Integrated Pest Management

IPM Manual for Landscape Pests in British Columbia

Chapter 9: IPM for Insects & Mites in Ornamentals & Trees

Learning Objectives

When you have completed this lesson, you should be able to:

Classify sites with ornamentals (including trees) into three categories according to maintenance level.
List five methods that prevent insect (and mite) problems in ornamentals. 3. Know where to look for help in identifying pests.
Know where to look for help in identifying pests.
Describe three general monitoring methods used for pests of ornamentals.
Describe the use of biological controls on ornamentals.
Give three examples of physical / mechanical controls used for ornamental pests.
List general guidelines for using insecticides and miticides on ornamentals.
Describe the role of evaluation in an IPM program for pests of ornamentals.
Describe monitoring, give examples of action levels and treatments for aphids, scale and tent caterpillars.

Introduction

This chapter describes pest management in trees, shrubs and ornamental plants in yards, gardens, parks and institution grounds, playgrounds, golf courses, boulevards and natural areas. Common pests in such plantings are various species of aphids, spider mites, scales, leaf-chewing caterpillars, root weevils, leafminers and borers. In parts of the south coast, winter moth (Operophtera bruceata) and jumping gall wasp (Neuroterus saltatorius) on Garry oak are local problems, while elm leaf beetle (Pyrrhalta luteola) and fall webworm (Hyphantria cunea) are common problems in the southern interior.

As described in Chapter 2, using a system for categorizing sites according to maintenance level can help in planning an IPM program.

Facility Categories

Examples of sites that might be included in each category include:

Class A - High level of service: rose and specialty gardens, display areas of parks and boulevards, residential front yards, golf courses and institution grounds.
Class B - Moderate level of service: plantings in neighbourhood parks, playgrounds, residential backyards, along boulevards.
Class C - Low level of service: greenbelt areas, vacant municipal land, highway plantings; natural areas of yards and parks.

The following section describes the general steps in an IPM program for insects and gives examples of techniques currently available. Outlines of IPM programs for three common insect pests of ornamentals are also included. This information is intended as a starting point, to be adapted to suit specific sites and improved as new products and methods are developed.

Prevention

Roses in shade Compared to natural growing conditions, urban environments tend to have higher temperatures, less air flow and more disturbed and compacted soils that reduce the supply of oxygen and water to plant roots. Winter road salt and air pollution from traffic exhaust also pose problems. With a careful choice of plants and efforts to correct poor conditions, it is possible to design healthy, pest-free landscapes even for difficult conditions. Unfortunately, however, it is all too common for plants to be chosen without considering whether they are suited to the site or are resistant to pest problems. Thus, boulevards are still being planted with pest susceptible Prunus and Liriodendron trees that saddle those responsible for maintaining them with future pest management costs. In the Okanagan region, for example, Prunus and Malus trees are prone to many pests that cause problems for landscapers and gardeners. They also harbour pests that can spread to nearby agricultural crops.

The elements of prevention (also called "cultural controls" in some references) for ornamental pests are:

a) Use optimum site design

Ensure there is the right drainage, soil preparation, fertility and pH for the intended plants.
Select plants suited to the sun exposure, soil type, drainage, climate and other environmental conditions. Consider growth habit and height of mature trees when choosing plantings under utility lines. The importance of choosing the right plants for the site cannot be overstated. Studies have shown that when trees adapted to the sun are planted in shade their resistance to pests and disease attack drops; when shade-adapted plants receive too much sun they also become more likely to be attacked.
Choose a diversity of species and families of trees and shrubs. When there are many plants of the same species in an area, pest populations can build up to high levels.
Select healthy, well-grown planting stock that has been fed and shaped appropriately for the type of plant. Inspect all planting stock before purchase or delivery and check roots as well as foliage, to avoid bringing in new or exotic pests.

