WEEDS AND THEIR IDENTIFICATION.

New Zealand Journal of Agriculture, Volume XII, Issue 3, 20 March 1916, Page 175

WEEDS AND THEIR IDENTIFICATION.

CONTINUED.

ESMOND ATKINSON,

Biological Assistant.

THISTLES. IF we consider their great abundance throughout the country and their powers of spreading rapidly both by seeds and roots, we must rank the various species of thistles found in New Zealand as among the most important weeds with which the farmer has to deal. In this article' six of the commonest species are described ' and illustrated. These are : Spear thistle (Carduus lanceolatus). Nodding thistle (Carduus nutans). Winged thistle [Carduus ftycnocefthalus). Californian thistle [Carduus arvensis). Milk thistle [Carduus ■ Marianus). Woolly-headed thistle [Carduus erio-phorus).

IDENTIFICATION. ! Stems winged. ■ Heads large, upright, with narrow spines- '. . Carduus lanceolatus. Heads large, drooping, with -broad spines . . Carduus nutans. Heads small, clustered . ■ .. . . . ■. . Carduus pycnocephalus. [ Stems not winged. ' ’£■ . Plant with creeping underground stems . . Carduus arvensis. . Plants without creeping underground stems — J Leaves very large, with white veins . . . Carduus Marianus. Leaves smaller, without white veins . . Carduus eriophorus. This key is not intended to show the botanical relationships of the different thistles, but merely to provide a quick means of distinguishing them from one another. The genus Carduus is divided by some botanists into' two genera, Cnicus and Carduus proper, „ the species of the former genus haying feathery pappushairs, while . those .of the. latter have simple pappus-hairs. By this classification two of the species, nodding thistle and winged thistle, would remain in the genus Carduus, the others being placed in Cnicus, except milk thistle, which is often separated from the rest and made to 'constitute, .the genus .Silybum. The differences between ' the three genera are not important, however, and in this article all will -be -included under Carduus. SPEAR THISTLE. Spear., thistle ,is . a rather stout and much-branched plant, growing usually to a height of from 2 ft. to 4 ft. Being biennial, this thistle does not produce flowers : till the second season, the first-year plant consisting of a stout and long, only slightly branched tap-root, bearing at its crown a rosette of spreading leaves which are strongly lobed and prickly, dark green above and whitish beneath. ' ■ The stem, which is stout at its base, though rather slender in the ultimate branches, and is everywhere hairy, is irregularly winged for most of its length. The stem leaves are unlike the radical leaves in being shorter, narrower, and more pointed, and in having fewer, narrower, and longer lobes. The heads are rather large (1 in. to i|in. long by about’ the same in diameter), erect, solitary or two or three together at the tips of the branches. The involucre is egg-shaped, and each of the numerous bracts ends in a narrow, spreading spine, those , towards the base of the head being recurved. A slight cottony web is found on the involucre, but it is insignificant in comparison with that of woollyheaded thistle. The florets are purple inclining to reddish. As the achenes : ripen, the involucre opens out and becomes cup-like

