Official Statement On Opotiki Experiments In Control Of “Soldier Fly”

Bay of Plenty Beacon, Volume 12, Issue 21, 13 February 1948, Page 5

Official Statement On Opotiki Experiments In Control Of “Soldier Fly”

(By E. R. Marryatt for the Beacon)

The Entomology Division of the Department of Scientific and Industrial Research in conjunction with the Fields, Division of the Department of Agriculture undertook an investigation of the “soldier fly” in maize at Opotiki in an endeavour to demonstrate clearly whether or net it was a serious crop pest.

The insect is present in numbers in the soil of the Opotiki area and has been considered to be responsible for abnormally early deterioration of pastures and injury to maize crops. The effec.t of the insect on pastures is difficult to determine quickly since the changes in composition of the pasture due to the insect would take place slowly over a period of years and since falling off in production of a grazed pasture is difficult to demonstrate to occasional visitors. Attempts which were made to kill the' grubs in pasture plots and to observe the growth of the grub-free pasture were unsuccessful since no one of the insecticides used killed the grubs and left the pasture unharmed. Maize Problem Work was therefore concentrated on the maize problem. The cooperation Df Mr J. Baird enabled the carrying out of an experiment on a paddock which was broken out of grass and sown in oats in the autumn of 1947. The oat crop was largely a failure apparently owing to a high production of grubs in the soil. In order to demonstrate the

effect of time of cultivation one half of the paddock was ploughed early and the other half left until a week before sowing the maize. There was little or no difference in the strike or establishment on the two halves of the paddock but the growth of the maize in the early ploughed half was very much better than that on the late ploughed half. The grub population was much lower in the early ploughed half as a result of the early ploughing. The use of effective insecticides against the grub on the early ploughed half produced little or no improvement in growth as compared with the untreated portions. Four Insecticides On the late ploughed half plots were set out on which four different insecticides were used* in the hope and expectation that at least one of them would materially reduce the grub population and so give a comparison of maize growth on grubfree and grub-infested soil.' The maize plots in which two of the insecticides were used showed, in early January, 1948, a height growth of at least 18 inches greater than that on the untreated plots. The grub population on these plots was very much reduced by the insecticides used. Considerable stunting of maize plants is therefore apparently due to this insect. The comparisons of grain yields from these plots will not be available till later in the yeai\

The infestation on*the paddock in which the experiments were made would probably be classed as medium since although there was stunting of plants there was little or no loss of plants after establishment. Other crops in the area were more seriously affected.

Early Cultivati«n It must be emphasised that the insecticides used in these trials are unlikely to provide a practical solution to the protection of maize cropfe from the soldier fly owing to their high cost; Great interest therefore is being taken in the apparent beneficial effect of early cultivation in reducing grub populations. Further confirmation is being sought on this* point since if the insect is not controllable by cultural methods the prospects of controlling.■ Pit by the application of insecticides to the soil are not -good.