Hopeful About Grass Grub Control

Press, Volume CIX, Issue 32032, 5 July 1969, Page 9

Hopeful About Grass Grub Control

“Although I have been working on this problem for only a year and naturally one year’s results must be treated with a certain amount of caution, I feel pretty certain that we have the control of grass grub within our grasp at a reasonably low cost,” an officer of the Department of Agriculture, Mr T. E. T. Trought, said this week.

Mr Trought, who is stationed at the Crop Research Division at Lincoln, was referring to what he calls “turf treatment,” or the introduction of chemicals below the surface of the ground, and also a surface application method with what he calls a “jet squirt.”

An Englishman, who was testing new. chemicals for the Shell Chemical Company before he came to New Zealand a little more than two years and a half ago, Mr Trought was an agricultural chemicals officer with the Agricultural Chemicals Board for a year and a half before coming to Lincoln a year ago. He is now working as a scientist on insect control as a member of the field research section of the Research Division of the Department of Agriculture.

He admits that his knowledge of the grass grub is of relatively short duration. One of his early introductions to the problem was when he visited Canterbury about two years ago when the province was in the throes of a major outbreak of grass grub and porina caterpillar damage. His work in the last season in Canterbury has been mainly with a machine built some eight years ago by the late Mr H. W. T. Eggers, an engineer to the Department of Agriculture, to control soldier fly in the Whakatane district and to overcome problems with D.D.T. residues.

It works on the basis of 10 discs, four inches apart, cutting grooves in the soil into which the insecticide is introduced below ground level. It almost certainly gets over the problem of herbage contamination with insecticide.

Mr Trought has a natural interest in building machines and once held a patent for a gadget—a spot applicator for insecticide. He said that to him the principle of the Eggers machine seemed to be right and he wanted to test it

So since September Mr Trought and tris technician assistant, Mr A. L. Wood, have been using the old machine—he believes that it is the original—to apply eight different chemicals including diazinon, lindane, fensulfothion and parathion, but not

including D.D.T., at generally about 21b active ingredient to the acre. This work has been done in the Southbridge district and north of the Hinds River in the Carew area, which is well known for its grass grub problems. This is what Mr Trought calls his turf treatment

AU of the treatments, except where no grubs have shown up at all, have given most striking responses, with all Insecticides giving a remarkably uniform HU.

The reduction in grub populations has been considerable—from, say, 40 to the square foot down to five after treatment not being an uncommon experience. Late in the season Mr Trought also tried another technique. This involved a simple spray boom with nozzles about every three inches and a half along its length with the boom being held about three inches above the pasture on skids at either end. This is what is called the “jet squirt” The nozzles issue a squirt rather than an over-all spray. It appeared as though the jets penetrated through the pasture well and even to the ground, although this might not happen with a particularly thick mat of a sward. The results of this form of approach were virtually identical with the turf treatment, but Mr Trought believes that there may be more limitations with it. He started using it

about the middle of May when moisture conditions were more favourable, but under dry conditions or if the grubs remained deep in the soil and did not come up, he thinks it would break down. It would also be a method that could require the imposition of some withholding periods when stock would have to be kept off pasture after treatment He say? that more work is required on this particular method.

* The Idea of laying the insecticide in lines, however, means that a greater concentration is achieved which is likely to remain active for longer and the heavier the population the . more grubs are likely to be killed as they move about even in a relatively confined area. Mr Trought is naturally very optimistic about these results. He, however, readily agrees that they have come from only one year’s work and that next year’s responses may pot be in line with the last season’s, but he feels that these developments should not necessarily await the results of another three or four years of confirmatory work as is often required in scientific investigations.

He is hopeful that In the next year they can be translated into practical form that can be applied on a farm scale.

“I think I am justified in making an all-out effort in the coming year to produce an answer that can be translated directly into the field,” he says. It is hoped that the Agricultural Engineering Institute at Lincoln will be able to give priority to the development of a machine along the lines of the Eggers machine. In the meantime Mr Trought will try to further his knowledge of the techniques so that they can be

applied with more exactness. While the applications have ben made at mainly 21b of active ingredient of the chemicals to the acre, Mr Trought believes that considerably lower rates may be as satisfactory—even down to a ilb to the acre for some materials. For Instance, fensulfothion gives much the same result whether 11b or 21b of active ingredient is used to the acre and this could apply with other chemicals, too. The liquid applications used should naturally be cheaper than use of granulated formulations. The cost for the cheapest chemical at the 2lb rate, he says, would be $3.80 an acre but at half that rate the cost would be reduced to $1.90 and in addition there is now the concession announced in the Budget to be taken into account.

If these are compatible, Mr Trought also sees the possibility of perhaps incorporating urea with an insecticide to give the pasture a boost at the same time as grub control is achieved and the technique might also lend itself to the distribution of such a material as a larval attractant should that be developed in the future. Mr Trought has made the observation that there has been a pasture response in some cases where insecticide has been applied but there are no grubs present. He feels that this may be due to these insecticides also killing nematodes.

There is still testing of chemicals to be done and new and better chemicals may come i’rom those being continuously screened by the Department of Scientific and Industrial Research. It will also be necessary to look at possible effects on bird life and on beneficial soil organisms. Both systems may also require the use of withholding periods for stock.

Neither the turf treatment method er the jet squirt have given worthwhile results with porina caterpillar, but Mr Trought believes that in a year’s time he may also be able to reduce the cost of porina control by spraying by something like 30 per cent

He has had some promising results with a machine made in England and costing £45 there. Weighing 81b and dispersing insecticide by means of a spinning disc in the centre of a fan, it is known as a “Turbair Tot.” Mr Trought has used it to drift insecticide. In still air its distribution has been 10 yards and in a light breeze 20 yards. By walking up and down a paddock with the machine an acre has been treated in about three minutes and a half. It could conceivably be mounted on a truck or van. Mr Trought says that in some instances it has done as good a job as any conventional boom spray, and with some chemicals it has also given very good results with clover case bearer moth. In the next year or two it is hoped to be able to determine the climatic conditions under which the machine will work most efficiently. While it appears to be very economical to use, it has, however, limitations from a drift hazard point of view and because the chemical may drift back on to the operator it is essential that he be clad in protective clothing.

Mr Trought is also working on the development of a machine to treat potatoes at harvesting to prevent damage to them from the tuber moth during storage. This is a problem particularly of the North Island.