Killing Weeds.

Horowhenua Chronicle, 30 May 1910, Page 4

Killing Weeds.

(My E. V. -AYileox, Special Agent in Hawaii Agricultural Experiment Station, United States Department of Agriculture). 11l tlie perpetual conflict with weeds it becomes necessary to make use of every weapon which slkjws efficiency in destroying them. Tho conditions under "which different crops are raised indicate different methods as best .adapted to the various conditions of each case. During the past year -a number of experiments have been made with carbon bisulphide in studying its effects upon, various herbaceous and shrubby weeds. In these experiments, the amount of carbon bisulphide to be used varied according to the size of the plant to bo destroyed. On small stemmed plants like Crotalaria, about a teaspooiiful ol commercial bisulphide was poured down the stem, from about six inches above the ground. The amount was increased for larger plants up to two tablespoon fills for guava bushes three or four inches in

diameter. The plants upon wincii most of the t.'S'ls were made were lantana, va, prickly-pear, Stachytairphota. r'lirotoina (one of the plants known by the native name Oi), and Crotakiria incana. In all cases, as just indicated, the carbon 'bisulphide was poured on the stem at .a point about six inches above the surface of the ground. On most plants carbow bisulphide shews no effect until after the lapse of a considerable period ; on large guavas sometimes two or three months. The effect of oonring carbon bisulphide on Oro'lalaria was to cause the death of the plant, root and branches, within fourteen days. The plants remain gr'ivn, and .apparently normal, until shortly after death, when the leaves ■nirldenly turn yellow a.nd shrivel up. If the plants are then carefully removed from the soil, it is found that all of the root-system is dead, and the inner tissues of the roots anl lower part of the stem avu brown or otherwiso discoloured. Lantana bushes, about two inches in diameter, died wiitbiu seventeen to thirty-two days after the application of carbon bisulphide. About the same length of time was required for the destruction of Oi. Young prickly-pear plants, about two feet in height, wore found to he exceedingly sensitive to carbon bisulphide. In some cases, the plants fell over on the ground within twenty-four hours after beiiuc moistened with 'the liquid, and in other cases wvw dead within two da vs.

"WiHi guava, tin* effects of carbon bisulphide were net manifested iVr ,n much longer period, in smno case* even not for two or three months. Fiiiiilly. however, in all but two '•ases the halves it urn cd yellow, withered up. and tli» plants died. The dead iind dying trees were dug out find tin' roots examined. Tn overy case the roots were found .to be dead to the tip and tilieir whole ti-'.sue discoloured. In one cii.se. i - 1 !e guava tree ws over six indie* in diameter at tli.> I rise. Apparently the effect of carbon bisulphide, when applied to the stem if plants, i.s due to artificial freezing. As is well known, the liquid vclatises aluinst instantly, and cools the surface so suddenly that th" living bark is destroyed. It was found '> be a simple matter to pror'u"e ice at ii'>on on liol days op the surface of guava.s and ether plants by slmvlv dripping carbon bisulphide along the trunk. The death of la rye guavas from an application of a sin.all ouantitv of carbon bisulphide to the ba.se of the trunk, a few inches abave the "round, can hardlv be attributed ei>Mrelv fo th" freezing effect. It sc'.'iis a'so to evercise a unisonous .action, otherwise it would be difficult to explain the complete destruction of the reefs to their tips, in some instances, six or e'mlit feel" from the point whore the carbon bisulphide was .applied. Tt was found, for examp'e. that, guava btHies wonlrl live for five to .seven months after the bark and cambium had been entirely removed from .the surface of the ground up to n height of two foot. Moreover. the destruction of the bark at the base of the trunk by concentrated sulphuric acid was iv. .t .suflicien.t to cans,, the death of a guava bush for about .six months. Apparently, therefore, carbon bisulphide cause;, the death of plants by its freezing effect and also by a poisonous action.

'I'v.v- use of carbon bisulphide few (li.strnying underground insects is a fiiuiiiiar practice. It may be into resting, therefore, to inquire what effect, if any. tilio extensive iiko of carbon bisulphide may have upon the soil and its adaptability 1.0 ritl.tiva.tion. It is well known,' lor example, (hat the application ol carbon bisulphide to the soil around fruit trees and other plants lias nu injurious effect upon the plants: in faot, Hiltner »nn-cl Stormer have bliowii that carbon bisulphide reduces de.iitrilieation and the fixation of nitrogen. Similarly, Heiiizo demonstrated that carbon bisulphide promotes the activity of nitrogonfixi.HK organisms. In experiments carried on by Xubbo. the yield of peas and various other crops was increased as a result of the application of carbon bisulphide, and the plants absorbed more ash ami nitrogen. Ile::.ry found that when -100 cr. of carbon bisulphide per square in: it re was injected into the soil at'icu.t locust trees, beneficial effects upon growth of the trees were observed for several years. On the, other hand,_ heavy fninj<i;iiH;i<jii witji carlion bisulphide has frequently proved injurious or fatal to young fruit 't'i'eL'S. In a series 01 experiments by Oberlin, carried on tor I on'ghteen years, in treating grape phylloxera, it was found that carbon bisulphide had a remarkable effect in increasing the yield of grapes. When other crops were rotated with <;rape.s for example, legumes, sugarbeets, and cereals, a considerably increased, yield was also noted in these plaints. In a few instaiiioos, it appeared that soil made "sick" by ctmtiimou.s culture of the same crop was restored to productiveness by the use of carbon bisulpliicle. Apparently the only previous experiments with oarbon bisulphide, as a weed-destroyer, wave carried out by "Walker in Arkansas in destroying sasafras sprouts, and by the writer in Maryland, also on sassafras. In both of these localities the chemical was found to produce the death of the plants within one

month. Til I'.nijio; carbon bisulphide it c '!n!'H always he remembered that •the fumes, if inhaled, continuously, nny produce, serious effects upon the workmen, and also that the mn.teri.al is highly inflammable, and should he protected from accidental !I-:!n-.'!. ] T're effects of the fumes npo:i ihi! -workmen include, headache, I:;. • | eri:"-l excitement, a.nd finally a rather sarioius woakiK'rs, a feeble pnl.se, and other symptoms of prostration. If it is used, therefore, the eradication of weeds, those efi."ts .'vlianhl bo b::me in order to protect the workmen. It is obvious that carbon l bisulphide, a I though an effective mourn of destroying certain weeds, cannot be i:si).l economically in all localities. There are many steep slopes covered with gi lavas in which it would lie a very difficult matter to operate with this chemical. It is al-. ways necessary for the workmen ito keep to the windward, in order to

avoid the fumes, and in some localities the difficulty ol\'kaiisporting containers would render tho method entirely impracticable. On the oil her hand, the u.se of oa.i'bon bisulpaide in the dost ruction of sueh plants as the <j;iiavn has the advantage that new rprouts do not come. i:p from the rots. The necessity : of grubbing out all tlie roots is thus j obviated. Under such eiroumj stances it would merely ho necessary j to allow the gnavas to stand, until I they are dead, after which the trunk a.nd large romts would he removed, as is .necessary in any case in clearing land. I——MB