Integrated Pest Management

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). Contact the laboratory for specific instructions on how to collect and package plant samples. When sending samples to a lab provide as much background information as possible about weather conditions, cultivars, any pesticide use, fertilizing, irrigation and other management practices. See Appendix I for a lab submission form.

To help in future identification it is a good idea to keep photographs and descriptions of disease symptoms that occur on various sites.

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Monitoring

Unlike other kinds of pest problems, once the symptoms of diseases are visible, it may be too late to control it on the infected plant. This means that, in addition to looking for disease symptoms, monitoring should include looking for growing conditions that favour disease. Monitoring for diseases in ornamentals includes visual inspections of plants, keeping weather records and using counting methods.

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Visual Inspections

Use a hand lens to take a close look at the plant. Use tools, such as a soil probe, shovel or pocket knife as needed, to explore around roots, dig into soil or cracks in bark etc. Look for conditions that favour disease, such as:

• injuries to bark or foliage that could allow pathogens to enter the plant
• soil that is compacted, overwatered, too dry, too cold or too warm for the plants on the site
• conditions that allow leaves or roots to stay wet for long periods, such as dense foliage, poor drainage or water runoff from other sites
• presence of sucking insects, such as aphids, whiteflies, leafhoppers, that might spread viruses between plants
• alternate host plants with infections that could spread to the landscape plants (i.e., pears that harbour pear trellis rust, which also infects juniper)

Look for signs and symptoms of disease, such as:

• wilted, distorted or abnormally shaped shoots and leaves
• spots, streaks or discolourations on leaves, stems and flowers
• discoloured, distorted or damaged roots
• presence of fruiting bodies or visible mycelium

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Weather Records

The right conditions of humidity and temperature are key factors in the development of many diseases, particularly those caused by fungi and bacteria. For this reason, monitoring may also include keeping records of temperatures (daily minimum and maximum, if possible), rainfall and relative humidity. These records will help you know when conditions have been favourable for specific bacterial or fungal disease infections so that you can monitor or treat accordingly (see text box for examples of rose diseases).

Conditions Favouring Diseases of Roses Pathogen Optimum Temperature Optimum Relative Humidity (RH& Moisture) Blackspot (Diplocarpon rosae) 18 - 24°C Spores must be continuously wet over 7 hrs to germinate Powdery mildew (Sphaerotheca pannosa) Day 21 - 26°C Night 16°C RH*: Day 40 - 70%; night 90 - 95% Rust (Phragmidium spp.) 18 - 21°C Continuous moisture 2 - 4 hrs Downy mildew (Peronospora sparsa) < 18 °C RH*: over 85% *RH = relative humidity

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Counting Methods

Counting diseased plants or plant parts may not be as useful in most landscapes as careful visual inspections and monitoring weather conditions. This is because landscapes are usually planted with a variety of plant species and, since most pathogens attack only particular species, diseases are usually limited to those few susceptible plants. Where there are large numbers of the same plants in an area, however, counting methods are useful in making decisions about treatments. This is because they tell you whether a disease is getting worse or spreading. For diseases that appear every year, start inspections early to detect the first infections and use counting methods to track the progress of the disease. This information, along with weather records, can be used to time preventative fungicide applications and other treatments.

Examples of counting methods include:

• count the number of leaves, branches or plants with symptoms
• measure the severity of symptoms using a scoring system (see text box) for estimating area of leaves affected by symptoms

