Steel in the Field: A Farmer’s Guide to Weed Management Tools

	Dryland Crops: The Farmers Long Rotations, Tall Crops, Right Steel Suppress Northern Dakota Weeds Terry Jacobson Wales, North Dakota 640 acres, flat fields organic grains and livestock glacial till, clay loam soils 5 to 6 percent soil organic matter one of the shortest growing seasons in continental U.S. 18 inches precipitation crops: spring wheat, barley, oats, flax, sweetclover, rye, sunflowers, alfalfa. Weed management highlights Strategies: crop rotation... tall varieties... delayed planting... pre-plant weeding... mechanical cultivation... soil structure management... fallow tillage residue management Tools: rod weeder at planting... stiff-tine drag harrow... field cultivator... row-crop cultivator... chisel plow... wide sweep plow Wild mustard loves the cool springs of northern North Dakota. It comes on strong just when annual crops are getting started. Innovative farmers elsewhere could use winter grains to suppress the early invaders, but it’s too cold here for milling grains to survive. Lots of other operators would use a non-selective herbicide to get a clean start, but organic farmer Terry Jacobson has long ago forsaken that option. Instead he weaves together a flexible rotation of tall grain varieties, underseeded cover crops, carefully applied tillage, and delayed crop planting to thwart weeds. The givens of his crop rotation sequence are wheat (Year 1 and Year 4) and disked-down yellow blossom sweet clover (Year 3 and Year 6). These rotate through the sequence that stretches to six years to keep confectionery sunflowers (Year 5) from appearing on the same soil any more often. The other two slots are flex years for short-season annuals that allow him to respond to market opportunities. Year 2 is open for oats or flax. Year 5 can be sunflowers, rye or barley. In ’97 he added crambe to his farm for either of the swing years. The oilseed crop is better suited than canola for organic production because it is resistant to diseases and tolerant of flea beetles. He underseeds oats or flax in Year 2 with the soil-improving clover at 10 pounds per acre. He also underseeds his Year 5 crops with the clover. Its deep rooting tendency opens subsoil macropores and brings up deep nutrients to the surface. Killing the cover crop deposits these minerals on the surface within the abundant residue, which breaks down to build soil fertility and organic matter, stimulating biological activity. Jacobson disks down the weed-smothering, biennial legume in late June after it has overwintered then regrown to early blossom stage. The stemmy biomass breaks down through the summer fallow season as the soil also absorbs water throughout summer. “In my rotation, I have early crops followed by late crops followed by green manure,” he explains. The rotation design shifts tillage and times when soil is not covered with crops each year. “The sequence give me a whack at early weeds in the second year [after fallow] with a late-seeded crop. Then I get them all in the third year with the cover crop.” “Our family has chosen not to expand acreage, but instead to intensify and diversify our operation. This priority supports community and allows us to intimately know our farm.” — Terry Jacobson Harsh winters and a four-month growing season require spring-planted crops. Weed control, however, starts in October. “The last cultivation in fall is our first weed management for spring,” Jacobson says. He uses 4-inch beavertail shovels (pointed at the bottom, wide at the top) on his Chisel Plow. The shovels leave soil roughly ridged with some incorporation of residue. The pass exposes roots of fall growing weeds such as quackgrass and field bindweed to winter’s wrath. He makes a second fall pass if weeds begin to regrow, or if quackgrass is a problem. Jacobson sees additional benefits of the pass: over winter, ridges trap more snow and lessen wind erosion; come spring, there’s faster soil warming and residue breakdown. To stimulate weed growth, he harrows in late April as soon as soil dries out. His Herman stiff-tine harrow has round tines about five-sixteenths of an inch in diameter. He controls the subsequent weed flush with a Field Cultivator outfitted with 9-inch sweeps. He makes a second pass if weed pressure is heavy and if he can delay planting. Planting is also a weeding pass. A favorite tool is his Morris Seed-Rite hoe drill. The 18-foot unit drops seed behind hoe-point openers, then runs a rod weeder over the rows about an inch below the surface. The turning rod firms in the seed, leaves a fluffy dust mulch, and spins up any weeds to dry out on top. The drill is a good load for his Case 1070, a tractor with 108 hp. (The Seed-Rite line, with units up to 40 feet wide, was discontinued in 1990.) “My grain comes up two to three days ahead of my neighbors,” Jacobson boasts. But he’s quick to admit that the newer air drills that most farmers of the area use are easier to transport, easier to load, much faster and have much larger seed tanks. “But the drill fits my farm perfectly because I don’t farm a huge farm,” he explains. “I need the fast emergence and extra weeding action I get with the Seed-Rite.” Jacobson watches the seeded fields closely to determine the last possible day he can do a postplant, preemergence return trip with the Herman harrow. Set at its least aggressive angle, he pulls the drag harrow over the fields at a 45 degree angle to the rows. Tines penetrate about three-fourths inch, not threatening the seeded grain which is rooting at its planted depth of 1.5 inches. This pass knocks out small