Implementation of Pheromone-based Pest Management
Programs in Washington

Larry J. Gut and Jay F. Brunner
Washington State University
Tree Fruit Research and Extension Center

and

Alan Knight
United States Department of Agriculture
Agriculture Research Service

Introduction
Chosing an appropriate orchard
Selecting a pheromone product
Applying pheromone
Monitoring codling moth
Managing codling moth
Monitoring non-target pests

Mating disruption as a commercially available option for codling moth (CM) control was first available in Washington in 1991. Suppression of CM populations by mating disruption entails dispensing sex pheromone into orchards in quantities sufficient to interfere with the normal process of mate location. In 1991 pheromone was applied as the primary control for CM on over 1,500 acres of apples and pears in Washington. The use of mating disruption has steadily increased over the past four years with about 18,000 acres untreated throughout the state in 1995.

During this five-year period we have evaluated CM mating disruption in over 200 apple and pear orchards in Washington. Treatments have included several products or dispenser types application rates, and combinations of pheromone plus conventional or organic insecticides. Based on our experience, we have identified six basic steps in implementing a pheromone-based CM pest management program in Washington: orchard selection, product selection pheromone application, CM monitoring, CM management, and non-target arthropod monitoring and management.

Choosing appropriate orchards Codling moth mating disruption is influenced by several physical factors, including orchard topography, size and shape, wind conditions and canopy structure. The best control is achieved where physical conditions allow for uniform distribution of pheromone within the orchard. Thus, sites that are relatively calm and flat are better candidates for CM mating disruption than sites that experience frequent winds or have steep slopes. Orchards with large numbers of missing trees or uneven canopies are considered poor candidates for CM mating disruption. Using CM mating disruption in a large contiguous area is considered a better strategy than in small, individual orchards. However, good control of CM by mating disruption has been achieved in blocks as small as two acres. The benefits of applying pheromone uniformly across large contiguous areas will be addressed by the areawide panel later in the program. We know that the borders of mating disrupted orchards are especially vulnerable to CM. Thus, when implementing a pheromone-based CM control program we recommend that you maximize the amount of orchard interior relative to orchard edge as illustrated in Figure 1. If only a single orchard is to be untreated, the best choice is the one with least amount of border exposed to open areas. Long narrow orchards are poor choices for mating disruption.

A key factor determining the efficacy of mating disruption is the initial density of CM within or adjacent to an orchard being considered a candidate for CM mating disruption. We often refer to this initial density of CM as the level of CM pressure. Controlling CM by mating disruption alone becomes more difficult as CM pressure increases. This is thought to occur because as CM densities increase the number of successful matings increases, resulting in unacceptable level of fruit damage. Three criteria each related to CM activity or controls the previous year, can be used to characterize CM pressure in an orchard. Codling moth fruit injury from packout records or field counts provides the best measure of CM pressure in an orchard. A seasonal count of CM moths captured in pheromone traps also gives an indication of CM pressure. The number of insecticide applications required to control CM can also provide an indication of CM pressure, especially if treatments were based on some measure of the need for control (e.g. fruit injury or pheromone trap catch).

Using these criteria, we have attempted to characterize orchards in Washington into four risk classes (very low, low, moderate and high) with respect to CM mating disruption (Gut and Brunner 1994a). Very low and low risk orchards are the best candidates for CM mating disruption. Very low risk orchards are characterized as having CM fruit injury of less than 0.1%. A very low risk orchard would typically have a seasonal moth catch in pheromone traps below a treatment threshold and require none or one application of insecticide for CM control. Low risk orchards are characterized as having CM fruit injury between 0.1 and 0.4% the previous year. Moth catches in pheromone traps would usually exceed treatment threshold, especially in the first flight, necessitating one or two insecticide treatments to control CM. Mating disruption alone can provide satisfactory control of CM in very low and low risk orchards.

