IPM Basics for Christmas Trees

The aim of this article is to help Christmas growers combat their pest problems
by using integrated pest management (IPM) methods.
IPM Basics for Christmas Trees - Articles
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IPM Basics for Christmas Trees

Christmas Tree Farm in Schuylkill County, PA.

Integrated Pest Management Basics

Christmas tree growers everywhere face obstacles to growing healthy trees. Perhaps the largest challenge is controlling the pests that feed on and live off of conifers. The aim of this information is to help growers combat their pest problems by using integrated pest management (IPM) methods. IPM is a multilayered approach to keeping pests and pest damage to a minimal level with the smallest cost to health, environment, and budget.

IPM attempts to improve on some of the common problems with traditional Christmas tree pest control. One problem is improper timing of pesticides. Traditionally, growers may use two unsuccessful timing methods: calendar spraying and reaction spraying. Calendar spraying is making pesticide applications at the same time every year regardless of the actual pest situation. Reaction spraying is making a spray immediately upon discovery of a pest problem. Both of these methods are generally incorrect because they may not coincide with the target pest’s vulnerable life stage.

Another problem IPM attempts to correct is the overuse of broad-spectrum, or nonspecific, pesticides. Broad-spectrum pesticides kill a wide range of insects, not just the target pests. Beneficial insects that help keep pest populations in check may be eliminated by these harsh pesticides. If spray timing is not correct, growers may make multiple broad-spectrum applications and possibly still not get control. Using the steps of IPM addressed on the following pages, growers should be able to implement safer, more effective pest control.

IPM Basics: Step 1. Preparing for IPM - Planning and Prevention

IPM practices are generally aimed at an established crop, but some pest prevention can occur before the crop is even planted. Most growers know what species they intend to grow at their location. However, since a tree grown in a suitable location is a good defense against pests, consider the following points before planting:

  • Property assessment. Identifying the challenges to growing trees on a property will help growers determine the best locations for tree blocks. Assessing the property may include collecting and testing soil samples, surveying property slope and topography, and determining water drainage rates and sunlight levels. Historical meteorological information and knowledge of past crops can be useful. Talking to area growers about possible pest problems (insect, mite, disease, mammal, etc.) to expect would also be beneficial.
  • Tree species. Selecting tree species best suited to the property is the next step. This will involve research and may mean that the site is not appropriate for the intended species. By using printed publications, Web resources, and information from other growers and seedling nurseries, growers can predict the success of the intended crop. For instance, knowing that Colorado blue spruce may grow best in a fl at, sometimes wet field can help a grower decide not to plant Fraser fir, which could be susceptible to root rot issues in this same location.
  • Seed source. In addition to choosing tree species, growers may have options for the seedlings based on seed source. Seed sources generally refer to different geographical regions where the trees grow naturally. The trees resulting from these seeds may be adapted to certain growing conditions or may show some pest resistance in addition to foliage and growth attributes. Growers selecting seedlings from a particular seed source for its pest resistance need to understand that resistance characteristics may change when the tree is grown outside its natural range.
  • Planting. The success of a tree block has a lot to do with proper planting of seedlings and transplants. Consider the following factors when planting:
    — Spacing. Adequate spacing between the trees will provide good air circulation, which can prevent disease development and allow for good spray coverage during pesticide applications. Other factors to consider when spacing trees are the minimum requirements for mowing, harvesting, and shearing equipment. A spacing of 5½ feet by 5½ feet or 6 feet by 6 feet will allow for fewer trees than a spacing of 4 feet by 4 feet, but the trees with wider spacing will be healthier through harvest time. Spacing needs will vary depending on the final desired age of the trees in a block.
    — Depth. The depth at which seedlings are planted will greatly affect tree health. Planting trees so that the root collar is at or just slightly below the soil line and not planted too deep or too shallow will be a factor in preventing pest attack.
    — Method. Some planting methods are more prone to future problems. Mechanical planters may encourage J-rooting. In this situation, roots do not spread out but actually grow in a “J” shape (Figure 1). As a result, trees are unable to establish a good root system, which after several years will lead to poor tree health. J-rooted trees are also more susceptible to insect and disease problems.

Figure 1. J-rooted tree resulting from improper planting. Courtesy of Tracey Olson, PDA

IPM Basics: Step 2. Identification and Understanding of Pests and Problems

After the Christmas tree block is planted, the focus of an IPM approach will be on preventing losses due to pest damage. The term “pest” may include any organism— diseases, insects, mites, nematodes, mammals, birds, or weeds—that is detrimental to the health of the tree. Environmental factors such as air pollution may also cause damage. Knowing which pest or what factor is causing damage to a tree is essential to finding a means of stopping or controlling that problem.

