Identification and Control of Rushes

New Zealand Journal of Agriculture, Volume 95, Issue 1, 15 July 1957, Page 20

Identification and Control of Rushes

IT may surprise some people that J- rushes can be regarded as serious weeds of established pastures, as there is a common misconception that they grow only on swampy areas. Though almost ' all rushes thrive in waterlogged conditions, the 6 species listed above also grow well in conditions of soil moisture and fertility which are ideal for the growth of high-producing pastures. They, can also grow in conditions which are much drier than this, as is demonstrated by the fact that they are sometimes found on sand country and on dry, northerly hill faces. Any conditions which lead to the opening of the sward, such as summer drought or winter poaching, allow rushes to invade the pasture, and, as they are perennial plants and well adapted to survive under grazing, they can be extremely difficult to get rid of. With the use of hormone weedkillers, however, plus the adoption of pasture management practices to ensure the maintenance of a vigorous and closeknit sward, the pasture rushes can be quickly eliminated, except where conditions are too wet for the betterproducing species of pasture plants. Though a number of low-growing rushes, principally J. bufonius and J. articulatus, appear in newly established pastures before the sward has had time to thicken up, they do not persist into the pasture’s life unless soil conditions are too moist to be suitable for the growth of highproducing pastures. Susceptibility to Weedkillers Rushes vary widely in their susceptibility to hormone weedkillers. For

example, J. effusus and J. pallidus can be readily controlled, but J. vaginatus is fairly resistant. Farmers are often puzzled by the excellent results obtained from spraying rushes in one pasture and the poor control obtained in adjacent ones. This variation in results is often due to the different species of rushes present. For this reason it is important to identify the rushes present before spraying. The best time to do this is when the rushes are growing freshly in the field, as identification becomes much more difficult once they have wilted. IDENTIFICATION The following are the main points used when identifying rushes in the field: I. Pith Continuous or Interrupted If the stem of a rush is split along its length with a razor blade or sharp knife, the split stem in some species will be found to be filled with a continuous white pith and in others with pith that is not continuous but is interrupted with numerous regularly occurring air spaces. In J. vaginatus there are often so many air spaces that the pith is virtually lacking, being reduced to small remnants clinging to the inside of the stem walls. As a result this rush appears to have a hollow stem. Identification by the study of pith in the stem can be made satisfactorily only with stems of mature rushes which are carrying flower heads or seed capsules. Undamaged stems should be selected, as the attacks of caterpillars can greatly modify the pith characteristics.

2. Stem Colour When healthy pasture rushes in vigorous growth are viewed with the sun behind the observer some species are seen to have smooth, shiny green stems and others much duller stems of a bluish green. Closer examination will show that the shiny green rushes have very faint parallel striations (fine longitudinal lines) down the stems, whereas the striations on the stems of the bluish green species are much more distinct. 3. Size and Length of Capsules All rushes have 3-valved seed capsules, that is, 3 scale-like leaves have joined their margins together to form a hollow capsule, within which the seeds, which are extremely small, are lying free. These 3-valved capsules, each containing numerous tiny seeds, are a characteristic of all Juncus species. They are a useful aid in distinguishing rushes from other plants, such as sedges, with which they are often confused. Sedges and other members of the Cyperaceae family have relatively large seeds which occur singly or in clusters, but never lying loose in 3-valved capsules. Each capsule is held round the base by six perianth segments, which form a little cup. (The perianth, is the outer part of a flower.) In some species, notably J. pallidus, the capsules are very large and so long that their tops project well past the tips of the perianth segments. In other species, such as J. luxurians, the capsules are equal to or shorter than the perianth segments.

