Aphis, Virus, Warning Service Again

Press, Volume CV, Issue 31042, 23 April 1966, Page 9

Aphis, Virus, Warning Service Again

The cereal virus warning service which has functioned for the last three years to assist wheat growers in Canterbury will do so again this year.

A committee representa- . tive of the various sections : of the Department of Sden- ; tific and Industrial Research at Lincoln, the Department of Agriculture, .and Lincoln College will meet at regular intervals from the beginning of May and offer information on the prevalence or otherwise of cereal aphides on traps and in cereal crops, and on control measures. Aphis traps are operated by the Entomology Division at Lincoln and Annat on a year-round basis, and these will be supplemented by district traps operated by officers of the Department of Agriculture. The information thus gained will be made public through press and radio and should enable fanners to assess the severity of cereal virus in their own district and in relation to i sowing dates of their own I crops. This service, which has i become widely known as the "cereal aphis warning service," is intended to alert growers to the need to guard against the possibility of infection from cereal virus reducing their yield and hence the profitability of their wheat crops. The service has operated for the last three years and is based on the findings of Dr. H. C. Smith, now director of the Crop Research Division, that yields may be increased by as much as 25 per cent by a well-timed chemical spray application. The flight pattern of the cereal aphis has now been recorded over eight years at Lincoln. This shows quite clearly that very few aphides are flying in any year after the end of May, and is the basis for the now common recommendation to sow wheat where possible after June 1. Emergence after mid-June almost guarantees freedom from cereal aphis in any year. Delaying sowing, however, is not practicable in all districts, especially on heavy land. There are also some grounds for farmer opinion that earlier planting gives a better crop. The grower’s ow’ convenience may frequently determine the time of cultivation and hence of sowing. Practical Use To cover all these possibilities, the aphis-virus committee has sought to give advice which is of practical use to all farmers who sow wheat in the autumn. A study of the numbers of aphides flying will show that farmers who plant early—some as early as mid-April—are almost sure to experience trouble from aphides and yellow dwarf virus, since April is a period of peak flights for this insect. At the other extreme, those who can delay sowing till June will almost always escape aphides and virus. In between will be many growers who, for a variety of reasons, sow wheat in May. All growers can profit from the information made available through the warning service, which usually covers three points: (1) Good Crop Hygiene: Volunteer cereals should be grazed off and kept to a minimum during April and May. If this is not done aphides build up on them and they become a source from which these insects fly into adjacent paddocks of emerging wheat. Similarly, clean cultivation is important in paddocks being prepared for wheat. Grasses or cereals showing green in such paddocks are often infested with aphides, and from such sources wingless aphides crawl on to surrounding wheat plants. These infestations within the paddock can often be seen in young wheat crops as stunted patches of plants which develop yellow leaves in November and black heads with shrivelled grain in January. (2) Sowing Dates: Where it is possible, late sowing—after

June I—will lessen the risk of infestation with flying aphides. From early in May the committee issues weekly reports which serve to alert farmers as well as inform them. The information given compares the current flights with aphides numbers in previous years and provides district information as well. An “all-clear” is given when it is known that flights are finished for the season. (3) Spraying: Where other measures cannot be taken to alleviate the attack of cereal yellow dwarf virus on wheat

This article was written bv Mr A. D. Lowe, of the Entomology Division of the Department of Scientific ana Industrial Research, on behalf of the aphis and virus committee

crops, in some seasons a greatly increased yield will be possible with a single welltimed application of a chemical spray. The information issued by the committee offers guidance in this matter. Usually crops sown in April are likely to require spraying, often in the autumn. Those sown in May may need treatment depending on district and season. In very favoured areas, such as inland valleys, even June-sown crops may be infested by flights on warm winter days.

Winged aphides will fly, if they are present on the plants, whenever there are light air currents and the temperature exceeds 60 degrees F. All farmers should be aware of the need to inspect crops for the presence of aphides. If

they are not familiar with their appearance, they should seek the help of advisory officers, many of whom are well acquainted with the symptoms <rf infestation. In some winters, for reasons not yet fully understood, quite heavy infestations of aphides have failed to survive on wheat crops, and there has been no carry-over into the spring. Spraying is therefore frequently delayed until the early spring. Experimental work at Lincoln has shown that it is quite effective at any time up until early September. The committee therefore continues its activities through into the spring period, and alerts farmers at that time to the need for a final inspection of crops before the opportunity for spraying passes. Sprays are effective only if they are applied before head formation begins in the growing plant This is of course long before the head can be seen emerging and varies with seasonal temperatures. The only way to be certain that virus damage does not decrease yield is to control the aphides with a spray applied before this damage can occur. The necessary information on this timing is issued each year in the committee’s reports. In short, the committee’s work will cover the two allied activities of collecting information and issuing reports. These reports remind farmers of the need to practice good crop hygiene, and to sow late if they can. Where this is not possible, growers are alerted to the need to spray if aphides are present, and given guidance as to correct timing. Where this advice is followed, it should ensure that damage from aphides and virus are reduced to a minimum and the profitability of wheat-growing in Canterbury is maintained.