The 20-10 Planting Rule

A rule of thumb for ensuring diversity in a landscape is to choose no more than 20% of plants from any one family and no more than 10% from any genus. For example, 20% of shrubs and trees might come from the family Rosaceae, but no more than 10% from each genus, such as Photinia, Pyracantha, Spiraea, Rubus, Malus. etc.

b) Choose pest resistant plants

Weevil resistant rhododendron Select cultivars that are most resistant to common pests. For example, plant rhododendron and azalea cultivars resistant to feeding by adult black vine weevils. A long-term pest management plan may include replacing the most susceptible plants with less susceptible species and cultivars wherever possible. This is particularly important for long-lived, woody plants because the total cost of managing pests on susceptible plants can be very high over the lifetime of the planting.

Cypress Tip Moth? Think Resistance!

Cypress tip moth (Argyresthia spp.) attacks juniper (Juniperus spp.), arborvitae and cedars (Thuja spp.) and cypress (Cupressus spp.). On highly susceptible plants, such as American arborvitae (Thuja occidentalis), Pfitzer juniper (J. chinensis 'Pfitzerana') and Chamaecyparis lawsoniana, it can make an unsightly, brown-tipped mess of an evergreen hedge. Once the tip moth is established the only controls are annual spraying with residual insecticides when the moths are activeor removing the hedge and starting over. It would be much better (and cheaper and easier) to avoid the problem by starting with resistant species, such as western red cedar (Thuja plicata), or by choosing a different family of plants altogether for the hedge.

c) Use planting practices that give plants the best start

Set plants at the correct depth (usually the same level as in the nursery).
Plant far enough from building foundations to allow for the mature size of plants.
Remove turf from the planting area where plants are set in lawns and control weeds around trunks for the first 1-2 years.
Dig generous planting holes to accommodate roots (don't forget to remove plastic pots or burlap root ball covers).
Stake and protect trunks of young trees.

d) Follow management practices that keep plants healthy

Use fertilizing and watering practices suited to the site and the needs of the plants.
Install irrigation systems that can accommodate the differences in water requirements between turf, shrubs and trees in the landscape. Ensure regular and adequate water during establishment of new plantings.
Use correct pruning methods to speed wound healing and prevent insects and decay organisms from entering.
Protect trees from injury by mowers, line trimmers, vehicles, construction equipment, etc. by using barriers, trunk protectors, temporary fences or other measures. One way to cut down on mower injury to trees in turfed areas is to keep a circle of mulched or bare soil around the base of the trunks so that mowers do not need to work close to the tree.

Keeping up the Defense

Fertilizing and watering for healthy plants does not necessarily mean encouraging rapid or vigorous growth. While drought or nutrient stress can make trees more susceptible to borers and other pests, studies have consistently found that too much water and fertilizer also makes trees more susceptible to pests. The explanation lies in the fact that woody plants produce a range of chemicals in their tissues that help defend them against pests. Tannins in oaks and terpenes in pine, are examples of chemicals that are repellent to pests. When trees are growing rapidly, they have less of these defense chemicals in their tissues. Maintaining healthy trees and shrubs involves achieving a balance between growth and defense. This is a basic principle of the Plant Health Care Management System developed by the International Society of Arboriculture (for more information, see Further Reading at the end of this chapter).

Identification

Due to the wide variety of trees and shrubs grown in BC, a landscape manager may encounter many different pests. Generally, they fall into four main groups:
sucking insects and mites (e.g., aphids, scales, leafhoppers, spider mites)
root / crown feeding insects (e.g., root weevils)
leaf-eating insects (e.g., leaf miners, tent caterpillars, fall webworm, leafrollers)
borers (e.g., shot-hole borer, bronze birch borer)

Correct identification is essential because monitoring and treatment methods must be tailored to a particular species. Some pests cause very similar damage, which can also be mistaken for diseases or disorders caused by poor growing conditions. Once a problem species is identified, then information about it's life cycle can be used to pinpoint when treatments will have the greatest effect and what preventative measures would be most effective.

If you suspect an insect or mite problem, inspect damaged leaves and nearby shoots and branches, carefully, under magnification. Collect insects and samples of damaged plants to inspect under a microscope. If no suspects are visible on the damaged tissue, it may be because they are no longer present. This may be because larvae have left the plants to pupate or the pests might have been eaten by natural enemies. If this is the case, no further damage will show up in later inspections. If leaf damage continues, however, and no pests are found, it may be necessary to look for the pests at night, when nocturnal insects such as black vine weevils and cutworms come out to feed.

