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Ministry of Agriculture, Food and Rural Affairs

Integrated Pest Management

An integrated pest management (IPM) strategy is one that combines all available tools to reduce pest populations to an acceptable level in the most economic and environmentally friendly fashion. These tools include cultural, mechanical, biological and chemical pest control measures, as well as regularly monitoring for pests. It is important to note that most of these tools do not involve pesticides. For many specialty crops there are few registered chemicals and biological controls. The lack of registered products makes the adoption of cultural practices to minimize or overcome these production challenges very important. There are numerous non-pesticide options that can be used to help prevent or reduce the impacts of pests, including cultural and natural controls. While many of these measures on their own might not provide sufficient control, in combination they may help in reducing pest populations.

IPM programs make extensive use of information collected in the cropping system and require careful management by the grower. To implement an IPM program it is important to understand:

  • pest identification, biology and behaviour
  • beneficial organisms
  • monitoring and diagnostic techniques
  • use and timing of appropriate management tools
  • record keeping
  • sprayer calibration (if products are registered on the crop)

Integrated pest management is a broad term that encompasses a wider variety of techniques, many of which are crop-specific, then can be adequately covered in one document. What follows is a general introduction to some of the basic elements of IPM.

PREPARATION AND RESEARCH

Successful integrated pest management is greatly enhanced by adequate preparation - determining what pests are likely to be attracted to a crop and planning methods for avoiding them. This should be done well in advance of planting the crop in the field. This is particularly important for specialty crops with few registered pest control products, as often the only available management tools are preventative tactics that must be in place before the crop is in the ground.

Unfortunately, this step is often overlooked by growers of new or unusual crops, because they often experience a "honeymoon" period where pests are not a problem. Pests are often not a problem for the first few years of production of a new crop. There are many reasons for this. It may take time for local pests to recognize the new crop as a food source, low acreage may make the crop difficult for pests to find, there is little pest inoculum in the soil initially, etc. Regardless, it is easy to be lulled into a false confidence that the new crop has no pest problems. Unfortunately, pest populations usually do build up to damaging levels eventually and it is important to be prepared to deal with them. Do not assume pests will not be a problem on a crop just because they are not observed in the first few years of production. The best way to prepare for pests in a new crop is to be proactive - use preventative strategies to avoid pests, scout regularly and be prepared to deal with arriving pests early.

It is impossible to predict all the possible pests of a new crop, but a little research can go a long way. Look up the major pests of the crop in the areas where it is traditionally produced. If these pests are also present in Ontario or have close relatives that are present here, it's a potential pest of the specialty crop. If the crop is closely related to a crop already being grown in Ontario, then prepare for the possibility that pests of the conventional crop will also attack the new one. For example, many specialty cucurbits such as oriental cucumber, bitter melon and bottle gourd are affected by some of the major Ontario cucurbit pests, including cucumber beetle and downy mildew. Each of the crop profiles included in Specialty Cropportunities, includes a list of potential pests for that crop in Ontario. These have either been observed on the crop in Ontario by crop specialists, researchers or growers, or are considered to be likely problems due to their impact on the crop in its native growing region or on related crops. More detailed information on some of these pests can be found in the general insect and disease sections on the main page.

Once potential pests have been identified for a crop, determine the available management options. Growers who would like to rely on pesticides to control pests, should determine what products are registered on the crop of interest before you plant it. Many non-traditional crops have very few registered products. Determining what pest control products are registered on a low acreage specialty crop can be challenging. More detailed information on this topic is provided in the section on Pest Control Products for Specialty Crops. For crops with few pesticides but serious pests, consider whether you are willing to take the risk of losing your entire acreage to pest damage.

If there are no registered chemicals available and damage cannot be tolerated, then the only option will be various non-chemical methods of pest control. These techniques can effectively reduce pest populations in many situations; however they can be labour-intensive and costly. Additionally, many of these techniques are preventative, which means they will not be effective after the pest has been found in the crop.

Perhaps the most effective defence is to avoid getting the pest in the first place. Opt for pest-resistant varieties and high quality seed, if possible. For some crops, certified disease free seed or transplants are available. These may be more expensive, but are often worth the cost. Keep a clean field - use vigilant field sanitation and management of crop residues.

