Clean Weeding.—Intimately connected with the growth and development of the rubber tree one has to consider the conditions under which it is allowed to mature. The argument has been used that, since the habitat of Hevea Brasiliensis is in the jungle, we should be proceeding against nature by introducing conditions unlike those under which the “wild” rubber tree grows. It is difficult to treat such an argument seriously, as by quoting parallel instances in arboriculture it could be shown that growth, development, and yields are improved by cultivation of “wild” plants.

It needs small experience with rubber-tree plantations to be convinced of the necessity for dealing with other growths, which would otherwise soon surround and overshadow young rubber trees.

Apart from checking and preventing woody undergrowths it is considered advisable to keep the ground more or less free from light vegetable growths, which are roughly grouped under the heading of “weeds.”

Naturally, if these weeds are allowed to flourish and seed, their eventual eradication may be a matter of extreme difficulty and expense. It is the aim, therefore, of properly conducted estates generally to institute such a system of work that the weeding-gangs cover the whole estate at regular intervals; and, as a general rule, it may be accepted that the shorter the interval between successive visits by the gang to any particular area, the easier it is to keep weeds in check, and the cheaper the work will eventually be done. This procedure defines roughly what is implied by the term “clean weeding,” and it is the policy adopted by most estates.

Strict adherence to this practice in rubber cultivation has been inculcated by the older school of planters who obtained their experience in the cultivation of other crops such as tea, coffee, tobacco, etc.In latter years the wisdom of scrupulous clean weeding under all conditions has been questioned; and there can be no doubt that under certain special conditions a continuation of the policy of clean weeding is calculated to produce, in course of time, more harm than benefit. As an instance, the case might be cited of steep slopes on poor land. Continual clean weeding on such areas will lead eventually to a great loss of the surface soil, unless some precautions are adopted for catching and retaining the fine silt particles. It is to be noted that such a type of soil and slope, when the shade is appreciable, often produces no weeds heavier in growth than a very light grass. It is urged that the necessity for strict clean weeding on such soils does not exist, and, in fact, that it would be an injurious policy. Such arguments appear to be well founded in experience, and the writers are in thorough agreement that such special cases deserve special consideration. Rigid adherence to a policy of clean weeding, without regard to special conditions, would be most inadvisable.

Nevertheless, such exceptional cases do not detract from the wisdom of clean weeding in general. Every planter of experience realises how easily fields become infested with weeds if the regular work is suspended or delayed. It is probably quite true that the harm due to the presence of some weeds on an occasion is negligible; but apart from this debatable point, there is the solid fact that if once an area is allowed to become weedy it may soon demand a much greater expenditure to bring it back to normal condition than if it had been regularly weeded. This is common experience, and for that reason alone a general policy of clean weeding is thoroughly sound; especially if combined with some system of silt-retention.Grass Squares.—On some estates the practice of clean weeding is undertaken in combination with a system of silt-retention, which depends upon the development and maintenance of ridges. These are built up from the dÉbris of weeding in the form of hollow squares. Grass is allowed to sprout and grow in these ridges, and when it attains a certain height it is trimmed down so as to keep it within bounds. The soil within the hollow square is clean weeded; and it is maintained that loss of soil by wash is avoided. Under certain conditions there is a great deal to be said in favour of the method, but in the opinion of the writers it should be regarded only as a method of expediency. It is not to be preferred to the more thorough practice of soil-retention by means of silt-trenches, although the latter method may be slightly more expensive in the end.

“Lallang” Eradication.—The greatest bugbear of the planter in connection with weeding is the incidence of lallang. Many proposals have been put forward at various times for the complete eradication of this pest; but at present, under ordinary circumstances, there would seem to be no better method than by heavy and deep digging, followed by regular attention. The method is acknowledged to be expensive, but any half-hearted measure otherwise taken will eventually prove to be even more costly.

One has to differentiate, of course, between the incidence of lallang attributable to negligence on the estate itself, and the occasional outbreaks near boundaries, due to seeds having been wind-borne from patches of lallang outside the boundaries But, in general, it would be safe to remark that the appearance of lallang could be taken as evidence of a failure to cover the area at sufficiently short intervals.

As already intimated, the usual method of eradication of areas of lallang is by thorough digging, and the exposure of the strong root system to the sun. As a matter of interest it may be noted that recently some success has been obtained by another method[1] on areas which one may have in view for planting at some future date.

It consists in the employment of Mimosa gigantea, which eventually smothers the growth of lallang.

The seeds are sown broadcast, in drills, or in pockets, amongst the lallang. In the course of about three months it overtops the grass and proceeds to travel. At this stage the whole mass is pressed down, and the pressing is repeated at regular intervals. Under favourable conditions, in about twelve months, an impenetrable mat has been formed, which gradually forms a good mulch. When it is desired to remove the Mimosa, the mass (pressed down) is cut and rolled up like a carpet. Cleared in this manner, the area then needs regular weeding, in order to check the development of any stray lallang shoots. In actual practice it was found that the cost of this method was approximately two-thirds that of the usual digging method.Green Cover Plants.—Some years ago it was quite common to find green cover-plants employed on estates with the primary idea of minimising weeding costs. With most of these it was found later that their value was not real, and that they harboured diseases, and pests. Moreover, when they were removed, it was often found that an abundant crop of lallang and weeds resulted.There can be no question that certain plants can be employed with advantage, not only in the control of weeds, but also by reason of benefit to the soil in which they are established. These plants are leguminous, and their use is restricted almost entirely to young areas, inasmuch as they will not continue to grow when shade becomes marked. Of those best known in modern practice might be mentioned Tephrosia candida (Boga bean), Centrosema Plumerii, and Dolichos Hoseii (Sarawak bean).

It is wrong to imagine, however, that the establishment of such leguminous cover-plants obviates weeding. So far is this from being the case, that in practice it is found that the weeding “rounds” must be conducted at first with the same regularity as in ordinary working, but that naturally there is much less work to be done.As the plants develop, they can be pruned or dug into the soil, as the case may be. The addition of the green material to the soil, either by digging or by burying in open trenches, is calculated to cause improvement in the condition of the soil. There may thus be a close connection between weeding, soil conservation, and soil improvement.