Integrated approach to grub problem needed

Press, Volume CXIII, Issue 33252, 15 June 1973, Page 14

Integrated approach to grub problem needed

Grass grub should be considered as a factor in the overall management programme of a farm and use made of all the various possibilities that are available for reducing its damage to a minimum.

The accompanying item on a field day on the grass grub problem in Mid-Canterbury has been contributed by A. G. Leith, a farm advisory officer with the Ministry of Agriculture and Fisheries in Ashburton.

Mr P. G. Fenemore. a scientist from the Entomology Division of the Department of Scientific and Industrial Research, Nelson, made this comment during a recent Ministry of Agriculture and Fisheries field day held on the property of Messrs G. A. and G. D. Rountree at Alford Forest, Mid-Canterbury. Mr Fenemore reviewed the current grass grub research being conducted in the Entomology Division and other divisions of the D.S.I.R. He said that the prospects of improving on currently available insecticides are not bright, but that testing will be continued as long as new prospective materials become available. The small number of these which have reached the farmer all have their limitations, such as high toxicity to humans and wildlife, inconsistent performance and high cost. Referring to biological control and the search for possible parasites for use against the grass grub. Mr Fenemore said that there is very little prospect of success with this type of procedure, but promising material would be considered. The major interest at present, he said, is concentrated m development of pasture and crop plants which are resistant to the feeding of the grass grub and other insects. Plants can be tolerant to damage, or can contain substances which are distasteful or even toxic to insects. Lucerne and Lotus pedunculatus have shown more resistance than ryegrass. red clover and black medick. in spite of the fact that grubs are strongly attracted to them Chemicals present in the roots

include saponins, which depress grass grub feeding, and these may be the factor responsible for resistance, but other chemicals are also being tested. Mr Fenemore outlined a new development, still in the early stages. This is the use of a technique where the reactions of the grass grubs to a whole series of chemicals can be recorded, using minute electrodes attached to nerves. This allows rapid screening of many chemicals, but it is expensive in time and does not tel) whether a chemical is attractive or repellent. The Applied Biochemistry Division of the D.S.I.R. is continuing work on the chemical and other aspects of grass grub nutrition. Mr Fenemore said that moisture and temperature effects of the soil are being studied, and one factor that has emerged is that Canterbury grass grubs are more drought resistan, than grubs from Nelson Saturation of the soil with water has no effect. A lesson learned from the D.D.T. era, Mr Fenemore added, was that research would continue even if an immediate practical answer, as D.D.T. had been, was found. Failure of this answer would not then leave us years behind in research aspects. Mr Fenemore concluded that an attempt must be made to develop a totally integrated approach t< the research and combine the efforts of entomologists, agronomists, plant breeders, biochemists, other scientists and farmers in the grass grub programme. In the meantime. all methods available should be used by farmers to alleviate the problem Mr George Rountree,

who has leased a block of land to the Ministry of Agriculture and Fisheries for research, gave a background to the problem on his property, and pointed out that the grass grub had been present for many years and had been tolerated, but that the failure of D.D.T. through residue problems and resistance of grass grubs to the chemical, combined with the series of dry seasons, had led to a rapid build-up of the pest. Mr Dallas Rountree described the series of events during this build-up, which had led to a reduction in stocking rate to maintain stock performance. and to use of the techniques of overdrilling and various chemical applications to combat the problem. More than 100 acres were overdrilled last summer. All these techniques were costly, but inevitable under the circumstances. Mr Rountree welcomed the research on sex attractants being conducted on the property. Mr T. Trought and Mr R. French, field research officers with the Ministry of Agriculture and Fisheries, outlined the cultivation trials under way and the management trials planned. Mr French said that the pupal stage of the grub was very fragile, and M.A.F. trials showed significant reductions in grub survival if the soil was disturbed in September and October. Reductions in survival of up to 96 per cent were recorded in one trial, with October ploughing, and this significantly reduced subsequent populations. The management alternatives, which are then possible, include either a summer fallow to allow good estab-

lishment of winter feeds in late summer/early autumn, or a summer greenfeed, such as maize. Maize is highly resistant to grass grub, as it has a very unpalatable root system with a high fibre content. Since the grass grub lives on the cell juices and cannot break down and use the cell walls, this gives maize a high resistance. Mr I. Ritchie, farm advisory officer with the ministry in Ashburton, said that maize offered four possibilities — as feed for cows with calves at foot and weaned calves; feed to allow earlier buying of fattening cattle in late summer / early autumn; flushing feed for ewes; and silage. Weighing trials were being carried out to determine the suitability of maize as a flushing feed. Mr French displayed infra-red photographs of the trial areas, which gave a good indication of the amount of damage. Management trials will continue, he said. Mr Trought spoke on various aspects of grass grub populations and emphasised the variable density of populations. Grass grubs are found in heavy numbers at central points and numbers decline in samples taken starting from the centre and moving out. This means that counting grass grubs in a few holes across a paddock has little meaning because of the scattered groupings of the grubs, so that it is difficult to establish levels at which chemical treatment becomes economic. Mr Trought outlined the chemicals available for treatment of grass grub damaged pastures. These included Lindane. Diazinon, Prophos and Fensulfothion. A summary of the chemicals is as follows: Lindane is recommended for long term protection where light to moderate grub numbers and damage are present in April. May and June. Disc drilling of Lindane or Diazinon with

seed and fertiliser up till the end of June is a good method of renovating damaged paddocks. A permit is required for Lindane. At high populations. Diazinon prills give both porina and grass grub control when rain follows application, and the liquid 80 per cent Diazinon has a gooff effect under favourable conditions using the jet squirt technique on loose soil. 40 per cent Prophos (trade name “Mocap”), has given good results with turf treatment, particularly in porous soils in the North Island. Fensulfothion (trade name “Dasanit”). as a 10 per cent granule, drilled with the seed, gives encouraging results and may be mixed by farmers, but it is highly toxic and protective clothing must be used. It is suitable with higher populations where other in-! sect problems occur, such as Argentine stem weevil and porina. A permit is required for use between May 15 and December 31, 1973. Mr G. McFadden, a farm advisory officer with the ministry, discussed the use of over-drilling techniques to renovate damaged pastures. A disc drill was most suitable, and this could be used in combination with the spraying of the pasture with a dessicant, unless the grass had died back from drought. Where no dessicant was used, results were still reasonably good and in grub damaged patches, the establishment was excellent. Standard seeding rates of ryegrass and clover with nitrogen super, to give the grass an initial boost, along with an insecticide, either Lindane or Diazinon, at 5-101 b per acre (6-11 kg per ha), down the spout, has given good results in the past. Mr I. Woolley, a local contractor, gave a demonstration of direct drilling with both disc and tined implements and a number of these are being used in the district bv contractors. < (To be continued) I