HILL PASTURE WEED

Southland Times, Issue 23942, 7 October 1939, Page 14

HILL PASTURE WEED

Control of Biddy-Bid METHODS OF REDUCING SPREAD One of the worst weeds in many hill pastures of both the North and South Islands is piri piri, or what is commonly known as Hutiwai, or biddy-bid. Piri piri belongs to that group of plants which spread by means of overground runners. These root as they grow, and require a close-eaten or bared-out turf to do so. - . It can safely be said that in the South Island the spread of the weed has been largely due to the rabbit pest, for during the Great War period many of the hill country farms became badly infested with rabbits, and it was a common sight to see whole faces of countryside, and especially sunny faces, eaten bare of grass. Replacement of herbage on these faces was, in the main, by piri piri. There are other causes of the spread of the weed in the South Island, and no doubt the continual burning of the tussock country has been one of them. In the North Island, except in certain localities the rabbit pest has never been such a menace, and the spread of piri piri is due mainly to close and continuous grazing by sheep, making conditions ideal for the spread, of the weed. Sheep will not penetrate into patches of piri piri, and will graze only the grass arofind the edges, while cattle are not averse to eating the weed, and will readily graze in the patches. CONTROL IN PASTURE For successful spread the runners of piri piri must have full light, and by spelling pastures for a period the runners are kept from the ground surface and run along the top of the grass as loose, trailing stems. Control is effected by systematically spelling areas during the summer to allow the grass to lift the runrters up, forcing them away from the ground. The heavy stocking of such areas with cattle in the autumn and in the winter results in the cleaning up of a great deal of the weed which has been prevented from rerooting. By working over the farm, spelling a paddock or two at a time, it will be found that the weed is lessened to a large extent, and further, that the pastures will have benefited considerably by the spelling. It is necessary to repeat this process, and a scheme of systematic spelling and heavy cattle stocking of paddocks in turn, in order to repeat the process every five or six years on each paddock, will be found beneficial to the pastures to a marked extent, as well as controlling piri piri. The topdressing of pastures is also of extreme benefit in controlling piri piri, and this is due to the increased carrying capacity and the strengthening of the grass and clover sward. Pastures which have been badly affected with the weed and which have been topdressed for two or three seasons are seen to have benefited considerably, and the piri piri is weak and gradually dying out. CONTROL B’.' INSECTS The only native insect attacking piri piri to any marked extent is a species of mealy bug, and this infests the roots, but it is only occasionally that this insect markedly checks the weed. During the last few years an insect known as the Chilian saw fly has been imported from South America and is being bred at the Cawthron Institute, Nelson. Field liberations have been made in Taranaki and in Poverty Bay, and the insect is being concentrated to build a sufficient population under field conditions. Under experimental conditions the saw fly has considerable powers of control, but it is a slow breeder and will require time to build up its population. The work of field establishment cannot be hurried beyond importing, rearing, and liberating the insects in countless numbers. Apart from this, the matter lies with the insect itself and with its environment.