Crop rotation can keep levels of certain damaging soil insects and diseases lower, as is the case for verticillium wilt in eggplant. It may be tempting to shorten or eliminate crop rotations if a non-traditional crop shows no signs of pest damage in its initial years of production. However this will usually lead to problems in the long run, as it encourages the build up of pest populations in the soil.

A number of other techniques can sometimes also be used to reduce pest populations, including intercropping, varying planting dates and densities, tillage, trap crops and natural enemies. More information on these techniques can be found in the Cultural and Natural Controls section of this document, or on the OMAF and MRA website.

MONITORING

Systematic monitoring of pest populations, weather conditions, plant health and disease symptoms are critical components of an IPM program. This will allow early detection of pest populations, before they become too big. The accurate and timely diagnosis of a plant problem is important if the most effective control measures are to be selected and implemented. This, in turn, will minimize the damage to the plant's yield and aesthetic value. This is particularly true with a specialty crop, when you cannot be sure of all the pests that are likely to attack it or whether chemical controls will be available.

A. Scouting

Crop monitoring in IPM is commonly referred to as scouting. Scouting is the routine, systematic inspection of a field to monitor crop development, plant health, pests and beneficial organisms. Routine inspection is important, as this allows for observations of how pest populations change throughout the growing season, which can have important impacts on control decisions. This can be done by professional scouts, the grower or an experienced farm worker.

Before beginning a scouting program, review the potential pests identified in initial research. Learn to identify life stages and damage caused by the likely diseases and insects and understand their biology and life cycle. Learn to recognize beneficial and harmless insects. If previous crops planted in the field may share pests with the specialty crop, use historical data to identify hot spots and previous problems. Become familiar with the crop's normal appearance and growth pattern. This helps in identifying any abnormalities.

The following are some general tips on scouting taken from OMAFRA's CropIPM Resource and other publications. Consult the OMAFRA website for more detailed information on scouting.

  • Assemble your scouting tools and carry them with you into the field:
    • a 16-20x hand lens
    • traps
    • collection bags and vials
    • field maps
    • flag tape
    • shovel or sturdy trowel
    • pocket knife
    • scouting forms and record sheets
    • soil corers and a bucket can be useful if sampling for nutrients or nematodes
  • Monitor at least once a week and preferably twice a week during critical stages.
  • Monitor at approximately the same time each day and keep the light behind you.
  • Inspect plants in several areas across the field to get an accurate idea of pest pressure.
  • Scout the edges of the field and interior of the field separately. Give special attention to border areas
  • Stand back and look for patterns, such as patches or areas of poor plant growth or where colour is off.
  • Get close and examine fruit clusters, the underside of leaves and inside the canopy, etc.
  • Some symptoms to look for or other considerations include:
    • Does the plant show wilt, dieback or discoloration
    • Moulds, mildews, mushrooms and other spore producing structures; these are the signs of fungi. Look for the presence of a cloudy fluid (bacterial ooze) which might indicate an infectious disease.
    • Inspect the plant(s) closely for webbing, cast skins, excrement, and other signs of insects, as well as for the pest themselves. Many insects, such as aphids, caterpillars and beetles can easily be seen on plants. Others such as maggots are not likely to be seen until damage is done. If these pests have been a problem in the past, preventive measures will be required
    • How are symptoms distributed on the plant, and on other plants in the area; which non-crop species are affected (if any)
    • Don't forget that many pest problems occur out of sight, under the soil surface. It may be necessary to dig up a plant to look for root damage or soil insects.
    • Bear in mind that weather conditions, site, soil conditions and cultural practices such as chemical use, fertilizer application, and watering practices will also affect plant growth. Often, it is a combination of factors that create the problem. Plants under stress from poor environmental conditions, for example, are more susceptible to infectious diseases and pests.
  • For each visit, take detailed records, including:
    • the stage of crop development
    • disease severity
    • population levels of insect pests and beneficials
    • damage observed
    • record the location of damage on a field map
    • rainfall amounts, daily highs and lows, and weather events
    • pesticides applied and other control measures used
  • Scouting can include the collection of samples. Sample collection involves the collection of data to represent the entire area being monitored. This involves collecting plant material to bring to a microscope or magnifying glass for closer inspection or counts of very small pests (e.g. number of mites per tree). To sample:
    • Divide large areas into sample blocks.
    • Walk in a W or zig-zag pattern across the field to collect samples from a representative area.
    • Look away from the plant when you take samples of leaves and fruit, etc., otherwise you will tend to choose damaged leaves or fruit and bias the sample

