WEEDS.

Northern Advocate, 5 August 1924, Page 3

WEEDS.

THEIR HABMFUL EFFECTS.

HOW TO COMBAT THEM,

Mr W. A. Given's lecture on weeds, -delivered in the Whangarei County Chambers' on Friday night, served to convey a great deal of useful information to a fairly large audience.

The lecturer said that Dr Brenchley, of Rothamstead, classified weeds into two groups—weeds of arable land, and weeds of grass land. He defined the former as "any plant other than the crop sown,'' and the latter as '' a plant of low feeding value,' 7 or as "a plant that grows so luxuriantly or plentifully that it chokes out other plants that possess more valuable nutritive j properties." For the purpose of the lecture a weed might be broadly defined as an undesirable plant. Weeds followed with a. stubborn persistence in the footprints of man. Wherever he J pitched his tent, or wherever he built I a more pretentious home, weeds would J entrench themselves about him, and as i often as he cultivated his land weeds at once challenged possession with the sown crops. In spite of man's labours, the intruders would continue with an almost uncanny persistence to harass and perplex him, and to place in Ms way a serious obstacle to the eco- j nomic subjugation of the soil. In the prolonged struggle for existence the I ■weeds had waged a winning battle, | mainly because they had eliminated the characters accessory to the struggle, and had at the same time abnormally developed those characters more essential to the development of a robust constitution and of a quick and certain reproduction.

Directlv or indirectly weeds must cost the New Zealand farmer a large annual sum. They were tacitly declared enemies to agriculture, and it was therefore a duty to so study their characters and Txa"bits as to "be better enabled to take effective measures against them. So far the weed question liad not "been given its proper measure of study. Literature on the subject was Still very incomplete. In the case of several of the worst North Auckland weeds there was little "beyond a bare mention. Tn Shaw's book, for instance, A such weeds as blackberry, gorse, and oxalis cernna were left alone, perhaps 'because there was no "All "Bed Tonte'' "to their eradication, j HARMFUL EFFECTS. The harmful effects of weeds could i be classified under a number of headings. They seriously interfered with' the natural functions of useful plants ' by overcrowding and "by shading them, j "Weeds generally grew much, more quickly than economic plants did. They shut -j out the sunlight, they interfered with the free circulation of air about the plants, and they limited the amount of available root space. Some weeds formed a kind of mosaic on the surface of the ground; for example, swine cress (particularly at the present time) and catsear. Mt Given showed a specimen of catsear which would flatten out over a square foot of ground, and mentioned an instance in which catsear "had choked out perennial ryegrass.

"Weeds might provide shelter foT injurious insects, and act as temporary hosts for the spores of fungoid diseases. Diseases and pests affecting cruciferous plants such as turnips and cabbages were seriously -encouraged by the presence of related weeds such as> winter cress, wild mustard and shep herd's purse. Winter cress, Mr Given added, had crept into this distract during the last few years and was making rapid headway. It had a fairly long growing period and belonged to the cabbage tribe.

"Weeds robbed growing crops of their due. .share of moisture and plant food, for weeds appropriated the same soil elements as did growing crops. They were generally remarkably well equipped for this work, as they naturally developed a more vigorous root system and one that was able to penetrate to greater depths. Amaranthus retroflexus and phytolacca ■decandra (ink weed) might be quoted as examples. . The former was very prominent in the High School gardens and made rapid headway during the summer holidays. It had a strong root and was a bad weed in light land if neglected.

Weeds were rarely of much value as fodder plants. Farm animals generally fotwnd them unpalatable or distasteful on account of the prevalence in their-substance of bitter juices and on «e<eourtt of their early development of woody "tissue. Milk weed, sorrel, and oxalis -oernua might be quoted as examples.

