Managing Greenhouse & High Tunnel Environments 2016 PDF

University of Kentucky College of Agriculture Plant Pathology Extension Cooperative Extension Service University of...

University of Kentucky College of Agriculture Plant Pathology Extension Cooperative Extension Service University of Kentucky College of Agriculture, Food and Environment Plant Pathology Fact Sheet PPFS-GH-01 Managing Greenhouse & High Tunnel Environments to Reduce Plant Diseases Emily Pfeufer Nicole Ward Gauthier Philip Konopka Extension Plant Pathologist Extension Plant Pathologist County Extension Agent Introduction Greenhouse and high tunnel environments, which tend to be warm and humid, often create ideal situations for disease development. Environments favoring infection and spread of many disease pathogens include one or more of the following: high relative humidity (90% or above), free moisture (e.g., leaf wetness, wet soil), and/or warm temperature. Because diseases can cause extensive damage, their management is essential to production of high quality, marketable products. While challenging, these environments can be managed to simultaneously encourage plant growth and discourage pathogen spread. Managing Relative Humidity & Temperature High relative humidity promotes development of many leaf, flower, and fruit diseases, including powdery mildew and gray mold (Figure 1). Figure 1. Many plant pathogens, (such as Botrytis, shown Daytime relative humidities of 25% to 70% are here) are favored by the warm, humid conditions that often low enough that pathogen infection is can develop in greenhouses and high tunnels. Pathogens inhibited. However, when humidity rises above allowed to multiply on diseased tissues serve as sources of infectious material for further disease spread. 90%, especially for long periods, disease incidence can also increase. The following practices help manage humidity and temperature. Agriculture & Natural Resources Family & Consumer Sciences 4-H/Youth Development Community & Economic Development Figure 2. Ventilating high tunnel (left) and greenhouse (right) structures is important to reducing internal relative humidity. High humidity encourages the development of many diseases, such as powdery mildew and Botrytis gray mold. Air Circulation breezes to facilitate ventilation. Prevailing winds Fan-jet or horizontal air flow systems should will dictate orientation of a ridge vent. operate continuously in greenhouses during periods of high humidity, which often occur Plant Spacing at night and during rainy days. Exhaust fans, Closely-spaced plants and overlapping canopies when present, can be used to circulate air in can create microclimates different from the rest greenhouses and in high tunnels when sides are of the structure. These microclimates are often closed. higher in relative humidity than surrounding air and are typically the first place disease develops. Ventilation Plants should be adequately spaced to allow for Exchange air in greenhouses and high tunnels air movement during all stages of development. with fresh outdoor air (Figure 2) in order to This facilitates drying of foliage and makes it reduce internal relative humidity. easier to obtain good spray coverage when fungicides are required. Hanging baskets placed Heated greenhouses overhead also reduce normal water evaporation Most winter evenings are cool enough to raise and contribute to high humidity in crop canopies. humidity to 100% and result in considerable Bushy or suckered ornamentals should have condensation in greenhouses. Condensation wider spacing, especially if plants are not pruned can be reduced significantly with late afternoon regularly. On determinate tomatoes, suckers and ventilations. Ventilation fans exhaust warm old leaves (up to first bunch of fruit) should be moist air from the greenhouse, replacing it with removed to facilitate air flow. cooler outdoor air. When this fresh air is heated, it becomes much drier and less favorable for For specific recommendations on vegetable disease development. spacing, see Vegetable Production Guide for Commercial Growers (ID-36). High tunnels Ventilation in high tunnels is manipulated by Air Temperatures opening sidewalls, endwalls (Figure 2), and/or Temperatures outside the normal range of ridge vents, if applicable. For new construction, growth induce stress on plants, and stressed choose a site with good air drainage and gentle plants are generally more susceptible to  Surface Sterilize Benches, Pots, & Tools Disease-causing pathogens are often spread through used pots, dirty tools and work surfaces, unswept floors, contaminated hoses (FIGURE 3), and even on human hands and clothing. Avoid any introduction of natural soil from dirty boots. Surface sterilize all work benches and tools regularly to prevent spread of pathogen inoculum. A dilute solution of household bleach (9 parts water to 1 part bleach) or commercial disinfectant will eliminate most pathogens. If using landscape cloth, thoroughly sweep it between cropping seasons and clean by spraying with high pressure water. Landscape cloth should be replaced as soon as it begins