The Grass Grub

It is important to understand the life cycle of the grass grub. The adult beetle, commonly known as the brown beetle, is on the wing in November to early January. Eggs large and white are laid at least 3 inches in the soil and the young grubs hatch out in 7–16 days to start feeding on the roots of pasture plants. These grubs grow over the summer, autumn and spring, feeding all the time, and remain within 2–3 inches of the top of the ground until September or October, when they burrow to a depth of from 4–10 inches to pupate—a new generation of beetles appearing in November to start another cycle.

Most farmers are familiar with the type of damage done to pasture by large numbers of grass grubs. In such circumstances most of the grass is killed and the dead turf can be rolled up like a carpet. This type of damage is so obvious that no effort is required to persuade the farmer to use an insecticide to bring the grubs under control.

Recent investigations, however, carried out by the D.S.I.R., which involves the sampling of 70 paddocks in the North and South Islands, showed that whereas in grub-free pastures the leaf length could be as much as 6–8 inches in 4–6 weeks, areas of the same paddocks harbouring 1–9 grubs per square foot had leaf lengths of only 1–3 inches. The average reduction was over 3 inches in any 4–6 week period between the end of January and the end of August. The pastures at no stage showed what farmers usually consider to be typical grass grub damage. This rather startling discovery emphasises the necessity to treat pastures with D.D.T. where grubs are known to exist in the district even though no damage is visible on a farm.

If D.D.T. is properly used it will proof the pasture against grass grub damage.

One pound of 100 per cent D.D.T. per acre should be used where no evidence of grub can be seen but where there is a likelihood that they do exist. In other words this dressing will be an insurance and should be used particularly where new pastures are sown down. Where a pasture has been attacked and grubs are working actively the application rate should be doubled to two pound of 100 per cent D.D.T. per acre.

During March and April farmers are advised to go over the farm with a spade digging bits of soil to see if any grubs are present. It should be remembered that they will be working in the top 2 inches of soil and that they will be very small at that time of the year.

D.D.T. prills have proved an efficient insecticide and make it possible to apply accurately a comparatively small amount of D.D.T. required per acre without first having to mix the insecticide with fertiliser. The recommended rat of application in 16 lb of prills per acre, which contains 2 lbs of 100 per cent D.D.T. But good results have been recorded from the use of 12 lb prills, that is, 1 ½ lbs of 100 per cent D.D.T., and this lesser amount may be an economic proposition. The total cost including application should not exceed 25/- per acre.

Crickets

The main effect of the cricket is felt in the Auckland province particularly about Hauraki Plains and the North Auckland Peninsula where soils and climate are ideal for this pest. When seasons are favourable the cricket population can build up to immense hordes which cause widespread damage to pastures. It usually occurs around dry autumns when pastures plants have little power of recovery and it continues until the cooler weather when again the plants lack the vigour required to repair damage.

From February onward the light coloured cigar-shaped eggs about a tenth of an inch long are deposited by the female into the turf or just below the soil surface. Some eggs hatch in the following few weeks if conditions are satisfactory but generally it does not begin until October. A nymph emerges from the egg which is similar to an adult but is wingless and very small. It begins to feed immediately and as it feeds passes through a succession of moults until it becomes a winged adult. It is usually near the adult stage before damage is noticed.

The cricket is a surface feeder. It lives on rye grass as the most favoured pasture and although cocksfoot is readily eaten by the cricket, it has strong powers of recovery from damage. Clovers are much less attractive and are usually left until

other species are eliminated. As this damage is always associated with dry weather and as the crickets will also consume any seed which has fallen, there is little hope of recovery of the pasture.

Dieldrin applied as a dust in dieldrin superphosphate at 2 cwt to the acre kills crickets quickly and effectively. In this form 6 ozs. of dieldrin is used per acre. Dusting with D.D.T. is not effective.

Early February is the most effective time to treat affected pastures as if they are treated too early in December or January a second crop of crickets may infest the area. But on the other hand treatment should not be delayed until pasture damage is severe.

The Army Worm

The army caterpillar which is often referred to as army worm is the caterpillar stage of a common native night-flying moth. It has often devastated crops in summer or early autumn and in a number of districts has severely damaged pasture on river flats, and swamp areas usually after summer flood followed by warm muggy weather. An attack by army caterpillar cannot be predicted with complete precision but we can tell when conditions are suitable for the pest and keep a close watch for it. Hay after mast, especially paspallum, newly sown pastures or cereal crops or land subject to summer flooding are all vulnerable to army worm infestation and should be watched very carefully with a view to making remedial measures. Caterpillars usually confine their feeding to sunny faces on hill country and shady faces are generally not depleted. They prefer plants of the grass family and the way in which they avoid patches of dominant clover pasture is really remarkable. Thus areas of pasture showing high fertility with plenty of clovers are usually not affected. If unchecked they may continue to feed well into June.

Caterpillars can be controlled by spraying with either D.D.T. or Dieldrin and either killed off completely or prevented from moving on to fresh areas. Effective sprays applied by helicopter or aeroplane are 1 ½ pints of 15 per cent Dieldrin in 5–10 gallons of water (according to the lankness of the growth) where water is being used, or else 2 pints of 20 per cent D.D.T. in similar quantities of water per acre. Dieldrin is much quicker acting than D.D.T. but the latter is quite effective. A method of control is for a band of 50 to 60 feet in width to be sprayed with one pass of the aeroplane or helicopter and the perimeter of the advancing caterpillars. Half of the band is applied on the advancing caterpillars and half on the pastures ahead of them.