Insects and Mites

The largest groups of Christmas tree pests are two classes of arthropod pests, or organisms with jointed body parts and an exoskeleton. These two classes are the insects and the arachnids. Arachnids include mites, spiders, and ticks, but only the mites can be detrimental to tree health. Experienced growers are familiar with the insect and mite pests that may affect their trees. They have, or know where to find, information about the life cycle and habits of these pests in order to determine the best method and timing for both detection and control, if necessary (Figure 2).

Figure 2. Balsam twig aphid life cycle. Courtesy of Sarah Pickel, PDA (photos courtesy of PDA)

For example, spider mites (Figure 3) and (eriophyid) rust mites feed openly on tree foliage without any extra protection. It is easier to control these pests than one that spends most of its life covered by a protective coating, such as pine needle scale. In addition to the mites, pests that feed openly include aphids, gypsy moths, and sawflies.

Figure 3. Spruce spider mite feeding openly on tree foliage. Courtesy of Rayanne D. Lehman, PDA

The larger group of insect and mite pests includes those that are only exposed for a short time during their life cycle. Timing sprays to target susceptible life stages is critical for effective control. Pests that fall into this category include all the scale insects, most adelgids, bagworm (Figure 4), weevils, bark beetles, and midges.

Figure 4. Protective casing containing bagworms. Courtesy of Rayanne D. Lehman, PDA

Knowing these and other insects is essential for growers to protect their trees from pest infestation. In addition, recognizing which insects and mites are beneficial and taking steps to avoid killing these organisms can limit or even eliminate the need for chemical control measures.

Stinging insects, such as wasps and bees, are also a major concern on Christmas tree farms, especially during summer mowing and field maintenance. These insects are frequently attracted to trees infested with aphids and scale insects. Recognizing both the pest and the stinging insects and understanding their biology are important when considering employee safety.

Diseases (Fungi and Nematodes)

Numerous diseases of Christmas trees are caused by fungi and nematodes, with the majority being caused by fungi. Fungi are simple organisms that survive in soil, water, and dead or living organic material. Cool temperatures, high moisture, and low air circulation will encourage fungal development. In Christmas tree plantations, these factors often occur together, making disease development common. Symptoms include swelling or shrinking of the wood tissue, discolored or deformed needles, early needle drop, and wilted foliage. The disease types are referred to as cankers, galls, needle casts, rusts, rots, and blights.

Fungal diseases spread from tree to tree by microscopic spores. At a specific stage in disease development, mature fruiting bodies on the diseased host release the spores. Wind, rain, or other physical contact will spread these spores to other trees, initiating a new disease cycle. Growers should be aware of the diseases that may affect their trees and have an understanding of the symptoms (Figures 5 and 6).

Figure 5. Rhabdocline needle cast symptoms on Douglas-fir. Courtesy of Rayanne D. Lehman, PDA

Figure 6. Reddish-brown splotches, symptoms of Rhabdocline, found in late winter. Courtesy of Tracey Olson, PDA

Unlike the insect and mite pests, diseases are not usually controlled—they are prevented. Fungicides will not kill the fungus but only protect the plant tissue from infection. Therefore, most fungicides must be applied before spores would contact the healthy tissue.

Less common are the diseases caused by nematodes. Nematodes are microscopic, simple worms. They damage plants by sucking out the contents of plant cells. In the case of pine wilt disease, a wood-boring beetle transfers nematodes to the tree.

Vertebrates (Mammals and Birds)

Vertebrates are animals with backbones. The vertebrates of concern for Christmas trees are birds and mammals, especially deer and rodents. Birds may damage tree leaders by perching on the tender growth, resulting in broken or bent leaders. Deer may severely damage shoot tips by feeding on them. Bucks can also cause injury by rubbing their antlers on the main trunk (Figure 7). Rodents may kill trees by girdling the lower trunk as they feed on the bark.

Figure 7. Buck rub on a young fir. Courtesy of Rayanne D. Lehman, PDA

Weeds

Weeds are undesirable plants that interfere with the growth of a crop such as Christmas trees. Generally herbaceous, they reproduce and spread through seeds and rhizomes (underground stems). Weeds compete with trees for soil nutrients, water, and sunlight (Figure 8). They inhibit good air circulation between trees—a contributing factor for disease development. Weeds also hinder the movement of people and equipment through and between rows, making good pesticide coverage difficult. Through good mowing practices and the assistance of herbicides, growers can control weeds to a manageable level.

Figure 8. Common milkweed, a familiar nursery weed in the Mid-Atlantic and Northeast United States. Courtesy of Theodore Webster, USDA Agricultural Research Service, Bugwood.org (#1552251)

Weed control will not be covered in this manual. Information on weeds can be found in the Penn State publication Controlling Weeds in Nursery and Landscape Plantings by Dr. Larry Kuhns. Growers can also look to their state land-grant universities for additional weed resources.

