Masters Theses

Date of Award

5-2000

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Dennis E. Deyton

Committee Members

Donna Fare, Charles Pless, Carl Sams

Abstract

Pest management strategies within the ornamental industry differ greatly from those of other agricultural crops. Farmers of most agronomic and horticultural crops control pests to minimize economic crop loss (Doutt, 1983). However, ornamentals are widely used in both urban and rural landscape settings. Since ornamentals fulfill aesthetic purposes, instead of nutritional needs, responses to pest presence are often chemical sprays, regardless of their appropriateness (Sadof et al., 1993; Freeman et al., 1997). Plant retail customers and homeowners have low tolerance of pests in their gardens and yards (Owens, 1986), and constitute 27% of all pesticide users in the U.S. (Freeman et al., 1997). Coffelt and Schultz (1990) reported that a mere 5% defoliation of woody ornamentals by the orange striped oakworm (Anisota senatoria J.E. Smith) increased homeowners' requests for pest control by >50% in Norfolk, VA. Sadof and Alexander (1993) concurred with the interrelationship between leaf discoloration and aesthetic value, stating that 50% of 134 nursery customers surveyed believed burning bush (Euonymus alatus Thunberg Siebold 'Compacta') plants with ≥ 5% leaf discoloration from spider mite infestations were damaged and unsalable.

Urban pest management poses potential problems for environmental pollution, health hazards, and ecosystem disruption (Bradley, 1991; Owens, 1986). The UCLA Center for Environment Risk Reduction indicates that on a per hectare basis, urban pesticide use often exceeded that of agricultural applications (Freeman et al., 1997). The majority of pesticide applicators are untrained homeowners and landscape gardeners, who rarely heed attention to the chemical's appropriateness or safety precautions (Bennett et al. 1983). Modem gardeners and nursery growers use synthetic pesticides due to their speed and efficacy of pest control (Smith, 1991). Problems from over-spraying exist in urban environments as well, and are similar to historical agricultural situations, including soil and water contamination, pest resistance and resurgence, and acute / chronic human health problems (Freeman et al., 1997). Modern agricultural ecosystems possess relatively low diversity in comparison to that found in landscapes, parks, vacant lots, gardens, and other urban communities (Owens, 1986). It is critical that alternative pest management strategies be developed and implemented, so as to better manage ornamental pests without environmental toxicity and ecosystem disruption, particularly of beneficial arthropods.

Oil sprays were first used agriculturally in the 1780s to control overwintering insects in orchards (Chapman, 1967). Oils differ from synthetic pesticides in that they are nontoxic to mammals, possess little to no residual pesticidal activity, control pests with a physical mode of action (suffocation), and are usually less expensive than their competitive pesticide counterparts (Hesler et al., 1986; Johnson, 1985). Advanced refinement procedures have created lighter petroleum oils (known as superior or horticultural oils) that control arthropod pests year-round on many plant species with minimal phytotoxicity (Baxendale et al., 1988a, 1988b; Mizell, 1991; Nielsen, 1990). Modern nursery growers use horticultural oils, such as Sunspray Ultra-fine Spray Oil %reg; or Success Naturalyte Insect Control ®, at label-suggested rates to control common horticulture and nursery insects and mites (Miller, 1997; Bisabri et al., 1997). Early research on citrus indicated that natural plant oils possess insect and mite controlling properties similar to petroleum spray oils (deOng et al., 1927). Many scientists have investigated insect and disease controlling properties of plant oils in efforts to find effective and safe alternatives to synthetic pesticides (Allen et al., 1993; Butler et al., 1988, 1989a, 1989b, 1990, 1991a, 1991b, 1991c; Chen et al., 1996; Flint et al., 1995; Hesler et al., 1986; Hill et al., 1981; Northover et al., 1996; Obeng-Ofori, 1995; Webb et al., 1994).

This thesis explores the potential usage of soy oil (Glycine max L. Merrill) as an insecticide and acaricide on ornamentals. Petroleum oils and soy oils were compared for their efficacy against soft-bodied haustellate (sap sucking) insects such as cotton aphids (Aphis gossypii Glover), sweet potato whiteflies (Bemisia tabaci Gennadius), and azalea lace bugs (Stephatiitis pyrioides Scott) , and two-spotted spider mites (Tetranychus urticaeKoch) on nursery stock. Soy oil was evaluated for effects on phytotoxicity, net photosynthesis, stomatal conductance, transpiration, and beneficial mites on various herbaceous and woody ornamental species.

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