A major challenge facing horticultural crop production is the need to provide field and postharvest disease control measures that help maintain high quality plant products. Producers and consumers also expect high quality produce with minimal or no pesticide residues and competitive prices. The chemical management of disease is further complicated by the development of fungicide resistance in many important pathogens. Because of these concerns, an alternative or complementary approach is the use of disease resistance inducers that activate the natural defenses of the plant. Induced disease resistance in plants has been studied in many different pathosystems for nearly a century. Resistance to plant disease can be induced systemically by prior infection with pathogens, by certain non-pathogenic microbes that colonize the surface of roots and leaves, or by chemicals. The application of resistance inducers should protect plants through the induction of defenses that are effective against a broad spectrum of pathogens. Over the last few years, a number of materials that could potentially be used as inducers of resistance in horticultural crops have been identified. Some of these materials are already commercially available. Although induced resistance is known to provide a broad spectrum of disease suppression, it may not be a complete solution because variation in the efficacy of disease resistance induction has been observed. The variation in the response may be dependent on the plant species and even cultivars, as well as variability in the spectrum of pathogens that resistance can be induced against. Induction of resistance depends on the activation of biochemical processes that are triggered in the plant, and therefore a lag time between treatment and expression of resistance occurs. This lag effect may limit the practical application of disease resistance inducers. Since the efficacy of the inducers also depends on the part of the plant that was treated, the product delivery (i.e., how the inducers would be applied in order to optimize their action) is another factor to be considered. Some studies have shown that there may be side effects on growth or yield characteristics when certain inducers are used. Understanding the biochemical interactions occurring between plants, pathogens and the inducers will provide information that may be useful for the optimization of this new approach on disease control. Approaches to integrate induced resistance with other management practices need to be investigated as a means to aid the development of sustainable disease management programs that are effective as well as economically and environmentally sound.
Andrea B. da Rocha and Ray Hammerschmidt
Victoria Y. Yokoyama
Scars caused by the ovipositional and feeding activities of the western flower thrips, Frankliniella occidentalis (Pergande), on ‘Thompson Seedless’ and ‘Calmeria’ table grapes, Vitis vinifera L., had no effect on many measurable quality attributes of the fruit. Scarred berries showed no apparent differences in size or average weight when compared to undamaged fruit. However, scarred ‘Thompson Seedless’ berries had a higher soluble solids content. The acid content was not affected by any type of scar and all fruit had soluble solids to acid ratios of at least 20:1. Scarring did not affect the weight loss of fruit in short-term storage at 0.6°C, and scarred berries were not injured by sulfur dioxide fumigation.
Rachel Leisso, Bridgid Jarrett, Katrina Mendrey, and Zachariah Miller
Codling moth (Cydia pomonella) is a major insect pest of apple (Malus domestica). If unmanaged, then codling moth can infest nearly all apples in an orchard, where the flesh-tunneling larva leave frass-laden tracks in the fruit. Insecticide-based management requires accurate application timing (typically based on adult moth and/or degree-day monitoring) and multiple spray applications. Both the season-long commitment to codling moth monitoring and management and limited familiarity with insecticides, application tools, and proper application procedures can prevent a small-scale or backyard grower from effectively limiting fruit damage. In addition, an increasing segment of growers is interested in nonchemical alternatives. Bagging fruitlets early in the season could be a simple and effective method of codling moth management for this subset of growers. At our research orchard in Corvallis, MT, we tested a method combining fruit thinning and bagging using plastic bags the first season and nylon bags the second season. Plastic bags reduced the incidence of codling moth damage to fruit from 34% to 10%, but european earwig (Forficula auricularia) frass, which was found in more than 50% of plastic-bagged apples, made harvesting the fruit unappealing. We tested nylon fruit bags during the second year of the study. These bags did not significantly reduce the incidence of codling moth. Both the soluble solids content and titratable acidity were higher in unbagged fruit during the second year of the study, whereas color measurements indicated bagged fruit were greener on the shaded side of the fruit. Failure of the nylon bags may have been attributable to eggs laid before bagging, eggs laid or larva burrowing through bagging, or improper bag application methods. Further research could assess whole-tree bags, the addition of rubber bands or twist ties when applying nylon bags, pretreatment of fruit with horticulture oil, and/or dipping nylon bags in kaolin clay before application; however, these steps add time and increase costs, which may discourage the small-scale fruit grower. Overall, results indicate that fruit bagging holds promise for codling moth management; however, further work is needed to optimize the methodology.
James D. Frantz, Jeffrey Gardner, Michael P. Hoffmann, and Molly M. Jahn
A replicated greenhouse evaluation of a range of commercial and noncommercial (Capsicum spp.) accessions for resistance to european corn borer (ECB) [Ostrinia nubilalis (Hubner)] was conducted. Percentage of fruit damaged was observed among 29 accessions four weeks after plants were artificially infested with ECB egg masses. Small-fruited peppers generally showed lower levels of damage, while large-fruited peppers were the most susceptible. Genotypes with elongate fruit were less damaged than those with bell-shaped fruit. Resistance to fruit damage was also associated with increasing pungency level, with two notable exceptions. The pungent genotype `Large Red Thick Cayenne' was significantly more susceptible than many of the other pungent accessions tested. The relative susceptibility of this accession may be related to large fruit size. The nonpungent pepper `Corno di Toro' showed significantly lower percent fruit damage than other nonpungent peppers including `Banana Supreme' with roughly similar fruit size, ranking amidst highly pungent peppers such as `Red Scotch Bonnet'. These results confirm that resistance to ECB can be identified in nonpungent Capsicum genotypes and demonstrate that pungency is not always correlated with ECB damage. Reported sources of aphid resistance or tolerance showed good levels of ECB resistance, but interpretation of these results was confounded by the presence of pungency.