Environmental Factors

Injury to Christmas trees is not solely a result of living organisms. Environmental factors can also have a negative effect. Damage from severe weather can be equally as bad or worse than a disease or insect problem. Extreme cold, wind, or hail (Figure 9) can cause needle discoloration, shoot dieback, or lesions on stems and twigs. Some unnatural environmental factors also exist. Pesticides and fertilizers applied at the wrong time of year or in the wrong amounts will also damage the trees. Air pollution, although hard to identify, may also harm trees.

Figure 9. Hail damage on eastern white pine. Courtesy of Rayanne D. Lehman, PDA

IPM Basics: Step 3. Monitoring Trees for Pest Populations

Monitoring is the key to any successful IPM plan. On farms not using IPM, the process of pest control usually involves pesticide applications based on a calendar date. These types of applications are made regardless of the verified presence of the target pest. Another type of pesticide application on farms not using IPM is the “see and spray” method: spray only when the pest or damage is seen. At times, applications are made based only on damage, not on actual pest presence. IPM looks at pest management differently. Monitoring to determine whether there is a need to take action is more effective than either of the methods above.

Figure 10. Scout conducting his weekly activities. Courtesy of Cathy Thomas, PDA

Monitoring provides growers with an accurate picture of pest situations on their Christmas tree farms. Monitoring includes the use of traps that catch pests to indicate their presence as well as direct observation by a scout. The process involves regular, close inspection of the trees on the farm for symptoms or signs of pest activity (Figure 10). “Symptoms” refer to the damage or evidence of activity, such as yellowed needles or wilted shoots; “signs” refer to the actual organism causing the damage, such as black fruiting bodies on the underside of a needle or a bagworm case hanging from a branch. By inspecting for these symptoms and signs, noting the stage of development, and evaluating the level of infestation or infection, growers can create an individualized, accurate, and timely plan of action for each field. Monitoring can be done by a farm employee whose time is committed to scouting activity or by a professional scout hired as a consultant. The key is to scout regularly, not just once or twice a season.

Growing Degree Days/Temperature

One method of monitoring specific pest populations is growing degree day (GDD) tracking. For insects, mites, and plants, development is influenced by daily heat accumulations from ambient air. (Disease progression is based on other factors such as host plant development, humidity, leaf wetting, etc.; therefore, the GDD method does not apply.) Tracking heat accumulation by monitoring daily air temperatures has proved useful in predicting the appearance of certain pest life stages.

The growing degree day method uses the daily average temperature (using low and high temperatures for 24 hours) to determine the heat unit exposure of the pest or plant. The GDDs accumulate daily until the required amount of heat for an event (hatch, emergence, pupation, etc.) is reached. This is not a specific number, but a range. For instance, spruce spider mite overwintering eggs begin to hatch around 50–121 GDDs. A scout can effectively monitor for a pest by knowing the range of GDDs for the target stage of each pest. Known GDD ranges for many Christmas tree pests can be found in the Growing Degree Days Chart on page 18 and on each individual pest fact sheet.

As a general rule, GDD recording should begin on March 1. Although each organism has a unique base temperature, most GDD calculations use a base temperature of 50°F. The base temperature is the minimum temperature required by an organism for development to proceed. Temperature should be tracked using a minimum (low)/maximum (high) thermometer capable of storing readings for several days. After calculating each day’s GDD value, add it to the accumulated total. Never include negative numbers.

GDD Formula

(Low Temperature + High Temperature)/2 – 50°F = Daily GDD Average temperature (for a 24-hour period), (Base temperature)

Daily Weather Log

DateTimeAir Temp. LowAir Temp. HighAir Temp. AverageDaily GDDGDD Running Total
3/245:30 pm45°F73°F59°F99
3/255:30 pm35°F55°F45°F09
3/265:30 pm46°F60°F53°F312

March 24 (45 + 73)/2 = 118/2 = 59 – 50 = 9 GDD Count positive number.

March 25 (35 + 55)/2 = 90/2 = 45 – 50 = -5 GDD Do not add negative numbers.

March 26 (46 + 60)/2 = 106/2 = 53 – 50 = 3 GDD Add positive number

Remember that temperatures may differ in different blocks. A tree block on a southfacing slope will experience higher temperatures than a block on a north-facing slope, which can result in several day differences in pest development.

