Survey Confirms Value Of Spraying Wheat For Aphides

Press, Volume CII, Issue 30028, 12 January 1963, Page 7

Survey Confirms Value Of Spraying Wheat For Aphides

QFFICERS <a the Plant Diseases, Division and the Crop Research Division of the Department ot Scientific and Industrial Research at Lincoln inspected more than 300 wheat craps for severity of infection of cereal or barley yellow dwarf virus last Saturday. They made the inspection from a Canterbury Aero Club Tn-Pacer flown by Mr John Brazier of Airwork (N.Z.) Ltd. The flight route extended from Omihi and Motunau in North Canterbury to south of the Rakaia river in MidCanterbury. Dr. Harvey Smith, a plant pathologist of the Plant Diseases Division, said on his return that about a fifth of the 310 crops would suffer yield reductions as a result of virus infection ranging from 10 to 30 bushels, but over the area as a whole the yield reduction would probably be only from 8 to 10 per cent, compared with 10 to 20 per cent, in the last bad season for virus in 196061.

The survey served to contain the excellent results that have attended spraying of crops to kill aphides and limit the spread of the virus which they carry. Dr. Smith said that the reduced tom this season as compared with two years ago was largely due to the big area that had been sprayed. It had been estimated, he said, that about 30,000 acres of wheat had been spreayed tn the province last year and from the survey it seemed that at least another 30,000 to 40,000 acres could have been sprayed with advantage.

Dr. Smith was accompanied on the flight by Mr L. G. Copp, senior cereal breeder of the Crop Research Division, and Mr John Patterson of Pyne, Gould Guinness Ltd. The route was from Harewood to Rangiora, Ashley, Waipara, Omihi, Motunau, Waikari, Loburn, Cust, Oxford, Sheffield, Darfleld, Hororata, Highbank, Barrhill, Dorie, Southbridge, Springston, Prebbleton and Templeton.

As had been expected from earlier aphis incidence in crops, Dr. Smith said, the most severely affected crops were in the areas from Rangiora to Motunau and Southbridge to Templeton. There was a modereate infection in a number of crops about Darfleld and Hororata and betwen Barrhill and Rakaia and

only a slight Infection in crops between Cust andO*" ford, Sheffield and DarfieM and Highbank and Barrhill. AH crops in-Jhe Waipara, Waikari and Motunau districts which had been sprayed with a helicopter befor mid-September were looking very healthy although many crops which had not been sprayed were showing between 50 and 90 per cent infection. A similar difference between known sprayed and unsprayed crops had also been apparent in the Springston and Lincoln district A great many of the healthy crops in the districts where there was severe infection were showing tractor marks probably resulting from ground spraying treatment. Dr. Smith said that similarly trial strips sprayed by helicopter at Springston were healthy while the unsprayed strips in the same paddoek were showing between 70 and 80 per cent infection. Heli-copter-sprayed strips and tractor-sprayed areas in Aotea and Hilgendorf (1961) trials at Lincoln College were 100 per cent, healthy compared with a 50 to 80 per cent, infection where no spraying had been done.

Well Worth While

Although there had been only one aphis to the chain of row in the Aotea crop when it was sprayed on June 22, it was estimated that the yield increase would be about 12 bushels to the acre obtained for a cost of about 45s an acre for helicopter spraying or 30s an acre for ground application. Samples taken from the Hilgendorf trial had indicated a difference in yield of 21 bushels per acre for a cost of about 30s an acre for spraying.

Six crops of wheat at the college which had been sprayed in early September were looking very ' healthy. Only two college crops had not been sprayed because they had very low aphis numbers and they had since developed a virus infection of between 15 and 20 per cent. From present indications, Dr. Smith said, it appeared as though it would be advisable to spray all autumn-sown crops in the Southbridge, Lincoln, Tai Tapu and Templeion district between June and mid-September if there were any aphides at all on these crops, and in the area between Rangiora, Waipara and Motunau between June and possibly mid-August to obtain best control, because in two seasons when there had been severe out-

breaks of virus these districts had had the bighat Incidence of infection. Applications of systemic insecticides within the periods mentoaed would control aphides before populations increased and caused serious infection.

As had been noted in the 1960-61 season Dr. Smith said that there had been a marked

difference between infection in earlier and later sown crops, with the infection being much more severe where crops had been sown before mid-May.

Recommendation In future he said it seemed likely it would be a D.S.IJI. recommendation that any crop in Mid or North Canterbury sown before May and thus liable to severe virus infection should be sprayed before mid-August in North Canterbury and mid-Septem-ber in central Canterbury. Where crops were sown between the beginning of May and tiie middle of June and after the middle of June they should be sprayed by midAugust in North Canterbury and mid-September in central Canterbury if aphides were found on them.

Dr. Smith said that in future aphis surveys would be made during May and farmers would be advised in which districts spraying would be required. From the trial at Lincoln College, he said, there was no apparent benefit from spraying as early as June 22 compared with a spray application on September 10. Dr. Smith recalled that aerial operators had indicated that if farmers gave advanced notice of intention of spraying so that all spraying in a district could be done at the same time it could result in more economical operation and lower rates to growers. Although trials in MidCanterbury with lower rates of systemic insecticides—about six ounces to the acre —had given 100 per cent control of aphides, Dr. Smith said it had been found that poor control had been obtained at this level of application in South Canterbury and Otago. Similarly it had also been discovered that reduced rates of application were not giving effective control of aphides in spring crops of barley where the aphides were mainly below ground level. It was therefore recommended that all systemic insecticides be used at

the standard rate of about 10 to 12 ounces of commercial material to the acra in aU cases. With barley. Dr. Smith said, it appeared as though spraying had to be done at a much earlier stage of growth than with wheat, and returns did not appear to be as spectacular as with wheat In the case of barley there did not appeertobe "mtoUcahtoa of ineecttoide sent weedicide because the insecticide should be applied within the first month after emergence whereas the weedlcide should be used much later. Returns for spraying for aphis control in barley were in terms of five to 10 bushels to the acre against from 10 to 30 bushels in a great many cases in wheat

Dr. Smith said that it seemed that cereal yellow dwarf virus was much more prevalent in a good season for what so that if it could be controlled in these seasons It should be possible to achieve record yields. While Aotea crops had by far the highest aphis numbers, Dr. Smith mid that Arawa crops with much smaller numbers had also been severely affected by virus in several localities.