Behaviour Of Grass Grub Beetle

Press, Volume CVI, Issue 31083, 11 June 1966, Page 9

Behaviour Of Grass Grub Beetle

“VTR Beattie’s observations ivl are sound on general principles of preference by beetles (and grubs) for soils of open structure as opposed to hard consolidated soils, but work of this station definitely shows that there is no preference by egg laying beetles for dense, rank pasture growth. I am aware that many farmers and Government agricultural

workers hold this view but our evidence does not support the belief.” These are the comi ents of Mr J. M. Kelsey, officer in charge of the Lincoln sub-station of the Entomology Division of the Department of Scientific and Industrial Research, on the observations of a farmer on the Inland road, Kaikoura, Mr D. H. Beattie, on the soil and pasture preferences of grass grub beetles. Understanding “A fuller understanding of the flight habits of the grass grub beetle and co-ordination in grazing management during the flight period, could well provide the much needed solution to helping determine the paddocks in which grass grub damage is likely to take place, and at the same time reduce the inaccurate and indiscriminate use of D.D.T., which if used on the same scale as at present could become a staggering burden on the cost of production as the incidence of grass grub increases,” says Mr Beattie. “Much has been written over the past few years on this growing problem, but little if any has been directed at any possible preferences the beetle may have for soil conditions, and the amount of cover grass or crop on a particular paddock. I believe it is in defining these preferences that a more accurate and economic measure of control is possible. “Farmers for some years have been consistently advised to treat a third of their farm each year, thus covering the property over a three-year period as an Insurance against grass grub attack. Surely this advice must worry many farmers and others as to the long term effect a policy of this nature could have. It is probable that many of these D.D.T.-treated paddocks would not have shown grass grub damage to the extent warranting the application of D.D.T. ‘1 believe the aim should be to treat only the paddocks that are likely to attract the greatest number of beetles during the flight period. To achieve this objective I would suggest the following guide. “All worked ground, grain, grass seed, hay or spelled paddocks should be regarded as potential homes for the grass grub beetle.

“It has been my experience that all pasture paddocks if they are closely grazed before and during the flight period will remain reasonably free of grass grub without the use of D.D.T. The exception could be areas of light, stoney, friable or sandy soils which are easily burrowed into by the beetle, or very large areas of the same soil or cover type. In the last case flight capacity

might confine the beetle to this area. “Where ploughing is planned and this coincides with the flight period it would be better to close graze then plough after the flight period. Such paddocks would then not require D.D.T. when sowing down. These paddocks the following season before closing for seed production, hay or fattening feed could then be treated with D.D.T. Where possible early closing of meadow hay paddocks would enable the cut to be taken in time to have it closely grazed before the flight period. “Irrigation areas should be managed to avoid soft soil and growthy pastures during this period.

“The grass grub population on dairy farms could be a contributing factor is causing pastures to become clover dominant thus creating a bloat problem. “Close grazing may be difficult on dairy farms as production would fall if paddocks were grazed to the extent necessary, but perhaps dry cattle 'or bought-in sheep could follow the milkers for some weeks before the flight period. Greater use of the harrows during spring would prevent cow pads developing into rank unpalatable growth, this being ideal beetle cover. Hill Country “Where hill country has been oversown with seed by air I would suggest delaying closing for seeding out as late as possible, preferably after the flight period. The cost involved in developing such country by this method would not be warranted if grass grub is allowed to destroy a large part of its future potential in the first critical year. “I have found D.D.T., if applied early, most effective in its first year but much depends on pasture management in subsequent years. I consider application after the grub has caused visual damage a case of getting 10s worth for 20s spent. “Pasture management along the lines suggested would automatically reduce the number of paddocks acceptable to the beetle and at the same time give an earlier Indication where the farmer would get a full pound’s worth of control. In other words a decision can be made during the flight period, on which paddocks D,D.T. treatment will be required. “It was during the 1958 drought in the Awatere, Marlborough, that this idea first occurred to me. . . “I have worked on this theory for eight years with a growing confidence in this belief. My conclusions are that the beetle does have preferences for a soil which can be freely burrowed into and foliage as food and cover play a major part”

Mr Kelsey said that flight habits and adult emergence habits as distinct from flights, reasons for flight and the percentage of adults that fly and their oviposition preferences for thick or thin, tall or short pasture, have all been studied closely over the full flight or emergence period from October to the end of March over a period of 15 years. These studies included soil structure influences also.

“Our surveys over 20 years have shown that all grassland —whether native or improved —is liable to grub attack. The heavy unworked clays harbour about one grub a square yard, but the same soil worked frequently and sown in introduced pasture can reach as high as 60 a square foot within ohe year of sowing down. Light sandy soils are more prone to grass grub attack and It is true that beetles prefer open structure soils to those which are baked hard, and the same thing applies to grubs—they prefer the light silty loams which permit more free movement.

"Beetles have no preference for tall or short, thin or dense pasture. “The only safe practice is to sample for grub presence and this is the thing that we have been trying to get farmers to do. Even if land containing grubs is ploughed the fanner, by cultivating where seagulls or starlings are present can reduce grub populations from over 50 to under one a square foot with this practice if five grubbings follow the initial ploughing. With such a scheme it is not necessary for treatment in the first year and whether or not it should be treated in the second year should depend entirely on soil sampling, and this could go on year by year but we have found that farmers in general will not sample. The result has been that grubs are present in damaging numbers before farmers realise it—hence the threeyear rotation technique. “Beetles will sometimes lay most eggs in close grazed pasture. Stock Effect “There is some evidence that presence of stock, particularly heavy sheep concentrations, deter beetles from laying eggs in such paddocks but this is due, not to close grazing, but the movement of stock during the short time beetles are on the wing on emerging at dusk. Though sheep are usually lying down then, they do move about in some instances throughout beetle flights and are even compelled to move by beetles emerging from the soil on which they are lying, and when hungry they tend to move in any case well after the beetle emergence period.”