The Elimination Of Twitch Is Long, Slow And Costly Process

Otago Daily Times, Issue 27266, 17 December 1949, Page 2

The Elimination Of Twitch Is Long, Slow And Costly Process

The Farm

The spread of twitches in arable land and grass pastures constitutes a problem which most farmers from time to time have to tackle. In the following article Mr A. H. Flay, senior lecturer in farm management at the Canterbury Agricultural College, sets out the most suitable measures for control and eradication. All efforts to control twitch should, as far as possible, work in with the ordinary rotation of farm operations so that the work may go hand in hand with crop production.

On cropping land, he says, continuous cash-crop production with reduced soil fertility favours the twitches. Improper cultivation often assists their spread. Wet conditions favour their growth, especially the wet land brownlop and creeping fog species. On the mixed farm, grass grub, drought conditions, and severe grazing, especially in the absence of liming and topdressing, are all favourable to the weakening of the clovers and better grass species. This results in the opening up of the pasture and the resultant occupation of these bare spaces by one or more of the twitches present. In paddocks, whether sown in rotational crop or in grass, the presence of twitch in fences and on sod banks is a fertile source of infestation for larger areas of the field. Twitches appear very strong and tenacious plants, but in reality they have some weaknesses. If left undisturbed for several years the greater proportion of the rhizomes of twitch will become confined to relatively near the surface —two to four inches is quite common. They mostly have a long winter period, and at this time their rhizomes cannot-withstand exposure to frosts. Likewise, in the summer or autumn, when under continuous cultivation, alternate wetness and dryness of the underground system soon causes a disintegration of these organs. Control Measures The farmer should direct his attention to the eradication of these twitches at every opportunity. Because of the practical and financial difficulties of an absolute kill, and because of re-establishment, slowly and steadily from a few surviving joints; seed; or from the spreading in from fence lines and hedge rows, the problem usually becomes one of control rather than complete permanent elimination. Control is costly* and often elimination might seem desirable, but with the free-seeding species such as browntop, both wet and dry, complete eradication from the farm is well-nigh impossible. Old man twitch, creeping fog, and onion twitch can be fairly well confined to fence lines. Every season on the mixed farm twitch and other weeds are killed in the ordinary cultivation programme. This programme involves the preparation of land for rape, for potatoes, wheat, barley and oats, for turnips and new grass. The cultivation is primarily carried out to enable the production of a given crop, and twitch control is not always very effective. Often the twitch is merely checked or partially killed, and as soon as the crop is sown the twitch commences new growth. Thus in a wheat stubble, especially after a light crop of wheat, twitch is often found to be worse than when the paddock was ploughed out of grass for the preparatory crop of peas or rape. Value of Plough Twitch killing methods may be divided into two distinct classes: — First, eradicating old man twitch, creeping fog, onion twitch and wet land browntop; and, second: r , controlling browntop and chewings fescue. The distinction must be clearly understood, as the methods used in the two cases differ widely. On every type of soil and in both high and low rainfall districts old man twitch, creeping fog, onion twitch and wet land browntop may be killed by the adoption of one method—ploughing. Operations are commenced by early summer ploughing out of lea or any other condition to a depth of three or four inches. The furrow is turned as flat as possible. After about three weeks the furrow is ploughed directly back again, and the operation repeated, gradually increasing the depth of the furrow up to perhaps six inches and at such intervals that the twitch never gets a chance to produce even one green shoot. Under conditions where clods form which may hold moisture and keep roots alive, grubbing and harrowing between the ploughing helps considerably. In an old pasture where the twitch is in to a depth of three inches ploughing to get all the runners and following this by crossploughing and repeated cultivating is a practice which has proved highly effective. In high rainfall areas the season may be so wet that a complete kill is not obtained in one summer fallow. Under such conditions the land should be sown in the autumn to some greenfed crop. Oats is the most popular and fits in best with the majority of farming practices. The oats will provide valuable late winter feed for pregnant ewes and a flush of early spring feed for ewes and lambs. A more effective crop from the twitch-killing point of view is oats and tares. This crop can be fed off once or twice in late autumn or early winter, but is often allowed to go without feeding. (A heavy crop of nay is taken in the following November). ' The oats and tares form a dense mat and are a fairly effective smother for twitch. After these crops the land is ploughed over in early summer and a second period of summer fallow commenced. The principle is the same; never allow the twitch to produce a green shoot; and the operations are identical with those outlined for the first summer fallow, but with oats and tares ploughing is delayed until after the hay crop in late November or early December.

