Grass Grubs Active Again

Press, Volume CIX, Issue 31984, 10 May 1969, Page 10

Grass Grubs Active Again

Since the rains have started to fall, grass grubs and, to a lesser extent, porina have been showing up again in pastures.

r year, apparently due to a forj mulation factor. Some grubs , have, however, proved com- - pletely resistant to such treatr tnent. i Mr Kelsey continues to ! be concerned about the pos- , sible effect of organephes- } phates on the bacteria and > other beneficial organisms . in the soil and the effect . that this may have on soil , structure, and he believes , that in 15 to 20 yean* ? time with their continued 1 use there might be «. let of i unhappy fanners. 1 From limited experience. • on population plots at the I college and elsewhere, Dr R. ! P. Pottinger, senior lecturer • in entomology at Lincoln 1 College, said this week the ! season had started off with good egg and larval popula- • tions of porina but in almost • every case there had been a 1 very high mortality. The ’ result was that there was really no population that they were studying that would really constitute a dami aging population. ! What was responsible for the mortality had not been ’ worked out and it was hoped I that it would form the basis of a study for a doctorate of . philosophy which would be . undertaken by Mr R. French. , It was possible that the mor- . tality was closely related to . the soil moisture levels that , had prevailed, he said. Dr Pottinger said that grass . grub populations at the college, in the Weka Pass and , at Winchmore being studied I by Mr R. East did not appear [ to be significantly higher or lower this year. During the . period before the recent i rains, he said, the activity of ! the grubs in the dry soils had seemed to be slowed down, i and the grubs were also at • greater depths than would have been expected. Mr C. P. Whatman, senior . farm advisory officer of the Department of Agriculture at Ashburton, said this week there was a certain amount i of grass grub throughout the • whole of the district, but the i damage was worst in the . Carew-Ealing area, which is , well-known because of the re- ; sistance of grubs to D.D.T. In • that locality, Mr Whatman I said, the grubs were extremei ly active and while not as bad t as in 1967 they were much > more serious than last year i and serious enough to be a s matter of considerable worry t to the farmers concerned. • The position was not com--1 plicated so much as in 1967 by serious porina damage, - but on the other hand D.D.T. s resistance had reached a r stage where control measures i were very difficult D.D.T. was i now practically useless and 1 other measures were slow act-

..‘From observations mainly in Mid-Canterbury and North Canterbury Mr J. M. Kelsey, oificer-in-charge of the substation of the Entomdlogy Division of the Department of Scientific and Industrial Research at Lincoln, says that the grass grub problem looks like being pretty bad over the plains country and only a little less severe titan in the bad 1966-67 season. It was certainly more severe titan farmers bad been hoping under the earlier drought conditions. Mr Kelsey said that grass grub and porina did not feed at the maximum rate until soil moisture conditions were favourable and earlier hopes that there <c~id not be a serious problem this season under drought conditions had not been borne out. Mr Kelsey said that on light country in. the Ealing area a paddock marked out for a trial area was so badly Infested with grass grub two days after rains began that the farmer asked if he could plough it up. On an adjoining paddock on which he had been given a trial area, Mr Kelsey said that the population was more than 80 grubs per square foot as well as 23 porina pe- square foot On thU country when half an inch of rain had fallen after a little earlier rain, it had been possible for a vehicle to get bogged down because of the activity of the grubs. On such country he suggested that rolling with a Cambridge roller might help in getting grass to root and come away again, provided that this was accompanied by application of an insecticide treatment against the grubs and stock were kept off for a period. Generally, he said porina populations were not so high as they have sometimes been in the past but because of the limited pasture growth in : the drought even these low numbers could be bad enough to cause trouble. Organophosphate materials < such as diazinon, trichlor-' phon and fenitrothion were available to give quick re- 1 suits against porina, he said, ' and with organophosphates and also the longer lastingmaterials such as lindane and DDT he had good results up to the end of June against grass grubs, provided there was rain within four to seven days. However, with lindane prills it had been stated that results were not as reliable as when they were applied

much earlier. Even on some so-called resistant grubs Mr Kelsey has found that DDT prills or pellets, while ineffective in the first year, have given good results in the second

ing and expensive. Elsewhere the situation was not so bad. Porina seemed to be mainly concentrated, in paddocks that had been closed up for ‘small seeds or for hay. In these paddocks infestations were high. However, paddocks that had been grazed hard into the late summer did not appear to be very bad. There had been quite a bit of porina control done and he expected that more would be done ini the next two or three weeks. ■