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in many production systems (Shishkoff Integrated Pest Management and Biological and McGrath, 2002). Control in High Tunnel Production Ensure that transplants pro- duced in greenhouses are free of fungus gnat (Bradysia spp.) and shore Laura Pickett Pottorff 1,2 and Karen L. Panter3,4 fly (Scatella stagnalis) pests. Growers have reported bringing these pests in on plugs purchased from greenhouse ADDITIONAL INDEX WORDS. disease control, pests, insects, IPM suppliers (Moore, 2007). To protect SUMMARY. Crops grown in high tunnels are just as susceptible to pests and diseases as transplants from fungus gnat and those grown under greenhouse and field conditions. Crops that lend themselves shore fly infestations, the predatory economically to this type of production system are edible and/or minor crops. mite Hypoaspsis miles is one of the best Therefore, labeled pesticides for these crops are limited and sometimes nonexistent. biological control agents on the mar- However, there is a wide range of integrated pest management (IPM) strategies ket and is a recommended manage- available to high tunnel producers. These strategies include biological control, which is often left out of traditional IPM programs when labeled pesticides are ment tool for these persistent pests. available. High tunnel production is very conducive to the inclusion of biological Hypoaspsis miles can also be used in controls and allows for a truly IPM system. This article provides a selective overview conjunction with beneficial nemato- of common arthropod pests and diseases encountered in high tunnels, as well as des such as Steinernema spp. strategies that have potential for becoming best management practices in high Excluding pests and diseases tunnels with additional research. from a crop is a very efficient mecha- nism for pest management. Screening ntegrated pest management the soil, controlling soilborne diseases from ground to ground with various (IPM) is an approach to manag- and pests. Clear plastic sheets are types of mesh sizes can help keep out Iing pests that uses appropriate placed on the soil during periods of many different insect and mite pests physical, cultural, biological, and high ambient temperature. In the (Bethke and Paine, 1991; Bethke chemical tactics that are safe, profit- western United States, solarization is et al., 1994). In Colorado, several able, and environmentally compatible most effective when soil is treated covering types, including single-layer (Thomas and Rajotte, 2004). Cur- from June through August for a polyethylene, have been used for the rently, literature on the efficacy of period of 4 to 6 weeks (Ellmore purpose of excluding pests from high IPM and biological control in high et al., 1997). tunnels (Fig. 1). In 2007, the LS tunnels is limited. This article pro- Soilborne diseases caused by Econet B aphid screening (Gintec vides a selective overview of IPM Pythium, Fusarium, and Rhizoctonia Shade Technologies, Birmingham, measures that have proven efficacious do occur in high tunnels (Zitter, AL) was used with success to exclude in greenhouse and high tunnel pro- 2008) and are best handled preven- flea beetle (Epitrix spp.) from orna- duction, or are likely to perform well tively, as suggested in the previous mental and cruciferous plants. Flea in high tunnels. paragraph. If extra protection against beetle populations were much lower Like any sound pest and disease these pathogens is desired, consider and plant quality was much higher in management system, IPM begins establishing transplants and seeded screened high tunnels versus roll-up with prevention. The soil one plants crops in soil that has been pretreated sided high tunnels. In trials per- in and the transplants one may bring with biofungicides (McSpadden Gar- formed at the Colorado State Uni- into a high tunnel must be pest and dener and Fravel, 2002) or other versity Horticulture Research Farm disease free. Introducing pests and types of bioantagonists. Many of in Fort Collins in July 2006 diseases into the high tunnel, or these products are available commer- (F. Stonaker, personal communication), planting in disease- or insect-infested cially and involve artificially introduc- screening increased temperatures as soil should be avoided. To minimize ing microflora, usually beneficial much as 2 to 4 F when compared the buildup of soilborne pathogens, fungi or bacteria, into the soil envi- with ambient air temperatures. How- appropriate crop