Figure 11. A minimum/maximum thermometer collecting temperature data in a field. Courtesy of Cathy Thomas, PDA

Using minimum/maximum thermometers (Figure 11) is the least expensive method of gathering data to calculate GDDs. Several other types of equipment will gather GDD in the field. These are commonly called biophenometers, data loggers, or weather monitors. The prices vary, but they are generally more expensive than a simple minimum/maximum thermometer. Weather services, both paid and free, can also provide required data. Skybit is a subscriber-based service located in Pennsylvania. The National Weather Service (NOAA) provides daily low and high temperatures from weather stations. NOAA data will not be specifi c to your area and should not replace on-farm temperature collection.

Soil Temperature

Research conducted in Pennsylvania on white pine weevil (Pissodes strobi) has shown that collection of soil temperatures is equally or more effective than GDD in determining the weevil’s spring emergence time. Temperatures were taken with a probe thermometer from soil beneath a tree in the target block. The probe was inserted to a depth of 2 inches on the sunny side of the tree (Figure 12). Once the soil temperature reached 50°F, weevils could be found in traps and on tree leaders. This method may also be effective on other insects that overwinter in soil.

Figure 12. A probe thermometer measuring soil temperature at a depth of approximately 2 inches. Courtesy of Cathy Thomas, PDA

Personal Monitoring Kit

When monitoring, a scout must have a few very important tools. Keep these tools together in a backpack or bag for convenient transport to the field on each visit (Figure 13).

Figure 13. Scouting tools and convenient zipper pack for storage. Courtesy of Brian Schildt, PDA

Hand Lens

This small magnifier allows a scout to see insects, mites, and fungal fruiting bodies that would otherwise be too small to see (Figure 14). These can be purchased in magnification strengths of 10X, 15X, and 20X. The 15X hand lens is a good strength to use and still has a reasonably sized field of view (see Appendix K for supplier information).

Figure 14. The number one tool for a scout: a hand lens. Courtesy of Tracey Olson, PDA

Notebook and Pen

Use these to record symptoms, signs, population stage and level, damage severity, field or weather conditions, and location. This information can be a reference for the current season as well as a resource that shows pest activity from previous seasons. Suggested forms for scouting observations and notes are included in the Appendix section of this manual.

Flagging Tape

Use brightly colored flagging tape to mark symptomatic trees so they can be readily located at a later date. Use a permanent marker to record specific information on the tape. Remember to use a color other than those used for digging or cutting purposes.

Clipboard/flat surface

Hold a clipboard or another flat surface under a branch to collect mites, aphids, or other insects dislodged by tapping the branch (Figure 15). The back of a clipboard that has been painted to have one half black and one half white is very useful when beating trees to detect pests. The inside back cover of this manual is a good flat surface to use.

Figure 15. Tapping branches over a white notebook or flat surface to dislodge and observe pests. Courtesy of Brian Schildt, PDA

Pruners/ Pocket Knife

Growers may need to clip symptomatic twigs or branches to observe them more closely for signs of insects, mites, or disease spores. Collecting samples for identification by a diagnostic expert (Figure 16) may also be necessary.

Figure 16. A good set of pruners. Courtesy of Joseph O’Brien, USDA Forest Service, Bugwood
.org (#5044044)

Bottles/plastic bags

Occasionally, growers need to collect samples to examine at a later date or send to a diagnostic laboratory. In addition to bottles and plastic bags for collecting samples, having a method of labeling the specimens (permanent marker, adhesive labels, etc.) is also helpful. Any sample collected in alcohol should be labeled with a pencil-written tag inserted into the vial.

Monitoring Tips

  1. During the growing season, a scout should be monitoring fields weekly to look for evidence of pests, diseases, and other problems.
  2. If possible, scout on cloudy days. The muted sunlight makes it easier to observe chlorotic, or yellowed, symptoms in the field. Some pests are also more visible in subdued light.
  3. When monitoring blocks for problems, scouts should walk through the field while keeping an eye out for obvious problems. They should also select non-symptomatic trees in a random pattern to inspect more closely. For these trees, be sure to look at the inside for discoloration.
  4. Prune a few twigs from the interior and lower portion of the tree for closer inspection.
  5. Tapping branches over a fl at surface will dislodge insects and mites, making them easier to see (use the tapping sheet at the back of this manual).

Trapping

Several types of insects can be monitored using traps. The traps are usually baited with pheromones (insect-produced attractants) or other chemicals (Figure 17) and placed in the field. They are designed to hold the insect until the trap can be checked by a scout. When monitored regularly, the collection data can help with the timing of control applications. Traps are used for monitoring purposes, not control. For more information on trapping, see Appendix E.

Figure 17. White pine weevil trap. Courtesy of Cathy Thomas, PDA

Sticky cards are another type of monitoring tool used to trap insects. These adhesive-coated index cards, which come in various sizes and colors, may be used to monitor the emergence of small pests (Figure 18). For example, in the case of some scale insect pests, 3-by-5-inch sticky cards are used to attract the adult male life stage. The cards are attached with clothespins to scale-infected tree limbs before the expected time of emergence. Cards can then be monitored regularly.