4. Head Characteristics The capsules are grouped into clusters called heads or inflorescences. The shape, general appearance, and number of capsules in each head provide valuable identification features. In some species, for example J. vaginatus, the heads are tightly clustered spherically; others, for example J. luxurians, have a large number of capsules in very loose, spreading heads. Farm Identification Procedure The following procedure is recommended for identifying rushes on the farm: First, select a mature undamaged stem bearing flower heads or seed capsules. Split it along its length with a razor blade or sharp knife and examine the pith. Rushes with Continuous Pith If the pith is continuous, the rush is J. pallidus, J. effusus, or the solid-pith strain of J. polyanthemos. Detailed identification points for these three species are as follow: J. pallidus J. pallidus is the largest of the pasture rushes, sometimes being more

than 7ft. high. The stems are extremely thick and are shiny green with faint parallel striations. In relation to their thickness the stems are fairly soft and easily broken, but they are not nearly as soft as those of J. effusus. J. pallidus occurs in broadbased clumps which contain relatively few stems. Many of the stems, particularly the outside ones, bend over toward the ground. The capsules are very large and project well past the perianth segments. They are tightly grouped into large spherical clusters. f. effusus The stems of J. effusus are a good deal shorter than those of J. pallidus, being rarely longer than 4ft. 6in. They are also much thinner than those of J. pallidus, though owing to their reduced height, they appear fairly plump. The stems are shiny green with faint parallel striations. They are very tender and can be snapped easily with the hand. The softness of the stems is a remarkably good identification feature, and the breaking test is the quickest way of verifying the identity of this rush. Possibly owing to its softness, it is frequently hard grazed by all classes of stock.

The stems are loosely arranged in their clumps and though they often bend outward from ground level, they do not droop, but keep straight along their length. The capsules are fairly small and do not project past the perianth segments. The bottom branchlets of each head cluster always, bend toward the ground. Often the capsules are undeveloped and persist unchanged throughout winter, giving the flower heads a characteristic feathery look. There are numerous capsules in each cluster and the clusters are usually fairly loose. J. polyanthemos (Solid-pith Form) J. polyanthemos (in either the solidor interrupted-pith form) is the most widely distributed and abundant rush in New Zealand, and as a species it is fairly variable. Some forms have continuous pith, but the pith is more commonly interrupted. Both types of pith have been known to occur on adjoining stems on the same plant. The stems are shiny green and extremely tough and wiry. This rush is probably the hardest of all to break. Owing to their stiffness, the stems usually do not droop, even when

leaning out from i the rush clump, though very tall specimens may droop a little at the tips. The capsules are about the same length as the calyx lobes or slightly longer, and they are always distinctly smaller than those of J. pauciflorus. Some heads contain few capsules in small, tight clusters, but others have numerous capsules in loose clusters. Though this species is fairly variable, it is easily distinguished in all its forms from either J. pallidus, which is much taller and thicker, or J. effusus, which is much softer and is easily broken. Rushes with Interrupted Pith If the rush has interrupted pith or the pith is virtually lacking, it is either J. polyanthemos (interruptedpith form) , J. pauciflorus, J. luxurians, or J. vaginatus. Detailed identification points for these species are as follows: J. polyanthemos (Interrupted-pith Form) The interrupted-pith form of J. polyanthemos is identical with the solid-pith form except that there are large, ragged air spaces in the pith. Little difficulty is experienced in distinguishing J. polyanthemos from the other three rushes with interrupted pith. The obvious differences between J. polyanthemos and J. pauciflorus are given in the description of the latter which follows. J. luxurians and J. vaginatus have bluish green stems which are not shiny. J. pauciflorus J. pauciflorus is the smallest of all the pasture rushes, ranging from 9in. to 2ft. high. It is not common in the North Island, but occurs fairly frequently in the South Island, usually in swards of low carrying capacity, such as on tussock country or dry, sandy soils. In appearance it resembles an extremely small and slender form of J. polyanthemos, but with the following differences: There are few stems and, though they resemble J. polyanthemos in being smooth with faint striations, they differ in that they are usually not green and shiny, but tend to be reddish brown. Though the stems are short, they are so thin that they cannot stand erect, but droop at the tips. The air spaces in the pith of J. polyanthemos are large and irregular in shape and distribution, but in J. pauciflorus they are very small, uniform in shape, and are regularly spaced, the general effect being of a row of tiny, neat dots running up the pith. The pith cavity is very narrow, being only a third as wide as the external diameter of the stem, compared with half as wide in J. polyanthemos. There are few capsules (“pauciflorus” means “few flowers”), but they are very large in relation to the size of the small plant. They project