in shape, and is filled with the whitish feathery pappus-hairs, which soon become freed from one another and from the involucre and float away as the thistle-down so common on windy days in the late summer. x It is not known accurately how far the “ seeds ” are carried in this way. It varies with the different species, and also depends on external conditions, such as the dampness of the weather and the strength of the wind. _. .. ; Spear thistle is Very commonly known in this country as Scotch thistle. . • ' NODDING THISTLE. , • Like spear thistle, nodding thistle is a tall and stout biennial, but it does not form, as broad or as symmetrical a plant, the branches arising, from, higher on the stem. In this respect it is more like woolly-headed thistle, presently to be described. : The stem is cottony, grooved, and, like that of the spear thistle, is winged for most of its length, but the wings are ' different in appearance, being much more deeply cut, very spinous, and often interrupted, so that often they are represented Only by a series of prickles with more or less expanded bases. The leaves are deeply cut into many narrow lobes pointing alternately upwards and downwards; both surfaces of the leaf are more or less clothed with short hairs, and the veins beneath are »woolly. The flower-heads differ from those of spear thistle in being larger (2 in. or more in diameter) and not so elongated, and also in their being drooping and not erect, this character having given the thistle its common name. The spines of the involucral bracts are also very distinctive, being three or four times as wide. The florets are of much the same purple colour as those of spear thistle, but the pappus-hairs are simple and not feathery. The flowers of nodding thistle have a ' rather strong and pleasant scent, which has given it the name by which it is sometimes known, “ musk thistle.” WINGED THISTLE. ' This thistle is a more slender plant' than the two preceding ones, and is an annual, ' flowering in the first season from seed. The leaves are broad in proportion to their length, cottony beneath, waved and prickly on the margin, but not so deeply cut as those of either spear or nodding thistles. In all three plants the leaves, are continued down the stem as wings, but winged thistle is aptly enough named, as the wings are very much broader than in the other two plants, and are more conspicuous through their being; continuous all down the stem. The flower-heads are altogether different, as they are much, smaller (1 in. or less long) and grow

in compact clusters at the tips of the branches. The involucres are narrow egg-shaped or oblong, the bracts rather broad but with slender recurved spinous tips, and the florets pinkish purple or whitish. As in nodding thistle, the pappus-hairs are simple and not feathery. CALIFORNIAN THISTLE. This thistle is the only one of the six under consideration which is perennial in habit. It, is a tall rather slender species, reaching the height of 4 ft. or more. The stems are smooth or slightly cottony, grooved and angled, and much branched, particularly towards the upper part of the plant. The leaves are deeply cut and waved, and very prickly, rather pale green above, and more or less whitish beneath. The flower-heads, which are abundantly produced in large open leafy bunches, have a strong honey-like scent. They are of two kinds, one producing pollen (male heads), the other having abortive anthers, and hence producing no pollen (female heads). The male and female heads are produced on separate plants, and, owing to the power this thistle has of spreading by creeping underground stems, a single plant may soon give rise, without the agency of seed, to a large patch. On account of this peculiarity, a whole district may be overrun with plants bearing exclusively one or other of the two types of flower-heads.* It is quite easy to distinguish the two kinds of flowers, the males ■ having roundish involucres, and showy spreading florets, lilac - purple varying to white in colour; while the female involucres are longer and narrower, and the florets less showy and darker in colour. In both kinds the projecting and prickly bracts of the involucre, so characteristic of most thistles,' are absent, the bracts being pointed but without spines, and instead of being reflexed the tips lie close against the involucre. Just before the achenes are ripe the feathery pappus - hairs project in a dense tuft from the slightly expanded involucre, the whole head looking rather like a paint-brush. MILK THISTLE. A short description of this plant should be sufficient, as it can be at once distinguished in all its stages by the conspicuous milkywhite veins which give it its common name. It is the largest and tallest of all the thistles naturalized in New Zealand, reaching

the height of 6 ft., and having leaves sometimes 2 ft. long, though they are often smaller. Besides being longer, the leaves are broader and less deeply lobed than those of the other thistles. The heads are large and solitary, with egg-shaped involucres armed with very long and stout spines, which spread to a diameter of 3 in. or more, and are themselves armed with prickles at . their bases. The florets are purple, .and the pappus-hairs of the achenes which follow them are rather short, and are not clothed with feathery hairs, but are quite simple. WOOLLY-HEADED THISTLE. Although in the key this thistle is placed in a different section from spear thistle, owing to its not having a winged stem, it is closer to that plant in general appearance than to any other of the naturalized thistles. It may be at once separated from milk thistle, which is next to it in the artificial key, by its narrow leaves without white veins, woolly stem, and clustered cobwebby heads. From spear thistle it is distinguished by its less deeply lobed leaves, which are decidedly white beneath; by its very stout strongly corrugated stems, which are entirely without wings; and by its densely woolly heads, which look as if a spider had been spinning its web on them. When the two species are growing together woolly-headed thistle may be picked out at a distance by its more upright and less bushy and spreading habit of growth. The heads of this species are usually described as much larger than the ones shown in the illustration, but the small-headed form is apparently the typical one in New Zealand. The pappus-hairs are feathery, and are like those of spear thistle, but have a brownish tinge. DISTRIBUTION AND IMPORTANCE AS WEEDS. Of the six thistles described above, three may be spoken of as widely distributed (spear, Californian, and winged thistles), one (milk thistle) as common in many places but rather local, while the two remaining plants (woolly-headed and nodding thistles) are at present confined to quite small areas.

