Most evergreens go year after year with little or no damage from insects. In nature, insects come and go and seldom have any long-lasting affect on the health of the plant. But in the home landscape, we aren't just interested in the health of our evergreens; their appearance is valuable too. Since evergreens hold the same foliage for several years, preventing or minimizing damage to their foliage seems more important than for deciduous plants. Concerns about chemicals and how they affect our environment and ourselves has changed our approach to controlling insects and diseases. Our heightened awareness has led to caution about applying chemicals and encouraged taking the time to understand the problem before choosing a plan of action. This planning involves several steps including prevention, detection, identification, evaluation and treatment options.
Prevention As the old adage says, an ounce of prevention is worth a pound of cure. Plants that are healthy are bothered less by insects. Not only are they infested less often, if they are infested, the damage is less severe. When a plant is plagued by problems, it is almost always an indication that the plant was already struggling. Knowing this helps us understand that we must treat the whole, not just the part showing symptoms. For the plant, this means being sure that its needs are being met. Whenever there is an insect problem, take a few minutes to evaluate whether or not the plant is getting adequate water, sun/shade or nutrition. Is the soil type right for that plant? Is the pH still correct? Is there too much root competition? Has there been any digging or construction nearby that might be compromising the plant's root system? Healthy plants that are getting all their needs met may still be bothered by insects on occasion, but the impact will be less than on an already stressed plant.
Detection If you suspect a problem with an evergreen, it is important to make sure it is an insect problem before doing anything about it. Look the plant over carefully.
Identification When you detect an insect problem, the specific insect should be identified if possible. This doesn't mean you need to know its scientific name. You may not even have to know exactly what type of aphid or sawfly you have. But it is important to know as much as you can about the pest so you can choose the best course of action. For instance, if you know it's sawfly larvae, and what the stage of development is, you can decide better if spraying will help or if they have just finished feeding and are ready to move on to another stage of their life.
Evaluation Once the culprit has been identified, the amount and type of damage it will do the evergreen can be evaluated. The damage of some insects is strictly cosmetic, affecting only the appearance of the plant. Other damage can affect the health of the plant. When you know what the pest is and understand what it does to a plant, an informed decision can be made as to how to approach the problem.
Treatment There is almost always more than one way to treat a problem and it helps to know the advantages and disadvantages of each alternative. Even when chemical treatments are the best answer, there are usually choices as to which to use.
What Bachman's Can Do For You Bring us a sample - in a sealed plastic bag, please! Bachman's employs knowledgeable horticulturists who are glad to help you diagnose an insect problem and advise you about alternatives for treatment. If one of our horticulturists is not available or unable to answer your questions, the sample will be passed along for another horticulturist to examine. Occasionally, even we are perplexed by a problem and we may refer you to a certified arborist or the University of Minnesota.
Below is a list of some of the more common insects associated with evergreens, along with a brief description of the pest, its preferred hosts and the damage it causes. If you need more information about any of these problems, please contact Bachman's, a certified arborist or the University of Minnesota. Check at our information desk for help with treatment alternatives.
Sawfly Larvae (Defoliating Insect) In early spring we often see sawfly larvae on pines, especially mughos. Then a few weeks later we see another type of sawfly larvae on spruce. The actual sawfly is a small, wasp-like insect that emerges from the soil very early in the spring and lays its eggs on the buds of its host. As the bud matures and expands, the eggs hatch into small, caterpillar-like larvae that then feed on the tender new growth. The larvae are almost all green/yellow and striped, maturing at about an inch long. Sawfly larvae feed in hordes and their damage can be done quickly. This damage is primarily cosmetic, but if it happens several years in a row, it can affect the health of the plant.
Spider mites (Sucking Insect) This is a serious pest of evergreens, especially during periods of hot, dry weather. Spider mites are most common on arborvitae and are occasional problems on pines, spruce and junipers. The insect itself is not readily visible. To check for spider mites, hold a piece of white paper under a twig and tap the twig hard. Look carefully at the piece of paper. If tiny specks begin to move, they are most likely spider mites. Anything big enough for you to identify as a spider is not the culprit. Spider mites feed on the foliage, leaving it looking rough and speckled. They can damage both the looks and the health of the plant.
Spruce Gall There is a type of aphid that injects its eggs into twigs on spruce. The injection sites then swell up and look a bit like a pineapple or a porcupine. Two types of this aphid exist. The Cooley spruce gall aphid attacks the tip of a shoot and the Eastern spruce gall aphid targets the base of the new shoot. While the gall is still green, the developing aphids are probably still inside. If the gall is brown, it is most likely empty. Spruce gall damage is primarily cosmetic but if it happens year after year, branching can be affected.
Scale (Sucking Insect) There are several types of scale that target evergreens. Scale are small sucking insects that form a protective shell over themselves during much of their lives. Some types of scale form on the needles, others on the buds or twigs. Scale will cause the foliage to look unhealthy or spotted or cause browning. Scale can damage a plant cosmetically and threaten its health.
Shoot Borers There are several types of burrowing insects that tunnel into the tender, young shoots of pines (and occasionally spruce) in our area. The larvae burrow in and the tunneling kills the shoot. Damage will appear as brown growth tips. It is important to confirm the source of the damage since similar damage can be caused by a disease. Shoot borers damage the plants cosmetically and can damage the branching and growth patterns.
There are several other insects that occasionally cause problems to evergreens in our area including: aphids, budworms, needleminers, zimmerman pine moth, white pine weevil, bark beetles and wood borers.
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