Yellow bristle-grass

Yellow bristle-grass is an annual summer weed from the monocotyledon class, whose seedlings appear in late spring (thermophilic species).

A characteristic feature of this species is its requirement for soil temperature, which should be warmed to 15-20°C for the plant to germinate.

It has a fibrous root system. The stem reaches 5-40 cm in height, erect or ascending, with slightly flattened leaf sheaths. The first leaf is narrow, with numerous veins, pointed at the tip, 15 to 20 mm long, without a ligule. Leaves are grayish-green, narrow, fairly wide, without auricles and ligule, with only a small hair at the base edges. The inflorescence is a spike-like panicle composed of ovate, single-flowered spikelets, 2 to 3 mm long, often with a reddish bristle. The fruit is an ovate caryopsis, dark gray, with small black dots.

Occurrence and harmfulness

Yellow bristle-grass is most commonly found in root crops, maize, and gardens, and less frequently in cereals. It prefers sandy and sandy-loam, non-calcareous soils. Its harmfulness lies in weakening the cultivated plants.

Control

Mechanical method

The long period between planting and potato emergence is critical (ideal conditions for weed growth), which can be used for mechanical treatments. These are carried out using available farm machinery, e.g., ridgers, light harrows, finger weeders, etc. Their main task is to create the most favorable conditions for rapid weed germination, and then destroy them through subsequent cultivation operations. The highest effectiveness (even over 90%) can be achieved when weeds are in the seedling stage, but effectiveness drops to around 40% as weeds grow. This system of weed control 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 couchgrass rhizomes are stimulated to stronger growth and branching. Additionally, the mechanical system is the most labor- and cost-intensive due to multiple passes. This method is most often used in small farms growing potatoes for self-sufficiency 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 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 allows savings on mechanical cultivations, which are used much less than in the mechanical system. After planting, usually two- or three-time ridging is performed, followed shortly before emergence by herbicide treatment, after which no further cultivation is conducted. At this growth stage, identifying present weed species can be difficult, so a treatment log kept by each professional user of plant protection products can serve as a basis for herbicide application. It allows identification of species that may pose a threat on a given field.

Chemical method

The most effective method is using herbicides, which are most effective on this species when weeds are in the seedling stage; the more vigorous the growth, the lower the effectiveness. Herbicides in potatoes are used in two main periods: before emergence and after emergence. After deciding to use a herbicide, read its label-instructions, which include information on timing and dosage. Some active substances in herbicides have medium effectiveness (average sensitivity of the species), and the control effect may be unsatisfactory, especially with high weed density or advanced growth stage.

On heavily infested fields, a non-selective herbicide containing glyphosate can be applied, known as the simplified system. Its success depends on the presence of weeds, as glyphosate is absorbed only through leaves and cannot contact potato seedlings (they would be destroyed!). Even potato sprouts just below the soil surface can be damaged (photos A, B). It is very important to adjust the application time to weather conditions, mainly temperature and rainfall, which often determine high effectiveness. Pre-emergence herbicides applied too late, when potato seedlings are just below the soil surface, can damage them after heavy rains. Some pre-emergence herbicides can also be applied in early potato growth stages, e.g., when plants are about 5 cm tall, such as prosulfocarb + metribuzin.

Active substances controlling yellow bristle-grass pre-emergence: pendimethalin.

Post-emergence herbicides should be applied no later than canopy closure to ensure weed coverage and prevent solution retention on potato plants. All typical herbicides for monocotyledon species (commonly called graminicides) are intended for post-emergence application. Follow the label-instructions carefully, as effectiveness depends on the growth stage of target species. Usually, this period is: for couchgrass from 2 to 6 leaves, and for other monocots (green foxtail, wild oats, volunteer cereals, bristle-grass, and foxtail) from 2 leaves to tillering. Due to pre-harvest intervals, post-emergence herbicides cannot be used for the earliest harvest!

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

Compiled by: dr inż. Janusz Urbanowicz