To identify insects and mites, use:

reference books, insect guides (listed at the end of this chapter under Further Reading)
resources on the internet
staff at garden centres, community colleges, botanical gardens
professional diagnostic services

Note: Professional services and companies can send samples to the provincial Plant Diagnostic Laboratory, Ministry of Agriculture and Lands, 1767 Angus Campbell Road, Abbotsford, B.C. V3G 2M3. Phone: 604-556-3126 (there is a charge for this service).

Monitoring

Monitoring provides the information needed to decide whether treatments are necessary, the best timing of treatments, and how the treatments are working. Most monitoring programs are based on regular inspection for pests, pest damage or other signs of their presence. It may also include monitoring for beneficial species. Examples of common monitoring methods for pests on ornamentals are:

Indicator Plants

Using indicator plants can reduce the time spent monitoring. These are plants that should be checked first because they are most attractive to particular pests. As long as these plants remain pest-free, there is likely no need for other plants to be checked. To use indicator plants with confidence, a pest manager must know what pests to expect and which particular plants are usually attacked first.

Visual Inspections

Regularly, usually weekly, inspect a representative sample of plants. Use a 10-15 X hand lens or headband magnifier to get a close look. Record observations.

Check the undersides of leaves, growing tips and lower leaves, along stems, leaf veins and in axils of leaves.
Look for curled, twisted, rolled or discoloured leaves and buds.
Look for webbing and yellowish "stippling" (speckled appearance) on leaves that would indicate spider mites.
Look for sticky patches of honeydew that would indicate sucking insects on the foliage above.
Look for holes chewed in leaves and for signs of caterpillar droppings (frass).
Check crowns of plants susceptible to root weevils for discolouration and damage.
Look for fine shavings or sawdust on trunks or base of plants that would indicate borer activity.

Counting Methods

The advantage of using counts in monitoring is that they give numerical (quantitative) measurements. If done carefully, these can be compared from year to year, regardless of who does the monitoring. The extra investment in labour to count and record pest populations can be well worth it for key pests in high value (Class A) sites. It may not be justifiable or necessary, however, on lower maintenance sites or for pests of little concern. Counting small species is more accurate if it is done under a dissecting microscope. Counting methods that give an estimate of insect populations, including beneficial species, include:

Count the number of insects found per leaf, per stem or per terminal shoot, then divide the total number of insects by the number of samples to get an average number of insects per sample.
Inspect pre-determined number (50, 100, etc.) of leaves, shoots or other plant parts and record how many had the target insects present. This is a quick method that gives a percentage or proportion of the total plant parts with an infestation.

The following sampling methods can be used simply to determine whether pests are present or they can be used to make more accurate population counts.

Traps

Pheromone traps can be used to monitor populations of cutworms, leafrollers, clearwing borers and other moths. These traps are usually inspected weekly for captured male moths and the counts would be recorded for comparison with previous counts.
Double sided sticky tape can be used to catch immature scale ("crawlers") in the spring as they begin to move to feeding sites in the foliage. Count the number of crawlers caught on tapes every week under a microscope or visually compare the relative number of crawlers on sample tapes from one week to the next (for more information on scales, see IPM Examples at this end of the chapter). Tape traps can also be used to detect when rust mites (Eriophyidae) become active in spring and early summer.
Pitfall traps are cans or plastic tubs buried with the top lip of the open container level with the soil surface. They catch large mobile insects, such as beetles, that travel over the surface. They fall in and cannot get out. Such traps can be used to collect adult root weevils for counting as well as beneficial ground beetles and rove beetles. Check traps often and release beneficial insects as soon as they are counted. To keep rain out of the traps, which would drown beneficial species, use a piece of shingle or other flat material as a cover. Support the cover 2-4 cm above the trap on small stones or pegs.

Honeydew Cards

The droplets of honeydew from aphids on trees can be monitored using cards to catch the droplets. Special cards with moisture sensitive coatings (such as used for spray droplet detection) are available. Cheap, reusable sample cards can also be made from sheets of clear acetate with a 1-cm² grid pattern photocopied onto them to aid in counting. Clip the cards onto branches below infested leaves or lay them on the ground beneath trees for a set period of time (such as 1/2 hour or 4 hours). Count the number of droplets of honeydew and record this figure — or keep the cards and compare them visually from week to week to find out whether the relative amount of honeydew seems to be increasing or decreasing.

