A HEADACHE FOR GRASS GRUBS

Press, 8 June 1979, Page 9

A HEADACHE FOR GRASS GRUBS

“I am sure that they are a bit sick even if they are not dead,” remarked Mr D. C. I. Edgar, of Ealing in Mid-Canterbury, the other day when he knifed up some grass grubs that were dead and disintegrating and others that were still alive out of part of a paddock, which the juggernaut photographed alongside had passed over sometime before.

Mr Edgar farms country comprising Lismore stony silt loam that is very amenable to grass grub attack and says that it has been the biggest bugbear in 26 years of farming in the area. But he believes that use of a heavy roller, like that in the photograph, may mean that although the grubs will not be completely eliminated they wiil no longer be a problem (in the grass root zone of the soil).

He has had a seven tonne truck heavily laden with shingle run over his country to compress the surface and hopefully kill the grubs in this zone of the soil, and where a paddock b.order-dyked for irrigation was treated in this way about two years ago there is still a marked visual benefit from this

treatment and the grass does not pull out so readily as on obviously badly affected areas. It has been observed that where a heavy truck has passed through a paddock there is less damage from grass grub in the area of the wheel marks. The grubs may dislike working in these compacted areas. Hence the likely value of heavy rolling. Heavy rolling against grass grubs is not a new development by any means, so Mr Edgar’s roller may be described as a modification or improvement of an old technique. It comprises four sets .of

rubber tyred wheels with each set carrying a concrete block and concrete posts reckoned to weigh four tonnes giving the “train” a total weight of 16 tonnes. Each of the four units is independent and follows the undulations in the ground. At a pass it covers a strip about 1.5 m or sft wide. Naturally compaction is best in the first 36 to 48 hours after rain but under dry weather these conditions could be simulated by irrigation, and this has been tried on the Edgar property. Certainly there seems to be a visual beneficial effect

on the pasture where the country has been heavy rolled in this way compared with where it has not. The pasture is much stronger and greener and there has been recovery where a paddock had been marked down for ploughing up because of grubs. Mr Edgar believes that quite apart from the effect on the grubs there may also be a spin-off from compaction in promoting better grass growth and he says that it may be desirable to heavy roll an area where a new pasture has been sown. The Edgar heavy roller

is pulled by a tractor of about 75 horsepower and almost two acres or 0.8 ha are covered in an hour.

One of the aspects ,of the treatment that Mr Edgar is interested in is how long the effect of heavy rolling lasts.

The Ministry of Agriculture is doing a pilot trial on the property. Dr R. A. French, district scientist (entomology) .of the Ministry, said this week that they had done some sampling of the soil on the farm and had found that there was a 50 per cent higher mortality among grubs Where the ground had been heavy rolled recently compared with an untreated area. But he added that the level of mortality between the treated and untreated areas tended to even out with natural mortality also occurring in the untreated areas. However, the farm is also being looked at photographically by false colour infra red aerial photography so more results will be available soon. Dr French agreed that there could be beneficial side effects on pasture growth on these soils resulting from compaction and he is hopeful of encouraging some investigations into this aspect also. Mr Edgar thinks that his roller may have some use in other parts of the country than Canterbury — in possibly the pumice soils around Rotorua, for instance.