Jeffrey H. Gillman, David C. Zlesak, and Jason A. Smith
Roses in nursery and landscape settings are frequently damaged by black spot, whose causal agent is the fungus Diplocarpon rosae F.A. Wolf. Potassium silicate was assessed as a media-applied treatment for decreasing the severity and incidence of black spot infection. Roses were treated with 0, 50, 100, or 150 mg·L-1 silicon as potassium silicate incorporated into irrigation water on either a weekly or daily schedule. Five weeks after treatments were initiated, plants were inoculated with D. rosae. Roses began to show visual symptoms of infection §4 days later. Roses that had 150 mg·L-1 silicon applied on a daily schedule had significantly more silicon present in their leaves than other treatments as measured by scanning electron microscopy and energy-dispersive x-ray analysis. In addition, roses that had 100 and 150 mg·L-1 silicon applied on a daily schedule had fewer black spot lesions per leaf and fewer infected leaves than any of the other treatments by the end of the experiment 7 weeks later. Although roses treated with higher levels of silicon on a daily basis fared better than roses in the other treatments, all of the roses were heavily infected with D. rosae by the end of the study. The results reported here indicate that using potassium silicate in irrigation water may be a useful component of a disease management system.
Raymond A. Cloyd and Amy Dickinson
Fungus gnats (Bradysia spp.) are major insect pests in greenhouses. The adult stage is primarily a nuisance whereas the larval stage is directly responsible for plant injury by feeding on plant roots or tunneling into stems. Insecticides are used to deal with fungus gnat larvae in growing medium, although sometimes with limited success. This study evaluated the potential of using a soil amendment—diatomaceous earth (DE) incorporated into growing media—for controlling the fungus gnat Bradysia sp. nr. coprophila. Two experiments were conducted by testing a series of growing media containing various concentrations of diatomaceous earth, and several without diatomaceous earth. The effects of the growing media containing diatomaceous earth on both the 2nd and 3rd instars of fungus gnat larvae were determined by recording the number of adults captured on yellow sticky cards (2.5 × 2.5 cm). Based on the results obtained from both experiments, the addition of DE to growing medium, at the concentrations tested, did not negatively affect or increase efficacy against both the 2nd and 3rd instars. This suggests that incorporating DE into commercially available growing medium may not be beneficial to greenhouse producers. However, further research is needed to assess whether differential larval susceptibility and moisture content influence the ability of DE to control soil-dwelling arthropods.
Raymond A. Cloyd, Cindy L. Galle, and Stephen R. Keith
In this study, we report on the compatibility of two commercially available predatory mites, Neoseiulus californicus and Phytoseiulus persimilis, with three miticides used in greenhouse production systems to control the twospotted spider mite, Tetranychus urticae. We determined the lethal effects of the miticides chlorfenapyr, spiromesifen, and bifenazate to both predatory mite species 24 hours after exposure to spray applications in petri dishes. Two rates of chlorfenapyr (0.40 and 0.81 mL/2-L) and spiromesifen (0.15 and 0.31 mL·L–1), and one rate of bifenazate (0.62 mL·L–1) were used. All rates were based on the manufacturer label recommendations for twospotted spider mite. Both rates of chlorfenapyr and spiromesifen, and the single rate of bifenazate were not harmful to N. californicus with percent live mite values ≥85% for chlorfenapyr and ≥95% for spiromesifen, and 93% for bifenazate. However, these same miticides were substantially toxic to P. persimilis with percent live mite values of ≤63% for all the miticides tested. Based on the results of this study, the miticides chlorfenapyr, spiromesifen, and bifenazate are compatible with N. californicus whereas these miticides are toxic to P. persimilis indicating a difference in susceptibility based on predatory mite species.
As an agroecosystem makes the transition from conventional to organic practices, changes in the pest management tactics used are often apparent. Despite varying degrees of efficacy among tactics, the issue of whether or not numbers of insect and nematode pests and their damage will become more severe in an organic system depends on the specifics of the pests and crops involved. Although many conventional systems rely on reactive strategies to deal with pest problems, an alternative approach is to redesign systems so that plant health is maximized, regardless of pest numbers, although this approach takes planning and time. An abrupt transition from conventional to organic may be risky if pest numbers are high and alternative practices are not yet in place. Hybrid systems, involving decreasing levels of conventional tactics and increasing levels of organic tactics, may be needed before the transitional period begins, in order to bridge the gap and lessen the impact of crop losses during the transitional period. The design of cropping systems with minimal pest impact requires a much more extensive and specific knowledge base than needed for reactive strategies.
Robert J. Hoard and Michael J. Brewer
The Environmental Quality Incentives Program (EQIP) administered by the U.S. Department of Agriculture Natural Resources Conservation Service (NRCS) was developed to encourage producer adoption of practices that promote resource conservation on lands in agricultural production. Reviewing the 2002 Farm Bill, EQIP rules, and local EQIP structure using Michigan as a case study, producers had ample opportunity to participate in EQIP. Yet past EQIP support of pest, nutrient, and conservation vegetation management was low among six states from 1997 to 2002, averaging 1.1% to 2.7% of total EQIP funds allocated. The past funding pattern and analysis of local resource concern priorities and incentive rates suggested that program modifications were warranted. The Michigan case study showed that participation in the NRCS advisory process, in partnership with commodity representatives and university specialists, was an effective avenue to recommend and obtain local EQIP modifications. After modifications were accepted in Michigan, increases were seen in producer participation in EQIP and in funds committed (about 15%) to adoption of a variety of techniques with pest, nutrient, and conservation vegetation value. This approach of analysis and engagement in the EQIP process is likely to work in other states, given common EQIP structure and governance, past funding patterns, and availability of supporting extension, research, and commodity partners.