GRASS GRUB MENACE.

New Zealand Herald, Volume LXIX, Issue 21224, 2 July 1932, Page 17

GRASS GRUB MENACE.

TOLL ON PRODUCTION.

PROBLEM OF CONTROL. The winter has brought to light a seasonal complaint— the ravages of the grass grub—in a seriously aggravated form. Tho depredations of this grassland pest have taken ail annual toll from thousands of acres of highly productive country in past years but apparently the extent of the damage has not occasioned the farmer any great degree of concern. We now find, however, that in one district in the North tho trouble has assumed such disastrous proportions that the very existence of the farmers, from the production viewpoint, is threatened. The grub is the larva of the brown beetle, which is so destructive to orchard trees and the leaves of root crops during the early summer, at which period it lays its f 'ggs at tho roots of the grass. The grubs when hatched, burrow into the earth and commence eating the roots, their presence being indicated in the early winter by tho appearance of patches of dead grass which scrapes otf easily. From May to September this effect becomes increasingly evident, but from then onward the grubs feed less vigorously and tho grass makes greater headway. By October the pupa stage has generally put an end to the grubs' destructive feeding, tho life history being completed when the beetle emerges from the ground early in November. It has been a very difficult matter to devise control measures. The grub has enjoyed a complete security while in the ground, chiefly becauso endeavours to eradicato it by the application of toxic materials have proved fatal to the pasture as well as to the grub. In cases in which applied specifics have proved effective in eradicating the pest without injury to the grass, the costs incurred liavo been of such magnitude that their adoption on a large scale has been completely out of the question Effect of Rolling. Heavy rolling has frequently been recommended as a means of extermination. This expedient may rid the soil of a few grubs which are very near the surface, but if it was efficient in killing large numbers, or even in restricting tho spread of the pest-, it would undoubtedly enjoy a far greater vogue. As a matter of fact, investigators have claimed that the grubs may be covered with only a quarter of an inch of loose soil and then trampled on with one's whole weight without causing them the least inconvenience. Grub patches have even been known to spread over marks left by the wheels of traction engines. Where good effects have been noted after rolling it is considered more likely that the action has been beneficial to the herbage rather than injurious to the grub. Boiling compresses the soil about damaged plants, remedying the friable condition created by the grubs and permitting fresh roots to strike. The grub is immune from the effects of cold and frost, and will also survive long periods of immersion in waterlogged soil. In the pupa stage, however, the pest is very vulnerable to any attack which disturbs the soil. The pupa is a fragile creature, and the mere passing of a plough through file soil will kill large numbers. Working the land during this period, of the "life cycle" —From October to tha early part of November—should therefore result in the destruction of a comparatively large number of potential beetles which otherwise would soon be laying eggs to the detriment of the succeeding winter's pastures. "War Against the Beetle. Such a policy could doubtless be adopted when only small portions of grassland are infested, but it is not altogether practicable to suggest that any considerable area of pasture be so treated just when the peak period of dairy production is approaching. In view of th:s, and in the absence of effective and economic expedients for coping with the grub, it seems that the best thing to do is to concentrate on combative effort against the adult beetle, which is far more vulnerable to attack and which can bo prevented, to a- certain degree, from laying the eggs which give rise to subsequent infestation. The chief essential in tho prevention of egg-laying is sound summer pasture control. Generally speaking, the beetle lay?; its eggs in only the longest grass, a fact which has been frequently illustrated by the serious infestation of paddocks which have been closed for hay cut about December. Farmers will generally find, also, that of two adjacent paddocks or farms, one of which is adequately stocked and the other understocked, during the time the hee'le if> on the wirif;. tho hitter will invariably be the most severely affected the following winter. Ihc avoidance ot as much rank growth as possible, by converting surplus grass into ensilage anil bv good grazing control, is the most practicable way of combating the post.

In certain districts it lias been found that the beetles fly readily to fires, lit in the dusk of the warm XovcmberDecernlier evenings. 1 his method has provided a means of wholesale destruction in the Ashburton and Hangiora districts, while successes have been reported from other parts of the country also, but it i> recorded that in some localities elaborate preparations along the same lines have been completely una vnimn< TlifTfrßnce in [t lias long been recognised that shal-low-rooted grasses, and particularly ryegrass, are especially susceptible io damage by tlie grub, but that good permanent strains are not so badly affected. Cocksfoot has shown itself to be perhaps the least susceptible, while recently if has been observed that paspalum also apparently enjoys a certain degree of immunity. At the moment the farmer is entirely dependent upon his own efforts in waging war against this foe. Energetic care oi his grassland during the critical early summer period must be his main line ot defence, as it obviously offers him the most effective means of restricting infestation. It will not give him complete security, however, and continued research into methods of combating (he pert in the grub stage is essential. Since current experience shows the menace to our key industry to be so great, the Department oi Agriculture—which already has the question of large-area treatments in hand with a view of evolving economical methods of applying expensive specifics—should place the problem among those calling for the most urgent attention.