"Weeds •aSfted much*to the labour of cleaning grain and seetf. Seed containing even a small percentage of certain noxious -weeds would be dear at any price. The work of removing most weed seeds -/rom 'bulk samples of grass, and clover seed was aggravated by the fact that there was not sufficient differentiation in .{faze between the economic and the weed seed.B. Dodder, a parasite on elover, wa«a a nuisance in -white clover seed, but it was now removed t>y a process of magnetic separation, which was described in a recent num'ber of tlkf "Journal of Agriculture.''' The dodder seed had a slightly rougher skin than the clover seed, so that when a quantity of seed was dusted with a

| magnetic materia! the-dodder seed at j traeted mora of St the clovei seed did. The use of electricity thee attracted tlwj dodder seeds and dreis them away from .the clover. Weeds increased (the labour and expense of inter J tillage, for to allow I them to grow unchecked on cultivated land, even far a short period, was a grave error. They 'were quick to mature, and in many cases the'r store of food was sufficient to ripen the undeveloped seeds, 'even after the plants had been cut down. For greater [ safety they should never be allowed [ to reach even 'the flowering stage, a ' measure which unfortunately was not | always practicable. Fumitory, a long ! straggling weed that was particular--Ily common in Whangarei, was remarkably quick to mature. "It is no sooner out bf 'the ground than it flowers," said the lecturer. "I know nothing like it. It is especially a nuisance to the cottage gardener." Mr Given added that he had a suspicion that fumitory had at least three or four generations in twelve months. Swine cress, a smothering -plant, and spurrey, might also be mentioned 'in 'this category. Spurrey radiated m aill 'directions from a central root, and it was a prolific seeder, the seeds "being close to the ground. Some weeds were parasitic or robber plants —for example, broom rape and clover dodder. They did not function ■as did other plants in making starch •and other plant foods for themselves. They attached themselves to suitable host plants, and extracted the food manufactured by the latter, which as a consequence might be depauperated, or evien destroyed. Mr Given stressed the prevalence of broom rape —a dusty-looking spike, he said, ' which attached itself to other plants j ! and would' not germinate unless it had j a host alongside. j

I Some weeds on account 6f the poisonous juices that they contained were directly harmful to farm animals. I'The apple of Sodom (solanium sodomj aeum), the thorn-apple (datura strajmoriium) :and 'black nightshade (soflanum nigrum) were examples. Black nightshade, the 'lecturer said, was the only one of the three he had peon growing in Whangarei, though a High School pupil last year had been able fo tg,*ke to him a specimen of apple of Sodom. Solanum nigrum was a native jof New Zealand, 'belonging to the potato tribe. The thorn apple was a very poisonous and dangerous weed. ! Some weed seeds possessed long-thin 'bristles, wliicli might do serious harm by finding a lodgment in the mucous membranes of the throats of animals, ! and might even form hair balls inside | the animal. FeStuca bromoides was Jan example. It was common in the district, growing particularly freely at Kensington Park. ' USES OF WEEDS. Weeds dug into'the soil served ikhe same purpose as green manure. Even weeds that were hoed up and left to chance on the surface must in time decay, and thus furnish useful humus. "Weeds might be 'the means of retain- j ing nitrates in 'the soil, especially dur- j ing bare fallowing. The weed roots | Tcept taking in soil solutions and so the I solutions were ndt allowed to waste. Weeds of a soft j wooded nature when gathered together and mixed with a J [Tittle soil formed 'a valuable compost. It. was, however, not always a safe 1 process to form a compost of weeds, for "the heat generated might not be sufficient to destroy the vitality of the seeds, j It was just possible, the lecturer J said, that a few of the weeds riiight j some day be put to a useful purpose. ! Beta marifima, a wild plant of the j seashore, had furnished the mangel, j Certain organs of the wild brassiea j oleracea w,eTe exaggerated, with ' the j development of Brussels sprouts. Sufch j weeds dandelion, spurrey, water- j •cress, deadly night-sha'de, aconite aiftil J poppy had been deliberately grown or ! harvested for economic purposes. Many choice garden flowers were weed derivatives. The little veronica agrestis («jt speedwell), which was prominent iivst now, was quite a pretty flower. Ferhaps the best service of weeds to ttciti 'lay in the fact that they enforced tillage operations, which in turn went ,a long way towards general soil improvement. Tillage meant r«oration, better drainage, conservation of moisture, send "-all that's 'good." | DISTRIBUTION OF WEEDS. !