B. Diagnosis

Accurate diagnosis of the pest causing a problem is critical to effective and cost efficient integrated pest management. Treating for the wrong pest costs a grower time and money, and a delay in treating the correct pest can lead to crop loss. Insects, diseases and abiotic damage can all be mistaken for one another. For example, mites and leafhoppers can both cause bronzing and distortion of hops leaves, as can nutrient deficiencies. Brittle and distorted leaves can also occur as leaves die from some diseases. Consequently it is important to remember that for specialty crops in particular, it will be easy to misidentify pests.

By following the steps outlined in the previous sections and routinely monitoring for likely pests, growers should be able to recognize emerging pest problems in new crops. However, growers of specialty crops are at a disadvantage because their crop is new to Ontario and there is no established body of information on the major pests, as there is for larger acreage crops.

There is a wide array of resources available to aid in identifying pests. Some of these include:

  • OntarioCropIPM, an online resource aimed at identifying pests of major horticultural crops in Ontario. Although targeted at larger acreage crops, there are many photos of pests that will also attack specialty crops. Note that this resource may mention pesticides that are not registered on specialty crops.
  • BugGuide is an online site with a large collection of photos of North American insects.
  • The American Phytopathological Society publishes a series of books with detailed plant disease information for specific groups of crops (e.g. Compendium of Brassica Diseases, Compendium of Lettuce Diseases, etc.). They can be found at their on-line store, at many university bookstores or at various online booksellers websites.
  • Some useful books include:
    • Howard, R.J., Garland, J.A. and Seaman, W.L. 1994. "Diseases and Pests of Vegetable Crops in Canada". Canada Phytopathological Society.
    • Koike, S.T., Gladders, P. and Paulus, A.O. 2006. Vegetable Diseases: A Color Handbook. Academic Press.
    • Datnoff, L.E., Elmer, W.H. and Huber, D.M. 2007. Mineral Nutrition and Plant Disease. American Phytopathological Society.
    • Marshall, S.A. 2006. Insects: Their Natural History and Diversity. A Photographic Guide to Insects of Eastern North America. Firefly Books.
  • A number of resources are aimed at aiding in identifying beneficial insects and distinguishing them from pests. These include:

Despite the array of resources available, it can still be difficult for growers of many crops, especially new crops, to accurately identify a pest. Where there is significant damage and a pest cannot be identified, professional help may be required. Places to seek help include:

  • Laboratories for Leaf Analysis
  • Laboratories for Soil Analysis
  • University of Guelph Pest Diagnostic Clinic
  • Local agrologists and crop consultants
  • OMAFRA specialists

THRESHOLDS

Thresholds are control guidelines that indicate when pesticides should be applied to prevent economic losses. Timing of control measures is critical. Spray guidelines for insect pests are based on an economic threshold where the lost income from not applying a control will be higher than the cost of applying a control. In other words, some damage to the crop is tolerated, as long as this damage does not exceed the cost of the control. For insect pests, thresholds are usually based on the presence of the pest at certain levels. Thresholds for direct pests, which feed on fruit and have an immediate effect on fruit quality, are generally lower than thresholds for indirect pests that feed on leaves, stems or roots. For diseases, guidelines may be based on the pest's damage potential. This is estimated through the use of weather models, crop tolerance, stage of crop development and field observation. Thresholds have not been developed or validated for all pests in Ontario. Even established thresholds require adjustment for different varieties, markets, and crop vigour.

Thresholds are not available for most specialty crops grown in Ontario. Thresholds may be established for specialty crops in other areas where they are grown on a larger scale, or for the pest on other crops grown in Ontario. While these can serve as a guide, in most cases, growers will have to use their own judgement as to how much pest pressure their crop can tolerate.

