Fat hen

White goosefoot, commonly called lamb’s quarters, is an annual spring weed from the class of dicotyledons, with a strong taproot. It germinates in spring but also in summer. The stem is highly branched, 20 to 100 cm tall, covered with a mealy coating and often reddish. Cotyledons are fleshy, reddish-purple underneath, silvery on the upper surface. True leaves are alternately arranged, petiolate with variable shapes – they can be triangular, rhombic, lanceolate, with a wedge-shaped base and slightly toothed margins, gray-green, upper leaves entire and lanceolate. The inflorescence consists of small, densely flowered clusters forming pseudo-spikes or false umbels. Flowers are greenish, composed of five perianth segments with clearly protruding ridges, five stamens, and short pistil stigmas. The fruit is a small grayish-black achene, roundish and lens-shaped. Seeds are shiny, black, about 1.5 mm in diameter.

Occurrence and harmfulness

White goosefoot most often occurs in root crop fields (beets and potatoes), legumes, maize, rapeseed, and to a lesser extent in cereals. It prefers fertile, well-cultivated, nitrogen-rich, humus-rich, clay and sandy soils. Its harmfulness is due to very high seed production, with one plant producing up to 20,000 seeds, which can remain viable in the soil for 10 to 15 years (up to 39 years in favorable conditions). It has a wide germination temperature range, 2 to 30°C (optimal 15-20°C). Additionally, this species depletes the soil of nutrients, especially potassium. If uncontrolled, it can hinder machinery during potato harvest, causing increased mechanical damage. Beyond its negative effect on yield, it may also host various pathogens and pests affecting potatoes, e.g., as a host for Potato virus Y (PVY).

Control

Mechanical method

The long period from planting to potato emergence is a critical time (ideal for weed growth), which can be used for mechanical control. This is carried out with available farm machinery, e.g., ridgers, light harrows, hoes, etc. Their main task is to create optimal conditions for rapid weed germination and then destroy them with subsequent cultivation. Maximum effectiveness (over 90%) is achieved when weeds are at the seedling stage, but effectiveness drops to around 40% as they grow. 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 stronger growth. Mechanical methods are also the most labor- and cost-intensive due to repeated passes. This method is often used in small farms or ecological systems. Before potato emergence, 3 to 6 treatments should be performed at 6-8 day intervals. After emergence, the number of treatments should not exceed 2-3, as delays can damage the crop and increase the risk of pathogen transfer and excessive soil drying (especially light soils).

Mechanical-chemical method

This is the most favorable and widely used weed control system. It allows saving on mechanical cultivation, which is applied much less than in the purely mechanical system. After planting, usually two to three ridgings are performed, followed shortly before emergence by herbicide application, after which no further cultivation is done. At this growth stage, identifying weed species may be difficult, so herbicide use can be based on a treatment log, maintained and stored by every professional plant protection user. This log helps determine which weed species may pose a threat in a given field.

Chemical method

The most effective method is herbicide application, which achieves the highest effectiveness when weeds are at the seedling stage; the more developed the weed, the lower the effectiveness. Herbicides in potatoes are applied at two main timings: pre-emergence and post-emergence. Before using a herbicide, always read the label instructions, which include timing and dosage information. Some active substances have medium effectiveness, and the control effect may be unsatisfactory if the weed occurs in high density or advanced growth stage.

On heavily infested fields, a non-selective herbicide containing glyphosate can be applied – this is the so-called simplified system. Its success depends on the presence of weeds, as glyphosate is absorbed only through leaves and cannot contact potato sprouts (they would be destroyed!). Even potato shoots just below the soil surface may be damaged (photos A, B). Timing according to weather, mainly temperature and rainfall, is crucial for effectiveness. Pre-emergence herbicides applied too late, when potato shoots are near the soil surface, may damage the crop after heavy rain. Some pre-emergence herbicides can also be applied in early growth stages when potato plants are about 5 cm tall, e.g., prosulfocarb + metribuzin.

Active substances controlling white goosefoot pre-emergence: flufenacet + metribuzin, fluorochloridon, linuron, linuron + chlomazon, metobromuron, metribuzin, metribuzin + chlomazon, pendimethalin, pendimethalin + chlomazon, prosulfocarb, prosulfocarb + metribuzin. Post-emergence herbicides should be applied no later than canopy closure to ensure coverage and avoid liquid retention on potato plants. Due to pre-harvest intervals, post-emergence herbicides cannot be used on the earliest harvest crops.

Active substances controlling white goosefoot post-emergence: metribuzin. This substance applied post-emergence may cause phytotoxic reactions on some potato varieties.

Compiled by: Dr. Eng. Janusz Urbanowicz