Figure 18. Yellow sticky cards used to trap flying adult male scales. Courtesy of Cathy Thomas, PDA

Diagnosis

Proper identification of the pests that have been found through the monitoring process is an important next step in the pest management process. With training, experience, and the use of printed and Web resources and guides, growers or scouts can usually make an accurate diagnosis. For difficult samples, consult an expert or a diagnostic lab. Regional inspectors for the state department of agriculture and county extension educators can be very helpful in obtaining necessary expert assistance. For contact information for select agencies, see Appendix K.

IPM Basics: Step 4. Setting an Action Threshold

The action or control threshold refers to the population level for a specific pest at which some control measure is justified in order to avoid economic loss or aesthetic damage to a crop. Christmas trees can sustain some damage and still be aesthetically acceptable to consumers. However, when the damage becomes unacceptable, the crop has passed what is known as the aesthetic injury level. The action threshold will be exceeded before the aesthetic injury level has been reached.

Because pests vary in the severity of damage they cause, action thresholds will also vary. A pest that has great potential to damage or disfigure a tree, such as white pine weevil, will have a lower threshold than a more minor pest, such as the balsam twig aphid, for which some damage may be acceptable. Action thresholds are further discussed in the individual fact sheets found in this manual.

The question of acceptable action thresholds will also vary depending on how the trees are marketed. If trees are sold as nursery stock, often referred to as balled-and-burlapped (B&B) trees for the way they are dug and bound, then the issue of threshold is no longer solely determined by the grower. All nursery stock in Pennsylvania is subject to state regulation, and the level of pest tolerance for the trees is based on a regulatory threshold. These regulatory thresholds are enforced by state or federal nursery inspectors. Some of these thresholds, such as those for pests under state or federal quarantines, are zero tolerance. Cut Christmas trees in Pennsylvania are not subject to regulation. However, if trees are to be shipped out of state, federal quarantines will be enforced.

Growers need to be aware of these regulatory issues when considering control actions on their farms. More information on state regulatory requirements can be found in the Conifer Certification and Quarantine Guidelines section.

IPM Basics: Step 5. Selecting Control Options

IPM does not usually rely on only one method or tactic. Often, growers employ a combination of methods to achieve a well-rounded, long-lasting management program.

Cultural and Mechanical Control

Best growing practices and physical methods of control are often the first defense to pest issues and can be the least expensive. Examples of these controls include:

• Mowing. Through consistent management of grasses and weeds by mowing, growers are able to facilitate good air circulation through tree blocks. Good air circulation helps prevent disease development and opens the lower portion of the trees to receive chemical applications, if necessary.

• Pruning. In addition to shaping trees, pruning can also help eliminate some pest issues. Pruning is one way to help eliminate the galls produced by adelgids or needles infested with needle midges. Growers may eliminate some of the feeding damage produced by balsam twig aphids, bagworm, or pine sawflies. Also, clipping out leaders infected by white pine weevil is an effective management method. Butt-pruning, or the removal of the lowest whorl of branches, opens the bottom of the tree to provide better air circulation, weed control, and pesticide application. It also permits heating of the soil and may make the area less attractive to certain insect and rodent pests.

• Culling. This is the practice of removing weakened, infected, and dying trees from the fields. Eliminating these reservoirs from the fields not only removes a source of infestation but will also allow for better air circulation among the remaining trees. It is an effective, low-cost method for reducing a recently introduced pest that has the potential to cause serious damage.

Biological Control

Biological control, or biocontrol, is the use of living organisms (parasitoids, pathogens, predators) to control diseases, insect pests, and weeds (Figure 19). Biocontrol plays an important role in IPM but does not define it. Many IPM techniques are geared toward enhancing or preserving biocontrols. A successful IPM program combines many methods aimed at keeping pest populations below damaging levels.

Figure 19. A praying mantis, a generalist predator. Courtesy of Cathy Thomas, PDA

In Christmas trees, no biocontrol agents exist for disease, and those for weed control are poorly understood. But numerous naturally occurring parasitoids, pathogens, and predators of insects and mites are present (Figure 20). Growers are often not aware of these natural enemies and continue to rely on insecticides to control pests. Excessive pesticide use may eliminate natural enemies, further increasing reliance on pesticides. The goal of a good IPM program is to recognize and preserve these biocontrol agents. The benefit is often a reduction of pesticides and costs.