Consider the health of the crop, as a plant that is stressed by other factors will be less able to withstand pest damage than a healthy plant. The timing of the damage will also be important, as plants are often more susceptible to pest damage at certain stages of their development. For example, vegetables are extremely vulnerable to insects, diseases and weed competition as seedlings, but can tolerate some damage later in development, particularly if it is a non-harvestable part. Consider also the location and degree of damage. Available control methods should also be considered. Control strategies that take a long time to take effect (for instance some natural enemies) or will only provide partial control, should be implemented when pest populations are lower.

Finally, remember that some pest damage is normal on plants and that minor damage usually will not have a lasting impact on them. Some non-traditional crops can tolerate more pest pressure than the conventional crops you may be used to. Two examples are prairie grass (for biofuel) and sea buckthorn. Though these crops may need some assistance in the establishment year, both eventually develop a sufficiently extensive root system that they can out-compete the weeds. Neither crop has any registered herbicides, so growers have had to rely on mowing to keep weeds down. Although the resulting field can look messy, the crops do not seem to be affected. Additionally, in some cases you can focus your pest control efforts on the plant part that is being harvested. For example, you may be able to tolerate leaf spot on kohlrabi if symptoms are restricted to the leaves, because only the stem is typically sold. This is not always the case, however, as excessive damage to non-harvestable parts can sometimes impact yield.

PEST MANAGEMENT

Successful integrated pest management emphasizes multiple tactics, including chemical, cultural and biological. Determining what chemical controls are available for specialty crops is complicated, and consequently is the subject of a separate section of this resource. Below, cultural, mechanical and biological control tactics are broadly discussed.

A. Cultural Control Methods

Cultural control methods involve manipulating planting, cultivation and other practices in ways that make the environment less favourable for the development and spread of pests. They are typically implemented early, sometimes even before planting, because the best way to manage pests is to prevent them from occurring in the first place. This is always more effective than attempting to control pests after they are infesting plants. Some of the most important involve keeping plants as healthy as possible, because healthy plants can withstand pest attack better than plants growing under one of several different environmental stresses.

Crop Rotation - Crop rotation involves the planting of non-related crops in a particular location in successive years to minimize the chances of plant-specific disease organisms and pests building up in the soil. Crop rotation is an important part of pest management because it meets objectives such as reduced pest habitat, soil improvement, and reduced pest food source. Rotation should involve crops that can successfully compete with weeds and those that can not, crops that are in different plant families, among other considerations. Crop rotation reduces the risk of plant disease, reduces the population of pests specific to one crop, increases yields, and reduces soil erosion. The longer the rotation, the less opportunity there is for pests to become established. By including a legume crop in the rotation, soil structure, organic matter, and nitrogen supply will improve.

Crop rotation is only effective on certain types of pest, namely those that have a limited host range, are not extremely mobile and do not survive in the soil for more than a year or two. Crop rotation is most effective at managing pests that are very host specific, are not very mobile and have a short persistence in the soil. Good examples of these types of pests include the Swede midge and the fungal disease Sclerotinia. Swede midge, a maggot that attacks crucifers and is not capable of long distance flight, can be managed by rotating out of Brassica plants for two years. Sclerotinia spores germinate with the first couple of years of being deposited, so rotating out of host crops for 3-4 years is an effective way of controlling this disease. Pests which can persist for many years in the soil, such as wireworms (3-6 years) or fusarium wilts (5-7 years), pests with a broad host range (e.g. tarnished plant bug, Botrytis) and pests which fly or are blown long distances through the air (e.g. cucumber downy mildew), are not well controlled by crop rotation.

Cover Crops - A cover crop can be defined as any crop that is included in a crop rotation with the primary purpose of providing a biological benefit, rather than to be sold for profit. Cover crops provide numerous benefits (e.g. adding organic matter, improving soil structure), that can include reducing pest populations, depending on the type of cover crop. Cover crops like pearl millet, marigold and sorghum sudan (make sure you have the right variety though for the sorghum eg. Sordan 79 or Trudan 8) can reduce nematode numbers in the pre-plant year for many crops. When cover crops are used to reduce nematodes, the goal is to establish actively growing, pure stands of these cover crops. Planting and establishment must be focused on getting a dense stand and achieving the most top growth possible. Use of cover crops to suppress pests requires very careful management. For example, while some varieties of pearl millet are used to suppress nematodes, others can actually increase populations. Good weed control is also necessary, as many weeds can serve as an alternative host for nematodes, thus allowing them to persist in the soil. Finally, proper mowing and quick incorporation is essential for the pest suppressive effects of many cover crops to work.