seeded weeds such as wild mustard and field pennycress—also called French weed or fanweed (Thlaspi arvense). This is the final mechanical weed control he can do on his grains with his present equipment. In ’96, it wasn’t quite enough to prevent an economically significant amount of wild mustard from surviving a wet spring. While his stiff-tine harrow is too aggressive to pull through standing grain, he believes a lighter flex-tine harrow would be ideal for uprooting the next flush of mustard and French weed. Also on his wish list is a rotary hoe for controlling tiny weeds in young standing sunflowers. The stiffer tines of his harrow don’t kill the grain, but they stress the plants enough to set back maturity about a week. “With my short growing season, that’s a serious issue,” he explains. Jacobson selects tall crop varieties for height to better shade out weeds. The decision is easier because some tall varieties also carry the superior milling and protein characteristics that organic millers look for in premium grains. The high-yielding semi-dwarf varieties grown around him are about 6 to 9 inches shorter. He notes an irony. Following high yield years, his neighbors worry about how to get their straw to decompose so that it doesn’t harbor crop disease organisms. “I’ve got lots taller stalks, but my biologically active soil means I don’t have to worry about whether my straw will decompose.” He explains that the robust microbial activity prevents harmful organisms from dominating and causing plant disease. Further, he has less green foxtail (pigeon grass) and wild oats—two varieties of weeds he says are symptoms of tight, unhealthy soil—than do his neighbors. Kochia, a drought tolerant escaped ornamental crop, is showing some herbicide resistance in his area. When excess nitrogen (N) is present in soil, kochia can emerge after wheat and overtake the crop. His organic soils don’t have extra N, a condition which attacks kochia at its vulnerable point, he says. “Good soil makes a difference in weed control. My soil flows well between cultivator sweeps for good weed kill,” says Jacobson. “You can walk the edges of my farm and see the lack of clods on my side of the line fences.” Other important tools include: • A Noble wide-blade sweep plow to manage the sweet clover residue during summer fallow. Two seven-foot blades undercut surface weeds. The flat V-blades sweep back at a slight angle from the leading center point. One or two diskings begin to cut up the residue, and coulters ahead of the Noble plow’s two vertical shanks help it to move through the material without plugging. “No weed gets past those sweeps,”Jacobson says, a trait he banked on in a recent year when a neighbor turned him in to local officials for having patches of noxious Canada thistles in a wheat field. He declined the spray order and turned to a time-tested protocol in an old USDA bulletin. “At purple bud stage, go in with the sweep plow and slice off every one of the stalks. Then work them up. After that, go back in every 21 days until frost.” • Foot-wide sweeps on his chisel plow. He exchanges the gouging, ridging beavertail points in favor of sweeps when he wants to attack quackgrass after wheat, or when he wants to partially incorporate especially heavy straw. The tillage starts a composting action over winter, he observes, and causes harvested weed seeds to germinate more quickly come spring. • Row-crop cultivator. His eight-row, low-residue Dacron cultivator has five S-tine shanks working between 30-inch row spacings. Two-inch shovels vibrate actively to kill weeds. He sets the inner sweeps to run within 3 inches of the sunflower rows and uses flat panel crop shields. He found in the wet spring of ’96 that wild mustard more than 8 inches tall had root balls that build up between and plug the close-set shanks. He cultivates sunflowers when they are about 6 to 8 inches tall—earlier if he wasn’t able to back-harrow weeds after planting. He will cultivate the crop as short as 3 inches tall if weeds threaten. Jacobson got better weed control than the S-tines give when he used to use an old four-row rolling cultivator. He tilted the spider gangs to throw his free-flowing soil away from the row at first pass, then at second pass to kick soil back into the row areas to smother in-row weeds. He’s not able to move soil with his wider, faster S-tine unit. But the narrower implement had its drawbacks. “The rolling cultivator has to be set so precisely, and you have to maintain two bearings on each spider gang,” he recalls. Part of the problem, he admits, is that row crops just don’t seem natural to him, even though sunflowers are his best commercial crop. But seeing soil between rows of crops instead of a solid crop is a practice his family and neighbors still regard with lingering suspicion. “I hate every minute in row crops. It’s just not something we’ve associated with ‘farming’ in this area.” Any tool requires an operator who sees the big picture of the farm and has the interest and desire to make the tool work within its capabilities. Jacobson is willing to do that adapting when it fits within his time constraints and his goals of building soil, profitability and long-term ecological sustainability. Toward that end, he intentionally cultivates more slowly than he could, keeping speed down to 5.5 mph—even 5 mph when he’s he feeling most disciplined. “Tillage for weed control is a necessary evil. I do as little damage to soil structure as I can and try to do as much in other ways to enhance soil health as a good defense against weeds getting started.” Next farmer All Farmer Profiles