Figure 20. Multicolored Asian lady beetle larva, an aphid predator. Courtesy of Cathy Thomas, PDA

In order for natural enemies to survive, they must not be 100 percent efficient. A small number of pests are always needed to keep the natural enemies around. Because the pests are not eliminated, biocontrol is not as popular when dealing with a crop such as Christmas trees where aesthetics can be important. However, biocontrol agents are extremely useful if dealing with a pest that either has a high threshold of damage or can be tolerated in a low-level population for a long time.

Not all pests are suitable for biocontrol. Borers, for instance, must be treated as soon as they are detected. White pine weevil has very few natural enemies, and none are known for pine root collar weevil. Some pests, such as aphids and mites, are easier to keep in check with natural enemies, but this is only applicable if regular scouting is used to monitor both the pest and beneficial populations. By monitoring, growers can take action if the pest populations are not being kept in check by their natural enemies.

Some research has been done with insect-pathogenic nematodes that grow in the bodies of their hosts (e.g., beetle larvae), eventually killing them. Neoaplectena carpocapsae (Weiser) has been extensively studied and tested, and Heterorhabditis heliothidis is receiving attention. In order for the nematode to do its job, it must occur with a bacterium since neither can survive alone. Sometimes the nematode-bacterium is not as effective as an insecticide, but that depends on the situation. The most critical factor restricting wide use of insect-pathogenic nematodes is overcoming nematode environmental sensitivity. Nematode success is greatest when moisture and temperature are at the optimum level for that location. Active research continues at universities and in private industries to increase the effectiveness of insect-pathogenic nematodes and make them a more cost-effective tool.

Chemical Control

When biocontrols are not suitable, not working as they should, or overwhelmed by a pest outbreak, chemical control is the next step. “Soft” or “reduced-risk” pesticides, such as insecticidal soap, ultra-fine horticultural oil, and neem compounds, are used for treating outbreaks that happen while managing with biocontrols. Consult with the biocontrol distributor before spraying to ensure compatibility.

The best control plan treats the pest populations with minimal disruption to the natural enemies. This can be accomplished several ways, including alternating insecticide classes, altering spray timing, or adjusting cultural practices. Another approach is to use soft insecticides that are not harmful to beneficial insects. Horticultural oils are effective in killing overwintering eggs and sessile insects but do little harm to natural enemies. Caterpillars, but not sawfly larvae, can be controlled with the bacterial insecticide Bacillus thuringiensis, or Bt. Some pest-specific insect growth regulators (IGRs) are also effective. There are three general types of chemical control: biorational, horticultural oil, and traditional.

Biorationals

As pesticide regulations increase and the general public gains awareness of pesticides used on Christmas tree farms, more attention is directed toward alternatives. Alternatives, otherwise known as biorational products, include insecticidal soap, pyrethrum, and rotenone (not an oil).

Insecticidal Soap
The insecticidal action results when fatty acids from plant oils are combined with the potassium bases to produce potassium salts of fatty acids. The inactive ingredients are water and alcohol.

Advantages:

  1. The mode of action (MOA) of insecticidal soap is physical, so pests are less likely to develop resistance. Soap acts on contact, penetrating body and cell membranes and causing quick death.
  2. Insecticidal soap has very few long-term negative effects on beneficial insects.
  3. Insecticidal soap is relatively nontoxic to wildlife and humans.
  4. It can be applied using a variety of application equipment, and disposal of unused material and containers is easy.

Disadvantages:

  1. The main drawback of using insecticidal soap is the lack of residual activity; therefore, more frequent applications are required.
  2. The effectiveness of insecticidal soap decreases when mixed with hard water.
  3. Soap will kill natural enemies on contact when plant surfaces are wet.

Neem Seed Extracts
Neem seed extracts are botanical or plant-derived pesticides. Neem oil extracts are from seeds of the neem or margosa tree (native to Asia). Azadirachtin, one of the active ingredients in neem oil, has growth-regulating properties. Neem oil has more than 12 other active ingredients that act as egg-laying deterrents, feeding inhibitors, growth regulators, repellents, sterilizing agents, or toxins.

Advantage:

  1. Various neem products affect more than 170 species of insects, mites, and nematodes that infest households, humans, livestock, plants, and stored products.

Disadvantages:

  1. The raw neem oil has an unpleasant garlic-sulfur smell, which is often eliminated in commercial production.
  2. Natural enemies of plant pests are slightly affected by these products.
  3. Effectiveness may be questionable.

Bacillus thuringiensis (Bt)
Bt is a bacterial or microbial insecticide that attacks the gut of Lepidoptera larvae. The caterpillars ingest the Bt spores, which, in the alkaline conditions of the insect’s gut, release toxins. This causes the insect’s own digestive juices to attack the gut wall, creating holes that allow the contents to poison the body. Death may take a few days, but the insect stops feeding soon after the Bt is ingested. It is best applied when the caterpillars are young. Other formulations of Bt exist that target other insect groups, but none have been successfully used in Christmas tree production. Bt is used to control caterpillars and has no effect on sawfly larvae.