Resistant Varieties - Plant varieties can be extremely variable in their response to insect and disease pests, with some being much more able to tolerate damage than others. The resistance to damage can be due to the possession of physical characteristics or chemicals that repel or kill pests, through an ability to remain vigorous in the face of heavy pest damage or for other reasons. For example, hazelnut varieties with tighter buds are less susceptible to invasion by bud mites. Plant breeders have incorporated some of this genetic resistance to various diseases and pests into plants. It is now possible, therefore, to select non-susceptible or resistant plant varieties. Information on resistant varieties may be available from seed suppliers or university or government extension sites from areas where a specialty crop is grown and bred. Remember, though, that some resistant varieties can still suffer damage if pest populations are extremely high. Additionally, resistant varieties will also vary in temperature, fertility and other requirements, and these should also be considered to determine if they will adapt to local growing conditions.

Site Selection - Choose sites less favourable for pest development through site selection. This involves knowledge of the conditions that influence the health of your crop and pest populations. Not all plants are adapted to all sites, climatic zones, soils, soil pHs, light availability or similar environmental conditions. Plants that grow in unsuitable locations are predisposed to diseases, insects and secondary problems. Woody and herbaceous perennial plants are given hardiness zone ratings that correspond to geographic regions of Ontario and Canada. Buy only those plants that carry a hardiness rating equal to or higher than your location.

Many crops (for example ginseng and lavender) are susceptible to soil borne diseases unless they are planted in well drained locations. Some fungal leaf diseases, such as downy and powdery mildews, will be less prevalent if crops are grown in open locations with good air movement. Wireworm populations are often highest in fields with a recent history of pasture, turf, forages or cereals. Crops that are susceptible to wireworms, such as sweet potatoes or oriental radish, should not be planted after these crops.

Crop Health - Anything you can do to keep the crop healthier will help the plant to resist and tolerate pests.

  • optimum nutrition - not excessive and not deficient. Proper fertilization is key to ensuring that plants are healthy enough to withstand pest attack. However plant fertility can influence pests in other ways as well. Excess fertilizer promotes excess vegetative growth, which can attract aphids and may also increase humidity, thereby favouring disease development. Finally, plant symptoms associated with over- or under-fertilizing can be easily mistaken for pest damage, which may lead to misdiagnosis
  • good soil conditions - good structure, no compaction, active soil OM.
  • no moisture stress - neither too much or too little. Many diseases are spread by spores which require moisture on leaves and stems to germinate and cause infection. Fungi and bacteria are also often worse when plant surfaces and soil are excessively wet for long periods of time. When, how and how much you water your plants can therefore be important in limiting the spread of disease. Ensure plants are neither over nor underwatered. Overwatering promotes root rots and other diseases, while underwatering contributes to the development of unhealthy plants which are less tolerant to pest attack. If diseases that are spread by splashing are present in your field, avoid overhead watering. Water in the morning so that plants dry before nightfall, or only on dry days. Do not work in the field when plants are wet, as you may unwittingly spread disease when you brush against them.
  • Maintain correct plant population. Planting at the proper depth ensures that seedlings emerge quickly and reduces the risk of damping-off fungi. Even, wide spacing guards against crowding, which can lead to spindly succulent growth, poor ventilation and poor drying conditions. These increase the likelihood that problems such as botrytis, white mould, root rots, damping-off and foliar diseases will develop.
  • use clean seed and healthy transplants

Adjusting Planting/Harvest Dates - It is sometimes possible to alter planting time to avoid or repel pests. If you know the biology of the pest attacking your plant, you may be able to time planting to avoid damage. For example, altering planting times to avoid the egg-laying or spore-discharge stage of some pests may prevent damage. In other cases, planting early (before pests arrive) may allow young plants to establish and develop to a point where they are better able to withstand pest attack. You may also want to time planting to avoid environmental conditions that are conducive to pest development (e.g. cool, wet early spring weather favors many fungal diseases and millipede feeding on seeds). Planting time can also be critical to minimize the potential for seed and seedling rot. Do not plant large seeded vegetables when the weather is cool and moist, as seed rot can easily overcome the seedlings before they emerge. Wait until the soil is warm and moist.

