Development of Biological Control of Tetranychus urticae (Acari: Tetranychidae) and Phorodon humuli (Hemiptera: Aphididae) in Oregon Hop Yards Woods, J. L., Dreves, A. J., James, D. G., Lee, J. C., Walsh, D. B., & Gent, D. H. (2014). Development of Biological Control of Tetranychus urticae (Acari: Tetranychidae) and Phorodon humuli (Hemiptera: Aphididae) in Oregon Hop Yards. Journal of Economic Entomology, 107(2), 570-581. doi:10.1603/EC13488 10.1603/EC13488 Entomological Society of America Version of Record http://cdss.library.oregonstate.edu/sa-termsofuse BIOLOGICAL AND MICROBIAL CONTROL Development of Biological Control of Tetranychus urticae (Acari: Tetranychidae) and Phorodon humuli (Hemiptera: Aphididae) in Oregon Hop Yards 1 1 2 3 2 4,5 J. L. WOODS, A. J. DREVES, D. G. JAMES, J. C. LEE, D. B. WALSH, AND D. H. GENT J. Econ. Entomol. 107(2): 570Ð581 (2014); DOI: http://dx.doi.org/10.1603/EC13488 ABSTRACT The temporal development of biological control of arthropod pests in perennial crop- ping systems is largely unreported. In this study, the development of biological control of twospotted spider mite, Tetranychus urticae Koch, and hop aphid, Phorodon humuli (Schrank), in a new planting of hop in Oregon is described over a period of 9 yr (2005Ð2013). Both the abundance and diversity of natural enemies increased over time. Known predators of hop aphid (Coccinellidae and Antho- coridae) were present in all years; however, stable biological control of hop aphid was not achieved in most years and aphicides were required to suppress populations at commercially acceptable levels in 5 of 9 yr. Populations of aphidophagous coccinellids developed synchronously with hop aphid populations, and temporal correlations indicated these are the primary predatory insect associated with hop aphid regulation. However, sampling methods did not assess levels of aphid parasitoids and hyperparasitoids and their contribution to biological control was unquantiÞed. Spider mite biological control was associated primarily with predatory mites (Phytoseiidae) and Stethorus spp. (Coccinel- lidae). The magnitude of temporal correlations of abundance of these predators with spider mites was found to be greatest on the same sampling dates and at lags of 7Ð14 d. Stable biological control of spider mites occurred after four Þeld seasons, suppressing spider mites to levels similar to those commonly achieved with chemical control. A survey of 11 commercial hop yards in Oregon documented pest and natural enemy densities under commercial management practices over a period of 4 yr (2008Ð2011). Natural enemy abundance in commercial hop yards was similar to that of a 2- to 3-yr-old hop yard with limited disturbance. Whereas total reliance on biological control for hop aphid is unlikely to be successful, there appears to be unrealized potential for biological control of spider mites in commercial production. Dynamic action thresholds that consider the value of natural enemies are needed for both pests. KEY WORDS conservation biological control, cross-correlation, integrated pest management Enhancing the environment through practices that longevity and efÞcacy of resident natural enemy pop- conserve natural enemy abundance and diversity has ulations to suppress pests (Barbosa 1998). The primary been termed conservation biological control (CBC; effort of CBC is directed toward encouraging the Ehler 1998). In the broadest sense, CBC seeks to resident natural enemy population to thrive through attract and maintain natural enemies and enhance the strategies such as use of selective pesticides, provision of refugia, and careful selection of cultural practices (Eilenberg et al. 2001). The use of trade, Þrm, or corporation names in this publication is for the information and convenience of the reader. Such use does not The hop plant, Humulus lupulus L., is a dioecious constitute an ofÞcial endorsement or approval by the United States perennial plant with annual shoots that can climb to Department of Agriculture or the Agricultural Research Service of heights Ͼ4Ð5 m in a single growing season (Neve any product or service to the exclusion of others that may be suitable. 1991). Female strobiles, termed cones, are produced 1 Department of Crop and Soil Science, Oregon State University, 109 Crop Science Bldg., Corvallis, OR 97331-3002. on lateral branches and contain the economically 2 Department of Entomology, Washington State University, Irri- valuable bittering acids and oils that act as a preser- gated Agriculture Research and Extension Center, 24106 North Bunn vative and ßavoring of beer (Neve 1991). This crop Rd., Prosser, WA 99350. offers a unique opportunity for assessing development 3 U.S. Department of AgricultureÐAgricultural Research Service, Horticultural Crops Research Unit, 3420 NW Orchard Ave., Corvallis, of CBC. The rapid growth habit of the plant, at times OR 97330. up to 15 cm per day, and production of copious 4 U.S. Department of AgricultureÐAgricultural Research Service, amounts of succulent leaf tissue are thought to make Forage and Cereal Research