Mediterranean Mustard, a New and Potentially Troublesome Weed in New Zealand

New Zealand Journal of Agriculture, Volume 96, Issue 2, 15 February 1958, Page 111

Mediterranean Mustard, a New and Potentially Troublesome Weed in New Zealand

By

A. J. HEALY,

Botany Division! Department of Scientific and Industrial Research, Christchurch

SEVERAL plants of Mediterranean mustard (Brassica tourneforti Gouan) were found in October 1956 on waste land at Timaru, their origin possibly being from seed accidentally introduced in Australian grain handled at the port. Because of the significance of this plant as a weed in cereal crops overseas attention is drawn to its appearance in New Zealand so that a close watch can be kept for any further occurrences and eradication measures adopted. The plants on which the identification was based were destroyed after specimens for record purposes were secured and the site will be examined this season so that any further plants can be eradicated.

A NATIVE of the Mediterranean region, this species has been accidentally introduced to other countries, where it has established and proved troublesome.

The weed appeared in Western Australia about 1914, but was not recognised as distinct from other weed mustards until 1928, by which time it was very aggressive, and in 1929 it was gazetted as a noxious weed in the

State. According to Currie (1936) this species was then “. . . the most important weed pest of West Australian

wheat fields”. It was thought to have come into South Australia about 1928, and according to Clarke (1939) it was widespread and aggressive, and by 1948 it was estimated that over 100,000 acres were infested. In Victoria the weed spread rapidly through the Mallee and was gazetted a noxious weed for the State in 1934, though according t<_ Sims (1945) it was not until 1936 that it became really serious. The weed was recorded from California, U.S.A., by Fleischman (1949), who states that it first appeared as a roadside weed in the Coachella Valley in 1938 and that by 1944 it had spread many miles along the sides of the highway. At the same time Californian farmers were warned to recognise the weed and take control measures.

Description An erect, hairy annual, the weed is 6in. to 6ft. high, with a long taproot and distinct turnip smell. The stems are erect, round in crosssection, branching, wavy, bristly-hairy below, and more or less hairless above. The basal leaves form a rosette Ift. to 2-2-ft. in diameter, are stalked, with 4 to 12 lateral segments (Fig. 1) and a large terminal segment often more or less three lobed; the lateral segments decrease in size toward the base of the leaf. The stem leaves are few and much smaller than the rosette leaves. The heads are many flowered, lengthening in fruit. The flowers are pale yellow and small. The seed pods or fruits are on stalks about Jin. long, the pod IJin. to 2-gin. long, containing 10 to 22 seeds. The pod has a long conical beak about a third the length of the pod proper, and carries 1 or 2 seeds near its base (Fig. 2). The seeds are small, globular, and pale purple-brown. How to Distinguish from Related Weeds Mediterranean mustard is liable to be confused with related cruciferous weeds already present in New Zealand; all have yellow flowers, a somewhat similar general aspect, and several a tumbleweed nature. Species which might be confused are listed on page 113 and a key which enables these weed species to be differentiated appears below.

KEY TO DISTINGUISH WILD MUSTARDS A representative weed specimen is taken and the pods checked against the first. option or statement under 1 below; if it does not agree with the first option, it is checked against the second option under 1, with which it agrees: pass then to 2 as directed by the number on the right-hand side. Check the first option under 2; the pods agree with the first option under this number, so pass on to 3 ; check against the first option of 3, and, as it agrees, pass to 4; check the first option of 4, and, since the specimen has “pods spreading from stem’’ and “stalk of pod very slender and J as long as pod’’, the plant is Descurainia sophia as given on the righthand side opposite this option. Any yellow-flowered mustard weed can be identified by working it through the key in this fashion, the drawings of the pods being used in conjunction. 1. Pod short, upper half globe shaped, bristly, much wider than lower half (Fig. 3 A) . . . . . . . . Raphanistrum rur/osum Pod short or long, upper half not globe shaped . . . .. . . . . .... . . . . 2 2. Pod lacking distinct conical beak (Fig. 3 B, D) . . . . . . . . . . . . . . 3 Pod with distinct conical beak (Fig. 3 L, K) 6 3. Pods Jin. to lin. long . . . . . . . . . . 4 Pods 2in. to 4in. long . . . . . . . . . . 5 4. Pods spreading from stem: stalk of pod very slender, about J as long as pod (Fig. 3 B) . . . . . . . . Descurainia sophia Pods closely pressed to stem: stalk of pod stout, short (Fig. 3C) . . . . Sisymbrium officinale 5. Upper stem leaves cut to narrow segments: tumbleweed (Fig. 3D) . . Sisymbrium altissimum

