Insect and Mite Control on Woody Ornamentals and Herbaceous Perennials

Bulletin 504

Detection and Monitoring of Insects and Mites
on Woody Ornamentals and Herbaceous Perennials

Introduction

Integrated Pest Management usually has an emphasis on the selection and use of the three control options - chemical, biological and cultural. However, even though a control option may be selected one still has to determine when to use the control. Therefore, monitoring pest populations (as well as the biological controls) becomes central to determining when controls are to be used.

Pest monitoring is simply using those techniques and tools that allow the pest manager to determine when and if control action is needed.

Preventive Pesticide Applications

Unfortunately, many pest managers simply apply a pesticide for control of anticipated insect and mite pests through regularly scheduled "programs." These applications may be called "preventive-," "round-" or "calendar-" timed applications.

Though there are numerous reasons stated for making preventive applications which seem appropriate, there are certain problems associated with this strategy: 1. a damaging pest population may not have occurred and therefore the pesticide application was not needed, leading to questions of environmental concern; 2. unnecessary pesticide applications may encourage development of pest resistance or accelerated pesticide degradation, and the usefulness of the pesticide may be lost; 3. merely having the pesticide in the tank or on the fertilizer granule increases the chance of pesticide misapplication; 4. making a pesticide application, whether needed or not, reduces the professional status of the manager/applicator because no effort was made to see if the pest was actually present.

Occasionally, preventive pesticide applications are warranted. Where pests are certain to occur (because of previous monitoring or predictive models indicate that a major pest outbreak will occur) or where pests under quarantine are present, preventive pesticide applications may be more effective than applications made after the pest has become active. Some pests, like borers and leafminers, are more difficult to manage after the larvae have entered the host plant. Therefore, preventive applications of pesticides to "protect" the plant from invasion is preferable. Some recently developed insecticides with sustained residual ability or those with insect growth regulator action are often more effective when used as preventives.

Reactive Pesticide Applications

On the other hand, many pests are not expected and applications are made after some damage has been detected. These applications are best termed "reactive" treatments. These applications are usually made because a damaging pest population was missed. Problems associated with making reactive applications are: 1. since poor sampling or monitoring was used, damage has occurred and people are upset; 2. damaging or noticeable pest populations may be more difficult to control; 3. if the preventive application didn't work, additional applications may be necessary to control the pest.

Alternative Tools and Strategies for Timing of Controls

Alternative strategies for timing of controls are available and should be used in order to reduce the problems associated with preventive and reactive pesticide applications. Active monitoring and sampling of pest populations is the heart of all integrated pest management programs. Before proper controls can be applied, one needs to know if a pest is present and if its population or potential population will cause significant damage. Unfortunately, in plant nurseries, where no pests can be allow on the plants prior to being sold, the mere presence of pests warrant pest management.

The single best monitoring device is the traditional visual inspection. However, because many of the pests or their eggs can be very tiny, a 10-15X magnification hand lens is essential when performing visual inspections. In fact, low cost dissecting microscopes (15-45X) should be obtained by persons making many inspections. These microscopes can also help determine if small mites or scales have been killed after a pesticide application. To assist in visual inspections, one should also have a strong, nonfolding utility knife (for checking under loose bark or splitting stems), good pruning sheers (to remove pieces of branches or splitting stems), a spade (for digging around plant roots) and several plastic bags (for taking samples back to the microscope or for mailing to a laboratory for identification).

In addition to visual inspection, several other trapping and sampling tools are useful for monitoring of insects and mites on trees, shrubs and perennials:

1. Beating Trays (=Beating Boards) are cloth sheets stretched on a frame, cardboard or plastic boards (often 10 to 20 inches square) which are held under plant foliage. The plant branch or foliage is struck sharply with a stick or hand to dislodge any insects or mites onto the tray. The number of pests are counted to determine if a treatment is needed.
2. Pitfall Traps are cups or cans sunk into the soil or turf near ornamental plants to capture crawling insects such as black vine weevil adults. The 16 to 20 oz. plastic cups used for cold drinks make ideal pitfall traps. These are easily installed in the ground using a 4.25-inch golf course cup cutter. Pull a soil or turf plug to the depth of the plastic cup. Obviously, a pitfall trap should not be used in areas where people may twist an ankle, but they can be used next to flower beds or under a tree.

3. Light Traps which use "black lights" attract and capture the adults of many moth, beetle and bug pests. Use of black light traps is not for the novice since hundreds of different species of insects can be caught in one night. However, nursery and landscape managers join local IPM groups which run a light trap in an area and report insect activity.
4. Pheromone Traps contain the sex and/or attractant chemicals used by clearwing moth borers, pine tip moths, Japanese beetles and other pests. These can be used, like light traps, to determine specific insect activity periods.

5. Trap Logs are often used to capture the adults of various wood boring beetles, especially bark beetles. Freshly cut pieces of host tree trunks or limbs are placed in plantations where the pest is suspected to be active. The trap logs are inspected periodically to see if the adults have moved to their oviposition sites so that treatments can be properly timed. Occasionally enough traps logs are used to attract the majority of pest insects for egg laying. After egg laying but before the larvae mature, these trap logs are burned or chipped, thereby destroying the pests.

Host Phenology Models are developed by monitoring plant (the host) activity compared to various pest activities. The flowering times of various trees and shrubs are commonly used to time applications of various insecticides. This technique is best used by keeping a yearly record of plant and pest activities. For example, if you find that pine needle scale crawlers appear at the same time that horse chestnuts bloom, then horse chestnut bloom can be your "trigger" for applying controls for the pine needle scale in your area.

Weather-Mediated Predictive (Degree-Day) Models are developed by monitoring weather parameters [usually temperature, as Degree-Days (DD)] and comparing these to insect or mite activity. Though these models help determine better timing of controls, they still do not answer the question of whether the pests are present in sufficient numbers to cause damage or warrant controls. Models have been developed and published for a variety of ornamental insect and mite pests. However, one should carefully keep local records of temperature and pest activity in order to better calibrate published targets. For example, a published DD target for pine needle scale first generation of crawlers is 298-488 DDbase50°F. If you find that the local pine needle scale crawlers are active from 350-500 DD, then you should modify the chart to reflect this later emergence pattern. See information below.

Pest Mapping is simply good record keeping. Most insect and mite pests require specific plants and weather or habitat conditions in order to build to damaging populations. Generally, trees, shrubs or perennials which have had insect or mite problems in the recent past are the most likely in need of attention. In short, if a damaging pest population occurred last year, the probability is much higher that the same thing will occur again. Keeping a useful record of pest occurrence is pest mapping.

Likewise, certain plants appear to be prone to certain pests. Little leaf lindens will certainly be defoliated if Japanese beetles are in the area. European birch is usually attacked by birch leafminers every year and, eventually, will come under lethal attack by the bronze birch borer. These plants are KEY PLANTS. Pest mapping for landscape management firms should be performed by making a plant survey of the customer’s property in order to determine what key plants are present. These plants should then be placed on a master routing schedule for inspection and treatment at the appropriate time.

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