Sole reliance on, and heavy usage of, organochlorine, organophosphate, carbamate, and pyrethroid insecticides has spawned environmental problems, and triggered public concern.  The events surrounding the Alar® (a plant growth regulator) incident suggest the potential for losing highly lucrative markets (O'Rouke 1990).  Ever-tightening regulations on pesticide use also point toward the need to develop alternative, less pesticide-centered pest management approaches.  The impact of intensive orchard spraying programs on ground and surface water and on soil biota has not been clearly assessed.  It is generally assumed, however, that pesticides provide a major non-point source of environmental pollutants (Figure 2 from Young et al. 1988).

Deciduous tree fruit orchards, because of their perennial habits, their tendency to be found in concentrated areas of favorable climate and soils (i.e., localized valleys), and their occurrence near riparian zones or natural resources such as forests, deserts, rivers and lakes, tend to be short-term and even semi-permanent habitats for many non-target organisms (Whalon & Croft l983, Rathman 1988, McDonald & Glynn l994).  These may include: a community of microorganisms involved in nitrogen fixation, detritus decomposition and pesticide degradation; a mesofauna of annelids, acarines, and insects important to soil health; an arboreal biota of arthropods critical to pollination and predation on phytophagous pests; a ground cover of grasses, herbs, forbes, and perennials, as well more visible wildlife such as amphibians, reptiles, birds, small mammals, and large mammals (beaver, deer, elk).  Many of these non-targets, as well as being "desirable," can become troublesome and targets of pest control.  Orchards may be sources of human exposure to toxins (farmworkers) and drift to areas of human activity.  Considering the heavy use of pesticides in orchards, it is clear why IPM has been a high priority goal of agriculturists and environmentalists.

Means of assessing the environmental impact of IPM or other large-scale systems of pest control (e.g., eradication) often involve both retroactive monitoring of key species and predictive analyses of impacts (Whalon & Croft l983).  Both types of assessment involve acute and chronic toxicity tests, while the latter sometimes use simplified representations of orchards (micro- or mesocosms) or modeling/geo statistical data for added analyses.  Because it is difficult to establish sufficient diversity to represent orchards in simplified micro- or mesocosms, most assessments of IPM in orchard ecosystems have focused on indicator species and modeling/spatial analysis (Whalon & Croft l983). Kovach et al. (1992) have proposed a scheme for assessing environmental risks (environmental impact quotient) which will be applied in environmental impact assessments under this areawide program.
 
Studies tracking abandoned orchards over time show that many of the insects feeding on fruit trees, especially aphids and mites, are regulated by natural enemies and other factors.  However, in the case of apple in the eastern U.S. and pear in the western U.S., the general equilibrium level of key pests was above the economic injury level for fresh market fruit (Glass & Lienk 1971, Westigard 1973).  Without intervention, a high percentage, nearing 100% in some years, would be lost to ravages of various pests.  In actuality, the level of pest damage to fruit which can be tolerated by growers for the fresh market is very low.  Levels of fruit damage due to pests exceeding 2 or 3% of the total crop slows the sorting process in fruit packing warehouses, reducing efficiency and adding to the cost of handling the fruit.  With increased levels of fruit damage comes an increased chance that fruit infested with pests will escape detection in the sorting process and thus enter the final packed product.
 

Pesticide Resistance

Codling moth larvae damage fruit directly making it a pest that can be tolerated at only very low levels.  For seven decades, chemical measures have been the mainstay of codling moth control, but insecticide use is beginning to fail on a worldwide scale due to evolution of pesticide-resistant strains.  For example, in California (USA) resistance to organophosphates is at a high level in some regions and spreading rapidly, resistance to carbamates and pyrethroids is known, and cross-resistance to most of the new chemicals (e.g., insect growth regulators), many of which have not even been registered yet, seems to be already present.

Development of resistance to lead arsenate and DDT in codling moth resulted in a shift to organophosphate insecticides (Croft 1979, 1982, Brader 1977, Barnes & Moffitt 1963).  Codling moth control with organophosphates, especially azinphosmethyl, has formed the basis for management systems in apple over the past 25 years (Hoyt 1969).  The argument has been made that organophosphate use should be maintained as long as possible (Croft & Hoyt 1978, Hoyt et al. 1978) as these products provide control of key pests while allowing survival of some natural enemies of secondary pests, particularly in apple orchards.  However, detection of organophosphate resistance in codling moth threatens the future of these systems (Varela et al. 1993).  Resistance, while not widespread, is well established in a number of California pear orchards (Varela et al. 1993, Welter unpublished).  The frequency (and to some extent the level) of codling moth resistance in Washington (USA) and Oregon (USA) is intermediate to that in California, although the differences may result from the way fruit drops are handled in California pear orchards (Knight et al. 1994).