markedly past the perianth segments. The heads are compactly grouped and each head usually contains not more than 6 capsules. J. pauciflorus is the least important of the pasture rushes and it is doubtful whether eradication of it with hormone weedkillers is warranted in the types of pasture where this rush is usually found. J. luxurious J. luxurians is a tall rush with dull bluish green stems with strongly marked parallel striations running along them. The stems grow very close together forming thick clumps, and the outside stems in particular tend to bend over toward the ground. The infertile stems (those which are not bearing flower heads or seed capsules) tend usually to have a much more bluish tinge than the fertile stems. The capsules are quite small and are never longer than the perianth segments. The capsules, which are very numerous, are crowded together into very loose, wide-spreading clusters. An important identification feature is that the continuation of each main stem past the clusters of capsules is very much longer than in any other rush, sometimes being more than Ift. long. J. vaginatus The stems of J. vaginatus are a dull bluish green with strongly marked parallel striations, but unlike those of J. luxurians the sterile stems are not more bluish than the fertile stems. This rush does not usually grow very tall (rarely more than 3ft. high) and the stems are fairly thick and loosely packed, forming open clumps. Stems always contain little pith and sometimes hardly any, the latter stems appearing to be hollow. Stock will often hard graze this rush. The seed capsules are large and usually about as long as the perianth segments, though sometimes slightly longer. The capsules are crowded into tight, spherical clusters sometimes only one per stem and sometimes five or six. CONTROL Rushes are more difficult to control with chemical weedkillers than highly susceptible weeds such as buttercups and annual thistles. This is due largely to the fact that buttercups and annual thistles have a bigger surface area to catch the spray than rushes. Because rushes are difficult to wet with spray, extra care is required if good results are to be obtained. Provided the following rules are followed carefully, good control of susceptible species of rushes can be expected. 1. Identify the rush or rushes present: J. effusus and J. pallidus are the most susceptible species, J. polyanthemos and J. luxurians are inter-

mediate in tolerance, and J. vaginatus is fairly resistant. Poor control is usually obtained if J. vaginatus is sprayed. 2. Always use an oil-soluble ester of 2,4-D: In trial work water-soluble salts of 2,4-D have given excellent control of susceptible species such as J. effusus, but in practice this treatment has not been reliable, because at least 3 days’ fine weather is required before the material is fully absorbed. The outer layer of a rush is often thick and relatively waterproof and can be penetrated best by oil-soluble esters. These should be applied at 21b. acid equivalent per acre. 3. Always use an atomised spray: Rushes should preferably be sprayed in the early morning or late evening, when the weather is calm, so that the spray particles may be atomised or fogged as much as possible. If 32 fantype nozzles are used at pressures of 351 b. to 401 b. per square inch, a fine spray will be obtained that will adhere to the upright rush stems; coarse spray particles fail to cling to the rush stems. For spraying rushes the boom should preferably be ■ covered so that the fine spray falls largely on the target and little is lost through wind drift. Spraying from two directions is recommended, 11b. acid equivalent per acre of an oil-soluble ester of 2,4-D being applied in each direction. 4. Always spray seedling rushes or rush regrowth: All species of rushes are probably susceptible at the seedling stage. Mature rushes, particularly the more resistant, species, require prior cutting. The rushes should be cut in spring and sprayed when the regrowths are 12in. to 18in. high and before the onset of dry weather. For susceptible species, such as J. effusus and J. pallidus, prior hard grazing is an alternative to mowing. The regrowths after grazing should also be sprayed when 12in. to 18in. high. 5. Always follow up spraying with good pasture management: The oilsoluble esters of 2,4-D applied at 21b. acid equivalent per acre are particularly severe on clovers, which may be checked for several months. Every endeavour should be made to encourage the clovers after such an application by topdressing and preferential grazing management where practicable. If this is not done, the area will usually revert strongly to rushes after several years. Spraying of rushes should always be followed by pasture improvement, as chemicals have only the power of controlling the rushes present at the time of spraying. They have no control over a subsequent invasion of rushes. These can be kept out only by improvement of pastures.