Moderate risk orchards are characterized as having CM fruit injury between 0.5 and 1.5% the previous year. Moth catches in pheromone traps exceed treatment threshold more than once, necessitating two or more applications of insecticides to keep crop loss at acceptable levels. Mating disruption alone will most likely not control CM under these conditions. Supplementing mating disruption with insecticides, primarily during the first CM generation, is recommended as a standard practice in a CM mating disruption program in moderate risk orchards.

High risk orchards are characterized as having CM fruit injury greater than 2.0% the previous year. Moth catches in pheromone traps would exceed treatment thresholds, necessitating a full season control program for CM, 3 to 5 insecticide treatments. Insecticides should be the primary control tactic used for CM under these circumstances. It may be possible to transition some high risk orchards to moderate and eventually low risk categories by using combinations of mating disruption and insecticides. While this represents an intensive and expensive program for the grower, it may provide long-term benefits by establishing a more stable pest management system.

Selecting a pheromone product In 1995, three registered CM mating disruption products ( pheromone dispenser systems) and at least two experimental products were used in Washington. The commercially available products were Isomate-C+ (Pacific Biocontrol, Inc.), Checkmate-CM (Consep, Inc.), and NoMate-CM (Ecogen, Inc.) Three or more products will probably be available to growers in 1996. What kind of information will help you select the product that best fit your needs? Manufacturers should be able to provide you with three critical pieces of information: the amount of pheromone emitted under different environmental conditions (i.e. cool, warm and hot temperatures), the longevity of their product under Washington's growing conditions, and the level of CM control expected in low and moderate risk orchards at the rate they recommend.

Codling moth mating disruption products can be classified into two groups based upon characteristics of pheromone release rate and longevity. Group A dispensers are characterized by a moderate rate of pheromone release (i.e. 0.5 to 1.5 mg of CM pheromone per day) and a longevity of 140 to 150 days. Group B dispensers are characterized by a high release rate of pheromone (greater than 2.0 mg of CM pheromone per day) and a longevity of 60-75 days. Strategies for using the two dispenser groups differ. Group A dispensers are intended as a season-long product and are applied one time at the beginning of the first CM flight. Group B dispensers are used in a strategy of multiple applications, usually one against each CM generation.

Two products used most extensively in 1995, Isomate-C+ (Pacific Biocontrol, Inc.) and Checkmate-CM (Consep, Inc.) illustrate the relative performances of group A and group B products. The rates of pheromone loss from field aged dispensers were determined by residual analysis (Checkmate) or gravimetric analysis (Isomate), and are plotted in Figure 2. Residual analysis consisted of determining the amount of pheromone remaining by extraction and gas liquid chromatography from five dispensers collected every other week. The gravimetric technique consisted of an initial weighing and placement in the field of 25 dispensers, followed by collecting, weighing and replacing them weekly over a period of 140 days.

The Checkmate dispenser released an average of 2.7 to 3.4 mg of pheromone per day (mg/d) during the first CM generation (Figure 1). Due to this high rate of pheromone loss, the dispenser was empty after about 60 days in the field. Release of pheromone from the Checkmate dispenser increased with increasing daily temperatures, suggesting that dispensers applied for control of the second CM generation may have released codlemone for less than 60 days, but data on release rates during this period are not yet available. The peak release rate from the Isomate dispenser was about half that observed for the Checkmate dispenser (Figure 1). However, this dispenser continued to release a substantial amount of pheromone throughout the season. The amount of CM pheromone released fluctuated between 0.7 and 1.5 mg/day and depended on weather conditions. The highest release rates occurred during the hottest part of the summer, between days 42 and 98 post-application.

Isomate-C+ is designed to provide season-long control of CM under typical conditions in Washington with a single application, while Checkmate-CM must be applied at least twice. The recommended application rates are 400 dispensers per acre (d/a) for Isomate-C+ and 120-160 d/a for Checkmate-CM. In 1995 we directly compared the effectiveness of both products in six orchards with low to moderate CM pressure. Isomate-C+ was applied once at 400 d/a, while Checkmate-CM was applied twice at 160 or 200 d/a. Isomate-C+ provided significantly better CM control than Checkmate-CM. An average of less than 0.1 % CM fruit injury at harvest was recorded in the Isomate treated orchards; the highest level of injury was 0.3%. In paired Checkmate-CM treated orchards CM fruit injury averaged nearly 1%, with a highest level of 3.0% damage.

