Monitoring Insects in the Landscape and Nursery

Table of Contents

• Introduction
• Monitoring
• Control
• Record Keeping and Evaluation
  

Introduction

There are four approaches to pest management in either the nursery or landscape. If customers did not object to the presence of insects on their plants, the natural populations could be left alone to fluctuate -- let nature take its course. When unattended, pest populations can reach disastrous proportions and the second approach is often adopted -- "spray 'em and stomp on 'em 'til none of 'em are a wigglin'. A third traditional approach is the weekly spray -- Just In Case, JIC. The fourth option, which has received much attention recently by both professionals and consumers, is Integrated Pest Management or IPM. Through monitoring populations, IPM determines optimum times and methods of control. This approach usually results in reduced pesticide use.

IPM programs integrate all suitable techniques to manage and reduce a pest population below levels of economic injury. Control practices are blended for compatibility, creating flexible and evolving systems (1).

IPM consists of 3 steps -- monitoring, controlling and evaluating.

| Top of Page |

Monitoring

Monitoring is an important step in an IPM program. Plants should be checked regularly, either weekly or biweekly. The same plants should be checked each visit in order to more easily notice changes and maintain continuity between inspections. The biology, including normal and abnormal growth, of the plants being monitored should be understood. When making observations, take note of the surrounding environment, neighbouring plants, types of mulches used, construction and traffic patterns, as these can all influence plant development.

Key pests and their damage to the plants being monitored should be identified. Knowing the life cycle of a pest is the best way to identify the easiest point of control. For example, the destruction of overwintering sites may reduce the need to spray subsequent stages. One should be acquainted with the environmental factors which favour or discourage the development of pest populations and how to integrate this information with the control program. In an IPM program, one should know what beneficial insects and mites are present. Generally, they are encouraged by IPM control strategies and help in keeping pest populations in check.

Monitoring should be performed on a regular basis. A 16X hand lens is helpful in identifying mites and other small pests. Other equipment which is useful include sticky traps and odour traps which may be sticky or non sticky.

A tapping tray made of a wooden frame covered with a white cloth or even just a white sheet of paper can be used to catch insects which fall from branches when shaken or "tapped" (Figure 1). A rubber hose should be used for tapping to avoid injuring plants.

Other traps can be designed to favour insect habits. For example, a board placed on the ground or rolled up burlap can be used to trap black vine weevil or strawberry root weevil adults.

Traditionally, calendar dates have been used for predicting pest development and timing of controls. Because weather is unpredictable from year to year, this method tends to be less reliable. When monitoring pest development environmental conditions such as temperature, rainfall and humidity should be considered as these may influence how quick or slowly a population may develop. Three methods which can improve pest activity prediction are:

• growing degree days
• phenology
• the key plants concept

Growing degree days (GDD)

This is a method used to calculate an accumulation of heat units over an established threshold temperature. Using daily maximum and minimum temperatures and subtracting the threshold or base temperature GDD are calculated:

[(max. temp + min. temp.)/2] - Threshold temp. = GDD

When using GDD it is important to know what threshold or base temperature was used in the calculation and what the starting date for temperature collection was, ie. Jan. 1 or April 1.

Phenology:

A second method of monitoring, which can be combined with GDD, is phenology (3). This uses plant development as an indicator to predict pest development. Since plant growth responds to temperature, rainfall and length of daylight, it is a good indicator of general pest development.

The "key plant concept"

This method utilizes certain plants in the landscape or nursery that are more susceptible than others and can serve as a focus for a management program (4). For example, Juniperus chinensis "Blaauwi" and Picea glauca "Conica" (Figure 2) make good indicators for mite development. Although some plants are relatively problem free, they are considered key plants because of the importance placed on them by a client. Key plants will change with location, number of plants and diversity of plants in an area. Each situation will be unique.

Figure 1: Monitor for spruce spider mite by shaking interior branches over a white sheet of paper and look for tiny specks (mites) that don't move very quickly. Use a hand lens to make sure they are mites (8 legs, two body parts etc.)

| Top of Page |

Control

The decision to control a pest must be made when a population reaches a control threshold. In fruit, vegetable and field crops, thresholds are designated when economic losses occur if the population develops beyond that threshold. Unfortunately with landscape plants, the threshold tends to be rather subjective because of aesthetic criteria threshold ie. how much damage a plant can withstand before it is visually unacceptable.

In an IPM program, control methods may be either genetic, biological, cultural, chemical or usually a combination of these methods. The methods chosen usually depend on the stage of insect development and how well it integrates into the system without making a great impact on beneficial insects or mites. Control strategies should be aimed at the weakest link in the pest's life cycle.

Genetic control utilizes plants or cultivars resistant to diseases, insects and tolerant of the growing conditions of the site. Biological control includes using beneficial insects, mites, or nematodes, properly timed to keep pest development in check. Cultural practices used such as cultivation, mulching, pruning, eradication and diversification of plants within the landscape should be adopted. Reducing and avoiding stress on the plants will help in minimizing pest problems. Chemical controls should be selected for least impact on beneficial insects and specific to the pest and stage of development. Broad spectrum chemicals should be avoided.

| Top of Page |

Record Keeping and Evaluation

Control methods and pest population developments should be evaluated regularly in order to access the effectiveness of control strategies. By recording populations, stages of development and general plant health with each visit, control methods and pest population developments are evaluated. Regular inspections allow one to access the effectiveness of control strategies.

| Top of Page |