Scoring Disease Symptoms Developing a scoring system is a good way to monitor for diseases with readily identifiable symptoms, such as leaf spots or blotches. Scoring systems can be based on any number of categories of damage. To be practical, however, they usually divide the range of damage into 4 to 6 categories. The categories range from "no symptoms" to the most severe. A monitoring system developed for hawthorn blight in Victoria*, where over 11% of the boulevard trees are hawthorns, is based on 6 categories of leaf symptoms. When trees are inspected, the severity of the symptoms are scored on a scale starting with 0 (no symptoms), 2 (some brown spots), 4 (more spots), 6, 8 and 10 (defoliation). A simple way to analyze these records is to calculate the proportion of inspected trees that scored in each category. For example, if a total of 60 trees are inspected and 15 had no symptoms, 25% would be in the "0" category. Do this calculation for each category. The percentage of trees in each category can be displayed in a table or bar graph for comparison with other monitoring dates. It is a good idea to make a score guide with pictures or drawings that clearly illustrates the amount of damage to associate with each score. This will standardize the scoring and reduce the differences in interpretation between people doing the monitoring. The same scoring system should be used each time so that results can be compared from year to year. *Information from Dr. Michelle Gorman, IPM Coordinator, City of Victoria

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When and How Often

The monitoring schedule depends on the category of the site, what diseases are expected to occur on the plants, the weather and on other conditions that promote disease. Monitoring for disease symptoms is usually done weekly, or more often, during the seasons or periods of weather that favour disease development. It is important to be familiar with what diseases to expect on various plants in the landscape so that you can plan an efficient monitoring program.

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Injury and Action Levels

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: A higher level of damage may be acceptable in plantings that are less noticeable or important in the landscape, providing disease is not likely to kill the plant.
• Class C Sites: A relatively high level of plant injury is acceptable before actions are required. Action might only be taken if there is a risk of losing a plant to severe injury or where a disease outbreak might spread to related plants in nearby, higher profile site.

Given the wide variety of climate zones, plants and possible diseases, 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, which in turn depends on where the damage is and how visible or severe it is. For diseases, an important factor is whether or not the long-term survival of the plant is threatened or whether there is a risk of the disease spreading to another site. In practical terms, how much it costs to treat or replace the plant will also affect tolerance for damage.

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

The action levels depends on what type of controls are planned. For example, most fungicides work by preventing the pathogen from infecting healthy tissue, rather than by killing the pathogen directly. This means that on high risk plants, such fungicides would be used when there is a sound basis for expecting infection to occur (such as poor weather conditions).

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Treatment

When a disease occurs that must be treated, the manager should re-evaluate the plant management program with the aim of strengthening the plant's natural defenses or altering the plant's environment to reduce damage or prevent the problem from occurring in the future.

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Cultural Controls

The main cultural controls for plant diseases (in addition to measures also described above, under Prevention) are sanitation methods including:

Pruning: Not to be confused with pruning to shape plants and increase air circulation, sanitation pruning is done to remove infected branches, foliage and other plant parts. It is usually done as soon as infections are found, at any time of year. For some diseases, however, it is important to time pruning so that it is done when there is less likelihood of spreading the disease. For example, the greatest number of bacteria are present on plants infected with bacterial blight in the spring; pruning at this time has a much higher risk of spreading the infection than pruning in mid-winter or on a dry day in mid-summer.

Burn or bury infected material, well away from susceptible plants. When working on plants with disease symptoms (or suspected symptoms), disinfect pruning tools between cuts using rubbing alcohol, a 10% household bleach solution or other disinfectant. When the job is done, thoroughly clean tools and equipment, wash soil and leaves off of shoes and wash hands before working on other plants.

Plant Removal: Always remove and destroy infected plants before planting new stock at the site. Take care in selecting replacement stock to ensure it is not susceptible to the same disease. Where the ongoing cost of managing plant disease is high, or treatments do not provide satisfactory control, it is often best to replant even if the disease does not kill the infected plants. For some plant diseases, removing alternate host plants that keep infections going in the area is preferable.