Crops left too long in the field are more susceptible to pests or storage rot diseases. It is important therefore both to harvest on time and to properly prepare the crop for storage. Avoid rough handling of fruits and vegetables. This can cause wounds which, in turn, can become infected by secondary disease agents. In some cases it may also be possible to avoid applying pest controls by harvesting the crop early, before pests reach damaging levels. This will only be effective if the pest occurs late in the season. For example, if summers are relatively dry, completing basil harvests by mid August may reduce losses to downy mildew.

Sanitation - Sanitation involves the removal of material which allows pests to survive or be transported between plants or crops. Because many insects and diseases overwinter in plant debris and in weeds, the most important sanitation measure involves the regular removal of such material. Pull up all infected plants and weeds promptly and dispose of them outside the field. For larger plants, such as trees, cut off diseased or damaged branches. Pest-infested plant material should be destroyed. Do not compost diseased plants, or leave them in the field, as the sustained high temperatures required to kill problem-causing insects, nematodes, fungi and weed seeds cannot be guaranteed. Some insects overwinter under boards, bricks, stones and similar objects. Remove all such hiding places and store them away from the soil. Additionally, do not leave vegetables or fruits on the soil from one year to the next, and dispose of prunings from woody plants promptly.

Sanitation also includes careful attention to the health of new plants or seeds introduced to your field. Use only high quality, pest-free and disease-free planting material and seeds. If possible, quarantine new transplants for a period of time before placing them in your field to allow time for possible pest symptoms to develop.

Some insects and diseases can be transferred between fields on tools, farm equipment or worker clothing. Take appropriate steps when moving between fields to ensure potentially infested soil is not being transferred from one field to another. Try to enter and work in pest infested areas of fields last, and disinfect equipment, hands and shoes after working with infected plants. Thoroughly wash and disinfect all pots and planters before reusing them, ensuring all soil is rinsed off.

Some weeds serve as reservoirs for insects and diseases. They also compete for nutrients and moisture. Always keep weeds under control both within the field and in surrounding areas. Weed control should begin before plants emerge, to avoid pests moving onto them from the destroyed weeds.

Crop Diversity - If a wide variety of plants are grown in a small location, it is more difficult for flying insects to find the right plant on which to feed. This can also slow the spread of diseases and provide a habitat for beneficial insects. For this reason, inter-cropping, or planting alternating varieties of crops, can help reduce pest problems more than if crops are planted in large blocks. This can include trap crops, intercropping, farmscaping and other methods.

Trap crops or plants can sometimes be used to lure an insect away from the plant you wan to protect. Plants that the insect prefers to eat are planted near the crop, luring the insect over to the trap crop. The trap crop may then need to be destroyed or a control applied. For example, mustard trap crops have been used to help reduce flea beetle populations on cole crops and eggplant can be used as a trap crop for Colorado Potato Beetle. However, to be effective the trap crop has to be much more preferable to the insect than the specialty crop, and you need to ensure that the insect has no way of moving back to the crop after the trap crop is destroyed. For example, mint has been used as a trap crop to lure four lined plant bugs away from ginseng. Mint is less likely to be effective as a trap crop for lavender, as both these crops are in the same plant family and appear to be equally attractive to four lined plant bug.

B. Mechanical Control Methods

Mechanical control methods are those that physically prevent the pest from attacking or injuring the crop. Hand weeding and use of fences to exclude deer and other wildlife are examples of mechanical, or physical controls. Mechanical controls such as vacuums, flaming, row covers, hand picking can all work but may have high cost. Some strategies work well but must be suited to the crop situation and scale of production.