Spear thistle is by far the most widely spread and abundant species, being found in a great variety of soils and situations throughout both Islands. It is perhaps the most characteristic constituent of the plant covering that so constantly appears a few weeks after a bush burn, and it is usually during the first few years of settlement in bush country that it is most abundant, since it does not survive more intensive cultivation. . For the same reason it is not found as a crop pest, though it. is one of the most

frequent occupiers of all waste ground on the farm . and elsewhere. It is spread entirely through the agency of seed, but this is produced in large quantities and over a long period, besides being well adapted for ~ dispersal by wind.

It seems probable that the achenes are capable of remaining dormant for some time, and then germinating when favourable conditions arise. The fact that spear thistle appears in enormous quantities within a few weeks of a ' bush burn, and also after the reploughing of old pastures, affords evidence to support this view, since the bare ground may become populated at a time when no seed-dispersal -is taking place. Achenes of spear thistles as well as of woolly-headed and nodding thistles germinated strongly in a few days after being kept for four years, and this power, together "with the fact that the achenes of all these thistles have seed-coats containing oil (which protects them from decay) makes it likely that they may lie dormant in the ground for a number of years. It should be mentioned that goldfinches are great destroyers of thistle “ seeds/’ especially those of spear thistle. In many districts it is quite difficult to find whole achenes. Little need be said here of the economic position of Californian thistle, since this subject has been fully dealt with in the Journal from time to time. . The thistle is now widespread throughout New Zealand, and is still on the increase, though its distribution is not even. Certain districts may be called its strongholds, while it is still quite rare in others. In Marlborough lucerne has proved very effective in destroying Californian thistle, and where the former plant can be grown there is no sounder way of getting rid of the pest. Californian-thistle rust JPuccinia suaveolens) has done good work this season, and the Biologist will send supplies of the fungus (as long as it is available) to any one requiring it.

Winged thistle, though very abundant in many localities, is not nearly as generally distributed as either spear or Californian thistles. It is the most ephemeral of all the introduced thistles, ground which is covered with it in one year often being entirely free from it the next. “ Seed ” ripening in autumn will produce flowering plants the following spring and summer, while from spring “ seed arise plants flowering in the autumn. In many parts of the denuded areas of Central Otago it occupies a position of great ■economic importance, since it affords the only available winter feed lor sheep. Milk thistle is ' abundant in many parts of the North Island, but it is local in its distribution, and is less common in the South. It often grows in large and dense patches, smothering all other vegetation, but it never persists where thorough cultivation is carried on.

Both woolly-headed and nodding thistles are local plants. The former is at present confined to a part of the Wairarapa, and to the Otaki and possibly other river valleys to the west of the Tararua Range. Apparently this thistle has spread by means of “ seed ” carried over the range from the Wairarapa by the wind, as it is found only in the upper part of the Otaki valley in the country nearest to the original habitat. Nodding thistle is fairly common in South Canterbury, and is scattered through parts of Otago,, but has been recorded from nowhere else at present. The achenes of three of these thistles (spear, Californian, and winged) are found as impurities in various lines of agricultural seeds, both New-Zealand-grown and imported. For a full account of these impurities the reader is referred to .an article by Mr. E. B. Levy in the Journal for June, 1915. The “ seeds ” of the other three have not yet been recorded as impurities, two of the plants being rather rare and local, while the third (milk thistle) has achenes of so large a size that they would dress out of most lines.