Removing Cherry Trees with Little Cherry Virus Disease Little Cherry Virus (LCV) causes some or all of the fruit on infected trees to be smaller than normal, poorly coloured, and lacking in flavour and sweetness. Removing diseased trees is essential for control of this disease, therefore LCV is a declared pest under the provincial Plant Protection Act. This applies to the main cherry growing areas of British Columbia, including the Okanagan region and the Creston valley. Cherry trees with suspected symptoms should be reported to the local Ministry of Agriculture, Food and Fisheries office. Ornamental flowering cherries can be symptomless carriers of LCV so they are also prohibited within the control areas. Virus-infected trees cannot be cured, but controlling the insect that spreads the virus (apple mealy bug), will help prevent the spread of LCV. For more information see the Tree Fruit Production Guide for Commercial Growers, Interior Districts (under Further Reading).

Leaf Removal: Rake up and destroy fallen leaves from plants infected with pathogens that over winter on fallen leaves. This includes blackspot (Diplocarpon rosae) on roses and scab (Venturia spp.) on apples and other related plants. Removing infected leaves from plants and destroying them is also a sanitation step that can reduce the spread of fungi that attack leaves.

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Physical and Mechanical Controls

Water Washes (Syringing): Using plain water to rinse leaves is a long-established practice for suppressing powdery mildew. This is because free water on the leaves stops powdery mildew spores from germinating. Sprinkling or syringing is best done in mid-day to give plants time to dry off before nightfall and avoid other fungal diseases. Water sprays would not be advisable on plants susceptible to rusts, scab (Venturia spp.), bacterial blight or other diseases that are promoted by wet conditions.

Cauterization (Applying Heat): One research study found that using a hand-held propane torch to burn cankers caused by Pseudomonas on stone fruit trees limited the spread of the disease. This is experimental but may be worth trying.

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Biological Controls

Beneficial microorganisms that suppress plant pathogens are naturally present in the soil, the air and on leaf surfaces. These include:

• mycorrhizal fungi that colonize plant roots and protect the plant from infection. These prevent attack by pathogens and help plants take up nutrients from the soil. Most research on mycorrhizal products has been on seedling mixtures for forest nurseries and agricultural crops.
• microorganisms that attack, disable or inhibit the growth of pathogens (products containing these are registered as pesticides)

At this time, the use of soil amendments containing microorganisms is still experimental. There are very few biological controls registered in Canada for controlling plant disease. One is Agrobacterium radiobacter, which is a beneficial species of bacteria. It controls crown gall (A. tumifaciens) and is used as a root dip on nursery stock, roses, clematis, chrysanthemums, flowering Prunus spp., willow, juniper and other ornamentals (for more information see Chapter 3).

Other biological controls for plant diseases are available in the US and may be registered in Canada in future. Some of these include:

• the common, soil-dwelling fungus, Trichoderma harzianum, which suppresses Pythium, Fusarium and Rhizoctonia in soil mixes, turf and other applications
• the parasitic fungus, Ampelomyces quisqualis, which attacks many species of powdery mildew fungi

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Chemical Controls

Most chemicals available to control plant diseases are fungicides; a few products that contain copper as the active ingredient also work on bacteria. No products are available to control viruses directly. Some viruses are transmitted by insects, however, and these may be indirectly controlled by controlling the insects that spread the viruses. For some diseases, prevention and cultural controls are the only approaches available because there are no effective pesticides registered.

If a chemical treatment is required, select the product according to the following guidelines. Make sure the product selected is:

• effective and registered for the specific pathogen, and
• applied at the right time to provide protection or to have the greatest effect on target species

Timing is very important for applying preventative (protectant) fungicides because they have little effect if applied after the infection period has ended. Always check the life cycle of the pathogen to find out when the infection period occurs and time fungicide treatments accordingly.

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

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Evaluation

After any type of treatment, use visual inspections or counting methods to assess the effect. Follow-up inspections include checking for:

• further spread of disease symptoms
• reduction or elimination of disease symptoms
• restoration of plants to normal growth or appearance

Use this information, along with other monitoring records, observations from field staff, feedback from clients, budget records, etc. to assess the effectiveness of the IPM program and find ways to improve it for next year.

