Farmers' Fight Against Scrub

New Zealand Journal of Agriculture, Volume 60, Issue 1, 15 January 1940, Page 5

Farmers ' Fight Against Scrub

Methods of Controlling Manuka, Tauhinu, Bracken Fern and Hard Fern

E. M. BATES,

Instructor in Agriculture, Gisborne.

MANUKA, tauhinu, bracken fern and hard fern are some of Nature’s earlier volunteer plant forms in the natural succession of plant species back to natural forests from the artificial pastures placed there by man. There are in the Dominion several million acres in scrub of one form or another, much of which has reverted from sown pastures. Huge sums of money are. spent annually in a continual and often vain struggle to keep such growth in check. On unploughable hill country the difficulties are. many, and mistakes, once made, are not readily rectified. In any effort at control it is essential to have a knowledge of the growthforms and life-histories of the plants and their relation to local conditions if the most effective measure of control is to be obtained. The weeds under review usually make their first appearance in the youfig’Tjush-burn pastures two or three years after the primary burns. They may rapidly take charge, until eventually they are replaced by tallergrowing plants if Nature is allowed to take its course unchecked.

Manuka RED OR STUNTED MANUKA. (Leptospernum scoparium.) On much of the surface-sown, deteriorated grasslands, inadequate pasture cover, together with the ineffectual trampling of stock due to lowcarrying capacity, cannot check manuka aggression. In the Poverty Bay district manuka is kept well in hand on most of the hill country, but it is fairly prevalent along the. southern boundary of the Cook County and Wairoa. Odd patches occur on the East Coast and parts of the Matakaoa County. The higher

country frequently has a top layer of pumice. A small proportion is ploughable and is then easily brought in with swedes, followed by rape, before sowing down. One good ploughing will destroy the manuka if the seed is buried properly. The ground is not turned over again, and only surface cultivation is carried out. Stock droppings from the fed-off crops enrich the surface soil for the grass sowings. In the Waerenga-o-kuri district there is an excellent example of the conversion of ploughable, stunted-manuka country to high-class pastures of ryegrass and subterranean and white clovers. Afforestation Control is often very difficult and uneconomic because of high maintenance costs per acre in the incessant struggle against this persistent weed. On steep and difficult country with a low productive limit, where it is almost impossible to keep manuka in check, reafforestation appears the only reasonable solution. Control Factors Manuka is a particularly free seeder. The seed is shed during August to germinate in September. A proportion

of the seed heads retain the seed longer, and this will not germinate until the following spring at least. Fortunately, if manuka is cut below the lowest branches so that no leaves are left on the stump, further growth of the individual plant is stopped. Mature, standing manuka should never be burnt, as the green seed heads are ripened by the fire and reinfest the bare ground after the burn. Control Measures on' Unploughable Country Control measures must aim at destroying the plant in the seedling stage and preventing reseeding. With unploughable country, the essence of control is to cut, burn, sow, pull up young growth, and utilise stock for crushing. Cutting usually takes place from the beginning of Steptember to March. With early cutting there may be much green growth of thistles, grass, etc., to spoil the burn, and manuka seedlings will also be coming up. Early cutting may be satisfactory where there is little of this growth due to poor ground or dry conditions. Even with late cutting, green growth may spoil a burn or result in a poor burn in wet seasons, especially with light manuka. In such cases, much seed, seedlings, and small manuka overlooked by the scrub cutter will not be killed. Late cutting is much safer, but at this time labour is often a problem because of seasonal work. This is one reason why some cutting is carried out in winter and spring, which is not the best time. Where convenient, the lee sides of hills which are away from drying winds might be cut first, as this results in more even drying. Burning should not take place until the manuka

has dried out well, without, however, too great a loss of leaves. Good conditions for a burn are absolutely necessary and the best possible burn should always be obtained. In some places it is a practice to burn at any suitable time with the object of destroying the manuka and increasing the danthonia. This is a cheap method of destroying manuka and certainly has the desired effects, but continuous burning does not improve soil conditions, and a solid danthonia sward is likely to result. Sowing and Management Spring sowings are not usually successful, and autumn burning and sowing are safer. Sowing should follow immediately after the burn and should be as early in the autumn as possible, in order to give the pasture species every chance against volunteer weed growth, or before leeching of the ash from the burn occurs. Every effort should be made to obtain good pasture establishments, which is an important factor in control, as the closer the sward the poorer the establishment of manuka from seed. January may be the best month for burning and sowing grass seed in the lighter hill country of the higher levels. There is then a reasonable chance of rain in February and of the plants becoming well rooted before cold weather sets in. Plants have two good months to become established, and grow fast at this seasonable time. The fencing of sown areas is essential. If a fair pasture sward is obtained cattle will eat the young manuka with the grass. The trouble on manuka burns is to obtain a thick sole of grass. If possible, it is most desirable to topdress with available phosphate to assist establishment of pas-

