weeds Cropping out Tilling, mulches, cover crops and fabric barriers are among the non-chemical weed-control options available

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1 curt kipp Cropping out weeds Tilling, mulches, cover crops and fabric barriers are among the non-chemical weed-control options available There are few weeds in this picture, because Carlton Plants in Dayton, Ore., uses marigolds as a cover crop. They not only crowd out weeds but enhance the soil so that weeds are discouraged later on. By Miles McCoy Even with costly weed control, the weeds can still win. Nurseries face the challenge of controlling weeds in both field- and container-grown crops. Weeds such as liverwort also invade the greenhouse industry and are difficult to control. Growers often seek a more environmentally friendly way to control weeds, but there are difficulties. Other than herbicides, the toolbox of available weed management practices is the same for all growers, stated Steve Fennimore, an extension vegetable weed specialist with the University of California at Davis, in an online Western Farm Press article. Effective weed control requires an integrated approach based on knowledge of each crop and the weeds that threaten it. Effective weed control complex Weed control in field production starts with prevention. It starts with good field sanitation and preventing weed seeds from blowing in. Then, many nurseries use tilling, plus careful placement of water and fertilizers, to restrict weed growth. Containers are more of a challenge, 26 NOVEMBER 2011 DIGGER 25

2 Cropping out weeds Monrovia Growers uses hand weeding, combined with pre-emergent spray once a year, as a costeffective weed control method. curt kipp though. As the plants get larger, their canopy can create dense enough shade to slow or prevent weed growth. The Rodale Institute, an experimental farm located in Kutztown, Pa., surveyed organic growers and found that most use six different management strategies, with 85 percent using at least three. The study listed the six strategies as hand weeding, mechanical control, mulches, cover crops, crop rotation and dense planting. But, as growers know, there are disadvantages with all these alternatives, usually starting with cost. Most require not only added input costs, but also more labor a double expense hit. With mechanical control, or tillage, evidence shows drawbacks to frequently turning the soil. But first, what are most common practices in today s nurseries and greenhouses? Mechanical cultivation Hand weeding is as old as the industry as old as agriculture. Some of the earliest images of the Oregon nurseries show large crews hand weeding nursery crops. Hand weeding is often still used whenever chemical herbicides might cause damage. Most growers probably consider it one more added expense. However, Monrovia Nursery has long been committed to an intensive handweeding program, augmented by twice yearly use of pre-emergent herbicides. In the 1990s, the company studied the cost of hand weeding versus the cost of spraying herbicides, and found that a combination of the two BIRINGER NURSERY 26 NOVEMBER 2011 DIGGER

3 techniques is the least costly. Monrovia found it took workers 10 hours of hand weeding per acre, performed 10 times a year, to keep the nursery weed-free without using pre-emergent herbicides. Pre-emergents, applied once in spring and fall, dropped workers hand weeding to seven times a year, with only one hour of weeding each acre. This non-chemical approach does point to cost efficiencies with hand weeding low-level weed infestations. What we have found best is preemergent spray in the fall, combined with hand weeding and backpack spraying, said Walter Suttle, production manager at Monrovia s Farm in Dayton, Ore. We were able to get the most cost-efficient weed control. Meanwhile, tilling has long been a key weed control technique. It brings weed seeds to the soil surface, where they quickly germinate. Thus, the best is a multiple tilling strategy on fallow fields where the seeds are allowed to germinate, grow for a short period, and then tilled in to kill them. Repeat as necessary. However, research shows this frequent tillage can cause other problems, including erosion and robbing the soil of moisture. These issues alone have created extensive non-till strategies, now being tested throughout agriculture. And, according to the National Sustainable Agriculture Information Service (ATTRA), tilling can also disturb soil biology, increase runoff, decrease water infiltration, damage soil structure and even invite weeds by exposing bare ground. Tilling can also actually spread weeds. Several common nursery weeds produce either tubers, underground bulblets, or other vegetative structures. All these reproductive parts get divided and distributed during tilling, spreading the weeds and possibly even creating an infestation. Common examples include yellow nutsedge (Cyperus esculentus), Canadian thistle (Cirsium arvense), quackgrass (Elytrigia repens), wild Crop Production Services supports the nursery industry by supplying: Chemicals Dry Fertilizer Liquid Fertilizer Controlled Release Fertilizers Growth Regulators Horticultural Supplies such as: Greenhouse Films Nursery Containers Fertilizer Injectors Decorative Pots Propagation Trays Contact Kathleen O Hollearn George Mercure Gresham Office: NOVEMBER 2011 DIGGER 27