Our research strongly indicates that under low to moderate CM pressure the best strategy for mating disruption is to use a higher density of dispensers releasing a moderate amount of pheromone, a strategy best typified by group A products. Our combined experience during the past 3 years of field research is that a single application of Isomate-C+ applied at 400 d/a has consistently provided better CM control than two applications of Checkmate-CM at 120 to 200 d/a. These observations have been supported by results of recent studies conducted by Dr. Knight, who evaluated the relative effect on CM mating activity of the number of point sources and the rate of pheromone emission from each source under controlled conditions. Six pheromone treatments were compared: 100, 200 or 400 point sources per acre with each source releasing either 1 mg or 2 mg of codlemone per day. Each treatment was applied to four 0.3 acre apple blocks and was evaluated by comparing capture of CM in traps. Pheromone traps baited with a pair of virgin female moths were placed in each pheromone treated block and in the four 0.3-acre non-pheromone treated blocks. Four hundred CM males were released in each block over a six-week period. Treatment effects were evaluated by comparing the percentage of traps capturing at least one male moth. The results are presented in Figure 4. The average percentage of traps catching a moth was lower in all pheromone treatments compared to the non-pheromone control, represented by the thick black line in the figure. Increasing the number of point sources from 200 to 400 per acre resulted in a very significant reduction in moth captures. In contrast, there was very little difference between the 1 and 2 mg release rates at all point source densities.

The most commonly used group A dispenser type, Isomate-C+, has provided acceptable levels of CM control in low to moderate risk orchards at 400 d/a, though in the latter a supplemental insecticide treatment is occasionally required. This product has also provided acceptable levels of CM control in very low risk orchards at a reduced rate of 200 to 250 d/a.

The most commonly used group B dispenser type, Checkmate-CM, has provided acceptable levels of control in very low risk orchards at the company s recommended treatment rate of 120-160 d/a. However, in low and especially in moderate risk orchards this recommended density of dispensers is evidently too low, even with the high pheromone emission rate, to provide consistent CM control. The strategy of balancing a lower dispenser density per acre with a higher pheromone emission rate does not appear to be as good as maintaining at least a 200 d/a rate with moderate to high pheromone emission. The Checkmate-CM dispenser system is being engineered to better suit Washington conditions. Release rates of the newly engineered dispenser should be determined in the laboratory or in field-aged tests prior to large scale testing in grower orchards.

Applying the pheromone: To achieve the best control of CM with mating disruption, dispensers must be placed high in the tree canopy prior to biofix, the emergence of the first moths. CM activity and mating is concentrated in the upper third of the canopy. Weissling and Knight demonstrated that significant levels of mating occurred in the upper half of the tree when dispensers were placed at a mid-canopy height, 6 feet (Knight 1995). However, little or no mating occurred in the tree when dispensers were placed high in the canopy, at 12 feet (trees were about 14 feet tall). Dispensers should be placed near foliage to protect them from UV radiation and high temperatures. Our recommendation is that dispensers be placed within 2 feet of the top of the tree and in a position shaded by foliage.

Since mating disruption does not provide control once mating has taken place, its effectiveness is reduced if dispensers are applied late. To control the first generation of CM, pheromone dispensers should be applied prior to moth emergence in the spring. First moths usually emerge about full bloom of "Delicious" cultivars. Since CM can mate the first or second night after they emerge, late pheromone applications, such as at petal-fall, can provide an opportunity for a portion of the population to mate.

