Grass grub damage to grasses is not merely due to attack upon the roots. While feeding, the grubs swallow soil with the roots, rendering the former spongy, and so disturb the normal circulation of moisture about the grass roots. In the case of infested lawns, it is advantageous to roll infested areas in order to pack the soil pulverised by the grubs, and re-establish normal circulation of soil moisture. Another important feature in grub control is to stimulate root development by means of fertilisers. A recently-developed method of "grub-proofing" lawns is to broadcast over every thousand square feet of turf to be treated one bushel of screened sand or clean soil, in which 5lb. of lead arsenate powder have been intimately mixed. This is said to remain effective for a period of three years; but such fertilisers as nitrate of soda, superphosphate, sulphate of potash, and potassium chloride should not be used on "grub-proofed" turf, as they react with the lead arsenate, and reduce its effectiveness, though rotted manure or ammonia sulphate may be used.
The control of grass grubs damaging the roots of strawberry and other plants is a difficult matter, though some benefit is to be derived by making holes about four inches deep with a stick in the soil near to the infested plants and pouring in a little carbon bisulphide; the holes should be closed immediately. To protect strawberry beds, if they are not too extensive, the most satisfactory method is to cover the plants with scrim, stretched on frames, at dusk during November and early December, when the beetles are flying; this will prevent the insects from infesting the ground with their eggs. The use of sulphur smudges, already referred to, is of great importance in this respect.
SUBTERRANEAN GRASS CATERPILLARS.--These caterpillars are the larvæ of native moths (Fig. 12, f1) belonging to the genus _Porina_, and when they become epidemic they cause much more extensive damage to pasture and lawns than do the grass grubs. When full grown, the greyish-black caterpillars (Fig. 12, f2) reach a length of about three inches; they are soft-bodied and rather flaccid, and live in underground burrows of varying depth. After dark, these caterpillars come to the surface and devour the grass, eating it close to the ground, much soil being swallowed by the larvæ during the feeding. This soil is evacuated, and resembles earthworm castings, but is mixed with silk spun by the caterpillars; the emergence holes of the caterpillars, about the diameter of a lead pencil, are conspicuous on the surface denuded of its covering of grass. Pupation takes place underground, and when the moths emerge the pupæ first move to and project beyond the surface of the ground; these pupæ are large and easily recognised by the wing-cases, which are very short compared with the length of the body. The moths are on the wing during spring and summer, the rest of the year being spent in the larval stage. The moths are night-flyers, and are amongst the largest species in New Zealand, their wings having an expanse of from one to over two inches; they are heavy-bodied insects, and vary considerably in colour. One of the commonest, species is brownish-yellow, or sometimes a smoky-grey, with a white streak bordered with black on the fore wings; the hind wings may be pinkish.