Time of bloom: June to October.
Seed-time: July to November.
Range: Throughout the American Continent except the extreme
North, and in most parts of the world. Habitat: Soil either dry or moist. Invades nearly all crops.
The seeds of this weed form one of the most common impurities of commercial seeds, particularly of red clover. In a bulletin issued by the Agricultural Experiment Station of Nevada, concerning "Clover Seeds and their Impurities," it is stated that of red clover samples submitted for inspection (obtained in all parts of the country), 62.9 per cent contained seeds of Persicaria. (Fig. 61.)
Stems six inches to two feet tall, often red or purplish at base, nearly smooth, erect or sometimes spreading. Leaves lance-shaped, smooth or with fine hair roughening the edges, pointed at both ends and generally blotched near the center with a large brownish spot. It is related that Joseph once hurt his hand while working in his carpenter's shop. Mary wished to make a healing poultice with this plant, but
"She could not find it at her need And so she pinched it for a weed," since when its leaves have always borne the mark of the Lady's thumb; the sheathing stipules at their base are fringed with short bristles. Flower-spikes numerous, dense, erect, a half-inch to two inches long; calyx pink or purplish with four or five obtuse lobes, usually six stamens, and a two- or three-parted style. Achenes lens-shaped or sometimes three-angled, smooth, shining, jet-black.
In some localities the plant is said to harbor the corn-root aphis, the louse appearing with the first leaves.
Fig. 61.-Lady's Thumb (Polygonum Persicaria). X 1/4.
Prevent seed development. Even so expensive a process as hand-pulling is often worth the labor if it hinders so pernicious a weed as this from fouling the ground with its long-lived seeds. In grasslands and grain fields a spray of four-per-cent solution of Copper sulfate will greatly damage the foliage of the weed, checking growth and usually blasting the budding flowers. In cultivated ground it is readily subdued by the necessary tillage.