Undoubtedly dry seasons favour twitch eradication and a specially bad paddock of creeping fog may take three summer fallowings if damp summers are experienced. This is particularly the case if the area is heavily infested with onion twitch, the worst variety on cropping land. Twitch killing is a long-drawn-out process involving heavy expenditure in the shape of repeated cultivation. Foothill Areas The eradication of these twitches on foothill areas is a difficult problem. The two major difficulties are the high rainfall which prevents a satisfactory summer fallow, and the rolling nature of the country, as this makes ploughing backwards and forwards impracticable. There is also risk of wind blowing in foothill areas should the soil be worked too fine. Creeping fog is the most widely, spread of. the twitches in these areas. Where twitch is only moderate in amount some success has been obtained by summer fallowing with frequent strokes of a stiff-tined grubber, and sowing down

to grass about February or March. A complete kill is almost impossible to obtain in one year, and all that can be expected is a partial kill and a good cover with the new grass. Greenfield oats may be sown for sheep feed and a further summer fallowing carried out if desired. Sometimes as many* as three summer fallowings have been given before sowing down to permanent pasture. Dry land browntop and chewings fescue have the unusual characteristic of taking charge and forming a tight mat to the exclusion of other plants, both in the high rainfall areas of the foothills and on the dry, light land areas of the plains. The policy for these twitches on the foothill country is entirely different from the constant ploughing policy. Land is deep ploughed out of old pasture in early winter with a furrow of about six inches depth. It is essential to get a good deep furrow and turn it as flat as possible to get the browntop well buried. The furrows are later rolled to seal them down. The principle is to put the browntop down fairly' deep and leave it there. As soon as the paddock shows any greenness it is double disced. Further double discings and harrowings at suitable intervals follow and the seed bed-is ready for rape or turnips. The rape or turnip crop is followed by shallow ploughing and work as usual for a subsequent crop of rape or turnips or even oats for chaff. By following this up with green feed oats then summer fallowing after the oats from November to February, a good kill of browntop is obtained. The paddock is then sown to grass in February with or without lib of rape per acre. Sometimes the grass is sown immediately following the first rape or turnip crop. . In both cases shallow ploughing after rape or turnips is cultivated from September or October to November or December when usually 11d rape is sown with the new grass seed mixture Where light land is badly infested with browntop, and to a much smaller extent Chewings fescue, the deep ploughing method adopted on the foothills is most useful where old standing, shallow rooted browntop Is growing on soils deep enough to allow a 5 or 6-inch furrow. The procedure outlined for browntop on the foothills can be followed with success on these deeper light soils—i.e., a deep flat furrow, rolling, double discings an harrowings, and sowing to rape, turnips or grass. On shallow light soils and on boulder soils there seems to be no other method than repeated ploughings in the driest time of the year. Usually three ploughings are sufficient to dry out the topsoil thoroughly and hill the browntop. Control Is C-stly The (Smallest loss in the matter of a season’s production from a given area is obtained where an old pasture is ploughed 2-4 inches below the twitch in early November and summer fallowed. This is usually followed by sowing wheat and sometimes Italian ryegrass or oats. A similar summer fallow occurs where a grain "crop is followed by greenfeed (oats and oats and lupins) so necessary for lambing on our arable farms and a further fallow where this is followed by new grass—i.e., rape and grass, turnips and grass. In each case, there is the cultivation expense and there is no cash crop return for that season. It might be argued that without this treatment it would be impossible to carry on and maintain production. This is frequently true, and so summer fallowing becomes an annual charge on mixed farms. Many progressive farmers nowadays, especially on the better soils, fallow annually up to 10 per cent, of their farm, and the length of this fallow and the frequency of cultivation vary considerably with the soil type and the climatic conditions.