Few !STew "Zealand native plants, Mr. Give-n said, had entered the weed class; they evidently resented artificial interference resultant on methods

of soil cultivation. Those tiiat might be inenthioaicd as weeds were haiorffgis alata, which was common on the roadside; tauhiiua, or Tvireweed-; makomako, which came up prominently after •>, burn; towai,. which -was rather common', and gnaphahtim keriense, or cudweed, a composite weed belonging to the daisy j family, which threw a lot of seed. v j Most of the worst weeds hud been introduced with important soeds in varions cargo commodities. New Zealand, he believed, was particularly afflicted. The general intolerance of the native plants to cultivation methods had left a clear field for the incursion of Wfjeds.

I ■ ! Moreover, the Dominion's isolation ' • ; might in part be responsible for many i j of the prominent weeds by compelling r New Zcalandess to take so many mixed cargoes. [ Animal manure might be an instru- - ment for weed seed distribution, for the exposed manure furnished an ideil arrestment for errant seeds, many of which were probably unaffected by the ! heat of the fermenting heap. High winds also were doubtless responsible for much seed dispersal. Regional storm columns must be capable of carrying seeds almost any distance. Water also would oarry them. Apart from these adventitious agencies, most weed seeds were specially adapted for the purposes of survival and of reproduction. Many weeds were low-grow-ing and quickly reached maturity. Fertilisation was quick and sure, and the ripened seeds Ml directly into the soil. A few seeds were winged, and thus assisted in distribution, for example, toad flax (linaria vulgaris) and perhaps spurrey (spergula arvensis). Some seeds had hairy or woolly appendages, which assisted in transport, for example, dandelion, catsear, ground sel, willow-herb, and thistles generally, jln a few instances weed seeds were ! forcibly ejected from their cases, fo'r example, gorse, crane's bill, and the milk weeds. Some weeds were so small and light that they were readily transported by air movements, for example, broom rape and poppy. By swallowing certain seeds and voiding them intact birds and animals might be the instruments of dispersal. Indeed, the succulent matter surrounding some seeds would appear to function for this purpose. A few seeds under moist conditions j exuded a mucilaginous substance which aided the seed in sticking to any object with which it might happen to [ come in contact, for example, ribgrass

and some weed seeds of the cabbage j 0 tribe. Seeds, and sometimes fruits, '• were occasionally provided with spines or barbs, or with rough excrescences, which enabled them to become attached to the coats of passing animals. c Such were bidi-bidi, goose grass (some--3 times used for adulterating coffee), 1 danthonia, sedges and wild oats, dock, 1 wild carrot, and corn buttercup. The scarlet pimpernel (anagallis arveusis) developed a neatly globular capsule; at 5 maturity the top of this lifted cleanly ; | off, after the manner of the cultivated j portulaca, and the seed was gently . shaken out by air currents. 1 Concerning the carriage of seeds in : the coats of passing animals Mr Given I quoted the following passage from

''The Garden," of April 5 last:—"One of the most remarkable collections of alien flora in the British Isles—pos- . siblv in Europe—is to be found, nor j in a delightful country garden, but in a black,-soot-besmirched northern manufacturing centre. On a piece of waste j ground in the premises of one of Bradj ford's corporation .sewage works, Dr. ; Bruce, of Oxford University, the fainj ous botanist, had the pleasure of classi-

