Green bristle-grass

Green bristle-grass is an annual spring weed from the monocotyledon class, whose seedlings appear in late spring.

A characteristic feature of this species is the red-colored, ligule-less sheath of the first leaf.

It has a fibrous root system. The stem reaches a height of 5 to 60 cm, is thin, ascending, rough under the inflorescence, and branched at the base. The first leaf is oblong, with numerous veins, 15 to 20 mm long, without a ligule, with a red sheath. Leaves are narrow-lanceolate, grass-green with a bluish bloom, with a tuft of hairs instead of a ligule. The inflorescence is a cylindrical spike-like panicle composed of single-flowered spikelets, 2 mm long.

Occurrence and Harmfulness

Green bristle-grass most often occurs in root crops, gardens, winter cereals, sometimes spring cereals, and on stubble fields. It prefers light, sandy-loam or sandy, lime-free soils. Its harmfulness lies in soil infestation by seeds, which can also be spread with manure. One plant can produce several thousand seeds, which remain viable in the soil for up to 15 years.

Control

Mechanical method

The long period between planting and potato emergence is a critical time (ideal conditions for weed development) that can be used for mechanical treatments. These are carried out using available farm machinery, such as hilling machines, light harrows, inter-row cultivators, etc. Their main task is to create the most favorable conditions for rapid weed seedling emergence, followed by destruction through subsequent cultivation operations. Maximum effectiveness (even over 90%) can be achieved when weeds are at the seedling stage, but effectiveness decreases to about 40% as weeds grow. This system of weed elimination is highly dependent on weather and soil conditions. In very wet springs, mechanical methods are difficult to apply. On heavily infested fields, it may have the opposite effect, as damaged couch grass rhizomes are stimulated to stronger growth and tillering. Additionally, the mechanical system is the most costly and labor-intensive due to multiple passes. It is most often used in small farms, where potatoes are grown for self-consumption and in organic systems. Before potato emergence, 3 to 6 treatments should be performed at 6–8-day intervals. After emergence, the number of cultivations should not exceed 2–3, and any delay increases the risk of crop damage and pathogen transfer with sap, and can excessively dry out the soil (especially light soils).

Mechanical-chemical method

The most effective and widely used weed control system. It reduces the number of mechanical cultivations compared to the purely mechanical system. After planting, usually 2–3 hillings are performed, and shortly before emergence, herbicide treatment is applied, after which no further cultivation is conducted. In this vegetative phase, identifying weed species may be difficult, so a treatment record, maintained and stored by every professional pesticide user, is essential. Based on it, one can determine which weed species may pose a threat in a given field.

Chemical method

The most effective method of control is the use of herbicides, which achieve maximum effectiveness when the weed is at the seedling stage; the more vigorous the growth, the lower the effectiveness. Herbicides in potatoes are applied in two main periods: before emergence and after emergence. Before using a herbicide, read the label-instruction, which contains information about application timing and dosage. Some active substances in herbicides have medium efficacy, and control may be unsatisfactory if the weed is abundant or in an advanced growth stage.

On heavily infested fields, a non-selective herbicide containing glyphosate can be applied, known as a simplified system. Its success depends on the presence of weeds on the field, as glyphosate is absorbed only by leaves and cannot contact potato seedlings (they would be destroyed!). Even potato shoots just below the soil surface can be damaged (photo A, B). Timing must consider weather conditions, mainly temperature and rainfall, which are often decisive for high efficacy. Pre-emergence herbicides applied too late, when potato sprouts are just below the soil surface, after heavy rain, may damage them. Some pre-emergence herbicides are also registered for early growth stages, when potato plants are about 5 cm tall, e.g., prosulfocarb + metribuzin.

Active substances controlling green bristle-grass for pre-emergence use: pendimethalin.

Post-emergence herbicides in potatoes should be applied no later than row closure, to cover weeds and prevent spray retention on potato plants. All typical herbicides for monocotyledon species (commonly called graminicides) are for post-emergence use. Always read the label-instruction carefully, as efficacy is closely tied to the weed’s growth stage. Typically, this stage is: for couch grass from the 2–6 leaf stage, and for other monocotyledons (barnyardgrass, wild oats, volunteer cereals, foxtails, and panicgrass) – from 2 leaves to tillering. Due to long pre-harvest intervals, post-emergence herbicides cannot be used for the earliest harvest!

Active substances controlling green bristle-grass for post-emergence use: propaquizafop, cycloxydim, fluazifop-P-butyl, quizalofop-P-ethyl, and rimsulfuron.