Three growing seasons ago, during the middle of summer, I took a few soil samples on a southern Herkimer County dairy farm. One of the fields sampled that I found particularly interesting had been planted to a mix of forage soybeans and brown midrib sorghum two weeks earlier. There appeared to be more soybean seeds just sprouting – and laying on the soil surface – than there were emerged seedling plants boasting two, three or four true leaves. Emerged sorghum plants were few and far between.
In the preceding two weeks, local weather conditions had varied widely, from temperatures in the low 40s to the low 90s. Moisture conditions ranged from adequate to parched. For soybeans to germinate optimally, soil temperature should exceed 60º; sorghum seeds prefer a constant minimum of 65º for successful germination. While the host farmer and I were taking soil samples, about a hundred yards away a flock of pigeons was enjoying the sprouting soybeans.
I could see what looked like soybean plants with small but distinct true leaves. Examining this foliage closer, their surfaces felt soft and slightly fuzzy, ruling out soybeans. I told my host that these were velvetleaf (Albutilon theophrasti) seedlings. Researching the textbook “Weeds: Control Without Poisons” (Acres USA, 1996), we learn that this annual plant plagues growers in all but the coldest parts of North America. It reproduces by seeds, usually in tilled fields. It has a velvet feel on both sides of its leaves. When crushed, those leaves don’t smell good. Leaves alternate on the stem and can be up to 12 inches wide. Its flowers, mounted on short stalks, are orange-yellow and their resulting fruit splits upon maturing.
Quoting the textbook, “It proves troublesome in row crops. The remedy is cultivation, cutting or pulling. [Chemical] poisons are not particularly helpful, because their seeds retain their vitality for over 50 years. Only the well-inoculated compost pile will kill them. The appearance of velvetleaf is an early warning that decay has gone in the wrong direction, with methane rather than carbon dioxide the byproduct. Phosphates in the soil are complexed, and [beneficial] aerobic micro-organisms have gone off-duty.”
Most agronomists agree that soils making velvetleaf feel at home have a carbon problem. Moreover, fertilizing such fields with muriate of potash and commercial nitrogen ensures that this plant pest will stick around. Herbicides seldom solve the velvetleaf problem, since this weed skillfully develops resistance to them. Velvetleaf’s presence is usually proof that calcium and phosphorus levels are low or complexed and that potassium, magnesium and very likely selenium are high.
Quoting the textbook again, “With anaerobes in command, manganese, iron, sulfate, copper, boron and chlorine are cut loose and achieve a high profile. Low humus, low porosity and poor decay translate into high moisture, crusted and sticky soils and aluminum release.” Almost illogically, use of classic herbicides like alachlor and 2,4-D improve the overall vitality of the velvetleaf population.
Newer herbicides haven’t fared much better in this battle against A. theophrasti. This almost guarantees chemical failure because killing the inferior herbicide-susceptible specimens simply leaves the survivors to reproduce – the man-made selection of a super weed genotype.
This is a case where otherwise learned weed scientists keep failing Population Genetics 101. In addition to velvetleaf’s background, here’s some history. This weed originated in the Far East. Its use as a fiber crop in China dates back more than 2,000 years. Still grown there for fiber, it’s used to make ropes, coarse cloth, paper and caulking for boats. Whether as foreign material in desirable crop seed, or as an intended fiber crop in its own right, velvetleaf arrived in North America, likely before 1700, rapidly spreading on the East Coast.
Velvetleaf foliage. Photo courtesy of Rebekah D. Wallace, University of Georgia, Bugwood.org
Although attempts to process velvetleaf never succeeded economically, U.S. farmers continued planting it for more than 100 years. But in the minds of most farmers, A. theophrasti’s minuses far outweighed its pluses.
But there are some nutritional benefits. Seeds can be consumed raw or cooked; they can be eaten raw when they are under-ripe. Ripe seed can be dried and ground into powder, then used in soups, bread, etc. Seeds contain 15% – 30% oil, but those yields/acre basis compete poorly with oil yields from soybean, corn, sunflower and canola.
Also in southern Herkimer County is a farm where I used to cow-sit three decades ago. Since then, the farm changed hands twice. That farm stopped shipping milk, since a mega dairy operation nearby needed land for its expansion. Several months ago, I drove by this farm, passing by a field that, one owner ago, had been part of an organic rotational grazing program. The current crop grower had planted herbicide-tolerant soybeans, but it took great effort for me to find the beans because the beans were so swamped with velvetleaf. It was probably the worst infestation of that broadleaf I’d ever seen.
I know that this prolific stand of A. theophrasti had survived at least one barrage of chemical warfare. The seed had likely been delivered in liquid manure from the large dairy herd that the intended soybean parcel was supposed to support. A significant amount of now-herbicide-tolerant velvetleaf seed had apparently escaped the oxygen-free slurry environment as well as the cows’ digestive juices.
According to “Minnesota Wildflowers: A Field Guide to the Flora of Minnesota,” velvetleaf became a serious competitive weed of corn and soybeans, save for the use of modern herbicides. This weed not only sucks out large quantities of water and nutrients from soil, it also contains chemicals that inhibit germination and growth of other plants, allowing it to form dense monocultures.
Presently persisting in untreated field margins, disturbed waste areas and fallow fields, velvetleaf is also a very accommodating alternate host for the serious plant pest called soybean cyst nematode.
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