Monitoring codling moth: Monitoring is difficult in orchards treated with mating disruption products for CM control. A pheromone trap (Pherocon 1CP) baited with a red septum containing 10 mg of codlemone has been widely adopted as a component of pheromone-based CM control programs. CM activity in pheromone treated orchards is more effectively monitored with this high load lure than with a standard red septum containing 1 mg of codlemone. However, inconsistency of high load lure-baited pheromone traps to detect "hot spots" in mating disruption orchards has raised concerns over policies to recommend this monitoring system as a tool in pheromone-based pest management programs. We continue to recommend the use of a high load lure-baited pheromone trap as a tool in mating disrupted orchards but stress three factors that will greatly reduce the inconsistencies people have experienced in using it: use a trap for every 2 to 2.5 acres, replace lures frequently, and place traps high in the canopy. In addition, visual fruit inspections should be made in conjunction with moth capture results.

Effective use of a 10 mg red septum in commercial orchards probably will require changing lures every three weeks during the first generation CM flight and at least every two weeks during the second generation CM flight. Our research has demonstrated that moth captures in traps baited with 10 mg lures decline significantly after 3-4 weeks in the spring and 2 weeks in the summer. Analysis of release rates using ion mobility spectrometry (IMS) had indicated that reduced attractancy of these lures was closely associated with a decline in the codlemone release rate. In both spring and summer flights, emission rates dropped sharply during the first 10 days, from about 8 g/hour on day 1 to 3.5 g/hour by day 10. Emission rates continued to decline in the summer, with only 1.0 g/hour emitted by day 21. In contrast, emission rates above 2.5 g/hour were maintained between day 10 and day 31 of the spring flight. High summer temperatures appear to increase the rate of pheromone emission, thus shortening the effective life of the lure.

Codling moth pheromone traps used in conventionally managed orchards have typically been placed at mid-canopy, or lower because this position has resulted in good moth capture and they are easier to maintain than traps placed higher in the canopy. However, when high load lure-baited pheromone traps are used in mating disrupted orchards they are more sensitive when placed in the upper part of the canopy. The performance of traps placed at mid-canopy was compared with traps placed in the upper canopy in 12 orchards in the Howard Flat Codling Moth Areawide Management Pilot Project in 1995. An equal number of traps placed at each height was uniformly distributed in orchards at a density of 1 trap per 1.25 acres. Lures were replaced every third week in the first generation and every other week in the second generation. The "high" traps were 2 feet higher in the tree canopy than the midcanopy traps. This positioned them within 1 foot of the height at which dispensers were placed. The high traps captured about three times more moths in the first CM generation flight and almost seven times more moths in the second generation than the mid-canopy traps. The high traps were a better indicator of CM phenology, closely tracking the seasonal pattern of moth catch in standard traps placed in conventional orchards at Howard Flat (Figure 5). The increased effort required to place traps high in the canopy may be rewarded by their greater sensitivity and possibly improved reliability to predict the potential for fruit injury compared to traps placed at mid-canopy.

Monitoring with pheromone traps is not intended as a stand-alone method for accessing the effectiveness of CM mating disruption. Trapping should be used in conjunction with visual inspection of fruit for CM damage. Inspect fruit on as many trees as possible and primarily from the upper portion of the canopy, as this is where the majority of CM fruit injury occurs. Concentrate sampling first where CM damage is most likely to occur, on orchard borders, tops of slopes, near bin or prop piles, and in more susceptible cultivars such as Golden Delicious.


Monitoring Guidlines


Managing codling moth Mating disruption alone will not be sufficient for control of CM under certain circumstances. As discussed previously, supplemental control with insecticides should be planned in moderate risk orchards. Insecticides should also be applied if CM-injured fruit injury exceeds 1% at any time or if pheromone trap catch exceeds a treatment threshold. Using the monitoring protocols outlined in this article, and summarized below, the suggested treatment thresholds are a cumulative capture of 4 or more moths in the first CM generation. The efficiency of the high load-rate trap declines as the season progresses; thus, a reduced threshold of 2 moths is suggested for the second generation.

