Pines are unique. If you’ve worked on a Christmas tree farm or an evergreen production nursery, you probably have a good sense of their growth habits and features.
So what’s special about pines? They produce their own mulch, have 12-month foliage and don’t require much in the way of nutrition or pruning. Most species produce a pretty dense canopy, which gives them an advantage when it comes to competing with turf for sun, nutrients and water in a landscape, especially as they age.
My advice: Get to know pines up close and personal to gain some insights. Look at the trunk, follow the branches as they extend from trunk to the periphery, observe the inner growth — or lack thereof, note the average length of the needles and buds, try to find the various stages of pine cone development from flower to full-sized cone — most take three years to fully develop. After all, the more you know about a particular type of tree, the easier it is to figure out what might be wrong with it.
Consequences of damage
If you get to know specific features of a pine, it’s easier to fully appreciate the consequences of damage. If the needles are damaged from insects, diseases or abiotic causes, sure, the health and vigor of the tree can be reduced, but the greater impact can be imparted when the buds — which will produce new growth during the following year — are injured. Why? In general, pines do not produce much in the way of secondary growth as compared with deciduous trees, such as maple, crepe myrtle and oak. Pines only grow from the terminal ends of branches. For example, if an Austrian pine is infected with dothistroma needle blight, causing a disfigured appearance and needle droppage, the tree usually will become weaker, but survive until the following year and regain vigor as a result of new growth from the ends of the branches. But if a causal agent such as pine tip moth killed the terminal bud(s), new growth is unlikely to occur to replace it, and severe damage would result. Generally, trees recover from tip damage with the help of adjacent terminal buds that have not been damaged, as growth eventually extends and fills the void left by damaged tips.
In some cases, tip damage is not that straightforward. If it occurs in early or mid-season, and not to the entire new shoot, then embedded buds that are not visible at first glance may begin to grow and replace the terminal growth. Insects that damage a small part of the tip, birds and wind are natural causal agents of this growth response. Homeowners who prune new shoots to keep trees a certain shape and size, such as when a tree is close to a driveway or sidewalk, also can cause this to occur. Christmas tree growers do this, too — injuring the terminal stems every year by purposely cutting the new growth in half soon after it has finished extending to its full length. The result is a release of terminal dominance and subsequent growth of several side buds that fill in small voids between branches, producing the desired thickened exterior periphery.
In short, unless they are damaged, pines do not produce secondary growth; they grow only at the tips. The needles stay on a tree for two to five years, and then drop off forever. As such, damaged stems, buds and needles are of great consequence to the overall health and vigor of the tree.
The heart of the issue with pines is the process of diagnosis. Right off the top, at least a dozen possible causes must be considered. If a tree receives care only when it looks “bad,” diagnosis is reactive, lacks information about recent influential events and proves more difficult. If this is the routine in which you find yourself, it’s helpful to gather information about the history of the tree; neighbors and past property managers might be helpful. Ask about pesticide applications, construction activities in the area and watering habits of the homeowner/caretaker. A regular scouting/monitoring program will mean more complete information can be considered in the diagnosis. As well, a “freebie” consultation in exchange for a tree-fix job is replaced with a more profitable cost center, characterized by a set of routine inspections on a regular basis.
The progression of diagnosis itself can be started at least a couple of ways — “process of elimination” or “all things considered.” Really, neither is wrong; it depends more on the diagnostician’s level of comfort. The elimination procedure should begin with known problems for each species of pine, attempting to match up symptoms from experience and training with the appearance of the tree’s individual features. I’ve found that the more classic symptoms that can be matched, the better this process works.
The other way to go is more holistic, considering “universal” issues such as root girdling, slope, drought, compaction, wet soils, over-mulching, under-mulching, soil oxygen, planting errors, etc., equally along with the known insect and diseases.
As the diagnosis progresses, it’s important to note that commonly more than one causal agent is responsible for a tree’s appearance or lack of health and vigor. Both approaches are preferable to the random guessing in which some newly hired and/or inexperienced tree workers engage.
Stocking the tool kit
Whether it’s creating a document or changing the oil in your truck, tools are required. The same is true for monitoring pine maladies. Fortunately, most of these tools are inexpensive and not many are required. A simple tool kit should be set up for every service vehicle. In addition to ropes, saddles and other equipment required for climbing, smaller items such as a hand lens, fishing knife, screwdriver, binoculars and baby food jars for collection are helpful. A note pad and pen or electronic tablet should be included for note taking. An insect identification book would be a good inclusion as well.
Common pine problems
Dothistroma needle blight: I’ve always referred to this one as the “wedding ring” disease, in that one of the common symptoms is the presence of several tan to brown lesions that cross and surround the needle in several locations. In advanced cases, the browning extends to the end of the needle. Though this disease may make the tree unsightly, only severe infections that occur year after year are life-threatening. Cover sprays in mid-spring usually will interrupt the disease cycle.
Diplodia tip blight: Also referred to as sphaeropsis tip blight, this disease is more potentially damaging than dothistroma, as it kills the new shoots needed for the growth and development of existing stems and to fill in voids left by damage to others. Terminal shoots that appear to have died during expansion — usually a third of the size of unaffected shoots — and black dots (pycnidia) on the bottom of the cones are clues that diplodia is present.
Pine needle scale: Scales are tiny insects covered with a waxy coating; in this case, a white shell with a brown head. During most of the year, pine needle scales shield nymphs from predators and weather events, but are vulnerable and easy to control in mid-spring when nymphs hatch from eggs and crawl out looking for a suitable site to establish residency. During this roughly two-week period, many insecticides will control the scales. Horticulture oils and insecticidal soaps are particularly effective. Using a magnifying hand lens will help determine when the crawler stage begins.
Zimmerman pine moth: This pest causes damage when the larvae colonize the vascular system of the tree. First noticeable by the presence of white to light-pink globs of pitch in the tree crotches, Zimmerman pine moth is particularly damaging due to the interruption of the flow of water and nutrients. The pitch masses usually occur on the underside of the junction of the branches and the trunk in the branch collar area. Bark spray applications in early spring and late summer offer effective control.
Pine wilt: Pine wilt could be renamed “sudden pine disease,” in that trees often show few symptoms in spring, then, as the season progresses, the foliage exhibits a progressively lighter color. Pine wilt has a complex life cycle, involving feeding by pine sawyer beetles, the exit of pine wilt nematodes from their bodies, the entry of the nematodes through the feeding wounds and eventual clogging of cambial tissues, causing quick decline in health and vigor. Pine wilt is common on Scotch and jack pine; as such, identification of the pine species is helpful in diagnosis. Removal of affected trees is the recommended control method in most cases.
Pine tip moth: Another pest that affects the new shoots of pines is the pine tip moth. In the case of the southwestern pine tip moth, larval-stage feeding damages new growth after emergence from eggs laid in early spring. The tiny larvae bore into the fresh young tissues and, as they grow and develop, cause pine tips to die back beyond the feeding sites. Other species such as the common tip moth cause similar damage in mid-summer. The key to control is watching for damage to the shoots and inspecting for the presence of boring insects when symptoms are present. Cover sprays prior to boring activity are effective for control.
Read more: 6 Pine Problems and How to Identify Them