443092.5 Biorational Pest Management Tools and Tactics
443102.5.1 'Biorational' Controls
Biorational tactics begin with cultural and mechanical practices such as diverse cropping, crop rotation, and roguing of sick plants. Traps using food baits, light, and color as attractants can be useful. These methods may not stand alone, however, and additional tactics for control may be needed. The term "biorational" means to be environmentally conservative, that is, to protect the desired plant from pests while protecting other organisms from harmful side effects in the nearby and wider environment.
Some additional biorational tactics are:
Biological control using parasites, pathogens, and predators of the pest species. These are most commonly naturally occurring, although in some situations biological control agents may be added to the nursery or landscape. Such tactics often require a change in pest control attitudes. The biologicals depend on a reservoir of pest species to remain alive, but because the reservoir pests do damage, one must decide how much damage is tolerable. Parasites and predators need care and must be protected. A commitment to monitoring and maintenance is necessary to make biological control work.
Plant resistance to pests. Some plants have evolved both physical and/or chemical defenses against their arthropod enemies. Such defenses are genetically controlled. The leaf epidermis or bark surface is the first barrier between phytophagous insects and host plants. The foliage surface environment may be hostile to a food-searching insect. The epidermal glands of a leaf may produce defensive substances that are sticky or produce wax difficult for the mouthparts to penetrate. Some plants produce trichomes that make insect movement difficult, or they may produce quantities of defense chemicals that result in less insect feeding. Cells may make and store toxic substances such as tannins and steroids. Such plants have developed a natural resistance. Information on pest-resistant species may come from large nurseries or researchers at universities. Recent work in Michigan, for example, has provided evidence that our native birch, Betula papyrifera, is more resistant to bronze birch borer than any other white-bark birch. Gene manipulation or genetic engineering for obtaining pest-resistant ornamental plants is also possible now.
A functional knowledge of resistant plants may simply be a list of cultivars or species available to replace the nonresistant ones. These lists are available for plants resistant to euonymus scale; lace bug on cotoneaster, pyracantha, hawthorn, and mountain ash; and bronze birch borer as examples. Some of these (as well as susceptible plants) are noted in Table 2.9.1. Check with your local Cooperative Extension office or the NYS IPM Program (cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/ipm-areas/ornamental-ipm (scroll to bottom of page) for additional publications and information on this topic.
Kairomones are volatile chemicals produced by plants that attract insects, incite feeding or egg-laying, or otherwise induce the insect to remain on a host plant. An insect historically associated with a particular plant species is able to recognize such kairomone "odors" as originating from its food plant. Examples of kairomones include phenolic compounds found in conifer sap and resin that attract bark beetles; and the plant oil extract geraniol, which has long been used as an attractant in Japanese beetle traps. Commercial exploitation of this class of biochemicals for pest management purposes is mostly on the horizon.
Arthropod pheromones are chemicals or mixtures of chemicals released by an insect that elicit a certain behavioral response from other insects, usually of the same species. Examples include chemicals causing insects to disperse, aggregate or follow one another. Sex pheromones, mostly produced by females, lure males for the purpose of mating and are the most widely used kinds of pheromones. They are usually highly specific (with some exceptions); one type of sex pheromone may be completely ignored or repellent to another kind of insect. Synthetic versions of sex pheromones are now produced for many pest species and are useful in survey traps for determining insect periods of activity. They are often used to detect the presence of exotic or invasive species in new areas. In some cases, sex pheromones can even be employed at sufficiently high concentrations to disrupt mating and provide partial or complete control of a pest. Typically, however, sex pheromones are most used to determine when pests are active and when control measures should be applied. Examples of woody ornamental plant pests for which sex pheromones are available include clearwing borers (rhododendron, dogwood, lilac/ash and peachtree borers), common bagworm, spongy moth (formerly gypsy moth), Nantucket pine tip moth, European pine shoot moth, Japanese beetle, oriental beetle and elm bark beetle. Sex pheromone chemicals are deployed in various styles of devices (lures) that contain the pheromone while permitting it to diffuse out slowly over a period of time. Rubber caps (septa) are often used, the chemical(s) being absorbed into the rubber. Capillary tubes, plastic beads or bubbles, and low-density polyethylene bags or containers are other styles of lures commonly seen.
