Elymus repens
(quackgrass)

E. repens is a serious agricultural and horticultural weed mainly in temperate climates in the northern hemisphere, and to some extent in cool climates at higher altitudes within warmer regions. It is particularly important in the northernmost, cooler, agricultural areas, where it seems to be more competitive in perennial crops than further south (Håkansson, 1969b, 1982; Holm et al., 1977). It is reported as an important weed of coffee in higher, cooler areas of New Guinea and is found in scattered sites in the cooler mountain valleys of Central and South America (Holm et al., 1977). The occurrence of this species, a C3 plant, in temperate climates and its absence in the warm tropics may be due to difficulties in producing rhizomes at higher temperatures, which has been demonstrated experimentally (Håkansson, 1969b).

The species grows on many types of soil, both mineral and organic. It seems to be most competitive on fertile soils, rich in nitrogen and with a good water supply, and is less successful on very acid or very dry, shallow soils (Ellenberg, 1974; Holm et al., 1977; Wedin and Tilman, 1996).

E. repens ssp. repens is a rhizomatous perennial grass with both vegetative and sexual reproduction. It propagates easily by the rhizomes, even short fragments of which are regenerative if they include a node. The plant can therefore be rapidly spread and multiplied by soil cultivation, and where competition from other plants is not too strong, undisturbed plants can develop rapidly extending clones. In a short-term perspective, vegetative propagation dominates quantitatively and contributes to the special character of the species as a weed. However, following very thorough control of this weed in the field, surviving seeds will be important (together with surviving rhizome fragments) for initiating a new weed population. Furthermore, the seeds enable the formation of new genotypes, which is promoted by the prevalent cross-pollination. Because of a high degree of self-sterility (see Beddows, 1931), seed production is variable but on the whole high. Although the seeds have no, or no lengthy, innate dormancy (cf. Williams, 1968), a soil seed bank of considerable importance usually builds up (Korsmo, 1925; Palmer and Sagar, 1963; Håkansson, 1967, 1969a, 1970; Williams, 1970; Williams and Attwood, 1971).

Seedlings normally begin to develop rhizomes when they have four to six foliar leaves. Until then, they are as sensitive to mechanical disturbance as seedlings of annual plants. After rhizomes have developed, the plants are comparable to those developed from rhizome buds (Håkansson, 1970; Williams, 1970).

According to experiments by Håkansson (1967, 1969b, 1974, 1995) studying E. repens, its undisturbed growth and susceptibility to mechanical and chemical disturbance can be described as follows. In undisturbed clones, new plants or plant units (i.e. aerial shoots and attached adventitious roots) mainly develop from the apices of rhizome branches, whereas apical dominance prevents axillary buds from being activated. On the other hand, axillary rhizome buds are activated to a greater extent by soil cultivation or other disturbances breaking or wounding the rhizome system. Such buds then greatly contribute to the development of new plants. In studying 'late-spring dormancy' as described by Johnson and Buchholz (1962), Håkansson (1967) interpreted this dormancy to be merely due to shortage of food reserves in the rhizomes, a shortage which at the same time results in minimum capacity for regeneration in late spring to early summer. This minimum appears when primary shoots have developed 3-4 leaves and results in minimum tolerance to mechanical disturbance. According to studies in the UK (e.g. Leakey et al., 1978), rhizome buds can show two types of dormancy, a cyclical innate dormancy associated with the early summer season, as well as that due to apical dominance.

When the primary shoots of the plants or plant units have developed a foliage large enough for photosynthesis to compensate and increasingly exceed the consumption in the below-ground system, secondary tillers and new rhizome branches begin to develop from buds near or below the soil surface. In unshaded plants, this usually happens when the primary shoots have three to four foliage leaves. At this stage, or during a slightly extended period, the plants have a minimum regenerative capacity and are therefore more susceptible to mechanical disturbance by soil cultivation than earlier or later. The systemic effect of foliar herbicides is greater after application somewhat later, when the downward stream of assimilate is stronger and the foliage catching applied herbicides is larger in relation to the below-ground plant parts (Håkansson, 1967, 1969b, 1974, 1995).

