Barnyard grass is an annual summer weed from the monocotyledon class, whose emergence occurs in late spring and early summer (a warm-loving species).

A characteristic feature of this species is its strongly flattened leaf sheaths (similar to maize).

It has a fibrous root system. The stem reaches a height of 30 to 100 cm, is erect or knee-raising, with nodes bearing tufts of hairs.

The first leaf is broad-lanceolate, rolled, without auricles or ligule, gray-green or dark green, 15–20 mm long. Leaves are dark gray-green, narrow, lanceolate, fairly wide, without auricles or ligule, with only the base of the blade slightly hairy. The inflorescence is a panicle composed of single-flowered spikelets, densely arranged on the main axis in alternately or oppositely positioned pseudo-spikelets. The glume covers below the flower tip, usually with a long awn. The fruit is a caryopsis, oval, convex on the dorsal side, nearly flat on the ventral side, light brown in color.

Occurrence and harmfulness

Barnyard grass most commonly occurs in root crops, maize, and gardens. It prefers sandy-loam and sandy, fertile, and moist soils. Its harmfulness lies in strongly weakening the cultivated plant, especially when it emerges in spring. One plant can produce from 400 to 5000 seeds.

Control

Mechanical method

The long period from planting to potato emergence is a critical time (ideal conditions for weed development) that can be used for mechanical treatments. These are carried out using machinery available on the farm, such as ridgers, light harrows, and weeders. Their main task is to create the most favorable conditions for rapid weed germination and then destroy them with subsequent cultivation operations. The highest effectiveness (even over 90%) can be achieved when weeds are at the seedling stage; however, effectiveness decreases to about 40% as weeds grow. This weed control system is highly dependent on weather and soil conditions. In years with very wet springs, the mechanical method is difficult to apply. On heavily couch grass–infested plantations, it may produce the opposite effect, as damaged rhizomes are stimulated to grow and tiller more vigorously. Additionally, the mechanical system is the most costly and labor-intensive due to multiple passes. This method is most often used on small farms growing potatoes for self-supply and in organic systems. Before potato emergence, 3 to 6 treatments should be carried out at intervals of 6–8 days. After emergence, the number of operations should not exceed 2–3, and any delay increases the risk of damage, pathogen transfer with sap, and excessive soil drying (especially light soils).

Mechanical-chemical method

The most favorable and widely used weed control system. It saves on mechanical cultivation, which is used much less frequently than in the purely mechanical system. After planting, two or three ridging operations are usually performed, followed shortly before emergence by a herbicide treatment, after which no further cultivation operations are carried out. At this stage, identifying weed species can be difficult; therefore, the basis for herbicide use may be a treatment log, kept by every professional user of plant protection products. Based on it, one can determine which weed species may pose a threat in a given field.

Chemical method

The most effective control method is the use of herbicides, which achieve the highest effectiveness 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 times: before emergence and after emergence. Once a herbicide is selected, the label-instructions should be followed for timing and dosage. Some active substances in herbicides have medium effectiveness, and the control effect may be unsatisfactory, especially if a species occurs in high density or is at an advanced growth stage.

On heavily infested plantations, a non-selective herbicide containing the active substance glyphosate may be applied; this is the so-called simplified system. Its success depends on the presence of weeds, as glyphosate is absorbed only through the leaves and must not contact potato emergence (it would be destroyed!). Even potato sprouts just below the soil surface can be damaged (photos A, B). Adjusting the timing to weather conditions, especially temperature and rainfall, is crucial for effectiveness. Pre-emergence herbicides applied too late may damage germinating potatoes after heavy rain. Some pre-emergence herbicides can still be applied in early growth stages, e.g., prosulfocarb + metribuzin.

Active substances for pre-emergence control of barnyard grass: chlormazon, flufenacet + metribuzin, linuron + chlormazon, metribuzin (WG), pendimethalin, pendimethalin + chlormazon.

Post-emergence herbicides should be applied no later than the row closure stage to ensure weed coverage and avoid spray retention on potato plants. All typical herbicides for controlling monocotyledonous species (commonly called graminicides) are intended for post-emergence use. The label-instructions should be followed carefully, as effectiveness is closely related to the developmental stage of the target species. For couch grass, the period is usually from the 2–6 leaf stage; for other monocots (barnyard grass, wild oats, volunteer cereals, foxtails, and fescues) – from 2 leaves to tillering. Due to pre-harvest intervals, post-emergence herbicides cannot be used in crops for early harvest!

Active substances for post-emergence control: propachizafop, clethodim, cycloxydim, fluazifop-P-butyl, chizalofop-P-ethyl, metribuzin (WG), and rimsulfuron. Metribuzin applied post-emergence may cause phytotoxic symptoms on some potato varieties.