Pheromone traps are devices used to hold the lures and collect attracted insects. Traps come in various designs, such as clamshell-style wing traps with a sticky lower surface, funnel-like nets, milk cartons, 'bucket'-type containers and sticky panels. Usually, the trap type is specified for the particular kind of insect being surveyed. Check with suppliers on the appropriate trap type, where traps should be placed, the length of time they are used, how often they should be checked and when lures need to be renewed. Generally, place traps just prior to pest emergence at a height above ground where the insects are normally active. The pheromone should be unobstructed, allowed to freely move with prevailing winds from the lure into the area of interest. Be sure not to touch exposed lures or cross-contaminate by handling different kinds of lures using the same equipment or gloves, which may render them ineffective. If traps are being used to schedule insecticide applications, find out if the application timing varies according to whether a systemic or strictly contact insecticide will be used.
In addition to or instead of sex pheromones, some insect traps employ other chemicals, a distinctive shape, an attractive color or some knowledge of insect behavior. Examples include Lindgren funnel traps baited with alpha-pinene and ethanol or frontalin for bark beetles, yellow sticky panels that attract fungus gnats and whiteflies, and pitfall traps or trap boards for black vine weevils.
Insect growth regulators. (IGRs) were first recognized as useful with the discovery of the juvenile hormone biochemicals in insects. Some plants even use this chemistry as a form of protection. IGRs act on the hormonal system of immature insects; they generally do not kill adult insects and have a delayed effect. Therefore, timing applications to coincide with early immature stages is important and one should not expect to see immediate control. Treated insects may stop feeding, however. At least three major groups of IGR insecticides are now in use. Juvenile hormone mimics act like natural juvenile hormone in insects, the presence of which ensures that the next molt will be to another immature (larval) stage in treated insects. Affected insects usually do not reach adulthood or die while molting to the next larval stage. The insecticide pyriproxyfen (Distance) is a juvenile hormone mimic. Chitin biosynthesis inhibitors interfere with the production of chitin, an essential component of the insect shell or skin. Insects affected by these materials are not able to molt successfully. Novaluron and diflubenzuron are members of this group that primarily target butterfly and moth caterpillars, although they are also used for other kinds of insects. Diflubenzuron (Dimilin), for example, is used against early stages of spongy moth (formerly gypsy moth) and other caterpillars and also has some ovicidal activity. Cyromazine (Citation) is another kind of chitin biosynthesis inhibitor, disrupting molting of fly larvae such as serpentine leafminers. A third group called ecdysone agonists or ecdysone antagonists disrupt molting by interference with the normal operation of ecdysone, a hormone important in the insect molting process. Treated insects may not be able to emerge normally. Azadirachtin (Azatin O) is in this category. Derived from neem seed oil, azadirachtin has been used for thousands of years but only recently commercialized for horticulture in this country. It has some systemic activity when applied to roots and Ornazin is also labeled for trunk injection, although azadirachtin is primarily a foliar insecticide.
Microbial and other biorational insecticides. Some pesticides are microbes or derived from them. Bacillus thuringiensis kurstaki (Btk) bacteria produce a protein crystal endotoxin that disrupts the gut of butterfly and moth caterpillars. Formulations of the endotoxin are important insecticides used on ornamentals, vegetables, and other plants. Abamectin and spinosad are derived from the soil microorganisms Streptomyces avermitilis and Saccharopolyspora spinosa, respectively. Several commercial preparations are available that consist of spores of the insect-killing fungi Beauveria bassiana, Metarhizium anisopliae, or Isaria fumosoroseus. Successful use of microbial pesticides requires detailed knowledge of the pest's biology and phenology and its relationship to its host plant(s). When this knowledge is used in planning, effectiveness can approach that of synthetic organic pesticides in some cases. Some IPM specialists include horticultural mineral oils and insecticidal soaps as biorational pesticides. Both are environmentally friendly in spray dilutions and degrade quickly.
Remember that most ornamental plants in urban and nursery settings are growing in an artificial, contrived environment. Left on their own many of them could not compete and would not survive. Selection often results in the propagation of plants not suitable to the truly natural environment. Such plants generally require more maintenance, including pest management, and in effect are dependent on a range of horticultural inputs.