THE GRASS GRUB

Hawke's Bay Tribune, Volume XXIII, Issue 75, 10 March 1933, Page 11

THE GRASS GRUB

AUTUMN BOLLING NEEDED. LIFE CYCLE AND CONTROL. Not such a source of trouble in Hawke’s Bay as it is in the Manawatu, the grass grub is still to be reckoned with in some parts of the district, and the autumn is the ideal time for putting control measures into operation. In a later stage of life the grass grub becomes the turnip fly, which causes quite an amount of damage to Into sown turnip crops. The grass grub is a great nuisance to farmers whose pastures are attacked, and a knowledge of the life cycle of the grub is necessary, if the grub is to be suppressed. The eggs of the adult turnip fly are laid just under the surface of the soil, favourite spots being turnip fields, and in pasture. Hatching out, the emerged grub begins to feed industriously on the grass roots, the amount of damage done increasing till the end of the autumn months. As a result of this feeding on the grass roots, the growth of affected pasture is retarded. It is in the autumn months when the effects of the grubs are most noticeable, as it is then that the grubs are eating most rapidly. With the approach of winter the grubs go down into the soil to a depth of about ten inches, coming to the surface again in the spring. About October, the grubs descend to the depths once again, and go through a resting stage which occupies from two to three weeks. After this the adult turnip fly emerges, and commences laying eggs about December, the eggs being laid chiefly at night. SUGGESTED CONTROL MEASURES. The control of the grass grub depends on the fact that in the autumn the half grown grubs are very close to the surface of the soil. At this time it is possible to use a heavy roller on these areas, and crush the grub. A practice that is largely adopted in the Manawatu is to roll the pasture that is affected, and to feed out seed hay on the grub eaten areas. By concentrating stock on this area, they have a consolidating effect on the grass, the grubs are crushed, and at the same time the hay seeds are tramped into the soil and come away with fresh growth. This may sound rather severe, but results have shown the efficiency of this method. With badly affected land, where whole pastures arc affected it would probably pay the farmer best to plough up this pasture, and if possible crop it. sowing down grass the next season. Ploughing exposes the grubs to the birds, and as these are particularly tasty, the birds soon clean up the soil. Early topdressing, to stimulate growth, and thus make the pasture able to withstand the damage done by the grub has also been done with good results. Agricultural authorities recommend that any planting of cruciferous crops, or pasture grasses should be done either well before, or well after the flight of the adult turnip fly, which occurs in December. On lawns, where such severe methods cannot be practised, the best method of control is to use lead arsenate on the grass, washing it into the soil with water. There is a tendency with this method for the grass to be burnt up. Water-logging the soil can also be indulged in and is quite effective.