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Identifying and Controlling Weeds

By Charles Walters

Weeds have a nomenclature, much like a machine gun or an automobile. To keep it simple and still remain comprehensive, readers must be asked to master a few new vocabulary words. By now we are all familiar with common names for weeds. Spurge is such a name, one generally reserved for Euphorbia serpens, Euphorbia heterophylla, and Euphorbia hexagons. But there are other spurges: flowering spurge, or Euphorbia corollata; toothed spurge, Euphorbia dentata; leafy spurge, Euphorbia escula; mat spurge, Euphorbia glyptosperma; upright spurge, Euphorbia hysopifolia; spotted spurge, Euphorbia maculata; snow-on-the-mountain, Euphorbia marginata, etc. Usually, but not always, the scientific name will help separate and identify two weeds that have the same name.

It will be necessary to say something about habitat, general appearance, flower color, leaves, fruits, smell and juice or poison. Habitat designations become wearisome enough: fields, waste places, lawns, dry areas, wetlands. General appearance will be described as grass, bushy, creeping, erect, mat and so on, none of the vocabulary being troublesome. Flowers, of course, have a color, and leaves are opposite, alternate, lobed, succulent, verticillate, basal, narrow, medium, and so on. None of this will prove troublesome for the average reader.

As you read each entry in this cast of characters, remember that low biological activity is inherent in each weed problem. It is this lack of life in the soil that results in mineral imbalances. Each weed is keyed to a specific environment slotted for its proliferation. There are nutrient interactions and certain nutrients are needed to correct the weed problem. These may or may not be the nutrients indicated by the weed as deficient.

The farmer needs to read his fields like an open book. Weeds help define exactly what is happening. The information offered here will help the commercial crop producer become independent of the allopathic system, but it also forces him to move out into the field. The skills that backbone these biographies cannot be learned through a windshield or from local radio stations blasting their herbicide messages into the tractor cab.

With these thoughts in tow, here are a few notes on some specific weeds a farmer is likely to encounter*.


Jimson Weed
Jimson weed, Datura stramonium, is narcotic and poisonous, and
not the good cowfeed Gene Autry’s song suggests. Jimson weed is a
nemesis to soybean growers. It wakes up when decay has gone
wrong, producing ethane. Such decay releases too much cobalt. An
improved calcium level in colloidal position, a regulated pH, and
proper field decay of organic matter together provide control for
this weed without poisons. Illustrated is the upper part of the plant
(A); the cauline leaf (B); a ripe capsule (C); and seeds (D).

Datura stramonium, or Jimson weed, is narcotic and poisonous. According to variety, stems of this plant are green, corolla white (variety stramonium) or stem purple, corolla lavender or pale violet (variety tatula). Jimson weed is the nemesis of every soybean grower in the nation. It may be that northern states, because of sun angle, are less likely to have Jimson weed. It will grow in a very actively decaying organic matter complex, the kind of system one might relate to buttonweed. Buttonweed grows where there is methane gas production. Jimson weed wakes up and grows where gas production is ethane. Decaying organic matter can sequester and accumulate and govern the availability of cobalt. Improper decay will allow these things more freedom. Again, when conditions are adverse to the lifestyle of actinomycete molds, decay takes the hydroxide direction. Typical is the case of soybeans following corn, lots of undecayed stalks being left over. It is frequently a case of working the soil a bit too late in the fall, or late tillage in the spring. Under warm conditions with excess organic matter, and in the absence of bacterial activity taking decay in the proper direction, Jimson weed seeds are fired up and allowed to dominate. Of course if the calcium level were adequate, this alone would guarantee a different decay direction for trash. Thus the remedy is an improved calcium level in colloidal position, a regulated pH, and proper decay of organic matter. An injection of compost sees to it that decay proceeds in the right direction. This weed has a fibrous root, white to purplish flowers, and toothed leaves.


Russian knapweed
Russian knapweed, left to right, bracts, head, achene.

A perennial that reproduces by roots, rhizomes and seeds, that’s Centaurea picris, or Centaurea repens. Tradition says it came to the United States from Russia hidden in alfalfa seed. It still likes to travel that way, usually from Rocky Mountain and West Coast states. Before the age of hard chemistry, farmers controlled Russian knapweed exactly the way they handled field bindweed, with clean tillage and decay management. Faulty decay of organic matter is the culprit — in pastures because of over concentration of animals, in tilled fields because untreated soils impose limitations on the breakdown of organic matter. Inoculation of soil systems with predigested manures best manages this intruder and its well-developed branching root system. Russian knapweed grows up to almost 3 feet in height. Stems branch at the base, are striate, woolly, hairy to glabrous. Leaves of new shoots alternate and are little toothed and whitish underneath. Flowers are numerous, tubular, rose to purple in color. Composite heads are flask shaped, usually over an inch long. Flowers identify Russian knapweed from June to August. Seeds start staking out new territory in August and September. This weed grows best in soils with low calcium, humus, bacterial activity; calcium will be low or complexed; potassium, magnesium, manganese, chlorine will be high. Residual decay may be good, porosity high.


a.k.a. creeping bindweed, morning glory, climbing false buckwheat.