Many of the aerial shoots established during the earlier part of the growing season, particularly the primary shoots, develop a culm by stem elongation. In many cases, a great proportion of the culms are sterile, but are otherwise similar to the spike-bearing ones.

Animal feed, fodder, forage

• Fodder/animal feed
• Forage

Environmental

• Erosion control or dune stabilization

Human food and beverage

• Spices and culinary herbs

Medicinal, pharmaceutical

• Traditional/folklore

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Cultural Control

Cultural measures in the cropping system should always be considered. Measures improving the effect of competition in competitive crops such as small-grain cereals, oil-seed Brassica crops and many fodder crops are important. Using as small row spacings as is technically possible, and making all efforts to achieve an even distribution of the crop plants in the row, can reduce the plant growth of E. repens considerably, particularly in combination with a rapid and even emergence and establishment of the crop plants. To achieve rapid crop establishment, seedbed preparation and sowing depth adapted to soil type and climate are of the utmost importance (Håkansson, 1974, 1979, 1995). Systematic combination of techniques aimed at optimizing the competition from a potentially competitive crops, such as small grain cereals, may reduce the growth of E. repens by 50%.

Mechanical Control

Although considerable effects can be obtained by enhancing competition in certain crops, additional control is usually needed. When crops are harvested long before the end of the growing season, E. repens has its best period of rhizome production after harvest, in a period free of competition from the crop. Changing this period of production into reduction by mechanical or chemical control is a most effective measure in a control system for E. repens. When soil cultivation is carried out, the first operation (stubble cultivation) is preferably done immediately after harvest, with implements breaking the rhizomes as much as possible (Håkansson, 1968b; Boström and Fogelfors, 1999). When the growing period is long enough, operations are repeated at intervals. Ploughing is the last operation before winter or, on certain soils, it can be done in early spring if therew is enough time before the final seedbed preparation and sowing of the next crop. According to Håkansson (1974, 1982, 1995), combination of such tillage and competition in good stands of crops such as small-grain cereals will suppress E. repens and similar weeds by 90% or more.

Without effective tillage, E. repens, like other creeping perennial weeds, is hard to control sufficiently by any means except herbicides. This is illustrated in many experiments with reduced tillage in various forms (for example, Bachthaler, 1974; Cussans, 1976; Rydberg, 1992; Børresen and Njøs, 1994; Skuterud et al., 1996; Dzienia and Piskier, 1998).

Chemical Control

Where mechanical control is not desirable or not possible due to soil or climate, or for other reasons, different herbicides can be used for controlling grasses such as E. repens. Some of the more important ones are presented below.

A number of systemic foliar herbicides are effective on E. repens when the plants have sufficient actively growing aerial shoots in proportion to the attached rhizome system. The most important is glyphosate, a herbicide with low selectivity, used in a large number of countries with good effect in controlling E. repens. It is used in stubble fields after harvest, on fallow land, in orchards, on grassland in connection with ploughing (either before or following ploughing after sufficient time), in field margins and headlands, and in some countries, in ripe cereals e.g. by wiping or even spraying overall before harvest. Examples of other herbicides used for the control of E. repens are sethoxydime and cycloxydime, which are selective herbicides used in a number of dicotyledonous crops such as rape, turnip rape, beet, potatoes and peas. In recent years, other herbicides of this type, such as tepraloxydim (Kibler et al., 1999) have been used successfully in many of the crops mentioned. Foliar-applied herbicides of the sulfuro group may also be of interest for controlling E. repens, for example, sulfuron in potatoes (Kuzior et al., 1999), wheat (Rainbolt et al., 1999) and in fields of stubble (Rola et al., 2000). This and other herbicides of this group might attract an increasing interest in the control of E. repens in different cereals (e.g. Feucht et al., 1999). Various adjuvants are of interest for increasing the effect of sulfuron and other herbicides (Woznica et al., 1998). Among selective herbicides for soil application, EPTC has been used for several decades and is still used in some countries in dicotyledonous crops, e.g. in potatoes before planting. Propyzamide and terbacil are used in some countries, e.g. in orchards.