. fying more alien flora than at any i other spot he has yet visited in a j life-long devotion to botany and rej search work, while Dr. Stelling, of Zurich University, the famous German j botanist, expressed himself amazed at j the number of foreign plants found at | the place in question. No fewer than 500 flowering plants were found, and for a time their presence was 'hard to account for. The agent was the wool from Australasia, Argentina, and J Canada." j Some weeds, the lecturer continued, j spread and were perennlalised by the j development of underground stems or j rhizomes. Examples were C&'liforriiayi j thistle, bracken, sorrel, couch grass and t biml-weed. Sub-aerial runners or | stolons might be developed, as in the j case of creeping mallow and creeping j buttercup. Mr Given showed a piece jof creeping mallow taken from the '■roadway at Kensington Park. Though many motor-ears had passed over it, he said, it had still been holdmg oil-; it was a hard weed to get rid of. Onion couch (arrhenatherum tuber- j osum), a variety of tall oat grass, de- I swollen internodes at or just | beneath ground level. Those, if de- ! taehed. were capable of reproduction, j The bulbous buttercup (ranunculus ' bufbosus) developed a swollen stem » j base, from which arose young buds, ' ■ which, formed new plants by sending up j

aerial shoots. A few weeds —garlic ami oxalis cernua, for example —fie velope-cr bulbils or bulblets, which ou being detached were capable of produc-

ing new - plants. ME AS (7 REN AGAINST WEEDS,

The w.ned question, said Mr Given, offered a -wide field for intelligent observation rt'ud research, and thereby a'one migh't ?they hope to formulate basic facts -and principles on which to ,-! develop thft -surest measures wiMi the >1 least expenditure in capital and labour. <3ood drainage ;-.md rational manuring ■M ore helpful in uhat a more vigorous I iV'Oivth 9»d a r.vure resistant constitution was developed in the crop plant.

Where the land was not in permanent pasture crop rotation was a good measure, demanding as it did periods of enforced cultivation. "Weeds should, as far as possible, be prevented from seeding, for many strong-growing perennials once established could not be completely eradicated under a three years' limit. Good bulk seed only should be sown; it took very few seeds of a noxious weed to vitiate a sample. Spudding —severing the wje-ls a little below ground level —had been recommended as a measure, where it was not a case for the scythe or the mower. The object was to debilitate t l ie we?.! by destroying its leaf functions. Professor Shaw, whef advocated the use of this measure, said: "Many farmers look upon the use of the spud as a chimerical idea. They object to it op the score of the cost of the labour involved in its use; while the truth, in the mind of the writer at least, is beyond the shadow of a doubt that by no other conceivable means can freedom

from noxious weed intrusion be maintained so cheaply, or, indeed, be maim tained at all."

Where possible the use of smothering crops such as clover or lucerne might be a useful measure. Sheep might be commissioned as a measure against some 'weeds. In such cases they should be grazed on limited areas. Chemical weed killers such as sulphate of iron and copper, common salt, carbolic acid, petroleum products such as kerosene and benzine, unweathered gas lime, caustic soda, sulphuric acid and arsenite of soda had been used with

some measure of success. Once undertaken, the work of eradication should be as thorough and as expeditious as possible. When once a state of cleanliness had been secure 1, the maintenance of it thereafter should be as perfect as possible. The farmer himself could, if he would, Tender valuable service in regard to the weed

question, for he was in the best posi

tion to study the habits of growth anTl the associations of the "vyorst weeds. Mr Given added that the farmer was very mean in his attitude towards weeds; he should help far more than he did. SOME UNDESIRABLES. New plant arrivals should be viewed with suspicion and their identities at once established. If t'here was any doubt about new plants they should be destroyed. Some plants that had recently appeared in this district might be mentioned. Aster subulatus, a

member of the daisy family, which

grew to be a fair height and produce! a lot of seed, was one that he had only noticed during the last two years. It