Bacillus popilliae
Better known as milky spore disease, Bacillus popilliae was the first commercially introduced microbial insecticide. It has been used for many years to control Japanese beetle larvae in soil. The spores will remain dormant in the soil until future generations of Japanese beetle larvae are present. It is not effective against other white grubs.

Horticultural Oils

Horticultural oils work in two ways. The first MOA is suffocation. When the oil coats the insect’s body, it prevents the exchange of gases in the pest. Eggs are also affected in this manner. The second MOA is penetration of the insect’s external membranes and subsequent entrance into the individual cells, where cell functions are disrupted. Both dormant oil and the highly refined oils for use during the growing season are available.

Advantages:

  1. Economical—most oils are less expensive than pesticide products.
  2. There are no proven cases of insects or mites becoming resistant to oil. Even insecticide-resistant species are susceptible to oil.
  3. Oils are environmentally and applicator friendly, posing little hazard with their use.
  4. When used to control overwintering pests, growers have more opportunities to select a day to make an application.
  5. Early season feeding damage of overwintering pests will be eliminated or significantly reduced.
  6. A wide assortment of pests can be controlled on a large number of hosts.
  7. Oil has no residual effect and will only harm the organism by direct contact.

Disadvantages:

  1. Oils must come in contact with the targeted pest to be effective.
  2. Field conditions and weather during applications may limit efficacy.
  3. Eggs will only be controlled if they are present before the oil application.
  4. Oil has no residual effect.

Cautions:

  1. When temperatures are below freezing, oil can cause phototoxicity. Under these conditions, the oil and water cannot stay mixed and the water freezes, allowing oil droplets to accumulate. When thawing does occur, the water will evaporate, concentrating the oil on plant surfaces.
  2. Oil can also cause phototoxicity when temperatures are above 90°F. Burning is also a concern on the sunny side of the trees or during times of drought.
  3. Apply oils when conditions allow for prompt drying; be sure to avoid drift or overspray.
  4. Mistaken dormancy is a problem in early fall or late spring. In early fall, if the plant is not in dormancy and the leaves are water deficient, then the oil will burn the foliage. In late spring, new growth is burned if the dormant period ends before the oil is applied.
  5. Conifers known to be sensitive to dormant oils include Douglas-fir and spruce. Be sure not to spray oil on glaucous, or blue, varieties of conifers because the blue color will be removed and may not return for 2–3 years. Genetic variability may affect individual plants differently, even if the variety is known to be tolerant to oil.

When using oil, as with any pesticide, be sure to follow label directions. Some oils can be mixed with other pesticides to increase the level of toxicity. Never mix oils with dimethoate or any type of sulfur, as serious phytotoxic reactions will result. Most fungicides are not compatible with oils. Always consult the oil and insecticide labels for compatibility. Always choose “superior-type” oils to provide further insurance that these products are safe.

Traditional

This largest group of pesticides includes insecticides, miticides, fungicides, and herbicides. They can be the most effective materials available to prevent and destroy pests; however, they are frequently used when other options are available. For many years, broad-spectrum insecticides were the only tools available to growers. In recent years, newer, soft materials targeting specific groups of pests have been introduced. These materials are less likely to disrupt natural enemies while keeping the target pest in check.

The use of traditional pesticides should always be a last resort. If a traditional pesticide application is a must, choose the right product, time, and dosage to avoid problems. Inappropriate use may rid the area of pests now, but it may also cause a more serious problem later as pests become resistant and natural enemies are depleted. For maximum benefit and to avoid hazards, choose formulations that pose the least threat to nontarget species. Be sure to rotate classes of pesticides to decrease the chances of pests developing resistance. Always read the label before using any pesticide product.

IPM Basics: Step 6. Evaluating Results of Control Actions

The ultimate goal of any IPM program is to keep pests under control. Not all control measures will be met with success. Sudden rain showers, rapid drop in temperature, inadequate coverage, and poor mixing are only a few of the causes of control failures. In addition, pest populations may rebound quickly despite the best techniques of an applicator. Monitoring pests after a control application is equally as important as monitoring them before the application. Scouts should check the target pests 3–5 days after any application. Some materials may require a longer time period to be effective. Checking effectiveness of fungicides is very difficult, but trees should be examined to make sure a spray residue is on all areas of the tree. Heed reentry interval requirements on the pesticide label when scouting after an application.

