Leatherjacket Damage to Cocksfoot Stands

New Zealand Journal of Agriculture, Volume 99, Issue 6, 15 December 1959, Page 571

Leatherjacket Damage to Cocksfoot Stands

By

A. R. RANKIN.

Fields Instructor, Department of Agriculture, Invercargill

LAST spring there were three recorded . instances of leatherjackets attacking cocksfoot seed stands in Southland. Damage was so severe in two stands that they were subsequently ploughed up. One was only two years old, so that the economic loss was high. This article describes the damage and the results of the attack.

LITTLE is known of the life cycle and feeding habits of leatherjackets. They are grey, much wrinkled grubs up to f in. long when fully grown and are always found in the soil. They are without legs or any distinct head. Pupation occurs in the soil and when the adult is about to emerge the pupa wriggles to the surface and projects some distance out of it. The adult is a two winged fly commonly known as a crane fly or daddy longlegs. The insects prefer damp situations, the grubs -being often found in soil among the roots of plants on which they are suspected of feeding. Many species of leather jackets feed on decaying organic matter and apparently there is doubt about whether or not they cause significant damage to plants.

Severe Damage However, two instances of severe damage and one of minor damage to cocksfoot attributed to this insect have recently been recorded in the East Limehills district in Southland. The district is noted for its production of timothy seed and though several areas are saved for cocksfoot seed, the country tends to be wetter than normal for cocksfoot seed growing. The three areas attacked were all reasonably close together. Damage in each appeared to begin in the damper hollows and runners and spread outward in roughly circular patches. The cocksfoot became greyish and bleached, with no sign of green shoots.

. The plants were easily removed, indicating severe root damage. As these were seed stands, the cocksfoot plants were clumpy, and under normal circumstances considerable force would be required to pull them from the ground. There was a high population of leather jackets in the soil, and where the damage was severe the covering vegetation could be scraped away from the soil. Contributing Factors Two factors are thought to have contributed to the high population of jackets. Firstly, cocksfoot seed stands provide considerable quantities of litter in the form of decaying and dying leaf material. Based on present knowledge this would provide excellent cover and feed for the grubs. Secondly, the combination of this food supply with damp conditions has contributed to the incidence of this pest. However, in all three cases the grub in addition to feeding on the decaying litter and leafage, has apparently turned to the cocksfoot roots, with disastrous results. Two of the stands were so badly attacked that they were ploughed in. In the third the farmer, noticing the damage reasonably early, applied DDT superphosphate and this markedly arrested the spread of the damage. In addition a recent inspection has shown ■chat though the cocksfoot population has been reduced in the affected areas, young shoots are emerging from . a number 'of apparently dead plants. While it would seem that DDT provided an effective means of control in this instance, the possibility of more effective control with other insecticides must not be overlooked. DDT, the only insecticide tried yet, has, however, provided efficient control.