In the world of pine diseases, some are worse than others. Some, while causing the tree to take on an unattractive appearance, don’t do much damage other than preventing photosynthesis from occurring. In many cases, these cause more alarm from customers than the serious, highly infectious maladies.
On the other hand, some diseases are serious, and one in particular has proven to be almost always lethal. The keys to success in managing pine diseases are accurate identification of the causal agent, consideration of the severity of the infection, evaluation of the contributing factors within the landscape and, if justified, timely fungicide applications.
Effective control of pine diseases is much more likely to occur if trees are routinely inspected, rather than randomly or simply in response to customer inquiry. By the time most clients notice that something may be wrong with a particular tree, it’s highly likely that infection has already occurred, putting the tree care provider in a reactive rather than proactive situation.
Inspection, scouting, monitoring – do they all mean the same thing? Actually, they are different and the same. Inspection usually refers to a one time close examination of tree parts and the surrounding landscape for the presence of insects, diseases, odd symptoms or any significant change that may have occurred. Living and nonliving factors are part of an inspection. For the most part, the terms scouting and monitoring can be used interchangeably. Monitoring involves a series of regular inspections to detect early signs of pests and their damage. The primary goal is to detect, identify and describe pest infestations. All trees should be monitored on a regular basis during the growing season. The scouting interval may vary from once a week to once every several months, depending on the value of the trees to the customer and the nature of anticipated pest problems. Landscape monitoring can be delivered and invoiced for, replacing the number of pounds of insecticide or fungicide sprayed on a tree as your source of revenue.
Scouting and monitoring is important not only for your client’s property, but also for the early detection of potential pests in neighboring landscapes as well. If Zimmerman pine moth or Sphaeropsis tip blight are evident at the next door neighbor’s place, it would be wise to inform your client and suggest a management program to prevent damage to their trees. Diseases present in adjacent properties should be noted in the future problems section of an invoice to document the situation and keep it in the overall discussion.
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 meristems at the ends of the branches. If an insect, disease or adverse environmental condition causes a maple or linden 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 will easily 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.
Control Sphaeropsis blight by applying cover sprays of copper sulfate, propiconazole or thiophanate-methyl in midspring. Thorough coverage of the needles is required. If the disease has heavily infected the tree, consider two applications of fungicide, applied two weeks apart. Be sure to read and follow all label directions.
Dothistroma needle blight
While trees infected with dothistroma needle blight rarely die from the disease, they appear unsightly and are often weakened, resulting in infections from other maladies or damage from abiotic factors such as compacted soils, overwatering and competition. Infected trees often appear windburned 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: 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, and 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 a tree has, the less chance it has to remain a healthy part of the landscape.
Control Dothistroma needle blight in much the same way 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.
Brown spot and Lophodermium needlecast
These diseases are not caused by the same fungal organism; however, they carry many of the same symptoms and consequences of infection. Like Dothistroma, they produce “bar” or “band”-like signs and symptoms, beginning with small grayish brown spots bordered in yellow, and eventually covering the entire needle, causing it to fall off the tree, hence the name “needlecast” or a “casting of the needle.” Infection is more noticeable on older needles and generally begins on lower branches and moves upward in the tree canopy over time. The short-needled pines, especially red and Scots, are commonly affected. In severe situations, only the current season’s needles remain on the tree after infection. Typically, at least one year’s set of infected needles remains behind the current mostly unaffected needles.
The key to distinguishing between infections of brown spot and Lophodermium is the point in the growing season when symptoms are observed. Brown spot infected needles turn brown in the fall, while Lophodermium infections cause browning in the springtime. This underscores the importance of frequent inspection. The difference in life cycle of these diseases directly affects optimal timing of fungicidal spray applications. Brown spot infected trees should be sprayed in the spring when the new needles are half grown. On heavily infected or highly valuable trees, a second application three weeks later is appropriate. Chlorothalonil, liquid coppers and mancozeb products are recommended. Beginning in late summer, spray applications of chlorothalonil should be made to control Lophodermium infections and repeated every two to three weeks.
Pine wilt disease
This pine disease is caused by the pinewood nematode, which is moved from infested to noninfested pine trees by the pine sawyer beetle. The disease typically kills Scots pines within a few months after the pine sawyer beetle introduces the nematode to the tree. The needles of infested trees turn from grayish green to tan and finally brown. While primarily a disease of Scots pine, pine wilt can also occur in Austrian, jack and mugo pines with a similar pattern of symptoms.
Sanitation is the most important management practice to prevent or slow the spread of pine wilt disease. Pines dying from the disease should be cut down, and then burned, buried or chipped before pine sawyer beetles can emerge from the trees. High-value pines can be protected with trunk injections of the insecticide/nematicide abamectin.
Pine tree diseases can be among the most difficult to diagnose, second only to spruce and fir in terms of ambiguity. Adding to the difficulty in diagnosis is the presence of confounding or look-alike maladies such as root girdling, staking constrictions and insects like Zimmerman pine moth larvae. Success in sorting out the actual causal agent with inspection/monitoring/scouting is found to increase one’s knowledge of the telltale signs and symptoms of each pest as well as utilizing a good listening ear to pick up on comments the client may make that may otherwise be disregarded as fluff.