CONTROL OF THE BLACK CRICKET.

CALIFORNIAN METHODS WITH GRASSHOPPERS.

E. CLIFTON,

New Zealand Commissioner, San Francisco.

In certain northern districts of New Zealand the black cricket (Gryllus servillei) often commits . considerable depredations during the summer. The lands that usually suffer to the greatest extent are rich fertile swamps in the process of reclamation, also parts of the hilly country where, during dry hot weather, openings in the soil permit these insects to shelter. A very similar condition due to another insect, the grasshopper, causes very appreciable damage in the Imperial Valley of California. This grasshopper is somewhat similar in its propagation habits to that of the black cricket of New Zealand. Its eggs are laid in the soil, and in the season when the insects mature their depredations commence. The most serious harm is effected when imperfect or no cultivation at all is applied. In the Imperial. Valley fields of lucerne and maize, and gardens and trees, have been more or less injured. In lucerne fields from which an ordinary yield of a ton of hay per acre would have been obtained the stems alone

remain. Something similar has been seen in those northern districts of New Zealand, where areas have been stripped almost clean of vegetation.

It is recognized that although cultivation .is . the means of overcoming the pest in the districts, affected by the black cricket in New Zealand there are serious difficulties in the way; of this method. The land may have been but recently reclaimed ; considerable expense must be incurred in drainage or in . the ■ clearing of stumps before cultivation may be entered upon. Cultivation will come as these operations are completed. In the fertile , Imperial Valley, wherever thorough cultivation has been applied the grasshopper pest is almost entirely avoided, for the .. reason .that the operation has brought to the surface and exposed to the sun the eggs .of the ,■ insect. Such treatment will be the ultimate ■ cure in New Zealand; ’ • ‘ There remains another possibility of restriction'— namely, by poisoning the matured insect. This is effected in . California by the distribution of a mixture consisting of 25 lb. of bran, 1 lb. arsenic and 2 quarts molasses, in 4 gallons of water. The arsenic used is usually in the form of Paris green. The latter is mixed with, say,. 1 quart of water, poured into a tub, mixed with the molasses,, and the bran is added slowly until the compound becomes of the consistency - of - mortar.- - It is undesirable to pour the -water containing the poison on the bran; the arsenic is then not evenly distributed.- The quantity ‘ specified is estimated to be -sufficient for 5 acres of land—that is, assuming that the whole area was affected. In the • greater part of the country affected in New Zealand, however, the pest is not . distributed over the whole area. Therefore, this quantity would serve a much greater acreage if distributed on those parts that, the crickets affect. “ The poisoning method is being used over quite a large area in California, particularly for the ' protection . of commercial market-gardens and gardens generally. . ' .

It is claimed that this ' compound 'is not attractive to' stock or poultry, and therefore is not a danger to them. It may, however, be dangerous to children, and great. precautions should be taken in making use of it when such condition applies. ' !/ ? y ;

- In dealing with the grasshopper a greater difficulty is encountered than applies to the : cricket. The former moves in quite large flights! from place to place ; the cricket' has not this means of locomotion at its command. On the ! other hand, the ' grasshopper does not shelter itself in the ground as does the cricket. A grass-hopper-catcher is availed of by the farmer in the form -of a canvas screen covered with glutinous oil. The insects fly against the

screen and fall into a hopper below. Another means is a wide concave canvas screen of which the centre terminates in a bag net. The insects are usually caught in this and made use of for poultry-feed. This means, of course, could not be availed of in New Zealand, for on being disturbed the cricket at once seeks shelter in the ground. It is claimed that when sheep have been pastured on land during the winter and spring but a relatively small number of grasshoppers appear. This is supposed to be due to the trampling of the ground by the stock. The summary of recommendations for the farmer in California—and which may be applied with modifications to. New Zealand is in the first instance thorough cultivation/ and in the second poisoning.

* The subject of the production of seed by Californian thistle was dealt with by Mr. A. H. Cockayne, Biologist, in an article published in the Journal for May, 1912 page 351).