Pear production provides a sobering glimpse of what might lie ahead for pest control programs in apple given the development of organophosphate resistance in codling moth.  Recurring resistance by pear psylla has lead to the use of a series of insecticides with different modes of action (Burts 1985, Burts et al. 1989, Van de Bann et al. 1990).  The result has been an unstable management system, outbreaks of secondary pests, resistance problems, and high pest control costs (Hoyt et al. 1978).  As in pear, the negative effects of using synthetic pyrethroids in apple are striking (Hall 1979, Hoyt et al. 1978, Hull & Starner 1983) and their general use should only be viewed as a last resort.  Unfortunately, resistance in California (USA) and Nova Scotia (Canada) as already prompted some growers to apply synthetic pyrethroids for codling moth control with predictable disruptive consequences.

Resistance in codling moth has been identified and yet remains localized (Varela et al. 1993, Knight et al. 1994).  Historical data exist on resistance and codling moth population levels in several locations in western USA including California, Oregon and Washington.  There are regional and crop-influenced differences in resistance levels that provide an opportunity for identifying factors which influence the evolution of resistance.  Simple and rapid techniques are available for monitoring levels of resistance (Riedl et al. 1985, Meagher and Hull 1986, Suckling et al. 1985).  It is suggested that alternative control tactics such as mating disruption may be used before resistance in codling moth is widespread and before tactics detrimental to existing IPM programs have been widely adopted.

Organophosphate resistance in codling moth will encourage earlier adoption of alternative control tactics.  The potential of switching to insecticides with different modes of action, for example insect growth regulators (Westigard 1979), may be limited by cross-resistance evident in organophosphate-resistant codling moth populations (S. Welter & J. Dunley, unpublished).  Mating disruption offers a highly selective alternative for control of codling moth (Charmillot 1990, Rothschild 1982), and researchers have reported codling moth control in mating disruption programs using a "rope-type" dispenser system.  Even if highly successful for codling moth control, it is not likely that mating disruption would eliminate use of all insecticides in pome fruit orchards.  Insecticides would be used against pests for which alternatives are not available or when pest populations (including codling moth) threaten to exceed the economic injury level.

Organophosphates comprise 72% of insecticides applied to apple, with azinphosmethyl targeted at codling moth making up 35% (average of three applications per year) of the total insecticide use (Beers and Brunner 1991).  Many secondary pests of apple and pear have developed resistance to azinphosmethyl (aphids, leafminer, leafhopper, mites, pear psylla, leafrollers) requiring the use of alternative products for their control.  Environmentally benign control tactics such as mating disruption offer a resistance management strategy that could greatly reduce organophosphate use, slowing the rate of resistance development or even promoting reversion to susceptibility in the target, codling moth, and non-target pests as well.  Where mating disruption programs reduce overall organophosphate use, the impact of biological controls on secondary pests may be enhanced, thus minimizing the need for other insecticide applications.
 
 

Selective Chemical Insecticides

Among insecticides generally used for codling moth control, there are none with enough selectivity and effectiveness to be useful for integrated control programs.  During the 1980's, the agricultural chemical industry made a substantial effort to develop selective insecticides for codling moth control.  Development efforts focused on insect growth regulators such as the chitin-synthesis inhibitors and juvenile hormone mimics.  Research trials and limited grower use have shown that diflubenzuron, a chitin-synthesis inhibitor, provides adequate codling moth control on apple and pears without disrupting biological control of other pests (Westigard 1979, Alston 1992).

Fenoxycarb, a juvenile hormone mimic, is effective against codling moth, leafrollers, and leafminer (Charmillot & Brunner 1990, de Reede et al. 1984) and is selective and has a long residual activity.  A new group of chemicals referred to as ecdysone-agonists (e.g., tebufenozide, RH-5992; Science vol. 261, p. 158, July 1993), are highly specific, affecting only Lepidoptera.  Tebufenozide and related analogs have shown promise on laboratory and field tests against codling moth, leafrollers, and possibly leafminer.  The advantage of IGRs is that they are much more selective than conventional neuroactive insecticides and have few, if any, detrimental impacts on natural enemies of pests found in western apple orchards.

Petroleum oils have historically been used as pesticides in pome fruits.  These products have become highly refined and pure, reducing some of the phytoxicity concerns associated with former products.  The use of summer mineral oil applications to control codling moth has been shown to have promise on pear (Westigard, personal communication) and research on its utility on apple is currently being examined.  In pear, summer oils have provided suppression of spider mites in addition to codling moth, but the impact on other non-target organisms is not fully known.

Insecticidal soaps have been tested for efficacy against several pests of pome fruits with varying results.  While some products have demonstrated an ability to suppress pest species, e.g. white apple leafhopper, concerns about phytotoxicity have limited their adoption as selective controls.  Soaps are not known to have any efficacy against codling moth eggs or larvae.