Beating

As described in Chapter 1, insects that readily drop when disturbed can be knocked from foliage onto a beating tray below, by jarring the trunk or branches with a padded stick. This method is used to count adult black vine weevils (when done at night) as well as elm leaf beetles, thrips, leafhoppers and some species of caterpillars. It is also a good way to monitor for the presence of lady beetles, lacewings and other predatory insects. Mites on evergreen foliage can be detected by tapping the foliage over a clipboard covered with a sheet of light or dark paper.

When and How Often: The monitoring schedule depends on the life cycle of the problem insects and mites and on the time of year. Some insects, such as aphids and thrips reproduce throughout the growing season. Others, such as tent caterpillars have only one generation a yearonce the period of active feeding has passed they are no longer present or damaging. For a monthbymonth timetable for monitoring landscape and nursery pests in BC see the Nursery and Landscape Pest Management and Production Guide (see Further Reading at the end of this chapter).

Action Decisions

Injury levels also depend on the category of site. For example:

Class A Sites: Aesthetic injury levels may be quite low because plants are viewed at close range.
Class B Sites: Proportionately higher pest populations may be acceptable in plantings that are less noticeable or less important in the landscape.
Class C Sites: A relatively high level of plant injury is acceptable before action is taken. Action might only be taken if there is a risk of losing a plant to severe injury or where a pest outbreak might spread to a nearby, higher profile site or an agricultural crop.

Given the wide variety of climate zones, plants and possible pests, it is hard to generalize about injury levels. As for any landscape plantings, the injury level depends on how much damage the users of the site will tolerate. This, in turn, depends on where the damage is and how visible it is. Additional factors include long-term risk to the health of the plants and the risk of pests spreading to an another site.

To begin with, it may be necessary to set temporary injury levels based on a best guess or on information found in publications. As monitoring records and treatment evaluations accumulate from year to year you will be able to refine the injury levels.

Some ways to define injury levels are:

percentage or proportion of leaves damaged on a particular plant
percentage of plants affected on a site
number of pests counted
number of pests counted in relation to the number of beneficial insects found
number of complaints received from the public about a specific problem

The action levels depend on what types of controls are planned. For example, if biological controls are used, it is usually best to start releasing them while the target pest populations are still low. For a very damaging species, such as peach tree borer (Synanthedon exitiosa), the detection of one male in a pheromone trap might be the action level for an insecticide treatment to the tree trunk.

Treatment

One or several treatments may be coordinated into a management program for a target pest or for the entire complex of pests in a site or facility. Use biological, physical or cultural controls wherever possible to protect native beneficial species and reduce impacts on the environment. When a pest problem occurs that must be treated, the manager should re-evaluate the management program to determine how to prevent the pest problem in the future.

Physical and Mechanical Controls

Examples of physical and mechanical controls for insects on ornamentals include:

Strong sprays of water used to control aphids, spider mites and some sawflies, such as roseslug and pearslug (Endelomyi spp.).
Removal of infested leaves by hand or by pruning out infested branches to manage light infestations of aphids, scales, tent caterpillars or fall webworms.
Sticky tree bands used to trap winter moth (see Chapter 3 for instructions) or elm leaf beetles. They can also be used to trap ants where they are protecting aphid colonies.

Biological Controls

Only a few species of commercially produced biological control agents are practical for releases outdoors. As described in Chapter 1, conserving and attracting native beneficial species is the most useful approach outdoors. Useful commercial species are those that attack aphids (aphid midge, lady beetles and lacewings), as well as the insect parasitic nematodes (for control of root weevil larvae, borer larvae and cutworms) and predatory mites (for control of thrips, spider mites, rust mites and cyclamen mites). For detailed descriptions of the biological controls suitable for use in outdoor plantings, see Chapter 3.

In general, biological controls should be released as soon as monitoring shows target pests are present in enough numbers to support the predator population. Suppliers of biological controls provide monitoring and release rate information for using their products and should always be consulted before placing orders.