Physical Removal - Physically removing pests by hand or other means can be effective if just a few pests are present, the field is very small and it is done frequently. Soft eggs or soft-bodied insects such as aphids can be crushed when they are found, while caterpillars, slugs, snails, cutworms, grubs and other larger pests can be picked off and dropped into a bucket of soapy water. Caterpillar tents or webs can be ripped off trees and dealt with similarly. Larger groupings of pests can be dislodged from sturdier plants by aiming strong jets of water at them, however care must be taken that the plant does not get so wet that disease development is encouraged. Similar removal of diseased plant material may also be used to slow the progress of certain diseases, for example pruning of disease portions of branches, however this is generally not as effective with diseases as with insects. Some growers have experimented with vacuums to remove certain

Mulching - A mulch is any covering placed on the soil surface to help plants, including wood chips, fabrics and plastics of various colours. Mulches are often used to help warm the soil or prevent it from drying out, however they can also help in controlling weeds and some insect pests. Black plastic mulch is often used for weed control, however exercise caution as it also heats the soil and so can damage some crops. Reflective mulches made of aluminum foil or other silver coatings may help keep aphids and whiteflies from seedlings and smaller plants. Different colours of mulches can be used for different purposes.

Row Covers and Other Barriers - Various types of barriers can be constructed around and over plants to help protect them from insect and vertebrate attack. Row covers and plant cages, which are hung over young plants, are among the most common. Row covers have traditionally been used to promote plant earliness by increasing temperatures, however they can also be used to keep migrating pests, such as cucumber beetles, flea beetles and aphids, off young, vulnerable plants. Typically the covers are removed once plants are old enough to withstand damage - this allows pollinating insects access to flowers, and prevents plants from being overheated later in the summer. Homemade cages, often made of fine mesh fabric covering a wooden frame, are sometimes used. Alternately a variety of synthetic barriers are available for purchase.

C. Biological Control

Biological control uses a pest's natural enemies to help suppress populations. The natural enemies, collectively known as "beneficials", may be predatory insects, parasites, pathogens or nematodes. Predatory insects kill and consume multiple other (usually smaller) insects and include ground beetles, lady beetles, praying mantids and certain mites (Table 1). Parasitic insects or parastioids lay their eggs in or on the bodies of another insect, and the parasitoids young feed on the host insect, typically killing it (Table 2). Most parasitic insects are tiny wasps or flies. Pathogens are microorganisms which infect and kill insects and mites. Insects are naturally susceptible to a wide variety of bacteria, fungi, protozoa and viruses. Finally, nematodes are tiny worms similar to those that attack plants. However instead of plants, they invade insects through natural openings and feed on them from the inside out, killing them.

Many predators and parasitoids are closely related to the pest species and will look very similar. You would be wise, therefore, to get to know the more common beneficial species in your field. Pictures and information on beneficial insects can be found on the OMAFRA website or at the other sites mentioned earlier in this section. To determine whether an insect is the problem or part of the solution, look for feeding injury on the plant. Watch the insect to see if it is feeding on the plant or on another insect. Look at its movements; fast-moving insects are generally predators as they need to catch their prey.

There are two main ways to use biological control - by taking various actions to promote and conserve naturally occurring populations of beneficial organisms, and by augmenting these populations through the addition of commercially available natural enemies.

Promoting Beneficial Insects - The best way to encourage biological control in your crop is to promote natural enemy populations by providing them with favourable habitat. For many insect parasites, the adults will survive longer if they have a source of nectar to feed on, while some predators must feed on pollen before they can reproduce. Many natural enemies also do better when sources of shelter are provided. To promote populations of these insects in your field, plant a variety of flowering plants which provide pollen and nectar for adult beneficial insects. When selecting plants, ensure you have selected species that will not become weedy or invasive in your field. Native plant species may be a good choice for this purpose. Maintaining a diverse habitat in and around the field will provide beneficial insects with shelter. There are several tactics that you can use to do this, but there are risks. Mulch between rows of plants provides a natural refuge for predators such as ground beetles, but may also encourage slugs and sowbugs.

You must also be careful in your use of pesticides in the field, as some beneficial insects are killed by smaller doses of insecticides than are required to kill harmful insects. You must also take care to avoid pesticide drift to neighbouring plants which may harbour beneficial insects.

Augmentation - Numerous species of natural enemies are sold for release in crops and gardens as biological control agents. While release of these biological controls has been very successful in greenhouses, many have limited value in outdoor fields. Some, such as preying mantids, are generalist predators which feed on so many species that they will have limited impact on populations of the particular pest you want to control. Many introduced natural enemies will not remain in your field for long periods of time.