to wear. Plastic Figure 3. Puddling water on greenhouse and high tunnel liners in float beds should be replaced each year. floors increases relative humidity, encourages weedy growth, and can serve as sources of pathogen inoculum. Hoses left on the grouind may become contaminated with Clean Up Plant Debris plant pathogens. Most plant diseases cannot be cured, so it infection by disease-causing pathogens. Rapid may be necessary to discard diseased plant temperature fluctuations in structures should material. Bedding plants and vegetables with also be avoided to reduce plant stress. Consult root rots, vascular wilts, and viruses should be literature and production guides (e.g., Vegetable removed immediately after a positive diagnosis. Production Guide for Commercial Growers, This prevents pathogen spread to neighboring ID-36) for optimal temperatures for specific healthy plants. Diseased parts of woody plants, greenhouse or high tunnel crops. such as cankers, may be pruned. Plants with a few foliar leaf spots or powdery mildews may be salvaged if diseased material is removed and Avoid Standing Water plants are treated; however, any leaf removal on Water that collects or puddles under benches vegetables should be conservative in order to or in walkways (Figure 3) increases humidity. maintain production levels. Standing water also encourages growth of weeds and volunteer plants, which can harbor Diseased plant material and debris should be plant pathogens. Gravel, concrete, or landscape bagged and discarded (trashed or burned) as cloth covering dirt walkways reduces the soon as possible; do not compost. Tobacco overwintering (or overseasoning) capability of mowing should be completed with a sharp blade plant pathogens. to minimize plant injury, and then clippings should be removed and discarded; do not dispose Sanitation of clippings directly outside the greenhouse. Sanitation practices aid in eliminating sources of Develop a regular schedule to clean-up plant infectious plant pathogens and minimizing their debris on and under benches, in ground beds, spread. For more information on this topic, and on walkways. Immediate debris removal is refer to Greenhouse Sanitation (PPFS-GH-04). important because fungal pathogens can readily produce and disseminate spores on these The following practices can help reduce active materials. and dormant pathogen inoculum levels. Manage Weeds Avoid Wetting Foliage Remove and discard weeds and volunteer Whenever possible, opt for drip irrigation instead plants inside and outside of growing structures. of overhead irrigation; this keeps plant surfaces Excessive weeds outside greenhouses reduce dry. If using overhead irrigation, water early so airflow through vents, thus increasing relative foliage dries by midday. humidity in these structures. Weeds in ground beds can increase canopy density and result in Water Only As Needed higher relative humidity. Additionally, weeds Monitor plants closely and water judiciously, may harbor pathogens and insects that can but only as needed. Variations in light levels, transmit disease to greenhouse and high tunnel temperature, and humidity affect plant crops; insect-vectored viruses are a particular requirements for water. For example, plants concern. Gravel or landscape cloth may be used require less water during periods of cloudy to create a weed-free zone 5 to 10 feet around weather. In addition, plants arranged beneath the outside of structures; herbicides should be overhead hanging baskets (Figure 5) do not dry used with caution. as quickly as those exposed to bright light or full sun. Plants with similar water requirements Wash Hands Thoroughly After Using should be grouped together to maximize Tobacco Products irrigation efficiency. Tobacco mosaic virus (TMV) is a physically hardy virus particle that can persist on hands after Test Water to Ensure Fungicide Efficacy greenhouse workers use cigarettes and other Water used for tank-mixing or injecting tobacco products. To prevent introduction of fungicides should be tested for pH and this virus to commercially grown crops, workers alkalinity for maximum fungicide efficacy, as should wash their hands thoroughly with soap well as maintenance of application equipment. and water after using tobacco products. For more information on water quality, see Understanding Irrigation Water Test Results and Do Not Bring in Soil from Outdoors Their Implications on Nursery and Greenhouse Natural soil can harbor many soilborne pathogens Crop Management (HO-111) and Fungicide Tank- that may become serious problems if introduced Mixes and Incompatibilities listed in Additional into greenhouses; non-sterile natural soil should Resources. not be allowed into these structures. Sterilize any natural soil used in growing mixes or use a commercial soilless medium. Do not reuse potting media. Remove mud from boots and use foot baths (Figure 4) to prevent tracking natural soil. Water Management Many pathogens require free water to infect and reproduce. Wet plant surfaces are often at risk for foliar or fruit diseases, and overly-wet growing media favors development of