Control Of Grass Grub And Porina

Press, Volume CVI, Issue 31161, 10 September 1966, Page 8

Control Of Grass Grub And Porina

While in general D.D.T. superphosphate pelleted materials were slower acting they were fully as effective for grass grub control as the materials containing D.D.T. used earlier, Dr. J. M. Hoy, director of the Entomology Division of the Department of Scientific and Industrial Research at Nelson, told a meeting held in Christchurch last week to consider the grass grub and porina problem in Canterbury.

Called by North Canterbury Federated Fanners and presided over by the chairman of its meat and wool section, Mr W. N. Dunlop, it was attended by representatives of Federated Farmers from South, Mid and North Canterbury, the Entomology Division and Crop Research Division of the Department of Scientific and Industrial Research, Lincoln College and the Department of Agriculture.

For porina control the pelleted formulations were also slower acting and in some areas like Takaka they were not so good, Dr. Hoy said. However, Mr J. M. Kelsey, officer in charge of the Lincoln sub-station of the Entomology Division, had evidence that in the second season they were just as effective against porina. Dr. Hoy said that in the near future new restrictions might apply to the use of these materials. These could stipulate that not more than 50 per cent of a farm should be treated in one year and that in any one paddock not more than 21b of active ingredient of these materials should be used to the acre. If farmers complied with these restrictions and those applying to weather at time of application and the condition of the pasture, then there should be no appreciable residues in export products.

Among the range of organophosphorus materials available, Dr. Hoy said that there were materials that would give effective control in the season that an infestation occurred—in other words a quicker measure of control—but the economics of their use was not as good as for D.D.T. Mr F. C. Allen, an officer of the research division of the Department of Agriculture with particular responsibilities for pests and weeds, I said that his feeling was that farmers wotdd have to become more sophisticated in their control methods. He thought that farmers would have to sample their paddocks to determine whether or not they had a problem

and in the future they might be able to use chemicals only when in fact there was a problem there. At a later stage in the meeting Mr R. C. Jensen, lecturer in agricultural economics at Lincoln College, said an important question was related to the production of beef, sheep meat, wool or butterfat which would be obtained if pastures were treated as compared with if they were not treated. At about £3 an acre for treatment (the cheapest organophosphate costs £3 10s), and this charge recurring annually, the cost would amount to the gross margin from some 1} ewes. This led him to believe that farmers were going to have to live with these grubs much more than in the past. It was necessary to define a level where it was economic to come in with insecticides for treatment. It would be much higher with the more expensive organophosphates. These could not be used as a preventative measure. Farmers might nave to consider using control measures say, every six or 10 years. On the subject of time of application of newer D.D.T. formulations, over which it was alleged there was considerable confusion, Mr Kelsey said that in the past farmers had been advised to put on the older forms of D.D.T. as early as possible in the new year, in February or March, but with the pelleted materials the latest recommendation was that they should go on in October-Nov-ember. The idea of the Octo-ber-November application was to catch the young porina cater pillars as they were hatching out and in principle this was sound, but Mr Kelsey considered that this period was too restrictive with long residue materials such as D.D.T. He emphasised that rainfall was most vital to get the pellets to work and at that time of the year it did not always rain very much. But with organophosphates it was quite a good idea for porina control to put these materials on then as they would give quite good control.

Asked about what could be put on now in pelleted form and would give grass grub control, Mr Kelsey said that materials of the D.D.T. lindane group put on now would, in a great many cases, give no benefit whatsoever this year,

but would give control for the two succeeding generations. The fact that applications now would not be effective was due to the early cessation of feeding in the case of the majority of grubs. Mr Kelsey said that recent trials in the Te Pirita area using D.D.T. preparations applied on March 23 and at Carew on April 14 had shown no significant differences over the untreated controls.

Mr A. R. Dingwell, fields superintendent of the Department of Agriculture in Christchurch, said he thought that the reason for the recommendation that granular D.D.T. superphosphate should be applied not later than the end of October was as a preventative measure so that it could be expected to give some effect by the following March. Dr. Hoy. said that for most effective distribution there ideally needed to be separate distribution of the D.D.T. and fertiliser.

Mr Dunlop asked what course was open to the farmer who had left the application of a chemical too late and actually had damage now. Mr Kelsey said that there was Terracur. It would, however, last only a single season. At Carew, Terracur had reduced the grub population where there were 200 grubs to the square foot to 48 in 40 samples, Diazinon to 86 and Lindane to 124, whereas in the control there were still over 600 j At Te Pirita where there were also more than 200 grubs to the square foot Terracur had reduced grub numbers to 55 in 40 samples compared with 641 in 40 samples in the case of the control. Diazinon was again in second place. These results had been supported by pasture recovery. Dr. Hoy said they were not quite satisfied that these results were reproducable. Factors involved were the short life of the chemicals and the unknown effect of weather, including rain. On withholding periods—the periods that stock should be kept off a pasture after it had been treated —Mr Kelsey said that while a chemical which had a nil withholding period was very safe, it was still important to keep stock off the pasture while it was being treated, for although it would not kill the stock the effectiveness of the material would be reduced if some of it was eaten by stock. On the question of the upsurge of porina and grass grub in the past season, Mr Kelsey said he had been foolish enough to make a statement last year about the relative incidence of grass grub and porina then and a number of years previously. In 1945-46 one in five paddocks would have been badly enough infested to conduct a trial on, he said. But on the basis of the average for the previous five years he would have had to go to just over 200 paddocks to find one bad enough for a trial on porina and to just under 400 pad-

docks to get one for a trial on grass grubs. This year, however, he would be able to do a trial on grass grubs and porina in about one in every 10 or 15 paddocks, which meant that the position was not a lot better than in 194546.

Dr Hoy said he thought that with grass grub it was possible to have a bad year for the grubs but this did not necessarily have a bearing on what the position was going to be in the following year. With porina, however, there had been a slow upward trend in the numbers per square foot. Mr Kelsey said that there were always exceptions to the rule. At Te Pirita there had been grass grub and porina in the native tussock but there had been no porina in improved pastures on a farm there over the last eight years.