The borders of an orchard require extra attention when implementing CM mating disruption. Experience has indicated that orchard borders are often the Achilles heel of this pest control tactic. Two processes are thought to contribute to the frequent development of border infestations in mating disrupted orchards, immigration of mated females from nearby sources and successful mating of CM at orchard borders. Mating disrupted orchards are especially susceptible to invasion by CM from external sources. Usually no insecticides have been applied to control CM, and eggs laid by immigrating females have a good chance of survival. Pheromone concentrations on orchard borders are thought to be lower than in the interior, possibly because of wind sweeping away pheromone. Lower pheromone concentrations on borders may allow males to locate females more readily than in the orchard interior, leading to higher fruit injury in these areas.

Three tactics can be used to protect orchard borders. Additional pheromone can be applied to border trees or extended into adjacent orchards if possible. Our experience suggests that this approach is most effective when initial CM densities are low. In orchards that routinely sustain CM fruit injury, it is best to treat borders with insecticides in addition to using higher rates of pheromone or extending pheromone treatments into the neighboring orchards. An effective border treatment (insecticides or extra pheromone) in most orchards would be an area equivalent to 3 or 4 rows around the orchard perimeter or along the problem border.

Monitoring and managing non-targets: Mating disruption is a highly specific pest control tactic. Implementing this tactic for codling moth control, however, will have a significant impact on non-target arthropods, both pests and their natural enemies. The abundance of natural enemies is usually greater in mating disruption than in conventional control orchards (Gut and Brunner 1994a and b, Knight 1995). This is especially true where summer insecticides are used in the conventional control orchards. The potential for biological control of orchard pests in pheromone treated orchards is discussed by Nick Mills later in an article in these proceedings.

The specificity of mating disruption can have a negative as well as positive side. Pests that are kept at non-damaging levels by treatment with insecticides used to control CM will be released from all but natural controls in mating disrupted orchards. Natural controls may provide sufficient control of some non-target pests. For others, however, the removal of insecticides will mean their populations will increase, sometimes reaching damaging levels; and intervention with insecticides or other pest control tactics, such as augmentative releases of natural enemies, will be necessary. Leafrollers have consistently become the most important pest in CM mating disrupted orchards. Two species of leafroller, Pandemis pyrusana (pandemic leafroller) and Choristoneura rosaceana (obliquebanded leafroller), have caused high levels of crop loss, in many cases exceeding that of CM, in pome fruit orchards using CM mating disruption in Washington (Gut and Brunner 1994a and b, Knight 1994). The high potential for leafroller populations to reach damaging levels in the first or second year of transition to a CM mating disruption program was again made evident when the majority of Codling Moth Areawide Pilot Project sites reported a build-up of leafrollers and/or an increased level of fruit injury at harvest in the first year. The ability to monitor and control leafroller populations will be crucial to the success of pheromone-based pest management programs throughout the western region.

The use of azinphosmethyl for CM control has probably been the primary factor preventing many other pest species, such as tent caterpillar, lygus and stinkbugs, from becoming more frequent pests in commercial apple orchards. None of these pests have been reported as a serious problem in mating disruption orchards in Washington during the past five years. However, tent caterpillar colonized three of six mating disruption orchards for three

consecutive years in one of our studies (Gut and Brunner 1994). The distribution of this pest in orchards was clumped, and developing populations were effectively controlled by removing infested limbs. The regular occurrence of this pest suggests the need for more careful monitoring of rare or sporadic pests in pheromone-treated orchards.

REFERENCES

Gut, L.J. and J.F. Brunner. 1994a. Pheromone-mediated control of codling moth in apple orchards. Good Fruit Grower 45(9): 35-48.

Gut, L.J. and J.F. Brunner. 1994b. Implementation of pheromone-based pest management programs in pear in Washington, USA. Int. Org. Biol. Control/West Palearctic Reg. Sect. Bull. 17(2): 77-85.

Knight, A.L. 1995. What do we know about the use of sex pheromones? Good Fruit Grower 46(13): 37-44, 54.