Native predators such as ladybird beetles can be introduced, but if you buy beetles (Hippodamia convergens) imported from the U.S. you will realize little benefit. These beetles are collected while wintering in the mountains of California. Upon release here, they fly away before settling down to feed again. Few if any will remain in your field to provide the desired control. As well, the ladybird beetle can only help control outbreaks of non mobile insects such as aphids, and is only effective if introduced before the pest population is well established. On the other hand, there are beneficial parasitoids and predators that occur naturally in Ontario, and can be bought from suppliers. Routine introductions are necessary if they are to be successful.

A number of products based on insect-parasitic nematodes are available for sale in Ontario. These can be effective in helping to control populations of certain soil pests. Because these products are based on living organisms, close attention to storage and application instructions on the labels is important to their effective use.

A variety of pathogens of pest insects and plants are available commercially, however they are formulated and regulated as insecticides, and will not be discussed in this module.

If you do choose to introduce natural enemies, stick with commercially available products from reputable suppliers. Never introduce a beneficial insect you or someone else have collected from other areas and transported to Ontario. Introducing foreign organisms is against the law, and could lead to serious ecological problems in the long run.

Table 1: Common Predators and Their Prey

Predator Prey
Lady beetles and larvae aphids, mites, thrips and other small insects and insect eggs
Ground beetles caterpillars and small soft bodied insects
Syrphid flies aphids and small caterpillars
Lacewing larvae aphids, insect eggs, thrips and other small insects and larvae
Assassin bugs aphids, insect eggs, leafhoppers and other small insects and caterpillars
Other true bugs, including predatory stink bugs, pirate bugs, big-eyed bugs and damsel bugs mites, thrips, aphids and other small insects and larvae, insect eggs and caterpillors
Dragon flies and damsel flies mosquitoes and other flying insects
Praying mantis general feeders on a wide variety of insects
Frogs, snakes and mice a variety of insects

Table 2: Common Parasitoids and Their Hosts

Parasitoid Host
Ichneumonid wasps moth, butterfly, beetle and fly larvae and pupae
Braconid wasps moth, beetle, and fly larvae and various insect pupae and adults

Table 3: Commercially Available Natural Enemies

Target Pest Natural Enemy
Type Species
Mites Predatory Mites Phytoseiulus persimilis
Galandromus occidentalis
Amblyseius fallacis
Mesoseiulus longipes
Neoseiulus californicus
Predatory Flies Feltiella acarisuga
Predatory ladybeetles Stethorus punctillum
Whiteflies Parasitic wasps Eretomocerus mundus
Eretomocerus eremicus
Encarsia formosa
Predatory Ladybeetles Delphastus catalinae
Aphids Predatory Ladybeetles Hippodamia convergens
Adalia bipunctata
Predatory Lacewings Chrysoperla carnea
Chrysoperla rufilabris
Praying mantis (predatory) Tenodera aridifolia
Predatory fly larvae Aphidoletes aphidomyza
Parasitic wasps Aphidius colemani
Aphidius matricariae
Aphelinus abdominalis
Thrips Predatory mites Amblyseius swirskii
Amblyseius cucumeris
Amblyseius degenerans
Orius insidiosus
Caterpillars Predatory Soldier bugs Podisus maculiventris
Parasitic wasps Trichogramma pretisoum
Trichogramma minutum
Trichogramma ostriniae
Parasitic nematodes Steinernema carpocapsae
Various soil beetle larvae Parasitic nematodes Heterorhabditis bacteriophora
Heterorhabditis megidis
Steinernema kraussei
Leafminers Parasitic wasps Dacnusa sibirica
Diglyphus isea
Mealybugs Parasitic wasps Leptomastix dactylopii
Predatory ladybeetles Cryptolaemus montrouzieri
Scale insects Parasitic wasps Aphytis melinus
Metaphycus spp.
Predatory ladybeetles Lindorus lophanthae
Slugs Parasitic nematodes Phasmarhabditis hermaphrodita

Note that many, though not all, of these natural enemies are targeted more for greenhouse situations and may not achieve successful control in outdoor landscapes. Not all natural enemies are equally effective

A list of suppliers of beneficial insects and mites can be found on the OMAFRA website at the following link: http://www.omafra.gov.on.ca/english/crops/resource/beneficial.htm