If the target pest is still present in sufficient numbers to cause damage, a repeat application may be necessary. Consider the following factors when determining the need for reapplication of pesticides:

  • Pest life cycle:
    — Vulnerability of certain life stages
    — Timing of generations
    — Number of generations per season
  • Pesticide properties:
    — Mode of action
    — Residual effect
  • Weather conditions following the application
  • Number of applications permitted according to the pesticide label

Even the best method of control will not eliminate the need for continued monitoring of pests. Many pests are capable of reappearing at a later date. They may be blown in from neighboring fields or woodlots, arrive with new seedlings, or have been present in an undetectable level during regular scouting.

Pennsylvania Conifer Certification and Quarantine Guidelines

Note: Growers in other states should consult with their regulatory authority for their state quarantine guidelines.

Conifer/Christmas tree growers who plan to sell B&B trees, seedlings, and transplants must have a Pennsylvania state nursery certificate. Pennsylvania’s Plant Pest Act requires that all nursery stock (i.e., plants with roots) must be inspected and certified as apparently free of injurious plant pests before being removed from the growing site. To obtain a nursery certificate, contact the Pennsylvania Department of Agriculture Bureau of Plant Industry Regional Office nearest you to request an application. The inspector assigned to your county will inspect your trees, give recommendations for controls of any pest or disease problems found, and certify trees suitable for digging as nursery stock. This applies to retail or wholesale, including local sales.

Any conifer grower who ships trees across state lines should be aware of federal and state quarantines that may apply to cut and B&B trees, seedlings, and transplants.

Federal quarantines include the gypsy moth quarantine. Under this quarantine, all cut and B&B trees of any species moving from quarantined areas into or through non-quarantined areas must be inspected and certified free of all gypsy moth life stages. Movement of trees within the quarantined area does not require gypsy moth certification. Maps of the quarantined areas may be found on the USDA Web site.

Pine shoot beetle is another federal quarantine that affects the movement of all Pinus species—eastern white, Scotch, Austrian, and so on. All cut and B&B pine trees or any parts, such as branches, wreaths, etc., moving from a quarantined to a non-quarantined area must be inspected and certified free of pine shoot beetle. Maps of the pine shoot beetle quarantine zone may also be found on the USDA Web site.

Growing Degree Day Ranges for Christmas Tree Pests

This chart provides a list of growing degree day ranges that correspond with a particular pest life stage or life cycle event that is critical in the control of that pest. This information combined with scouting observations will help growers achieve the best control of pest problems on their farms.

Pest NameDegree Day RangeLife Stage Comments
Bagworm650–750*Larvae emerge from bags
Balsam twig aphid30–100Overwintering eggs hatch
Conifer rust mites (eriophyid)7–22Overwintering eggs hatch
Cooley spruce gall adelgid

22–81

2,800–3,000

Spring control of overwintering stage

Fall control of overwintering stage

Cryptomeria scale

600–800*

1,750–2,130*

First-generation crawlers emerge

Second-generation crawlers emerge

Douglas-fir needle midge200–400*Adults emerge from soil
Eastern pine weevil7–100Overwintering adults become active
Eastern spruce gall adelgid

22–170

2,800–3,000

Spring control of overwintering stage

Fall control of overwintering stage

Elongate hemlock scale360–700Crawlers first become active
European pine sawfly78–220Overwintering eggs hatch; larvae present
Gypsy moth90–448Overwintering eggs hatch; larvae present
Introduced pine sawfly400–600Overwintering eggs hatch; larvae present
Pales weevil7–121Overwintering adults become active;
treatment to prevent egg laying
Pine bark adelgid22–58Spring control of overwintering stage
Pine needle scale

298–448

1,290–1,917

First-generation crawlers emerge

Second-generation crawlers emerge

Pine root collar weevil300–350Overwintering adults become active
Pine shoot beetle450–550New adults emerge
Redheaded pine sawfly400–600Overwintering eggs hatch; larvae present
Spruce spider mite50–121*Overwintering eggs hatch
Striped pine scale (Toumeyella sp.)400–500Eggs hatch and first crawlers emerge
White pine weevil7–58Overwintering adults become active
Zimmerman pine moth121–246Larvae emerge from overwintering sites

*Based on observations in Pennsylvania.
Monitoring of GDDs begins March 1.

Insect and Mite Calendar for Christmas Trees

This calendar gives a range of weeks of occurrence for each pest and pest event. The purpose of this calendar is to show growers how dates of particular pest events relate to others throughout the growing season. Because only weeks are given rather than specific dates, these are just approximate ranges. The information in this calendar was collected from 10 years of scouting data in south-central and southeastern Pennsylvania, so these ranges will differ from the actual calendar dates in other areas of the country. This information should be combined with growing degree day calculations and scouting data to determine local occurrence. Bud break occurs from April to May and signals emergence of various insects, as well as infection periods of disease.

Calendar