RAGWORT DESTRUCTION.

Pahiatua Herald, Volume XLIII, Issue 13161, 20 January 1936, Page 2

RAGWORT DESTRUCTION.

EXPERIENCE IN WAIKATO. IDENTITY OF PAP A.SITES. The identity of a small fly that has been found to attack and destroy ragwort leaves has recently puzzled agriculturists in the Waikato and reports from different parts of the district indicate that the ffy ha,s caused damage to ragwort plants over a. wide area. It was suggested in s-ome quarters that the liy in question was a parasite that had been liberated by the Cawthron Institute, but this is not the o:-v.se (says the Waikato Times). The fly has been particularly evident 1 1 l the Matamata district and a. keen interest in the position was taken by the Matamata County Council, its engineer forwarding specimens of the fly to the. Cawthron Institute. As a result of a communication sent to the institute by the Minister of Agriculture, the Hon. W . Lee Martin, the Minister has received a letter explaining the position and giving further particulars of the insect and the ragwort- problem. The insect concerned, states the letter, is a small leaf-mining fly. the scientific name of which as Phvtomyza a.tricornis. The fly lays its eggs under the epidermis of the ragwort leaves and the larvae on. hatching tunnel exte.nsivo.ly between the upper and. lower leaf surfaces. It was found that an insect native to New Zealand was attacking the Cinnabar Moth caterpillars and it is to this that the non-success of the moth is attributed. The. ragwort seed-fly Pegohvlemyia with which the institute is at present- working promises to be a valuable agent in the control of the spread of ragwort. In laboratory experiments at the institute it has been found that a single larva of this fly is capable' of destroying 100 per cent, of the seeds in. thei infested head. The institute has now an open permit- for liberating this insect, the letter concludes, and though, supplies are not large the institute hopes to make a, start in regard to field liberations in a selected area, or areas during the present season. The announcement that the species of fly in the Waikato is itself liable to be destroyed by a natural parasite will be a disappointment to* many wlio had envisaged the entire destruction of the weed in the very near future. However, it is doing much to keep the weed in check in some quarters and in. co-operation with the parasite now being prepared by the Cawthron Institute it should do much to bring about the elimination of the menace of ragwort in the Dominion. AN ENEMY TO RAGWORT. The fly under favourable conditions may complete 15 full generations per \ ear and as it is capable of laying a large number of eggs it is capable of extensively damaging ragwort : indeed, it lias been shown that in very heavy infestations the larvae mine so thoroughly that rosette ragwort plants are completely destroyed in some cases, and ill other more advanced stages injured to such an extent that they are incapable of yielding normal numbers of seedheads. However, these experiments were conducted under conditions excluding the fly’s natural parasite which. unfoiTunately, is widely distributed throughout New Zealand This parasite emerges generation for generation with the fly and gradually asserts itself till the fly is controlled to such an extent that it is no longer of much value as a means of aiding in the control of ragwort. PARASITE CONTROL OF RAGWORT.

In speaking of the liberation of parasites the letter states that the Cinnabar Moth was liberated by the institute some years ago in the main areas of ragwort infestation of the Dominion, and though it showed great, promise in the initial stages of establishment, it gradually died out in most districts until now then* are only a. few places where it still exists.