Quackgrass is a perennial, rhizomatous weed from the monocotyledon class, with emergence occurring in spring.

A characteristic feature of this species is its very long underground runners, so-called creeping rhizomes, and a distinctive first leaf.

The root system consists of a strongly developed rhizome with numerous runners. The culm reaches a height of 30 to 150 cm, is erect, naked, and smooth. The first leaf is linear, dark green, 80 to 100 mm long, covered on both sides and along the margins with short, fine hairs, and the leaf sheath very often has a reddish tint. Leaves are flat, bright or bluish-green, with sharp auricles at the base of the leaf blade. The inflorescence is a short spike (10-flowered), with ovate, spreading spikelets 10 to 15 mm long; the lower lemma most often bears an awn. The fruit is a hulled caryopsis.

Occurrence and harmfulness

Quackgrass occurs most frequently in all crops and practically on all soil types. It prefers heavy, fertile, moist, and well-aerated soils. Its harmfulness results from very vigorous runners which, even when cut into very short fragments, produce new plants and spread intensively. It has high light requirements, therefore it develops very well in poorly established crops. Moreover, it is a very “greedy” species, as it can absorb annually from 1 ha of soil about 50 kg of nitrogen, 30 kg of phosphorus, and 70 kg of potassium. Additionally, quackgrass runners can grow through potato tubers (photo 1), which disqualifies them both for processing and direct consumption. Such damage may be incorrectly identified as wireworm feeding.

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 farm machinery available on the holding, e.g. ridgers, light harrows, weeders, etc. Their main task is to create the most favorable conditions for rapid weed germination and then destroy them with subsequent cultivation treatments. The highest effectiveness (even over 90%) can be achieved with this method when weeds are at the seedling stage; however, as weeds develop further, effectiveness decreases to about 40%. This system of weed elimination is highly dependent on weather and soil conditions. In years with very wet springs, the mechanical method is difficult to apply. On heavily infested fields, it may have the opposite effect, as damaged quackgrass runners are stimulated to even stronger growth and tillering. Additionally, the mechanical system is the most cost- and labor-intensive due to the high number of passes. This method is most often used on small farms where potatoes are grown for self-supply and in organic systems. Before potato emergence, 3 to 6 treatments should be performed at intervals of 6–8 days. After emergence, the number of cultivations should not exceed 2–3, and any delay in their execution exposes the plantation to damage, increases the risk of pathogen transmission with plant sap, and may excessively dry the soil (especially light soils).

Mechanical and chemical method

The most advantageous and widespread weed control system. It allows savings on mechanical cultivations, which are used much less frequently than in the purely mechanical system. After planting, two or three ridging operations are usually carried out, and shortly before emergence a herbicide treatment is applied, after which no further cultivation is performed. At this stage of vegetation, identification of weed species present may be difficult; therefore, the basis for herbicide application may be a treatment log, which should be kept and stored by every professional plant protection product user. Based on it, it is possible to 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 in the case of this species achieve the highest effectiveness when the weed is at the seedling stage; the more vigorous the growth, the lower the effectiveness. Herbicides in potatoes are applied at two basic timings: before emergence and after emergence. After deciding to use a herbicide, its label instructions should be carefully read, as they contain information on application timing and dosage. Some active substances contained in herbicides have medium effectiveness (medium sensitivity of a given weed species), and after their application the control effect may be unsatisfactory, especially when a given weed species occurs at high density or is at an advanced growth stage.

On heavily weed-infested plantations, a non-selective herbicide containing the active substance glyphosate may be applied; this is the so-called simplified system. The basis for its success is the presence of weeds on the plantation, as glyphosate is absorbed exclusively through leaves, while potato emergence must not have occurred (they would be destroyed!). Even potato sprouts located just below the soil surface may be damaged (photo A, B). It is very important to adjust the timing of treatment to weather conditions, mainly temperature and rainfall, which often determine its high effectiveness. Pre-emergence herbicides applied too late, when sprouting potatoes are located just below the soil surface, may damage them after heavy rainfall. Among pre-emergence herbicides, there are also registered products that can still be applied at early growth stages, when potato plants are about 5 cm tall, e.g. prosulfocarb + metribuzin.

Active substances controlling quackgrass for pre-emergence application: pendimethalin + clomazone.

Herbicides applied after potato emergence should be used no later than the moment when plants close the rows, which ensures weed coverage and prevents spray liquid from remaining on potato plants. All typical herbicides for controlling grass species (commonly called graminicides) are intended for post-emergence use. The label instructions must be carefully followed, as the effectiveness of these products is strictly related to the growth stage of the controlled species. Most often this period occurs: for quackgrass from the moment of producing 2 to 6 leaves, and for other grass weeds (barnyard grass, wild oat, volunteer cereals, foxtails, and bluegrass) – from 2 leaves to the tillering stage. Due to the length of the pre-harvest interval, post-emergence herbicides cannot be used in crops intended for the earliest harvest!

Active substances controlling quackgrass for post-emergence application: propachizafop, clethodim, cycloxydim, fluazifop-P-butyl, quizalofop-P-ethyl, and rimsulfuron.