Common fumitory is an annual spring or winter weed from the dicotyledon class, which mainly germinates in spring and autumn.

A characteristic feature of this species is the bluish or grayish-green color of leaves and a stem covered with a bluish-green bloom.

It has a spindle-shaped, poorly branched root system, white or yellowish-brown in color. The stem reaches a height of 10 to 50 cm, is angular, strongly branched, erect, glabrous, sometimes reddish, and covered with bloom. Cotyledons are lanceolate, 10–15 mm long, glabrous, bluish-green, sharply pointed at the tip. True leaves are bi- or trifid with narrow tips, bluish-green. The inflorescence is a raceme, composed of comb-like red, pink, or purple flowers, darker at the tip. The fruit is a small nutlet, inversely ovate, gray-brown. Seeds are oval, grayish- or yellowish-brown.

Occurrence and Harmfulness

Common fumitory occurs in root crop fields, less frequently in cereals and gardens. It prefers clay, sandy-clay, and humus-rich soils, well-cultivated, fertile, and with good air-water conditions.

The difficulty in controlling common fumitory is associated with the waxy bloom, which hinders herbicide effectiveness. Seeds can retain high germination ability for over 11 years. Optimal germination temperature is around 7°C.

Control

Mechanical Method

The long period from planting to potato emergence is critical (ideal conditions for weed development) and can be used for mechanical treatments. These are performed using farm-available equipment, e.g., hilling machines, light harrows, cultivators, etc. Their main task is to create optimal conditions for rapid weed germination, then destroy them with subsequent cultivation passes. Maximum effectiveness (over 90%) occurs when weeds are in the seedling stage, but as weeds grow, effectiveness drops to around 40%. Success depends strongly on weather and soil conditions. In very wet springs, mechanical control is difficult. On heavily infested plots, mechanical treatments may backfire, stimulating stronger growth of damaged perennial rhizomes. Additionally, mechanical control is labor- and cost-intensive due to multiple passes. It is most commonly used in small farms or organic systems. Before potato emergence, 3–6 treatments are recommended at 6–8 day intervals. After emergence, no more than 2–3 treatments should be applied, as delays can damage the crop, increase pathogen transmission, and excessively dry the soil (especially light soils).

Mechanical-Chemical Method

The most efficient and widely used system. Reduces the number of mechanical passes compared to the purely mechanical method. Usually involves two or three hilling passes after planting, followed shortly before emergence by herbicide application, after which no further cultivation is performed. At this stage, identifying the weed species can be difficult, so herbicide choice can be guided by a treatment log maintained by each professional pesticide user to determine potential threats.

Chemical Method

The most effective control method is the use of herbicides, which are most effective on fumitory in the seedling stage. Effectiveness decreases with more vigorous growth. Herbicides are applied in two main periods: pre-emergence and post-emergence. Labels and instructions must be followed carefully regarding timing and dosage. Some active ingredients are only moderately effective, particularly on dense or advanced weed populations.

On heavily infested plots, a non-selective herbicide containing glyphosate may be applied (so-called simplified system). Glyphosate is absorbed only through leaves and cannot contact emerging potatoes, as they would be destroyed. Even potato sprouts just below the soil surface may be damaged (see A, B). Timing must match weather conditions, mainly temperature and rainfall. Pre-emergence herbicides applied too late can damage germinating potatoes. Some pre-emergence herbicides can also be applied when potatoes are ~5 cm tall, e.g., prosulfocarb + metribuzin.

Active ingredients for pre-emergence fumitory control: fluorochloridon, flufenacet + metribuzin, linuron + chlomazon, metobromuron, metribuzin, metribuzin + chlomazon, pendimethalin + chlomazon.

Post-emergence herbicides should be applied no later than the row closure stage to ensure coverage and avoid retention of spray on potato plants. Due to long pre-harvest intervals, post-emergence herbicides cannot be used for early harvest crops.

Active ingredients for post-emergence fumitory control: bentazon, metribuzin, rimsulfuron. Metribuzin applied post-emergence may cause phytotoxic reactions on some potato varieties (link).

Compiled by: dr inż. Janusz Urbanowicz