Horticultural Crops - Understanding the Basics - Pest Management

Table of Contents

1. IPM Systems
2. Resistance
3. Summary

Pesticides are often used to control pests in horticultural crops. However, they are often viewed as environmental hazards by the public. Integrated Pest Management (IPM) promotes the responsible and reasonable use of pesticides in combination with non-chemical controls. Relying only on pesticides for control has several disadvantages:

• Insects, diseases and weeds can become resistant to pesticides.
• Resurgence of the pest when the pesticide application kills a high proportion of its natural enemies. The pest population increases rapidly because natural enemies no longer provide control.
• Secondary pests are created when pesticides kill the natural enemies of a non-target pest. Without natural enemies, the pest population increases to where it becomes a problem.
• Possible environmental contamination (e.g. pesticides in well water).
• Input costs for growers.
• Potential health hazards.
• Negative public attitude towards pesticides.

Figure 1. Secondary pests are created when a pesticide applied to control Pest A also kills many of the natural enemies of Pest B. Without natural enemies, the population of Pest B increases to become a problem.

IPM Systems

There are four components to an IPM system:

• Pest Identification
• Monitoring
• Control Guidelines
• Control Methods

IPM can reduce pesticide use and yet, maintains quality standards by treating pests as part of the total management system. Components of the system include the physical and biological environment of the crop and pest. Pest management practices are combined with production practices to achieve economical, long-term solutions.

Pest Identification

Identifying the pest properly helps decide which method of control is best. Nutrient deficiencies or physical damage can cause symptoms similar to those caused by pests. Also, the presence of pests does not always cause economic damage. Factsheets on pests are available from the Ontario Ministry of Agriculture and Food to help in identification.

Monitoring

Monitoring allows you to forecast and evaluate potential pest problems. It identifies the pests present, estimates numbers and examines conditions favourable to pests. Monitoring allows accurate timing of pesticide applications which may reduce pesticide use. Each field should be watched separately because conditions vary. Monitor at least once per week and preferably twice per week when the pest is usually most active. Scouts may be hired to monitor the crop.

Good record keeping is essential. Complete written records help decision-making by supplying information on previous problems and applications. It is useful to record:

• Crop health
• Pest species present
• Weather and other environmental conditions
• Population level of pests and beneficials
• Sprays and other controls applied

Figure 2. Weather conditions can be monitored by systems such as this TOM-CAST station. The information can then be used to predict some diseases.

Methods of Monitoring

There are several ways to monitor pests.

• Pheromone traps contain a chemical that attracts only the species of pest being monitored. This makes pest identification easier.
• Physical traps are visually attractive to many types of insects. This can make pest identification time consuming.
• Direct counts check the number of insects or the amount of disease on a set number of plants. Weed counts across the field will aid in herbicide selection.
• Weather monitoring calculates when insects will first emerge in the spring or when a disease is most likely to occur (e.g. BOTCAST predicts when Botrytis leaf blight infection takes place in onions so fungicides can be applied at the best time).

Control Guidelines

Control guidelines, or thresholds, indicate when pesticides need to be applied to prevent economic losses. Timing of control measures is critical. Guidelines for insects are based on an economic threshold where the cost of not applying a control will be higher than applying a control. Guidelines for diseases, weeds, nematodes and vertebrates may be based on weather, history of the field or region, stage of the crop and other field observations.

Figure 3. Eggplants are currently being used as a trap crop in tomatoes. Colorado Potato Beetles appear to prefer eggplant and potatoes over tomatoes.

Control Methods

There are three types of controls used in IPM systems: cultural, biological and chemical (pesticides). Cultural and biological controls are used wherever possible. When these are inadequate, pesticides are usually used. The most economical and reliable way to deal with pest problems is to avoid them when possible.

Figure 4. Removing pear suckers will reduce psylla numbers.

Cultural Control

Many cultural practices reduce pest damage. They prevent problems and are effective and economical. Examples are:

• Site selection - choose sites that are less favourable to pests.

• Cultivar selection - choose varieties that are resistant, when possible.

• Crop rotation - rotate away from crops of the same family (e.g. turnip, cole crops and canola) to prevent some pests and help control weeds.