Upper stem leaves not cut to narrow segments (Fig. .3 E) . . . . . . . Sisymbrium orientate 6. Pod transversely jointed, not opening by 2 valves (Fig. 3 F, G) . . .'. .'. . . . . 7 Pod opening from below upward by 2 valves, not transversely jointed (Fig. 3 C) 8 7. Pod narrow with shallow constrictions between seeds : easily broken into segments (Fig. 3 F) . . ... . . Raphanus raphanistrwn Pod broad with deep constrictions between seeds: not readily broken into segments (Fig. 3 G) ... .. •• Raphanus maritimus 8. Pod tightly pressed to stem (Fig. 3 H) . . . . . . 9 Pod spreading from stem (Fig. 3 K, L) . . . . 10 9. Stem hairs downward directed (Fig. 3 H) . . . . . . . . • ■ Hirschfeldia incana Stem hairs spreading or absent (Fig. 3 I) . . . . . . . . . . . . Brassica nigra 10. Pod valves 3 to 7 nerved, beak half as long as pod (Fig. 3 J) . . . . . . . . Sinapis arvensis Pod valves with middle nerve only (Fig. 3 K, L) 11 1. Upper stem leaves stalked or with stalklike base (Fig. 3K) . . . . . . Brassica tourneforti Upper stem leaves rounded at base or with base clasping stem (Fig. 3 M) . . . . . . 12 12. All leaves without hairs: flower buds overtopping the open flowers (Fig. 3 L) Brassica oleracea Lower leaves at least bristly: opened flowers overtopping the buds (Fig. 3 M) Brassica campestris

SPECIES WHICH MIGHT BE CONFUSED WITH MEDITERRANEAN MUSTARD Brassica campestris (wild turnip) B. nigra (black mustard) B. oleracea (wild cabbage) Descurainia sophia (flixweed) Hirschfeldia incana (hoary mustard) Raphanistrum rugosum (turnip weed) Raphanus maritimus (sea radish) R. raphanistrum (wild radish) Sinapis crisis (charlock) Sisymbrium altissimum (tumbling mustard) (S', officinale (hedge mustard) S. orientate (oriental mustard) Why Regarded as a Weed From Australian experience the following reasons are given why Mediterranean mustard is regarded as a troublesome weed: — 1. The free-seeding habit and quick maturity enable it to spread rapidly.

2. A robust, spreading initial rosette of leaves which crowds out other plants. 3. The ability to mature earlier than a wheat crop in which it is growing. 4. The tumbleweed character at maturity; the stem breaks off at ground level and blows with the wind. 5. When the weed is present in a wheat crop its early maturity allows the stem to break off and the dried plant to blow across the top of the wheat crop, broadcasting seed as it tumbles. 6. The dried stems are difficult to handle with harvesting machinery. 7. The dry, wind-blown plants pile up against fences and plantations, fill up drains and depressions, and could constitute a fire hazard.

8. The plant grows equally well on roadsides, in waste land and cropped land, and, owing to its tumbleweed character, it can spread readily from waste land to cropping, areas. 9. While some farmers state the plant is grazed, others contend that it is unpalatable and avoided. Means of Spread The tumbleweed character at maturity enables the weed to spread widely on waste land and individual properties, and highlights the need to prevent seeding. Transfer of farm produce as hay, chaff, grain, etc., has proved important in Australia in the spread of the weed from district to district. In Western Australia it was found that second-hand sacks were significant in spreading, seed from farm to farm and district to district; this spread was counteracted by dipping the sacks in boiling water or into a 5 per cent, bluestone solution, these treatments killing the seed. Means of Control The following methods of control have been used in Australia: — 1. Pulling and hoeing scattered plants. 2. Clean fallow. 3. Taking heavily infested land out of cropping and using it for grazing. 4. Refraining from sowing of crops until as late as possible to allow seedlings to germinate with the autumn rains.

5. Use of hormone weedkillers: Meadley (1953) reports that in Western Australia the amine salt of 2,4-D at 6oz. acid equivalent per acre applied at 1 to 2g gallons per acre by both aerial spraying and land spraying proved successful in controlling the weed. Literature Cited Clarke, G. H. 1939. Important Weeds of South Australia, Part 11. Department of Agriculture, South Australia, Bulletin No. 343, pp. 43-45. Currie, G. A. 1936. A Report on a Survey of Weed Problems in Australia. C.5.1.R., Australia, Pamphlet No. 60, p. 30. Fleischman, G. C. 1949. A New Weed Brassica Appears in California. Department of Agriculture, State of California, Bulletin, vol. XXXVIII, No. 3, pp. 111-113. Meadley, G. R. W. 1953. Journal of Agriculture, Department of Agriculture, Western Australia, vol. 2, No. 3 (3rd ser.), p. 293. Sims, H. J. 1948. Wild Turnipa Serious Mallee Weed. Journal of Agriculture, Department. of Agriculture, Victoria, vol. 46, No. 2, pp. 82-86.