Porina, Grass Grub Bad Again This Year

Press, Volume CVI, Issue 31333, 1 April 1967, Page 8

Porina, Grass Grub Bad Again This Year

Infestations of porina caterpillars and grass grubs in pastures throughout Canterbury are worse than last year, which was recognised as being a bad year, according to Mr J. M. Kelsey, officer in charge of the Lincoln substation of the Entomology Division of the Department of Scientific and Industrial Research.

Dealing first with the porina situation, Mr Kelsey said he thought that most fanners realised that last year was a bad year for porina. About one in 10 paddocks in Mid, North and South Canterbury was bad with porina, with quite a lot having populations from 10 to 22 caterpillars per square foot. The situation had been particularly bad in Mid-Canterbury. This year the position was even worse with one in five paddocks being bad and with the average Infestation higher than last year. The highest number of caterpillars in a square foot sample was 68 and over the whole of this paddock the average was more than 30 per square foot. Once again the three areas of Canterbury were badly affected with the situation once more being most severe in Mid-Canterbury. The populations also tended to be higher on the inland side of the main south railway line. The observant farmers had got in early in making their treatments this year and most of those had achieved very good control of the pest, but because these people had made their treatments early and also because of the general severity of the problem supplies of some insecticides had already run out, which meant that some commercial interests Lad to apply for additional import licences. A great many farmers had, however, not realised that they had a porina problem and it was essential that they did something about it pretty quickly. Sampling While they should have started to sample their pastures with a spade in midFebruary to determine the level of infestation that they had, it was not too late to do something about it The sampling could be done by taking a spade square sample to a depth of seven Inches and this should be done at about 25 pace intervals over at least two rows or lines across a paddock to give a balanced idea of the position in the area. If they got only one caterpillar per three such spade square samples, which was equivalent to a square foot, they should treat the pasture. With one caterpillar per square foot up to a 10 per cent loss of cover could result.

On the basis of 22 years of observation of untreated plots in Canterbury, Southland and Otago and in the' North Island the average loss of pasture cover had ranged as follows: Catepillars Loss of cover per sq. ft per cent

Mr Kelsey said that the range was wide in a number of instances because the devastation was most serious in a dry season. When the average infestation readied 8 per square foot then there was never less than 100 per cent loss of cover. There were three materials that could be used for control of porina. They were Fenitrothion, Diazinon and Trichlorphon. Up to the middle of April each should be applied in the form of a spray. Where they were used before the end of March they could be applied at {lb of active ingredient to the acre in each case, but he did not think it was wise to continue with that rate of dosage from April onwards as with the onset of colder temperatures and the start of frosts the lib rate of each seemed to be much more reliable. Granular Form Each of these products was also produced in a granular form and if fanners delayed treatment until mid May or later they shotdd use the granular form as at 11b active ingredient it released the toxicant over a much longer period than was the case with the sprays. The position with grass grub was about parallel with that for porina. It was a very bad year again for grass grub in Mid, North and South Canterbury and again it was much more severe this year than last year, which wu also a bad year. Some paddocks which were in reasonably good shape last year had practically no roots left at all by mid-March this year, he said. Some areas which had up to 100 and 200 grubs per square foot last year had again become infested to about the same levels. This included the Te Plrita, Carew and Ealing areas. But on the other hand on some farms, where they had been persisting with routine applications of DDT over the last few years, they had no grass grub at all. When it came to treatment for grass grub control farms could be divided into those which could use DDT prills at the rate of 21b active ingredient per acre, and this was the great majority of farms in New Zealand, and those properties where DDT failure had been proved.

native materials to DDT were all granulated formulations of Lindane, Diazinon, Trichlorphon, and Fensulfothion, and these materials worked not only against the DDT-resist-ant grubs but also against those that were susceptible to DDT. Current trials showed that with Diazinon, Lindane and Fensulfothion dosage rates could be reduced to lib active

ingredient and with Fensulfothion to possibly a {lb per acre if these trials continued to show pasture improvement as they ought to. In the event of these trials with reduced dosages continuing to show improvement the cost of these materials at the 11b dosage would be: Lindane: 25s per acre. Diazinon: 40s per acre. Fensulfothion: 70s, or 35s if the dosage could be reduced to a jib. Of the alternative materials, Mr Kelsey said that Lindane was the only one that was likely to last into the second year and possibly into the third year also. The other two would last only the one year.

1 6 to 10 2 . 15 to 40 3 . 27 to 65 4 . 30 to 70 5 . 36 to 75 6 . 60 to 100 7-10 .. . 93 to 100 8 or over 10 . 100