Common chickweed is an annual spring or winter weed from the dicotyledon class that germinates throughout the year.

A characteristic feature of this species is very delicate cotyledons and leaves, which turn purple during cold periods.

It has a thin, weak root system. The stem is 5 to 40 cm high, thin, spreading, single-row hairy, and capable of rooting. Cotyledons are lanceolate, 5 to 7 mm long, hairy, green, with a sharp tip. The lower and middle true leaves are ovate, petiolate, opposite, while the upper leaves are sessile, glabrous or slightly hairy. The inflorescence is a two-branched cyme, consisting of small white flowers on long pedicels. The fruit is an oblong capsule, splitting from the base with six openings. Seeds are roundish or kidney-shaped, flattened, dark brown, and matte.

Occurrence and Harmfulness

Common chickweed occurs in all crops, especially in root crops and vegetables. It is found in almost all soil types but prefers moist, nitrogen-rich soils (nitrophilous species).

Its harmfulness is due to rapid growth and high vitality. In years with heavy rainfall, it forms flat clumps. It reproduces both by seeds and stem fragments (vegetatively), producing 2–3 generations per year. If uncontrolled, it complicates harvesting and increases mechanical damage to tubers. One plant can produce up to 15,000 seeds, which can retain high germination capacity for up to 68 years. Germination can start at 2°C, with optimal temperatures between 13–20°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 carried out using available farm machinery, e.g., ridgers, light harrows, hoes, etc. Their main task is to create optimal conditions for rapid weed germination, followed by destruction through subsequent cultivation. The highest effectiveness (over 90%) can be achieved when weeds are at the seedling stage, but effectiveness decreases to about 40% as weeds develop. This system heavily depends on weather and soil conditions. In very wet springs, mechanical control is difficult. On heavily infested fields, it can have the opposite effect, as damaged couchgrass rhizomes are stimulated to grow and branch more. Moreover, the mechanical system is the most labor- and cost-intensive due to multiple passes. It is most often used in small farms for self-sufficiency and organic farming. Before potato emergence, 3–6 treatments should be carried out at 6–8-day intervals. After emergence, no more than 2–3 treatments should be applied; any delay increases risk of crop damage, pathogen transmission, and excessive soil drying (especially light soils).

Mechanical-Chemical Method

The most efficient and widely used weeding system. It reduces the need for mechanical cultivation, which is used much less than in the purely mechanical system. After planting, two- or three-fold ridging is usually performed, followed shortly before emergence by herbicide application, after which no further cultivation is needed. During this growth stage, identifying weed species can be difficult, so herbicide use should be based on a treatment log, maintained by every professional user of plant protection products, which allows determining which weeds may pose a threat in the field.

Chemical Method

The most effective control method is the use of herbicides, which are most effective when weeds are at the seedling stage; the more vigorous the growth, the lower the effectiveness. Herbicides in potato cultivation are applied at two main timings: pre-emergence and post-emergence. After deciding to use a herbicide, the label instructions should be followed for application timing and doses. Some active ingredients have medium effectiveness, so results may be unsatisfactory, especially with high weed density or advanced growth stages.

On heavily infested fields, a non-selective herbicide containing glyphosate can be applied, known as a simplified system. Its success relies on the presence of weeds, as glyphosate is absorbed only by leaves and must not contact potato sprouts (which would be destroyed). Even potato sprouts just below the soil surface can be damaged (see photos A, B). It is crucial to adjust application timing according to weather conditions, mainly temperature and rainfall, which often determines herbicide effectiveness. Pre-emergence herbicides applied too late, when potato sprouts are just below the soil surface, can cause damage after heavy rain. Some pre-emergence herbicides are registered for early growth stages when potato plants are about 5 cm tall, e.g., prosulfocarb + metribuzin.

Active ingredients for pre-emergence control of common chickweed: chlormazon, fluorochloridone, flufenacet + metribuzin, linuron, linuron + chlormazon, metobromuron, metribuzin, metribuzin + chlormazon, pendimethalin, pendimethalin + chlormazon, prosulfocarb, prosulfocarb + metribuzin.

Post-emergence herbicides should be applied no later than canopy closure, ensuring weed coverage and avoiding retention on potato plants. Due to pre-harvest intervals, post-emergence herbicides cannot be used on early harvest crops.

Active ingredients for post-emergence control of common chickweed: bentazon, metribuzin, rimsulfuron. Metribuzin applied post-emergence may cause phytotoxic effects on some potato varieties.

Compiled by: Dr. Eng. Janusz Urbanowicz