• Inter cropping - planting a mixture of crops may reduce insect damage (e.g. underseeding brussels sprouts with clover). However, competition may reduce yields in some cases.

• Cover crops - can provide shelter for beneficials.

• Trap crops - plant crops to attract the pest away from the main crop. Pests can be killed with a localized spray. For example, in tomatoes, trap crops of potatoes and eggplant can be used for Colorado Potato Beetle (CPB).

• Tillage - provides weed control and may kill some insects and pathogens.

• Time and method of planting - may help to avoid a generation of the pest.

• Sanitation - remove pest habitat such as cull piles, dropped fruit or other plants. For example, potato cull piles provide a place for potato blight to overwinter.

• Pruning - removes a food source or a point for infection. For example, removal of pear suckers helps to keep psylla numbers down.

• Clean seed and transplants - avoid introducing pests. Use seed that has been certified disease-free.

• Plant health - healthy plants are less prone to infection.

• Irrigation - use good timing/scheduling to prevent disease.

Figure 5. Use of clean, disease-free plants such as these pepper transplants will help to prevent disease problems.

Biological Control

Biological control uses a pest's natural enemies to control the population of the pest. Natural enemies include predators, parasites and diseases. The term, "beneficials", refers to predators and parasites of insect pests. IPM systems take maximum advantage of control by natural enemies.

Figure 6. IPM systems take advantage of natural enemies such as this parasitic wasp which is emerging from an aphid exoskeleton.

There are two ways in which biological control is managed:

Encouraging natural enemies - provide shelters or food sources for natural enemies. For example, a sod or weedy cover in an apple orchard provides an overwintering site for predatory mites. These mites control European red mite and two-spotted spider mite.

• Select pesticides that have minimal effect on beneficials. For example, Bacillus thuringiensis (Bt) is specific to certain types of caterpillars.
• Time or schedule pesticide applications to have least effect on beneficials.
• Apply pesticides only when needed.

Adding natural enemies to provide control - adding natural enemies is not usually economical in the field. However, in greenhouse operations, it is often possible. For example, whitefly can be controlled with Encarsia formosa (a parasitic wasp). At present, work to develop pest diseases is continuing. In the future, more of these products may come on the market.

Figure 7. Another example of a natural predator feeding on an aphid in a greenhouse operation.

Resistance

Refers to the developed ability of a pest to survive applications of pesticides at rates that once killed most of that species. This ability is passed from generation to generation making the pesticide useless. Colorado Potato Beetle resistance, for example, is a major problem. With fewer new pesticides coming onto the market, resistance could become a more widespread problem. Resistance is most likely when pesticides are applied at lower-than-recommended rates and when either the same pesticide or pesticides with the same mode of action are repeatedly used.

Resistance Management

• Use pesticides only when needed.
• Avoid pesticide residues.
• Alternate pesticides with different modes of action.
• Use recommended rates of pesticide.
• Use other controls where possible (e.g. rotary hoe for weeds).
• Time pesticide sprays for the most vulnerable stage. For example, spray for the larvae of Colorado Potato Beetle rather than the adult.

Text equivalent

Chemical Families and Their Common Names

Chemical Family: Biological Control (Bacillus Thuringiensis)

• Common Names: Dipel, Thuricide, Trident, M-One

Chemical Family: Synthetic Pyrethroids

• Common Names: Ambush, Cymbush, Ripcord, Pounce, Decis, Belmark

Chemical Family: Carbamates

• Common Names: Pirimor, Lannate, Furadan, Sevin, Temik, Vydate

Chemical Family: Organophosphates

• Common Names: Guthion, Orthene, Metasystox, Parathion, Malathion, Cygon, Monitor, Lorsban, Diazinon

Chemical Family: Organochlorines

• Common Names: Thiodan, Methoxychlor

Summary

IPM systems can be effective and economical for horticultural crops. While the level of damage may be higher than when using chemical controls, long-term effectiveness is better. To be successful, IPM requires time and careful attention to pest identification and monitoring, control guidelines and methods of prevention and control.

Horticultural Crop Production