When I studied high school biology five decades ago, scientists only talked about three life form groups (called kingdoms): animals, plants and fungi. Halfway through that half-century, another kingdom was added, called protists. Protist life forms are universal, almost all of them microscopic – tiny critters with big names. Examples of protists include amoebas, ciliates, diatoms, Giardia, Plasmodia (which causes malaria), Phytophthora (the cause of Ireland’s Great Famine) and slime molds.

Crop Comments: Educated guess? Ignorance isn’t blissMost of these organisms are single-celled and beneficial. But Giardia can contaminate a harmless-appearing woodland brook so that its water should not be ingested by humans. (Many of us have ancestors who abandoned Ireland for America because the Phytophthora infestans blight destroyed their potato-based food supply.)

But I do like diatoms. When diatoms die, their skeletons left behind become diatomaceous earth (DE). This material consists of fossilized remains of diatoms, a type of hard-shelled protist. DE is used as a filtration aid, mild abrasive in products (including metal polishes) and toothpaste – and my favorite, mechanical insecticides. I dust it on growing vegetables and roses to kill Japanese beetles and other chomping insects; it works well. The jagged edges of these microscopic particles lacerate the insides of ingesting insects, as well as plug the breathing holes in their soft tissues.

Soil biology is very important to Mother Nature. If crop people abuse soil, traumatizing its biology, she makes a countermove: human-desired crops, such as corn and soybeans (lacking fibrous root systems) tend to rapidly deplete soil organic matter (OM). With waning humus, beneficial Actinomycete molds are discouraged. Mother Nature’s next move: With Actinomycete populations plundered, soil biology weakens in such a way as to encourage dormant Jimson weed (Datura stramonium) seeds to germinate. Jimson weed – unlike corn and soybean – boasts a fibrous root system, enabling this weed to better hang onto soil as well build OM. Unfortunately, all parts of D. stramonium are poisonous to one degree or another.

Of course, if the calcium level were adequate, this alone would guarantee a different decay direction for trash, thus un-inviting Jimson. This non-invitation consists mainly of an improved calcium level in the colloidal position – we’re talking about base saturation percentages, which help quantify the balance between soil nutrients. The non-invitation to Jimson also provides regulated pH as well as proper decay of OM. Fortunately, an injection of properly aged compost makes decay proceed in the right direction.

People call me up with questions like “Why is Jimson weed popping up all over my soybean field following corn?” I answer their question with my own: “What does your soil analysis tell you about the field?” That question is usually followed by loud silence. Thus far, I have been able to employ self-control to avoid retorting “That wasn’t a rhetorical question.”

Moving on to a pair of protists, we observe that the widespread use of the herbicide active ingredient glyphosate is increasingly linked to higher soil levels of pathogens like Phytophthora. Writing in the October 2009 European Journal of Agronomy, Don. M. Huber, Ph.D., Purdue Agronomy Department, explained that glyphosate stimulation of fungal growth and enhanced virulence of pathogens, such as Fusarium and Phytophthora, appear to be related. This relationship can have serious consequences against sustainable production of a wide range of susceptible crops, leading to the functional loss of genetic resistance. According to Huber, these two pathogens commonly increase mycotoxin levels in harvested crops – particularly corn and soybeans.

Another weed that Mother Nature employs to revitalize human-injured soils is Russian (spotted) knapweed (Centauria maculosa). This is another weed whose presence causes the involved crop person to ask me about the cause of that pest’s local appearance in their fields. My reply again centers on asking for information provided by soil analysis. More often than not, my question’s answer, again, is loud silence. C. maculosa is a biennial or short-lived perennial which forms a basal rosette in the first year, reaching four to five feet the second year. It reproduces by roots, rhizomes and seeds. Its flowers are pink to purple, usually half- to three-quarters-inch in diameter. During winter, all that remains of the original plant is dead stems with heads poking through the snow.

According to tradition, knapweed came to the U.S. from Russia, stowed away in alfalfa seed. During the pre-chemical era, farmers controlled this weed the same way they did field bindweed/morning glory – with clean tillage and decay management. Expect defective decay of OM to spawn a surge of knapweed in pastures because of over-concentration of grazing livestock – and in tilled fields because untreated soils tend to limit the breakdown of OM. Inoculation of soils with pre-digested manure (compost) best manages the antics of this Volga visitor, despite its well-developed branching root system which does function nicely as a soil retainer.

According to Charles Walters, writing in “Weeds: Control Without Poisons” (1996, Acres USA Press), knapweed’s stems branch at the base, are striated, woolly and hairy. “Leaves of new shoots alternate and are little-toothed and whitish underneath. Flowers are numerous, 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.”

Walters concludes that this weed grows best in soils that are low in calcium, humus and bacterial activity. Soils that have calcium that is low or complexed and/or are high in potassium, magnesium, manganese and chlorine will invite Russian knapweed, even if the residual decay and porosity are good. A knapweed-infested pasture – if left fallow and un-grazed – will likely host ragweed the next growing season, followed by goldenrod, then lamb’s quarters.

Occasionally unpalatable ragweed is followed directly by lamb’s quarters, which is fairly tasty, even to people. Overgrazed by cattle, desirable species slowly but surely fade away. Knapweed survives not because it’s toxic and kills its eaters. It’s actually quite non-toxic – it’s just very unpalatable.