Aim Grass Grub Control

Press, Volume CVIII, Issue 31730, 13 July 1968, Page 8

Aim Grass Grub Control

A North Canterbury farmer, Mr D. G. Allan, of The Sisters, Parnassus, is putting a lot of faith in this heavy, grooved roller as a means of controlling grass grubs, which are resistant to D.D.T., on his hill property. Tests with grubs from The Sisters, made at the Entomology Division of the Department of Scientific and Industrial Research at Nelson, have shown that it would be a waste of money putting more D.D.T. super on this country, and as he has been spending some $lOOO to $l2OO a year on D.D.T. super, Mr Allan says that at he is not overconcerned at the cost of this roller—s6so—as built by Mr I. Giltrap at Doyleston. Because of D.D.T. resistance in the grubs, Mr Allan has been forced to look for some other way of tackling the problem as he has some 300 acres affected in varying degrees. He recalls that in his home district, Southbridge, the heavy roller was used in paddocks with grub-infested patches closed for clover seed crops and he remembers that the grub did not have the same effect thereafter. Mr Allan’s aim has been to get the maximum compression of the surface of the ground to kill as many grubs as possible. In developing this roller, 15 or 16 strips of 3in by lin timber were laid down with a space between each one and a roller was put across

them, the grooves formed were subsequently rolled flat and it was reckoned that compression of the soil was being obtained to depths of from lin to 2fin. It is Mr Allan's belief that grubs are being killed to a depth of about 2|in in soft ground. Mr B. Withell, farm advisory officer of the Department of Agriculture at Cheviot, is showing a lively interest in the technique. He says trial diggings made about the end of May have shown that about 90 per cent of the grubs are in about the top Ifin of soil —hence the significance of what Mr Allan is trying to do. The roller, as built by Mr Giltrap to Mr Allan’s requirements, weighs eight tons and a half and has a diameter and width of sft. It is formed out of pairs of steel bands measuring IJin by IJin so that in the roller they are 2Jin across by Ijin deep. They are filled with a total of 4Jyd of concrete. Between each set of rings there is a scraper for cleaning the roller of soil which builds up in bare ground and reduces its effectiveness.

On flat going with a 55 or 56 horsepower wheel tractor Mr Allan has pulled the roller at up to 15 m.p.h. but a more normal speed is 7 m.p.h. or 8 m.p.h. in fifth gear. In more difficult going a crawler has to be used and on the hill considerable care is, of course, necessary. Mr Allan says that this roller seems to track well but irregularities in a paddock tend to reduce its effectiveness.

To iron out the grooves or

corrugations he now uses a borrowed lOf-ton roller which is Bft wide and filled with water, but he is envisaging having another sft by sft flat roller built at an estimated cost of $4OO.

Mr Withell says that in doing the two rollings Mr Allan can cover about two acres an hour, and not including labour, the cost would be about 25c to 30c an acre.

Mr Allan is optimistic about the use of the roller and says that there has been a quite marked recovery in pasture growth where the area has been

treated in this way. In fact, he believes that if a group of flat-land farmers acquired a roller like his they might not have to use D.D.T. again for grass grub. Where he has dug the ground up after treatment Mr Allan says that the odd grass grubs left are fat like cigarettes—probably due to the reduction in competition from their colleagues which are compressed into a tissue paper form. A few worms, too, are unhappily caught in the compression process. It is not thought that the heavy rolling will have a harmful effect on soil structure or will impede drainage. Mr Allan says that where he treated an area with the grooved roller about the end of May and then was unable to use the flat roller subsequently, the grooves have now almost completely disappeared.

Mr Withell says that at this stage the technique is at the experimental stage. It can be regarded as a first aid dressing as it does not eradicate the grubs. With Mr F. C. Alien, the officer of the department stationed at Lincoln who is concerned with pest and weed problems, he hopes to conduct a trial in which an accurate assessment is made of the grub population both before and after treatment.