rotations should be ronment to prevent attack or to con- ever, temperature within screened practiced. Alternatively, if soil is in- trol a pathogen or pest. Many of these high tunnels using Tuffbell brand fested with pathogens, soil solariza- products are labeled to help prevent (ground to ground; G&M Agricul- tion can be used, especially in warm, soilborne root rots caused by the tural Supply, Payson, AZ) was not sunny climates. Soil solarization, as pathogens Pythium, Fusarium, and significantly different compared with described by Katan et al. (1987), uses Rhizoctonia (Table 1). While not as the control (polyethylene with rolled- the sun’s radiant energy to heat up efficacious as synthetic fungicides in up sides). An additional benefit of some cases, biofungicides may be screens is reflective properties that 1Former Diagnostic Plant Pathologist and Regional combined with other management serve to repel certain insects such as Greenhouse Specialist, Colorado State University Extension, Adams County 9755 Henderson Road, strategies to provide adequate control western flower thrips (Frankliniella Brighton, CO 80601 2Pesticide Applicator Coordinator, Colorado Depart- ment of Agriculture, 700 Kipling Street, Suite 4000, Lakewood, CO 80215 Units 3Extension Horticulture Specialist, Plant Sciences– Department 3354, University of Wyoming, 1000 To convert U.S. to SI, To convert SI to U.S., East University Avenue, Laramie, WY 82071 multiply by U.S. unit SI unit multiply by 4Corresponding author. E-mail: [email protected]. ( F – 32) O 1.8 F C(1.8· C) + 32
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Table 1. Examples of commercially available biofungicides and the fungi they are occidentalis) (Antignus, 2000). Grow- labeled to control (McSpadden Gardener and Fravel, 2002). ers should be aware that exclusion Biofungicide Fungi controlled techniques may keep pollinators out of the high tunnel as well. This may Coniothyrium minitans Sclerotinia be problematic with insect-pollinated Streptomyces griseoviridis Fusarium, Botrytis, Pythium crops. Trichoderma harzianum Botrytis, Pythium, Rhizoctonia, Fusarium When pests and diseases enter Gliocladium virens Pythium, Rhizoctonia, Fusarium the high tunnel environment, there Bacillus subtillis Pythium, Rhizoctonia, are many strategies that can be Fusarium, powdery mildew employed to manage them. Most are (Erysiphe, Sphaerotheca, Phyllactinia, etc.) dependent upon the pest and crop. Burkholderia cepacia Pythium, Rhizoctonia, Fusarium Below are some of the common pests Erwinia amylovora Erwinia amylovora encountered in high tunnels and sug- HpN harpin protein gested integrated strategies to con- Ampelomyces quisqualis Powdery mildew sider in addition to the prevention and exclusion techniques listed above. Western flower thrips are of par- ticular concern to growers in all areas of the Unites States. This pest not only causes feeding injury to flowers and foliage, but it also is a potential vector of tospoviruses such as tomato spotted wilt and impatiens necrotic spot viruses (Figs. 2 and 3). These two viruses can affect over 500 differ- ent vegetable and ornamental plants (Smith, 2003). If virus-vectoring thrips such as western flower thrips are of concern, tolerance of this pest is too low to allow for the use of biological control. To manage virus-vectoring thrips, the following IPM strategies are sug- gested: screening for exclusion, re- flective mulches or screens to repel (Antignus, 2000), and insecticides such as spinosad (Greer and Diver, 1999). If virus is not a concern, then the addition of biological control to man- age thrips is possible. Two predators are commonly used with good success (Gill and Sanderson, 1998; Greer and Diver, 1999). These include the pred- atory mite Amblyseius cucumeris (Bessin et al., 1993) and the predatory bug Orius spp. (Weeden et al., 2002). Because A. cucumeris needs humidity levels above 65% to thrive, Orius spp. is preferredinaridenvironments.Natural populations of Orius spp. can be at- tracted by planting sunflower (Helianthus annuus) in proximity to high tunnels. Psyllids (Bactericerca cockerelli) are insects that induce a toxemia called psyllid yellows in potato (Sol- anum tuberosum) and tomato (Sola- num lycopersicum) (Fig. 4). This potentially devastating problem for tomato in the western United States (Al-Jabr, 1999) can be controlled using Fig. 1. High tunnel with LS Econet B ground-to-ground screening (Gintec Shade the following strategies: screening, Technologies, Birmingham, AL) (A) and traditional poly-covered high tunnel tolerant cultivars including Yellow (B) at the Colorado State University Horticulture Research Farm in Fort Collins. Pear (Liu and Trumble, 2004), sulfur