was a px-etty bad weed in parts of New South Wales. German ivy (senecio mikanioides) was a weed belonging to the groundsel family that did well in the district. In North America it was prized as a pot plant. Psoralea pinnata, which produced a handsome flower, was common on the Maungakaramea Road, and also at Parua Bay. It seemed to do well in the district. Ho believed, however, that it had been declared a noxious weed. It grew as much as 8 or 9ft. high and produce.! blue pea flowers. Tolidago canadensis, or golden rod, also did well—too well— and was hard to suppress. It should be burnt. Pennisetum longistylum, a. grass which came up in tufts,, could easily be done without. Mirabilis .Talapa (marvel of Peru) was a weed that was growing nicely in Norfolk Street. Carduus marianus, a spotted thistle, was to be seen flourishing in a section off Manse Street. Tar weed, with its yellow flowers, was a recent arrival and an unwelcome one. It was no good for fodder. It was spasmodic —thick and plentiful one year anl scarce the next year. The year be-

fore last it had been very common. It was said to depauperate the ground to

a great extent.

"With the help of sketches prepared by Master Reynolds the lecturer went on to discuss broom rape. Brenchley remarked, he said, that "broom rape deserves more attention than it usually 1 gets, for many farmers fail to realise the life history of the plant, and do not connect ihe poorness of their second cut of clover with the armies of dingy brown spikes that spring up in "their fields." He had seen clover with I broom rape 011 every root. Broom rape had a tiny seed, and as many as 9GO seeds had been counted in one capsule, a-nd perhaps there would be 100 capsules on a spike. Broom rape was found wherever there was a host plant; almost anything would do, though the parasite would have 110 contact with green peas. The damage it did wt>s not perhaps fully appreciated. The local climate suited it, and it was increasing at a rate to cause anxiety. Clover dodder was perhaps not present in the district. It germinated in the ground, threw up a shoot, and worked up round and round the host, then severed the connection with its root and lived on the host plant. Oxalis 'eernua was mentioned as a bad weed. With its thickened root It withstood drought, and it was so con- J structed as to make pollination almost j certain, and was therefore a free seeder, j It was never mentioned in books, bur ! it was a particularly bad weed in sour, j flat soil. Crabgrass (panicum sanguinale) was particularly prevalent in light warm soils. In the school gardens, for instance, it would take charge during

"'the six weeks of the summer holidays. [ It spread by means of runners, which rooted at the nodes, or joints, and it also developed a remarkable mass of fibrous roots, very long and deep. If a little of t'he root Avere left in the ground it would go ahead. It was a j prolific seeder, and sparrows might be j seen swarming on it. In light soils the seeds would lie under the ground 1 1 and probably survive for a number ! years. ; Sorrel (rumcx acetosella) flourished in dry, open places, especially on lighter soil. It was really an annual, Avhich seeded freely, but the underground runners also caused its persistence. Lime was a good measure against it. Toa toa annua (annual blue grass) was a bad weed, which had more than one generation in twelve months. Nut grass was bad in some parts of Auckland, where it could be seen lifting up the pavement. It was a harsh little grass, ami it was fortunate that there was apparently none of it in Whangarei. Flea bane (erigoron canadense) was beautiful when cultivated. Cattle would eat it and it was good on reclaimed land. It would help to consolidate swamp land if cattle were fed on it. Blackberry, of course, was wellknown, and according to t'he "Journal of Agriculture" goats properly graced j on it would eradicate it. Cape weed J (cryptostenuna calendulacea) was mentioned as a weed growing to a large size and producing rather pretty Cowers, and a few more weeds were noted and identified as plants to be avoided.

Specimens of many wp?ds were exhibited, while drawings of others were shown, and these added much to tin; interest of a very notable lecture, the conclusion of which was the signal for hearty applause.

Next Friday Mr Given will deliver tlio last lecture of his series, the subject being "Our native flora."

Competition has existed in some places as. to the discovery of the man deemed to be the meanest yet. One Palmerston North resident claims to have discovered one that will eclipse all comers (records the local "Times"). The other evening the resident paid a visit to some frineds, mid left his bicycle standing up against the fence. When he came for the machine a little later he found that the light had gone out, and upon investigation discovered that someone had removed the generator from the acetylene lamp, taken every bit of carbide from it, and carefully replaced the fitting. This certainly takes some beating.