Non-chemical Control of Weeds Inside Greenhouses
Weeds are a persistent problem in greenhouses, hoop houses, propagation houses, and other enclosed structures. Weeds can grow on the container media, competing with the ornamental plants for space, nutrients, water, light, and oxygen and thereby reducing the overall growth and market value of the plants. They can even be found growing in the drain holes of the containers, under the benches, on the ground-cloth floors, sides of the walkways inside the greenhouses, and even in the liners/stock plants. Not only do these weeds reduce the quality of the ornamental plants, but they also harbor insects, such as whitefly and thrips, and other pests such as mites, slugs, and snails. It is important to regularly scout for weeds. The following are some of the effective non-chemical methods for weed control that can be applied inside greenhouses and other enclosed structures.
Prevention and Sanitation Practices: Maintaining sanitation and adopting preventive measures are the first and foremost steps in an effective weed control program. It is recommended to use a clean and sterile substrate or media for growing ornamentals. The tools and equipment need to be cleaned thoroughly each time they are used to make sure that there are no weed seeds attached to them. Greenhouse workers should maintain proper sanitation practices and are recommended to disinfect their shoes/boots and gloves thoroughly as weed seeds can get dispersed via human beings. Weeds growing outside the greenhouse also need to be controlled to reduce the introduction of weed seeds and propagules by foot traffic and wind blowing. Screen exclusions on vents may help in reducing the amount of wind-borne weed seeds from entering the greenhouse. Make sure the storage areas for bulk goods and racks are not infested with weeds. Keep weed seeds and other propagules (tubers, rhizomes, etc.) out of the greenhouse by using weed-free plant materials and stock. Regularly scout for weed species inside the greenhouses and always monitor new shipments of plants and inspect them for small weeds before placing them inside the greenhouse. Concrete floors and weed barrier fabrics can help to reduce weed seed germination. Also, avoid storing/keeping container media under the benches and if reusing the containers, wash them thoroughly with pressurized water and chemical disinfectants to remove weed seeds, pathogens, and dirt.
Cultural Control Practices: Overwatering greenhouse crops can cause algae, moss, and liverwort to grow on the container media and spread rapidly as these species thrive well in moist conditions. Avoid overwatering the plants and ensure that uniform water is applied via proper irrigation practices. Drainage needs to be properly maintained inside the greenhouse so that water does not get collected on the floor and surfaces. Greenhouse ventilation and proper spacing of the ornamental plants can reduce humidity levels and may reduce weed germination rate. Chemical disinfectants such as quaternary ammonium chlorides can be applied to hard and concrete surfaces to avoid algae, liverwort, and moss growth. Strategic placement of controlled released fertilizers in the containers can further help to reduce weed germination, emergence, and growth. Instead of topdressing with fertilizers, subdressing is more recommended. Organic mulch materials such as pine bark and parboiled rice hull at a depth of 1 to 2 inches can act as a physical barrier and help to reduce weed emergence and growth in the containers.
Manual Removal or Hand Weeding: Frequent scouting and hand-pulling of weeds inside the greenhouse can minimize the chances of the weeds getting established and starting seeding. After hand-pulling weeds, never keep the weed materials on the greenhouse floors as these weeds are resilient and can re-root in the humid condition of a greenhouse. It is highly recommended to hand-pull weeds when young and avoid any seeds to be left over inside the greenhouse as they can germinate very easily under suitable conditions.
Debalina SahaAssistant Professor, Michigan State University
Debalina Saha is an Assistant Professor of ornamental weed management in the Department of Horticulture at Michigan State University. She has an appointment in research, teaching, and extension. Debalina provides statewide weed identification and management recommendations for ornamental plant production in greenhouses, nurseries, landscapes, and Christmas tree production. The primary goal of her research program is to improve upon current weed control practices and develop new effective methods of weed control using an integrated approach that involves both chemical and non-chemical strategies.