ture species. It is contended that this is the important time for applying fertiliser. Fertilisers Fertiliser has the effect of stimulating growth and giving a better pasture cover. This, in turn, increases the carrying capacity, with the ability to crush sown areas more adequately during the early years. Periodical crushing during this period is essential to success until the sward, mainly danthonia, becomes stabilised. After two or three years it is frequently necessary to grub and pull young manuka. This first pulling may cost 10s an acre on fairly bad manuka country. Usually, it is necessary to repeat the pulling and grubbing process every second or third year, but at a diminishing cost each year. Definite advantages of this practice over periodical burning and sowing every six or seven years are that there is no loss in grazing and no damage to wool, while there is the possibility of eradicating the manuka in time. Pulling and grubbing should be carried out when the manuka is small and scattered. Much of this work can conveniently be done in the early winter. The heavy white or tree manuka (Leptospernum ericoides) is treated as bush and cut in the winter. Tauhinu (Cassinia leptophylla.) Tauhinu is a native scrub with heavier foliage than manuka, and is common on the East Coast hill country along the coast. It is frequently found alone or scattered in the manuka.

Young growth, if only a few inches high, is usually pulled. Taller growth should be cut like manuka, but it is liable to shoot again if cut in the winter before the sap rises. fTauhinu burns well. , It is safe to burn young growth, but when mature plants are burnt. the seeds drop and germinate freely on the bare ground beneath, which restricts burning after cutting. The dense association common with manuka does not often occur with tauhinu, and the isolated plants are cut and the tops left to rot. Bracken Fern (Pteridium esculentum.) In one form or another bracken has a- world-wide. distribution. It is common throughout the North Island of New Zealand, and is too frequently allowed to grow unchecked on roadsides and railways. In the Poverty Bay district the steeper, higher country was originally in bush,, while the easier, more open country not in bush was largely in bracken fern. There was practically no native grass, as was the case in Hawke’s Bay. Control Factors Bracken fern is propagated by means of spores, which are noticeable on the under-surface of the leaves in the winter. A • single strong 'rhizome is developed underground, and from this, behind the growing point, a single tender shoot or frond, forming a leaf, is normally developed each year. The rhizome creeps forward below the ground at a depth of from 6in to Ift, while the older portions gradually decay behind. In the natural state fronds appear mainly in October-November, but under control measures such as burning, crushing, or cutting, the growing period is extended by the appearance of new fronds through to March, and in some seasons even a little later. On the developed leaf depends the vitality of the rhizome, and destruction of the fronds as they appear results ultimately in control. From about March to October bracken is dormant. Control When the young fronds are in the curl stage they are readily eaten by stock, especially by sheep, and being tender break off. These fronds do not grow again, but a fresh frond is forced up from a bud which normally would develop the following year.

Obvious control measures, are crushing with both' cattle and sheep over the period when the young fronds are appearing through the ground. Cattle are more important as the fern hardens. In a very short time a frond develops into a leaf. After the stems toughen tramping is less effective, and stock do not eat the growth readily. About March it is usual to ease up the stocking on fern country as much as possible. If the fern is allowed to mature in the summer it hardens, and stock will not eat it in the following winter. It is not a good practice to burn fern in February, and depend on the stock to eat the later growth in the winter. The burning is bad, and the season may be unfavourable. The young fern may become too hard before being eaten if conditions are dry in March. From March to October, when the bracken is dormant, light stocking will allow grass growth to come away, facilitating further crushing in the following spring. With a heavy growth of bracken fern it is possible to get a 99 per cent, burn in March, although this is also possible in September. In districts where the fronds appear strongly in February or early March it is wise to delay burning until the middle of March and to sow immediately the fire is out. Burning in spring is not recommended. If this occurs, crush perodically until autumn in order to control young growth coming through.

Sowing Sow in early March while crushing is in progress unless frond development is still strong, in which case mid-March sowing is safer. Sowing will depend somewhat on the season and the district, but the aim should be to have the seed distributed to grow with the autumn rains. If there is much young fern coming up in the new pasture further crushing will have to be undertaken next spring. An increase of cattle with a decrease in sheep gives more rapid control, which usually takes about three years. It may take more or less time to control the fern, depending on the seasons and the way in which the area is treated. Although fern can be crushed out with cattle without burning, this is difficult to accomplish, and is hard on the cattle. The poorer the country, the harder it is to crush successfully. Stock will eat fern less readily on poorer country, where it is known as “sour growth.” Crushing is not so difficult on better country, and stock eat the fern more readily. At one time, purchasing stock in the spring and selling again in the autumn resulted in financial loss, which did not assist in the control of bracken fern. Today, this difficulty is not present, as the stock market is more stable throughout the year. Pigs are useful in clearing up small paddocks of fern, as they root up the starchy rhizomes for food.

