Eradication of Mexican Devil Weed

New Zealand Journal of Agriculture, Volume 60, Issue 1, 15 January 1940, Page 53

Eradication of Mexican Devil Weed

COMMONLY known as Mexican devil weed, eupatorium glandulosum, which is described by Dr. Allan in the “Journal of Agriculture,” March, 1933, is causing anxiety to farmers in certain parts of the Auckland Province by its increase in growth and the difficulty experienced in eradicating it. It is a shade-loving plant, and grows thickly and vigorously in rough, shaded valleys. Here the pastures are' generally poor, and the land is covered fairly thickly with bracken fem. It also grows on the higher country where the rainfall is fairly heavy. Under these conditions • the sward is generally becoming invaded with bracken fern, and here it establishes in the shade of fern clumps. It is also found growing strongly in the shade along the edges of bush areas, but it will not thrive in the bush itself. Cutting and Pulling Cutting and hand-pulling before the .plant seeds is the usual , method adopted for eradication. The plant has a very shallow rooting system, and, when soil conditions are damp, it is fairly easy to pull. Control by this method has not met with much success. The roots appear hard to kill, ■as, when the plant is pulled and turned with the roots exposed to the sun and Weather, it has the power to re-root and exist until the. seeds have matured. A thick crop of seedlings

come away from the seeds during the following spring. . It is generally found in the shady valleys where the country is steep and carrying a poor sole of grass. It does not exist on clean country which is carrying ■' good grass and .is being effectively managed with . cattle and sheep with the addition of topdressing. Experimental Work Experimental work has been carried out during the last two years by the Department of Agriculture to see

whether the plant can be successfully eradicated 7 with sodium chlorate. The following . technique was adopted. A hillside, taken where the eupatorium was thick, and was divided into eight plots each 50 Iks. x 33 Iks. The eupatorium was cut just above the ground on , alternate plots, and half the cut plots were sprayed with a 5 per cent, solution of sodium chlorate, the others being dusted with . sodium chlorate and lime mixed at 1 to 10. The four remaining plots, where the eupatorium was left standing, were treated in a similar manner. ; Two applications of sodium chlorate were given to the plots, the first in October, 1937, and the second in January, 1938. The plots were cleared of all rubbish, which was burnt during the autumn of 1938, and the area was sown with a grass seed mixture consisting mainly of danthonia, browntop, and lotus major. Basic slag at at 2 cwt. per acre was also applied at the time of sowing. Results Because of wet, cold climatic conditions after sowing the establishment of grass was not very satisfactory, but the sodium chlorate treatments had shown their effect on the eupatorium.

Plots which were cut before dusting with sodium ' chlorate and lime mixture, and those sprayed with 5 per cent, solution, showed about a 60 per cent. kill. This suggests that if the applications were continued annu-

ally, a 100 per cent, kill should be obtained after three or four years’ treatment. The plots of standing plants which were treated with sodium chlorate in the same way as those in which the plants were cut showed that growth was checked, but very few plants were killed. Best Method Although no definite recommends-' tion can be given from the experimental work carried out, itappears that the most practical method of dealing with this weed would be to cut the plants before flowering and treat them with a mixture of sodium chlorate 1 part and ground limestone 10 parts immediately after cutting. This should be followed by another dressing in early February. In early March the areas should be burnt to clean up the dead and . dry foliage, and sown with grass seed together with basic slag at 3 cwt. per acre. > ' . ■ : ' Spraying is not practical, as water is often difficult to obtain and to transport on the steep country where eupatorium usually grows.

On many areas where eupatorium thrives, soil fertility is so low that it would be difficult for grass seed to establish. . Consequently, if a fairly tight sward cannot be obtained, eupatorium will no doubt continue to ap-

pear, thus necessitating continuous treatment with sodium chlorate or pulling to keep this weed in check.

E. B. GLANVILLE,

Instructor

in Agriculture, Whangarei.