The microbial insecticide, Bacillus thuringiensis kurstaki (BTK) is a biological control (and a registered pesticide) used to control leaf-feeding caterpillars.

Chemical Controls

Preferred insecticides are described in more detail in Chapter 3. Those of most use on ornamental plants in landscapes include:

insecticidal soaps for chewing and sucking insects and spider mites
pyrethrins for thrips, aphids and flying insects
summer formulations of horticultural oils for scales, mites, aphids and lace bugs (Tingidae) (check labels for phytotoxicity information before using)
dormant formulations of horticultural oils for overwintering stages of scales, mites, aphids and eggs of moths, such as leafrollers.

Generally, pesticides should be applied as spot sprays or in other targeted application methods. For example, systemic insecticides to control sucking insects can be applied as a band on the bark or injected into trees.

If an insecticide treatment is judged necessary, select the product according to the following guidelines. Make sure the product selected is:

registered for the specific pests and intended use (application method, host plant)
least likely to harm native beneficial insects and mites
applied as a spot treatment instead of broadcast application wherever possible
applied at the right time to have the greatest effect on target species

For more precautions and guidelines for using pesticides in landscapes, see Chapter 11.

Evaluation

Follow-up monitoring or inspections are necessary to find out how successful an IPM program has been. It is essential to review records to determine what worked, where improvements should be made and what preventative steps may be possible in future.

IPM Examples

Following are descriptions of three common groups of insects found in trees and ornamentals with notes on monitoring, action decisions and treatments that could be incorporated into an IPM program. In any IPM program, correct identification of the pests before taking action is critical, as is the evaluation step to determine how to improve the program in the future.

Tent Caterpillars (Malacosoma spp.)

There are two common species of tent caterpillars in BC. The northern tent caterpillar (M. californicum pluviale) occurs mainly in southern half of the province and along the north coast. It feeds on alders, poplars, willows and fruit trees as well as many deciduous ornamentals. The forest tent caterpillar (M. disstria), is mainly found in the interior regions of the province. It prefers trembling aspen, but in outbreak years will feed on a variety of deciduous trees and shrubs. Unlike the northern tent caterpillar, and despite its name, the forest tent caterpillar does not make a silken tent of webbing in trees. Another common species, fall webworm (Hyphantria cunea), is often mistaken for tent caterpillars because they also make large silken tents in shrubs and trees. They appear in late summer, however, 1-2 months after tent caterpillars have left the trees to pupate.

The following information describes northern tent caterpillar, but the monitoring and management information can also be applied to forest tent caterpillars as well as fall webworms.

Northern tent caterpillars are the larvae of a large, pale brown moth that lays its eggs in late summer on the small branches of deciduous trees (ash, birch, fruit trees, oak, poplar). The egg masses look like 1-2 cm long masses of hard brown foam, usually wrapped around branches less than 1 cm in diameter. The eggs hatch from mid-April to early June. The larvae feed together in large numbers, spending the night and periods of bad weather in a nest of silken webbing they spin in the crotches of branches. When the larvae reach full size (June to early July) they wander from the trees in search of pupation sites. The adult moths emerge in late summer. Webbing stays in the trees long after the caterpillars have left. Tent caterpillar populations naturally rise and fall in a 7-10 year cycle of outbreak, followed by a collapse as the population is wiped out by naturally occurring diseases and predators.

Monitoring

Inspection of dormant branches for egg masses can be done any time after the leaves drop. Before the leaves expand, hatching egg masses are particularly easy to see on branches silhouetted against the sky. In expected outbreak years, monitoring for hatching egg masses should start by mid-April.

Action Decisions

In peak outbreak years, trees may be completely defoliated. Although this may temporarily weaken trees, it usually does not cause long-term harm. Once the caterpillars leave in early summer, the trees produce new leaves to fill in the canopy. This means that the injury level mainly depends on the perception of the site users rather than danger to the trees. In practice, although defoliated trees are a source of public concern, by the time complaints are made to municipalities and parks departments, it is often too late to do much about the current year's infestation. Whether or not caterpillars are removed from individual trees, the tent caterpillar populations in the area will increase over several years and then collapse as diseases and natural enemies catch up with the population. In expected outbreak years, monitoring for egg masses and hatching caterpillars will make it possible to apply treatment early enough to protect trees from defoliation.