Hedge bindweed
Hedge bindweed, Convolvulus sepium, is both a terror and an
educational text. So is field bindweed, a blood brother. All the
bindweeds dominate when there is a short circuit in the energy release
of fouled decay systems. These soil limitations have to be corrected
via pH management. Microorganisms in well digested compost
help attack the shallow creeping rhizomes that make bindweed
such a crop destroyer. Pictured here is the plant (A); rootstock (B);
the flower showing structure (C); and seeds (D).

This perennial, Convolvulus sepium, reproduces from both seeds and shallow creeping roots. It is a blood brother to field bindweed or morning glory, Convolvulus arvensis. The sepium brother is also known as climbing false buckwheat. It grows almost everywhere, even on eroded hillsides that are well drained. Bindweed is a typical reflector of an improper decay of organic matter and excess accumulation of heavy soil metals. It may be that a bale of hay broke open in an area, and was left there. It may be that cattle were fed, and much organic matter was stomped into the ground. Morning glories function best in the presence of ample humus materials and an antagonistic decay system. Bindweeds tend to flourish more in an eroded low humus soil, which cannot support corrective decay systems for soil restoration. Low calcium, phosphorus, potassium and pH are benchmarks. Crusting and sticky soil are also consequences. Most creeping-vine-type weeds have extensive and fast growing rhizomes that develop to completely entrap the soil nutrient system in and around all the clusters of organic residues.

The biological energies contained in these foul, rotting residues support numerous dominating hormone enzyme systems that are “just right” for the vine weed families, and “not just right’’ for other species of soil and plant life. Such conditions can occur within soils of high exchange capacity (clay) or low exchange capacity (sandy) — with low or high organic material content — always in soils that impose limitations on ferment and breakdown of organic residue in the desired direction. Such soils are unable to govern the humus system. They also lack the capacity to support the right kind of nutrition needed for better plant and animal food, chiefly because of the imbalanced hormone-enzyme system that is sustained by improper decay. Field bindweed, morning glory, creeping bindweed all dominate the plant kingdom because of a short circuit in the energy release of fouled decay systems. These limits are generated by an accumulation of dry-dead organic substances either under dry fall conditions, or in wet spring soil — with compaction, sedimentation, and improper tillage timing figuring in the equation.

Cultural practices that relate to stress systems are greatly influenced by the pH character of the colloidal system involved and by the effect of drainage and air capacity of the decay medium. Correct these soil limitations through pH management and the bindweed-morning glory syndrome becomes completely dispersed. No herbicide chemical or fertilizer material can replace good soil management. Roots that go down 4 feet in the first year can’t be chased by phenoxy herbicides. Hedge bindweed is easy to identify. High twining with smooth leaves that alternate, are simple, long-petioled, triangular ovate, the plant has white to pink to almost reddish flowers. The fruit is glabrous and covered with bracts and calyx.


Pasture thistle
Pasture thistle.

This thistle, Cirsium altissimum, reproduces from seeds, sometimes in neglected fields. It grows to 6 feet in height atop a fleshy taproot. Leaves are slightly toothed with Pasture thistle.
weak prickles. Flowers are rose colored and terminal on the branches. Fruit with seeds is tipped with a parachute of plumose capillary bristles. The weed is easily expungable by the mowing machine, especially when this is done before seeds drop. This is not a serious problem weed, although the sharp spines are objectionable. Root reserves are lowest when the flowers are prettiest. Cutting at that time is lethal to the plant.


a.k.a., wind witch, common saltwort, Russian tumbleweed, tumbleweed, witch weed, saltwort, Russian cactus, prickly glaswort.

Russian thistle
The Russian thistle, sometimes called tumbleweed, would stair-step tumble into the loft of a western Kansas barn when the wind did its thing. Its classical name is Salsola kali, after Carolus Linnaeus, variety tenuifolia. This Regina Hughes art from USDA’s Selected Weeds of the United States does not illustrate the ball-like nature of the weed when it starts tumbling before the wind. Shown here is the weed itself (A); flowering branch (B); fruiting calyces (C); and seeds (D).

Even in the Latin identification system, Russian thistle has its aliases. There are some 60 species worldwide, 20 of them in the U.S. The most common scientific designation is Salsola kali, which USDA lists also as Salsola pestifer. There is also Salsola australis, a member of the goosefoot family. Another Latin designation is Salsola iberica, and there are at least 17 more such names in the United States alone. Whatever the name, Russian thistle, variety tenuifolia, is the one that the West, particularly Kansas and Colorado, made famous. It’s an annual seed machine and it provides weed lore with answers because its ubiquitous presence asked the right questions. As with Canadian thistle, the manganese to iron ratio is key.

Recognition is seldom a problem. Basically, this annual reproduces by seeds, usually in overgrazed pastures and drought stricken terrain. The plant has a spiny stem with reddish markings. It can grow up to 4.5 feet in height. Leaves alternate and for a time are succulent. Greenish flowers are not conspicuous.

I have stayed on to express the above notes because the plant is so well known and such a good teacher of the right questions. Managing the iron levels and cultivation, as with Canadian thistle, is the best strategy against this stubborn specimen. Russian thistle demands combat because it hosts the sugarbeet leafhopper, which in turn harbors the virus that confers curly top disease on beets and certain vegetable crops such as tomatoes, green beans, squash, cantaloupes, spinach, red beets, and many other receptive truck crops grown in the same soils. Rainbelt farmers do not need to worry about this weed.

*For the complete, unabridged list of weeds, their characteristics and how to control them, refer to chapter 13 of Weeds: Control Without Poisons.