4 Cropping out weeds curt kipp Northwoods Nursery keeps weeds under control by mulching with sawdust and planting living mulches a cover crop that is more or less permanent between the rows. The environmentally-conscious grower also leaves cuttings on the field to decompose, further feeding the soil. garlic (Allium vineale), and horsetail (Equisetum arvensis). If these are present, it might be better to remove them by hand, or cover with a thick mulch. Smothering weeds with mulches In the field crops, various mulches can suppress weeds, simply by limiting the light reaching the seeds in the soil. Again, chief drawback of mulches is the labor and materials costs. Still, the initial cost might be offset later by savings in both water use and herbicides. We have mulched all field-grown material with sawdust for decades, mostly Douglas fir, and found it conserves moisture and prevents most annual weed seeds from germinating, said Jim Gilbert, owner of Northwoods Nursery Inc. in Molalla, Ore. Gilbert agreed with the Oregon State University Extension s recommendation that mulches should be applied at 3 4 inches thick. They may need replenishing once or twice a year, depending on the material, though Gilbert replaces them less often. The weed-controlling effects of the mulch diminish somewhat in the second 28 NOVEMBER 2011 DIGGER year, but it still works well, he said. OSU Extension s weed website defines useful mulches as those that are regionally abundant and affordable, have no nutrient availability, hold little water and resist decomposition. Again, their decomposition rate is the key, since the longer the mulch can remain in place, the longer the nursery crop can grow with good weed control. OSU Extension rates Douglas fir bark as the most effective, but costly. They list large wood chips and sawdust as effective and less costly, respectively. OSU researchers also tested mulches made of oyster shell, Hazelnut shell and coppertreated geotextiles and found they provide good suppression of liverwort, one of the most challenging weeds to control. Gilbert has found similar success using simple mulches in containers. In our containers, we also use coarse bark mulch, which has the same beneficial effects as the sawdust mulch in the field, he said. Cover crops Weed control is one of the recognized advantages of many cover crops, mainly since they occupy and cover the soil, preventing most weed seed germination and growth. Bare soil just grows more problem plants. When one adds in the added nitrogen and organic matter in the soil after cover crops are tilled in, it becomes a cost-effective strategy. It is a mixed bag of positive benefits, said Allan Elliott, production manager at Carlton Plants in Dayton, Ore. We definitely hope that weed control is one of them. He said that cover crops research is also introducing new options, including new mustards from Idaho and eastern Washington, and sunflowers. Data from sunflower research indicates ability to suppress certain soil disease pathogens and insects, he added. Sunflowers seem to exude compounds into the soil that inhibits their growth, he said. Living mulches are more permanent cover crops planted between plant rows to hold the soil, provide traction, increase water infiltration and suppress weeds. They provide the same benefits as any cover crop, while reducing tillage activities. Northwoods Nursery uses

5 ASK ABOUT OUR CUSTOM SOIL BLENDS! 1275 Bailey Hill Road Eugene, OR Office: Fax: the technique. We also plant a cover crop between the rows and mow it with a modified flail mower that removes the weeds next to the sawdust, Gilbert said. Fabric weed barriers and disks There are now numerous fabrics that are used to cover the soil in horticultural growing. They are effective in preventing seed germination and slowing water loss. For certain crops, fabrics can add soil warmth. Cost remains a limiting factor, however. For containers, the physical disk barriers seem to be improving. Made of different materials, they are slit to fit around the plant stem and sit on the soil surface. Some disks are even treated with inhibiting chemicals that prevent seeds that land on them from germinating. Researchers at Virginia Tech used chemically treated Geodiscs placed on container-grown willow oaks suppressed all weeds completely. Meanwhile, the trees grown in those pots had higher top dry weights and root dry weights than trees grown without any form of weed control and trees sprayed with a conventional herbicide. These types of products are not considered organic. These last products are a few examples of newer materials for weed control. Research that advances our knowledge of the biology, ecology and management of weeds is fundamental to success on any farm, and it is vital that we do more of it, said Fennimore, the researcher at Cal-Davis. Scientific investigation gives us a broader base of tools that can be used successfully, regardless of the size of the operation or whether a farmer chooses conventional or organic growing practices. BARK FOR CONTAINER MIXES Various Sizes Available Top Quality Injection-molded Nursery Containers Sizes #1 #25 Bamboo Poles 3', 4', 5', 6' Call For Information and Free Samples Contact Rex for pricing at Performance You Can Rely On! Miles McCoy is the owner of Sustainable Hort LLC, a sustainable and organic products marketing firm. He has 25-plus years of green industry experience in marketing, communications and research. He can be reached at miles@sustainablehort.com Pringle Road SE (Salem, OR) nurserypots@msn.com NOVEMBER 2011 DIGGER 29