Treatments

Although treatment is usually not necessary to preserve the long-term health of trees, pruning out the egg masses and web nests may be desired on high visibility plantings. Remove webs in the evening after caterpillars have returned to the nest. Destroy the caterpillars by crushing them or dropping them in a bucket of soapy water.

To control the caterpillars while they are still actively feeding in the trees, the microbial pesticide, BTK is useful if applied carefully to ensure good coverage of the foliage. High pressure water sprays can also be used to remove caterpillars and webbing and to clean old webbing out of trees after the caterpillars have left.

Scales

Various species of scale insects attack woody ornamentals in BC. Scales are sap-sucking insects that look like tiny bumps or plates on twigs and leaves. Armoured scales (Diaspididae) have a harder shell and do not excrete honeydew. They include oystershell scale (Lepidosaphes ulmi) and San Jose scale (Quadraspidiotis perniciosis). Soft scales (Coccidae) are usually smooth or cottony and excrete honeydew (copiously!). They include lecanium scale (Lecanium spp.) and soft brown scale (Coccus hesperidum).

It is not easy to identify scale species, however, it is essential because there are important differences in behaviour and life cycles of the various species that affect timing of treatments. Some species overwinter as eggs that hatch in the spring. The immature "crawlers" move around the plants for a short period early in the season before settling down to feed. Other species, such as the main pests of fruit trees in the interior regions of BC, overwinter as adult scales. They mate in the spring and the crawlers hatch out in June and July and move to suitable feeding sites. Knowing when the crawler stage is on the move is key because this is the stage that is most susceptible to insecticides. Adult scales are well protected from sprays by their waxy shells, as are the eggs, which are also protected by the shell of the female.

Monitoring

For species that overwinter as eggs, start monitoring for the crawler stage 1-2 weeks before buds break in the spring. For species that overwinter as adults, start monitoring in mid-summer. Wrap double sided sticky tape tightly around twigs or small branches on susceptible plants. Fold over the end of the tape to make a tab to grip when removing the tape. Tie flagging tape or another marker near each taped twig so that you can find it again. Once a week, pull off the sticky tapes and stick them flat on a white sheet of paper. Look at the tapes under a microscope to distinguish the tiny, yellow or orange crawlers from specks of dust or pollen. If time permits, count the crawlers and keep the weekly records of counts. If not, keep all of the sample tapes on paper. Cover them with a clear sheet of acetate, labeled with dates and locations, and compare them visually from week to week.

Action Decisions

Injury levels have not been established for scale, however, with experience (and good records, of course) you should be able to establish your own idea of injury levels. If an insecticide treatment is needed, it should be done when the number of crawlers on the sticky tapes shows a marked jump upward in numbers from one week to the next.

Treatments

Biological Controls

For outdoor plants, naturally occurring predators and parasitic wasps often provide adequate control. Make the landscape more attractive to these beneficial insects by planting flowers that are good sources of nectar near trees attacked by scales.

Physical Control

Prune out and destroy infested branches.

Chemical Control

Used at the right time, non-residual insecticides are effective on the crawler stage of scales and cause the least harm to the natural enemies of scales. Spray insecticidal soap or horticultural oils when monitoring shows that peak numbers of crawlers are moving on the twigs. Applying horticultural oils when buds are swelling in the spring minimizes the harm to beneficials and is a useful control for overwintering stages of scales.

Several organophosphate and carbamate insecticides are registered as foliar sprays for scale. Use of these pesticides, however, will disrupt naturally occurring biological control of scale and should be avoided if possible. In extreme situations, a band of the systemic pesticide dimethoate can be painted onto trunks to spread through the plant (this is registered for use on only a few ornamentals, such as roses, lilac, birch). This application method affects the scales without disrupting populations of natural enemies.