damping- off and root rot diseases. Additionally, many pathogens are spread from plant to plant by splashing water or flooded soil. The following practices will aid in management of moisture in Figure 4. Use foot baths to prevent tracking natural soil greenhouse and high tunnel systems. (and potential pathogens) into greenhouses. Figure 5. Monitor plant water needs and irrigate accordingly. Variations in growing conditions affect plant water requirements. For example, plants produced under hanging baskets may not need to be watered as frequently as those exposed to more direct sunlight. Soil Management Salt buildup Salt buildup in soils that are intensively cropped Soilless Growing Media can stress plants and predispose them to disease. Commercially prepared soilless media are usually Monitor nutrient and salt levels with regular soil free of plant pathogens and are recommended testing and follow nutrient recommendations. for commercial production in flats and pots. To For more information on nutrient management, avoid contamination, bags of media should be see Vegetable Production Guide for Commercial stored where they will not become excessively Growers (ID-36). wet or have direct contact with natural soil. Fumigation Ground Beds (Natural Soil) Fumigation is broadly effective in reducing Growers should invest effort into maintaining a number of soilborne pathogens (e.g., root pathogen-free soils in ground beds by following knot nematode, Fusarium, and Verticillium), the recommendations below. but can also reduce populations of beneficial soil microorganisms. Only applicators with Crop and soil bed rotation specialized Category 1b licenses may utilize Rotate crops and soil beds to plants that are fumigants. As of the date of this publication, non-hosts of prevalent diseases in order to grower access to commercial fumigators in prevent buildup of populations of soilborne Kentucky is limited and costly. plant pathogens. Moveable high tunnels on rails allow alternation of the cropping site, which can Non-fumigant products reduce soilborne pathogens through natural Non-fumigant products have more specific modes weathering, fallow periods, or by using a non- of action against soilborne plant pathogens, host cover crop. and their efficacy relies on accurate disease diagnosis. These products are usually applied to Foot Baths for Animal Facilities: Easier Than soils via drip irrigation systems. Non-fumigants You Think! (University of California Division of suppress disease rather than broadly eliminate Agriculture and Natural Resources) soilborne pathogens, so regular applications are Note: While this publication was written necessary to realize yield benefits. These are for animal facilities, the foot bath design it most effective when combined with resistant describes could also be used in greenhouses. or tolerant varieties. For specific non-fumigant http://anrcatalog.ucanr.edu/pdf/8281.pdf options for vegetables, see Vegetable Production Fungicide Tank-Mixes and Incompatibilities Guide for Commercial Growers (ID-36). http://nicolewarduk.blogspot.com/2014/04/ fungicide-tank-mixes-and.html Soil solarization Greenhouse Sanitation (PPFS-GH-04) Soil solarization is another broadly effective http://www2.ca.uky.edu/agcollege/ approach used to reduce soilborne plant plantpathology/ext_files/PPFShtml/PPFS-GH-4. pathogen levels. For more information about pdf soil solarization, see Soil Sterilization for High High Tunnel Crop Profiles (Center for Crop Tunnels (Hort Fact-7003). Diversification) http://www.uky.edu/ccd/production/system- resources/gh-ht Additional Resources High Tunnel Webinar Series (Center for Crop Greenhouse Crop Diseases and Disorders Diversification) (Plant Pathology Extension Publications) http://www.uky.edu/ccd/training/webinars/ht http://www2.ca.uky.edu/agcollege/ Soil Sterilization for High Tunnels (Hort Fact- plantpathology/extension/pubs.html#GreenD 7003) Herbaceous Ornamental Diseases and https://www.uky.edu/Ag/CCD/HortFact7003. Disorders (Plant Pathology Extension pdf Publications) Understanding Irrigation Water Test Results http://www2.ca.uky.edu/agcollege/ and Their Implications on Nursery and plantpathology/extension/pubs. Greenhouse Crop Management (Hort-111) html#OrnamentalHerbaceous http://www2.ca.uky.edu/agc/pubs/HO/HO111/ Burley and Dark Tobacco Production Guide HO111.pdf (ID-160) Vegetable Production Guide for Commercial http://www2.ca.uky.edu/agc/pubs/id/id160/ Growers (ID-36) id160.pdf http://www2.ca.uky.edu/agc/pubs/id/id36/ id36.html March 2016 Acknowledgements—The authors are grateful to Shubin Saha, Extension Horticulture Specialist, for his review of this publication Photos—Emily Pfeufer (1), Cheryl Kaiser (2, left), Nicole Ward Gauthier (2, right), Steve Berberich (3), and Matt Barton (5), University of Kentucky; and Swen Halverson, Halverson Greenhouses, Jackson County, Kentucky (4) Revised from the original fact sheet, Managing the Greenhouse Environment to Control Plant Diseases, by Brian Eshenauer and Robert Anderson Educational programs of the Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability, or national origin.