Unit, and Department of Botany and hop a preferred host of several arthropod pests and Plant Pathology, Oregon State University, 3450 SW Campus Way, Corvallis, OR 97331. diseases (Mahaffee et al. 2009). The two primary ar- 5 Corresponding author, e-mail: [email protected]. thropod pests of hop in the northern hemisphere are April 2014 WOODS ET AL.: DEVELOPMENT OF BIOLOGICAL CONTROL IN HOP 571 the hop aphid, Phorodon humuli (Schrank), and the of the yard was Ϸ0.75 ha, and the yard was surrounded twospotted spider mite, Tetranychus urticae Koch. by mowed grass and annual cereal or vegetable crops. Management of arthropod pests typically involves an- Hop plants were arranged on a 2.1-m grid pattern and nual applications of miticides and aphicides. Numer- under a 5-m trellis. Several studies occurred during the ous applications of foliar fungicides are also made for 9 yr of data collection that evaluated the impact of disease management (Gent et al. 2009, Mahaffee et al. sulfur and other fungicides on twospotted spider mite, 2009). hop aphid, and their natural enemies. Details of two of The potential for biological control of aphid pests these studies are provided in Gent et al. (2009) and and twospotted spider mite is well supported in sev- Woods et al. (2012), but only data from plots receiving eral systems, including hop (Aveling 1981, Neve 1991, no miticides or sulfur fungicides are reported herein. James and Barbour 2009, Weihrauch 2009). Aphids are In a given experiment, plots were arranged in a ran- preyed on by numerous predator, parasitoid, and domized complete block design with four or Þve rep- pathogen species (Frazer et al. 1981, Obrycki et al. licates. An individual plot consisted of 16 plants during 2009). For example, an assemblage of aphidophagous 2005 and 2006 and other 8 plants in other years. In all organisms preying on pea aphid (Acyrthosiphon pisum experiments, the nontreated plots were separated by Harris) in alfalfa generally includes coccinellids, spi- at least one row of plants not treated with insecticides, ders, anystid mites, lacewings, syrphids, anthocorids, miticides, or fungicides. Standard production prac- phalangids, and aphidiids (Frazer et al. 1981). Hop tices for western Oregon were followed in all years. In aphids are commonly preyed on by members of coc- 2005, 2006, and 2007, irrigation was supplied by sprin- cinellids and anthocorids, although populations of at klers every 7Ð14 d as needed for crop development, least 50 aphids per leaf may be needed for the estab- whereas in subsequent years irrigation was supplied lishment of these predators. There is currently little daily by a surface drip system. In the planting year evidence to suggest stable and effective control of hop 2005, 46-0-0 fertilizer was applied to each plant by aphid can be achieved solely by parasitoids and patho- hand (Ϸ14 g per plant). Granular nitrogen, phospho- gens (Neve 1991, Trouve et al. 1997, HartÞeld et al. rous, and potassium were broadcast applied during 2001, Weihrauch 2009). 2006Ð2013 in April, May, and June according to stan- Predators of twospotted spider mite consist of many dard commercial recommendations (Gingrich et al. generalist arthropods, including members of the Ac- 2000), with total kilograms of nitrogen per hectare arina (e.g., Anystidae) and the insect orders Co- totaling 101, 54, 135, 135, 131, 137, 119, and 148, re- leoptera, Neuroptera, Hemiptera, Thysanoptera, and spectively. Basal foliage and weeds were controlled Diptera. Specialist predators include certain phyto- during 2006Ð2013 with applications of herbicides, as seiid mites as well as mite-feeding lady beetles, Stetho- described in detail in Supp Table 1 (online only). rus spp. (Pruszynski and Cone 1972, Strong and Croft Throughout the duration of these studies, selective 1993, Biddinger et al. 2009). In natural conditions, insecticides were applied in certain years to reduce twospotted spider mite generally is regulated by pred- confounding effects from other pests. During 2007Ð atory arthropods (James et al. 2001, Gardiner et al. 2009, Bacillus thuringiensis (0.15 kg a.i./ha, Javelin 2003), suggesting that this pest could be effectively WG, Certis USA, LLC, Columbia, MD) was applied in suppressed by CBC in managed agroecosystems. July for the control of lepidopteran pests. During However, no studies in hop have actually quantiÞed 2007Ð2009, 2011, and 2012, pymetrozine (0.034 kg a.i./ the temporal development of biological control or ha, FulÞll, Syngenta Crop Protection, Greensboro, attempted to identify the natural enemies most critical NC) was applied for the control of hop aphid when to its success. populations exceeded 90 aphids per leaf. An additional Our objectives in this study were to describe the application of imidacloprid was injected into the drip temporal development of biological control in hop, irrigation system (0.02 liters a.i./ha, Provado 1.6 F, identify the association of predatory arthropods with Bayer CropScience LP, Research Triangle Park, NC) hop aphid and twospotted spider mite, and assess the in July 2009.