerns that are site related (mower blight, leaving stakes on too long, deep planting, over mulching, etc.) and ones that are caused by fungi, nematodes and bacteria. Inspection packages go a long way toward avoiding tree troubles.
Pine wilt — Perhaps the most destructive disease, pine wilt has the capacity to completely kill a tree within two years. If that wasn’t bad enough, even more frustrating to property owners is the deceiving nature of the disease. In most cases, a tree can be healthy looking in April and May, start looking a bit off-color in June, and be entirely brown by July. All pines can become infected, but most cases involve Scots or jack pine.
Pine wilt is similar to Dutch elm disease in that it is carried to the tree by an insect. The carrier for elms is the elm bark beetle. The culprit for pines is the pine sawyer beetle, which carries the actual killer, the pinewood nematode. Once infected, the sap flow throughout the tree declines rapidly, causing death. It typically affects trees that are more than 10 years old.
The pinewood nematode is transferred throughout the disease cycle in two phases. Phase one is relatively straightforward. The sawyer beetles feed on young shoots of healthy trees. Then, the nematodes that are in the bodies of the beetles enter the pine tree through feeding wounds in twigs. Once inside the tree, the nematodes multiply and clog the resin canals, which quickly results in tree death.
Phase two begins when the sawyer beetles lay their eggs in the bark of dead or dying trees. The larvae develop, bore inward and begin feeding on blue stain fungi that have been transmitted by bark beetles that were attracted to the dead trees. After feeding, the nematodes move to the sawyer beetle pupae and are eventually carried along when they develop into adult beetles, after which phase two is complete, and the process starts over again with phase one.
Various approaches have been examined to control pine wilt, including insecticide injections and topical protective sprays. A satisfactory degree of control can be achieved with an injection of abamectin, or Greyhound insecticide. The injection must be made before the onset of symptoms and will generally protect the tree for two growing seasons. Be sure to follow all label directions.
A moderate degree of control can be achieved in a stand of pines if infected pines are removed as soon as possible after the onset of symptoms. To be certain that the nematode is not transferred by the sawyer beetle, it is recommended to burn, bury or chip the logs of the infested tree. Using the trees for firewood is not prudent, as the beetles can continue to emerge from the logs over time.
Sphaeropsis tip blight — Formerly known as Diplodia tip blight, this disease causes the new shoots to die before extending fully. Of course, this is a serious outcome, because unlike deciduous trees, all future growth to sustain the tree comes from the apical meristem at the ends of the branches. If an insect, disease or adverse environmental condition causes an oak or beech tree terminal to die, new growth will sprout from lateral buds and can usually be directed to replace the damage. The long-needled pines, such as Austrian and ponderosa pine, are most susceptible.
The first recognizable symptom is a dotting of brown throughout the silhouette of the tree. Closer inspection reveals that the fungus has killed the new shoots. The disease can be further affirmed by pulling the needles loose from the killed shoot. If infected, they can be removed with a gentle tug. Look closely at the base of the removed needle; several small, black spores will be present if Sphaeropsis is involved. Secondly, inspect a cone from the damaged tree, either fallen or attached. Again, small, black spores are likely to be present on the outer scales of the cones. Trees that have been infected for several years are likely to contain several branches that are entirely dead.
Sphaeropsis blight can be controlled by applying cover sprays of copper sulfate, propaconazole and thiophanate-methyl in mid-spring. Thorough coverage of the needles is required. If the disease has heavily infected the tree, consider two applications of fungicide, applied two weeks apart.
Dothistroma needle blight — A disease that is equally as problematic in aesthetic terms as the first two maladies is Dothistroma needle blight. Infected trees often appear wind burned or scorched from extreme heat. All pines can become infected, but Scots and Austrian are most susceptible.
As the name would indicate, the symptoms begin with discoloration of the needles. The blighting takes two forms:
1. Small, olive brown to dark brown markings that extend the circumference of the needles, encircling them as if the needle was wearing a thin, flat wedding band.
2. Needles that are brown, starting in the middle and extending to the tip. Some needles are completely brown.
Because the disease does not typically kill the buds, it is generally less worrisome than pine wilt or Sphaeropsis tip blight. However, a pine depends on its needles to photosynthesize and send sugars and carbohydrates throughout the rest of the plant. The more brown needles that a tree has, the less chance it has to remain a healthy part of the landscape.
Control Dothistroma needle blight in much the same as for Sphaeropsis tip blight. Because the disease overwinters on old needles, thorough coverage is required to prevent the disease from spreading. Bordeaux mixture and copper sulfate can be used. Be sure to follow all label directions.
Common Abiotic Maladies:
Desiccation — The drying of needles and stems, usually in winter is caused by extended periods of strong winds and cold temperatures. In many situations, consideration given to this potential malady during landscape design can prevent desiccation.
Drought Stress — The lack of adequate moisture in the root system leads to wilting and drying of all tree tissues. Probing the soil and checking for moisture content on a regular basis will assist in managing drought stress. Irrigation equipment that provides a slow soaking is best.
Herbicide Injury — Commonly caused by air-borne drift or overzealous applications by lawn care applicators, symptoms often appear as a twisting of new growth or a burnt appearance to older needles. Herbicide injury is only controlled through prevention.
Overwatering — As described above, the lack of separation of turf and trees often leads to overwatering. The root zone soil should be moist, not soggy or dry.
Over mulched — If a little is good, then more is better, right? No so with mulch. Two inches of wood chips, beginning 3 inches away from the trunk and extending to the periphery of the canopy is best.
Surrounded By Pavement — The growing conditions should always be taken into account when considering maladies of trees. If surrounded by impervious surfaces such as asphalt or concrete, air exchange and moisture infiltration are severely limited.
Editor’s note: This article was originally published August 2008 and has been updated.