Ploughable Country With Bracken Fern The cheapest and quickest method of establishing pasture on ploughable country, especially if one is prepared to topdress, is to burn in the autumn, disc, topdress, and sow as soon as possible. On virgin country it is usually necessary to effect establishment as early as possible, and expense is the deciding factor. Cropping with swedes and rape before sowing down will result in strong pastures, but this involves considerable expense, and can be carried out only by the more financial farmer. ' ’ ~ <■ Hard Fern (Paesia scaberula.) Hard fern (.Paesia scaberula), also known as ring fern, carpet fern, or sweet fern, is a native volunteer weed widespread in New Zealand on poor hill country pastures with a rainfall in the vicinity of 70 inches or more. Plants establish in places not usually tramped by stock, such as on the steeper faces or in the shelter of logs, etc. Control Factors Hard fern grows from spores, and the plants spread by means of surface rhizomes, which re-root outwards. From these the leaves grow to a height of about 18in, and the plants form more or less circular patches completely covering the ground. If moisture is low the fern may have a hard time, but in a wet season the patches may increase about Ift in diameter. After burning, the fern increases in size from the rings more rapidly than on the unburnt patches. Close grazing by sheep favours the rerooting of the rhizomes on the barer pasture, as in the case with piri-piri (bidi-bidi). Control Bracken fern forms strong, underground rhizomes, but on the other hand, hard fern forms numerous wiry, surface rhizomes. On this account control is largely different. Actually, effective burning is the only practical means of control with hard fern, while crushing with stock is the main line of attack against bracken fern. It is most unwise to burn in the spring, although after the winter the hard fern has much dead growth throughout and burns well. After

spring burning, the fern comes away rapidly as young green growth, and appears to be invigorated, or at least renewed, at this time. The surface rhizomes are succulent and difficult to kill. Young fern may also appear on the ground after spring burning, as there is usually sufficient moisture at this time for the spores to germinate. Time for Burning The best time for burning is in the late summer, autumn, or, on high country, between mid-summer and early autumn. Burning should be carried out, however, only when the rhizomes, as well as the ground, are well dried out. If conditions are such that a really hot fire can be obtained the fern may be killed outright, but at least there will be no growth until the following spring. If the season is not dry enough, burning is better left until a more favourable season, even if a year or two may elapse. In any case, burning should be delayed for two or three years’ growth, which is sufficient to make it possible to have a good fire to destroy the fern, and to allow for a good amount of ash to start the grass seed. Sow immediately on the burn. Superphosphate greatly assists the young grass and clover, inducing a denser pasture cover and stronger growth. Stock will then frequent the newly-sown patches more, and their tramping causes further injury to any remnants of the fern. There is no hard and fast rule for burning. Whether the operator starts at the top or the bottom will depend on wind and smoke, the density of the patches, and the steepness of the country. The ordinary blow-lamp is very satisfactory for lighting fires. It may be difficult to keep out hard fern when the sward is weak, and the land has not been logged, for the ground is usually heavily infested with spores. It is difficult to deal effectively with young plants and rings where patches have not been completely burnt out. Spraying Trials Interesting spraying trials with arsenic pentoxide were carried out several years ago at Whangamomona. A mixture of lib to 32 gallons of water proved the most effective strength. A stronger solution killed the tops without sufficient damage to the plants, while weaker solutions were also ineffective. Spraying round the edges of

patches and on isolated plants which are not strong enough to burn might be carried out in January during fine weather several weeks before firing to obtain a cleaner burn. If cattle make a bed on hard fern the centre dies out, but growth continues outwards from the edges of the rings. Stock would injure the fern by tramping, but they seldom frequent hard fern patches. Crushing is effective with bracken fern, but not with hard fern, and, actually, control of bracken fern in some localities paves the way for hard fern. Tramping may be effective with hard fern on very small areas, but it is as well to make the distinction between crushing' and tramping. Crushing involves tramping and eating, and stock never eat hard fern. Pasture Species in Hill Country Sowings Suckling clover, white clover, and subterranean clover usually establish much better under topdressing. In the secondary bush burn mixtures dogstail is always worth inclusion. Ryegrass affords quick cover and early feed, although its life may be short under hard conditions. A small proportion of Italian ryegrass also gives quick feed in the first year. Browntop is naturally suited to higher, damper country, and establishes well, but it is not suited to dry hill country, which runs to danthonia eventually. Danthonia is difficult to establish from sowings, but comes in as a volunteer with the opening up of the sward as other species die out. Cocksfoot is also difficult to establish, particularly under grazing after a secondary burn. A small quantity of yarrow is frequently included on poor hills. Lotus major is slow, but has proved useful under wet conditions. Paspalum is worth inclusion in warmer districts, and although slow to take hold, it is a valuable pasture constituent in the dry summer months.

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