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integration of the following manage- ment strategies will be successful (Greer and Diver, 1999): screening, soaps, oils, and neem-based insecti- cides. Biological control organisms such as ladybird beetle (Coccinelli- dae), which work best when aug- mented or inundative releases are used (Obrycki, 1998), green lacewing (Chrysoperla spp.), the parasitoid Aphidius, and Aphidoletes, a preda- tory midge, can be introduced. The warm, dry environment in high tunnels promotes rapid increase in two-spotted spider mite (Tetrany- chus urticae) populations. Spider mites require temperatures of at least 80 F and less than 50% relative humidity (White and Liburd, 2005). Monitor mites closely, because once estab- lished, outbreaks are quick to follow. Fig. 2. Symptoms of tomato spotted wilt virus (TSWV) on tomato in outdoor production. The following management strategies are often successful. Utilize irrigation to raise humidity levels and poten- tially decrease spider mite populations. Two predatory mites are commonly available for spider mite control. Amblyseius californicus (synonym Neoseiulus) does extremely well in hot, dry high tunnels, while Phytosei- lus persimilus does not (Henn et al., 2008). There is also a predatory midge on the market called Feltiella or Ther- idoplosis that will perform well in hot, dry environments preferred by spider mites (Osborne et al., 2008). Finally, the fungal disease pow- dery mildew (Erisyphales) needs to be considered (Fig. 5). Like spider mite, powdery mildew does very well in dry environments (Belanger et al., 2002). The pathogen requires a dry leaf sur- face, but higher relative humidity. There are several management strategies, but by far the most suc- Fig. 3. Symptoms of impatiens necrotic spot virus (INSV) on snapdragon cessful is to increase air circulation. (Antirrhinum majus). In a greenhouse, this can be accom- plished with the addition of horizon- dust application, and biological con- and biological control with parasitic tal air flow fans, but in a high tunnel, trol with Tamarixia spp., a commer- wasps (Greer and Diver, 1999). Para- without electricity, this addition is cially available parasitic wasp (Paine sitic wasps include Trichograma spp., not feasible. Consider the following and Driestadt, 2007). which attacks lepidopteran eggs, and management strategies to help com- Various caterpillars (Lepidop- Cotesia spp., which attacks larvae. bat powdery mildew: spacing plants tera) can cause damage on a wide Aphids (Aphidoidea) are another to allow for improved air circulation, variety of crops grown in a high tun- insect pest in the order Homoptera. rolling up the sides of the high tunnel nel. Fortunately, management of cat- Feeding on plant fluids, they can also or opening tunnel ends to improve air erpillars is not difficult if caught early. vector a number of plant viruses. If movement, neem-based or bicarbon- Therefore, regular monitoring is re- aphid-vectored viruses are of concern, ate pesticide materials, and biofungi- quired and when combined with the then, as with thrips, biological control cides such as Ampelomyces quisqualis following management strategies can may not be an option because pro- or Bacillus subtilis (Shishkoff and provide successful control: screening; ducers cannot tolerate the presence McGrath, 2002) (Table 1). application of pesticides such as soaps, of virus disease. However, if virus Crop production in high tunnels spinosad, and Bacillus thuringiensis; transmission is not a concern, then lends itself to a truly IPM approach.
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Belanger, R., W.R. Bushnell, A.J. Dik, and T.L.W. Carver (eds.). 2002. The powdery mildews: A comprehensive trea- tise. APS Press, St. Paul, MN. Bessin, R., L.H. Townsend, and R.G. Anderson. 1993. Greenhouse insect man- agement. Univ. Kentucky College Agr. Coop. Ext. Serv. Bul. ENT-60. 17 Sept. 2008.
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Osborne, R.S., N.C. Leppla, and L.S. detached leaf culture. Plant Dis. 86:915– insidiosus. Biological control: A guide to Osborne. 2008. Predatory gall midge 918. natural enemies in North America. 17 Sept. (unofficial common name), Feltiella acar- 2008.
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