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IPM Examples

Following are descriptions of two common plant diseases in BC, 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.

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Powdery Mildew

There are hundreds of species of powdery mildew fungi that may attack landscape plants (e.g., species of Erysiphe, Sphaerotheca, Uncinula, Podosphaera, etc.). Some are limited to particular hosts, such as Sphaerotheca pannosa var. rosae, which only attacks roses, while others infect a wider range of plants.

The disease usually appears as whitish or grayish powdery patches on leaves or young growing tips. The spores spread on the wind and can only live in plant tissue. Leaves do not need to be wet to enable the spores to germinate — in fact, the spores die in water. Spores overwinter in dormant buds and on fallen leaves, but not in the soil. Development of powdery mildew is greatest on plants in the shade and during humid weather. The fungus releases the most spores when dry warm days are followed by cool nights. Both rainfall and direct sunlight inhibit growth of powdery mildews.

How damaging powdery mildew diseases are depends on what species of fungus is involved, the species or cultivar of the host plant, the age of the plant tissue being attacked and the environmental conditions (i.e., relative humidity, temperature).

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Prevention

• The most effective measure is to plant powdery mildew resistant cultivars of roses and other plants where they are available.

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Monitoring

Visual Inspections

• Look for small, light-coloured patches on leaves and on growing tips, stems and flowers. In later stages, the patches grow together, covering the plant tissue with a powdery white growth. Plant shoots and flowers may be distorted or discoloured (often a reddish or purplish colour). Infected area of leaves may later die and turn brown.

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Treatment Thresholds

• Most trees are not significantly harmed by powdery mildew unless they have been repeatedly infected for several years.
• Moderate levels of infection may not require treatment especially if they occur late in the season or on isolated plants or in Class B or C sites.
• Highly susceptible plants, such as some cultivars of euonymus and roses, in high profile (Class A) sites may require treatment with fungicides at the earliest sign of the disease.

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Treatment

Cultural Control

• Don't over fertilize or over water plants. This produces excessive new growth and young tissue, which is the most susceptible to infection.
• Prune trees and shrubs to improve air circulation and reduce shade.
• Clean up dead leaves and foliage around plants in the fall to remove overwintering sites for the fungus.

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Physical Control

• Prune out infected plant material and dispose of it.
• Syringe plants with water in mid-afternoon to stop spores from germinating.

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Chemical Control

• Lime sulphur can be applied during the dormant season.
• Sulphur, copper, benomyl, triforine and other fungicides are registered for control of powdery mildew during the growing season.

A baking soda and horticultural oil spray developed at Cornell University has had promising results in some conditions but is not a legally registered fungicide in Canada (for more information, see the Nursery and Landscape Pest Management and Production Guide). Control of powdery mildew has also been observed where anti-transpirant products containing non-toxic polymers have been applied to plants [see Quarles (2000), below].

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Anthracnose (Discula spp.)

Many different species of fungi cause anthracnose disease of landscape trees. The Discula spp. are of concern in coastal areas, where they cause anthracnose on ash (Fraxinus spp.) and on dogwood (Cornus spp.). Other species affect sycamore, maple and oak. Symptoms appear as large irregular blotches on leaves. In severe infections, cankers may develop on twigs or stems and trees may be partly or entirely defoliated.

The fungus overwinters in buds and bark of trees, in cankers on stems and on fallen leaves. It produces spores in wet weather in the spring, which are spread by both wind and water to infect nearby foliage. From leaves, the fungi move into the stems to form a canker. Where cankers girdle the trunks or repeated severe infections weaken trees (as can occur in dogwood anthracnose) the tree may eventually die.

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Prevention

• Avoid planting highly susceptible cultivars, such as Modesto ash (Fraxinus velutina 'Modesto') and Pacific dogwood (Cornus nuttallii).
• Choose more resistant species and cultivars, such as Japanese dogwood (Cornus kousa), Eastern dogwood (Cornus florida) or Cornus 'Eddie's White Wonder'.

