PLANT PEST CONTROL

Poverty Bay Herald, Volume LXIV, Issue 19227, 20 January 1937, Page 5

PLANT PEST CONTROL

INSECTS AS AGENTS N.Z. EXPERIMENTS AUXILIARY ATTACK (Per Press Association.) AUCKLAND, this day. That experiments in the insect contvo! of three of the most important plant pests in New Zealand, ragwort, gorso and piripiri or bidibidi, had now reached the stage of field liberation and the establishment of the insects was stated in a paper read to the agriculture and forestry section of the Australian and New Zealand Association for the Advancement of Science yesterday by the assistant director and chief entomologist of the Cawthron Institute, Nelson, Dr. D. Miller, who indicated the results it was hoped, to achieve in the eradication of these weeds.

The losses from weeds through the reduced carrying capacity of pastures, the poisoning of stock, the rejection o! farm products duo to taint, and the money spent in fighting the advance ot pests came to a large sum annually in New Zealand, he said. The value of the wool clip was reduced by £250,000 a year, through piripiri burrs. Bracken accounted for a further loss of £1,300,000, and members of the twitch family for £2OO,(XX). Ragwort caused serious losses from poisoning and could reduce the butterfat production by 30 per cent in a short time. FUNDAMENTAL POINT A fundamental point to be considered in insect control of weeds was the relationship of the plant to others of economic value, since the more isolated the weed was botanically the less likelihood there was of its specialised insect fauna being a menace to other plants. Ragwort fulfilled this condition, hut blackberry and gorse were related to plants of economic value. It was, therefore, important to select carefully insects that were restricted to the weed in question.

In all cases, insects had to be carefully tested under quarantine on all economic plants likely to be attacked. The biological control of noxious weeds in the Dominion was begun at the Cawthron Institute in 1927, and since 1928 the researphes had. aimed; at blackberry, ragwort, gorse and piripiri. The work on blackberry was abandoned since no insect was found that would sufficiently control the weed and not attack related plants of value. POTENT GROUPS More success had been found with the other three weeds. The first insect liberated for ragwort, the cinnabar moth, failed to establish sufficiently and attention was now being concentrated on seed-fly, the grubs of which were a potent factor in the destruction of ragwort seed.

The attack upon gorse was also for the purpose of destroying seeds. The insect selected was the gorse-seed weevil, and it had already been well established in several parts of the country where it was destroying a very high percentage of seeds, in some places over £0 per cent.

The Chilean saw fiy was being used with excellent results to date in the control of piripiri. The grubs were active during the late winter and until the end of December, when they not only destroyed the flowers and burrs .but also attacked the foliage. It was yet too early to see the final results under field conditions, as the insects were liberated only last winter, but the establishment was taking place. BURRS AND LEAVES

Experiment carried out under natural conditions showed that, when the insects were at approximately the same concentration as in Chile, not only the burrs but also the leaves were destroyed, and it was expected that this state, of affairs would ultimately develop in the field.

“I must take the opportunity of advising farmers not to expect immediate and spectacular results irom this work, though this may happen, and to stress the necessity for maintaining a direct attack upon weeds by the usual practices of farm 'management,” said Dr. Miller. “The use of insects, when successful, is in most cases an auxiliary aid in weed control as in the case of ragwort and gorse. With some weeds which are beyond the reach of farm management, such as piripiri, the insect attack is a major controlling factor.”