Aphids

Aphid lifecycle Aphids are small, pear-shaped sucking insects, 2-8 mm long, with long, backward pointing antennae. Many different species of aphids occur on outdoor plants, including rose aphid (Macrosiphum rosae), spruce aphid (Elatobium abietinum) and maple aphids (Periphyllus spp. and Drepanaphis spp.). Most aphid species attack only a few closely related species of plants and won't spread to unrelated plants. For example, aphids attacking maples will not spread to roses. Some aphid species do alternate between two types of host plants. For example, black cherry aphid (Myzus cerasi) starts in the spring on cherry, moves to mustard family (Brassicaceae) plants in summer, then back to cherry in the fall to overwinter; leafcurl plum aphid (Anuraphis helichrysi) starts on plum, moves to sunflower family (Asteraceae) plants, then back to plum in the fall.

Aphids suck plant sap, causing distorted foliage and buds and dropped leaves. They also excrete a sweet honeydew which drips onto leaves and supports the growth of unsightly sooty moulds. Aphids reproduce continuously during the growing season. Most species overwinter in the egg stage on branches and twigs.

Monitoring

Visual inspections: Inspect plants weekly for distorted, curled foliage and shiny drops of honeydew on leaves. Use a 10-15 X hand lens to look for aphid colonies, concentrating on new growth and growing tips as well as the undersides of oldest leaves.

Counting Methods

Count the number or percentage of terminal shoots, leaves or plants infested with aphids. Start checking plants that are susceptible to aphids in the spring, before aphids are expected to appear. Every 1-2 weeks, check 5 to 10 leaves, or shoots, per plant. Inspect several plants in each area. While checking for aphids, record the number of aphid predators seen as well.
Count the number of honeydew droplets falling over a 1/2 hour, 2 hour or 4 hour period on cards placed under foliage. Special, water-sensitive cards used to monitor for spray drift are easy to use. Cheaper alternatives, such as sheets of acetate or dark construction paper, also show droplets well enough to allow droplets to be counted. Clip the card to clipboards and set them out in mid-day. Place them on the ground beneath trees or fasten them to lower branches.

Action Decisions

Examples of injury levels used by pest managers for various species of aphids on:

"Background" plantings: (i.e.,where honeydew will not fall on walks, patios, parked cars, etc.) 20- 40% of terminal leaves infested.
¥ Roses: 5-10% of terminal leaves infested.
¥ Other plants: less than 1 aphid predator per 50 aphids. This means that if there is more than 1 predator/50 live aphids, then it is likely that there are enough natural enemies present to control aphids without other treatments. The ratio of live aphids to dead aphids can also be used as an indicator of predator activity.

For sites where honeydew is the main problem caused by aphids, such as on boulevard trees, an action threshold might be established based on some number of honeydew droplets deposited on monitoring cards per hour. What that number is depends on the site. For example, if the honeydew is falling on a sidewalk, the tolerable amount may be much higher than if it is falling on parked cars.

Where biological controls are going to be released, the time to release predators is usually in the early spring, as soon as aphid colonies are found during regular monitoring.

Treatments

Biological Controls

Many species of aphid predators and parasites are native to BC and common even in urban environments. As described in Chapter 1, protecting them is the cheapest approach for long-term suppression of aphid populations.

Research in BC on releasing commercially reared aphid midge, Aphidoletes aphidimyza, has shown promising results on boulevard and shade trees, roses and other shrubs. Generally, aphid midges are released in the spring, 2 or 3 times at 7-10 day intervals to add to the naturally occurring populations of aphid predators. A late summer release of aphid midges on Malus and Prunus trees with established aphid colonies can be used to reduce the overwintering aphid population. Always consult biological control suppliers for their advice on release rates and timing.

Physical Control

Prune out infested branch tips or foliage.
Remove aphids by spraying the plants with a strong stream of water. Knocking the aphids loose from the plants damages their mouthparts and prevents them from feeding again.

Chemical Control

Aphids are difficult to control with pesticides because spray coverage must be very thorough to reach aphids on undersides of leaves and in curled leaves; if any aphids survive they quickly generate a new colony. Aphid populations readily become resistant to pesticides that are used frequently.

Avoid using residual insecticides, especially as foliar or broadcast sprays because this can cause a more severe aphid problem in the future by killing the native aphid predators.