GARDEN PESTS IN NEW ZEALAND 



KOUXD-HEADED BORERS. Apple, almond, and citrus trees, together 

 with gooseberry and such ornamental and shelter trees as poplars, 

 tree-lucerne, and goat-willow, are sometimes damaged by round-headed 

 borers, which tunnel in the stems and branches. These borers (Fig. 12d) 

 are white in colour, narrow-bodied, and cylindrical, the segments being 

 usually well defined, and belong to a group of beetles known as long- 

 horned beetles, a group of insects to which the common hu-hu beetle 

 belongs. These beetles are narrow-bodied, and their antennae are com- 

 paratively long and conspicuous. 



To control these pests, the only thing to do is to cut out and burn 

 the badly-infested parts. Where a borer is located (and this can be 

 frequently done by the presence of the powdered wood ejected from the 

 burrows)", the culprit may be killed by injecting into the tunnel some 

 carbon bisulphide and plugging up the openings with some clay or other 

 similar substance. 



LEAF-MIXIXG FLIES. -- Very often the leaves of cineraria and 

 chrysanthemum are disfigured by the tortuous tunnellings of the 

 maggots of minute flies (Fig. 12e). The adult insects are two- winged, 

 and in structure resemble in many respects miniature houseflies. The 

 eggs are laid in the leaf tissues, in which the whole development of the 

 maggots and pupae takes place. The white maggots are small, legless 

 and headless. Spraying with black-leaf 40 would act as a deterrent to 

 the flies, while infested leaves should be removed and destroyed before 

 infestation becomes general. 



GRASS GRUB (Odontria, zealandica). - - As explained in the pre- 

 ceding chapter, the grass grub is the larva of a native cockchafer beetle 

 (Fig. 11, 1). This grub, by feeding upon roots, causes extensive damage 

 to pastures and lawns, as well as to many garden plants, including straw- 

 berries. In the case of pasture and lawns, the presence of even a con- 

 siderable number of grass grubs is not detrimental unless they occur 

 concentrated in definite areas, when the damage is pronounced. With 

 garden plants, however, which are isolated when compared with the dense 

 root masses of grasses, the attacks of one or two grubs upon the roots 

 of a single plant may cause serious injury. 



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 witli 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 



64 