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Monitoring

Visual Inspections

• On dogwood, look for wedge-shaped blotches or irregular areas of dying tissue on leaves and twigs in late spring and early summer.
• On ash, look for leaf blotches and a scorched appearance around leaf edges.

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Action Decisions

Costs of control measures are not likely to be justified unless the disease occurs every year. On susceptible dogwoods, remove all infected plant parts as soon as leaf blotches or stems cankers are found and apply protectant fungicides if required. For nursery plants and other high value (i.e., Class A) sites with a previous history of anthracnose, protectant fungicides may be warranted; treatments should start at budbreak and continue at 1-2 week intervals during wet weather.

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Treatments

Cultural / Physical Controls

• In spring, remove infected leaves (on small, isolated plants) as soon as detected.
• Rake up and burn fallen leaves to remove overwintering spores.

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Chemical Control

• Dormant sprays of lime sulphur are available.
• Growing season sprays of chlorothalonil or mancozeb are registered for use.

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Further Reading

___. APS Plant Disease Compendia (Specific titles: Conifers; Apples and Pears; Stone Fruit; Flowering Potted Plants; Rhododendrons and Azaleas; Roses; Chrysanthemums; Turfgrass; others). APS Press. (From: American Phytopathological Soc., 3340 Pilot Knob Road, St. Paul, MN 55121-2097.

____ 1998. Nursery and Landscape Pest Management and Production Guide. BC Ministry of Agriculture and Land and BC Landscape & Nursery Association (From: BCLNA, Suite 101, 5880-176A St., Surrey, BC V3S 4E3. Tel: 604-574-7772)

____ 1997. Plant Health Care for Woody Ornamentals: A Professional's Guide to Preventing and Managing Environmental Stresses and Pests. International Soc. Arboriculture and University of Illinois. 223 pp. (From: University of Illinois, ITCS, 1401 South Maryland Drive, Urbana, IL 61801. Tel: 800-345-6087

____ 2000. Tree Fruit Production Guide for Commercial Growers, Interior Districts. Min. of Agriculture and Land and BC Fruit Growers' Assn. (From: BCFGA, 1473 Water St., Kelowna, BC V1Y 1J6. Tel: 250-762-5226)

Bobbitt, V., A. Antonelli, C. Foss, R. Davidson, R. Byther and R. Maleike. 1999. Pacific Northwest Landscape IPM Manual. Washington State University. 206 pp. (From: WSU, Cooper Publications Bldg., P.O. Box 645912, Pullman, WA 99164-5912. Tel:1-800-723-1763

Dreistadt, S. H. 1994. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. Pub. # 3359, University of California. 327 pp. (From: ANR Publications, Univ. of Calif., 6701 San Pablo Ave., Oakland, CA 94608-1239. Tel: 800-994-8849

Gerber, H. S., D. J. Ormrod and M. A. Waring. 1995. A Gardener's Guide to Pest Prevention and Control in the Home and Garden. BC Ministry of Agriculture, Food and Fisheries. 175 pp.(From: Crown Publications, 521 Fort Street, Victoria, BC V8W 1E7. Tel: 250-386-4636 [Revised edition available Fall 2000]

Olkowski, W., S. Daar, & H. Olkowski. 1991. Common Sense Pest Control. Taunton Press, Newtown, CT. 715 pp. (From: Bio-Integral Resource Center, PO Box 7414, Berkeley, CA 94707. Tel: 510-524-2567

Quarles, W. 2000. Antitranspirants as Least-Toxic Fungicides. The IPM Practitioner. Vol. XXII (1): 1-9. (From: Bio-Integral Resource Center, PO Box 7414, Berkeley, CA 94707. Tel: 510-524-2567

Pirone, P.P. 1978. Disease and Pests of Ornamental Plants. 5th ed. John Wiley & Sons, Toronto. 566 pp.

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