TURNIP FLY.

Timaru Herald, Volume CXXIII, 30 December 1926, Page 2

TURNIP FLY.

" PROVED TO BE BEETLE. Of the crops most intimately associated with animal husbandry 111 New Zealand turnips and rape are perhaps the most outstanding and universally cultivated; but they are more or less sevoroly assailed I by disease and insect depredations (writes David Miller, Entomologist, Biological Laboratory, Wellington, in the New Zealand Journal ot Agriculture). Among the insect pests 0110 of tho great drawbacks to suceces•ful turnip growing, is'the so-called-“tur-nip fly,” considerable areas of turnips in most parts of tho Dominion being annually laid .waste during the seedleaf stage,, necessitating one’or more resowings of the crops. Prior to recent investigation-of this problem nothing definite 'has been established as t the identity and-naturb; of the insert or insects responsible ad’id 'thc term “turnipily” lias been universally .used by farmers with reference to the trouble.

THE “FLY” AND ITS HABITS. The reports of damago from various turnip-growing districts of the Dominion, showed that; most of the loss Occurs during November and early December., .when, considerable areas ’of turnips are in the-first leaf." "This pointed to tho probability of the grassgrub bettle (Odontria ' Zeaiandica /White), notronibus for its depredations ’ upon the ioliago of ■ various plants, such as orchard trees, willows, etc., being the culprit, since at that period of tlio year largo swarms of the beetlo ’ are. on the w;mg. Subsequent observations proved this to be the case, although other - factors were found responsible for part of the.damage. The attack of- the “fly”—the grassgrub beetle-—is confined to the above ground portion' of tho plants affected, and practically any crop in tho seed-leaf stage during the flight of the beetle is liable to destruction. In many districts tho damage to rape is just as serious as to turnips,' but the former grows more rapidly and has better chances of recovery. At times the scedingly crop is damaged only within half a chain or so of headlands, particularly in the vicinity of hedgerows and tall grass; but though the beetle is responsible for this to a certain extent it is mostly tho work of the cutworm, Tho characteristic feature of the beetle infestation is that- the whole crop is completely destroyed, nothing being left but tho underground portion, or one or both of the seed-leaves may be partly or wholly removed from the stnlk The effect of the beetle on crops in full leaf is not so noticeable, as there is more leaf-surface to come and go on, but the attacks are neverthless apparent ,and may even result in more or less complete defoliation. The beetles eat the leaves along tho edges, so that tho latter, if hot destroyed, are noticeable on account of their serrated appearance. The beetle, as mentioned, is on the wing during November and .the first three weeks of December each year, though it may bo active in smaller numbers during the latter part of October and into January. It is nocturnal, flying usually close to the ground at dusk, when it creates the droning sound '.ohnractoiNtic of ills activity. Later in the evening they sott'e upon turnip and rape crops and other vegetation and commence to feed, and it is thus during tho night that young crops aro destroyed. On the approach of daylight the beetles cease feeding and seek shelter among the denser foliage of plants, or burrow into the ground whether covered or not by pasture.

CONTROL. The key to control should bo one of avoidance. As it is not practicable to stop tho lliglit of beetles, since they are widely Distributed throughout tho country, and their grubs breed in ground stocked with tho roots of grass both native and sown—and of many other natural and cultivated plants, tho process of control lies in regulation ot tho sowings of turnips and rape so that a few crops as practicable will he in tho seed-leaf stage during the beetle flights. That is,, in order to avoid damage, the crops sr.ould not be sown till after this period, or should be sown sufficiently early before tho flights to he so far developed in the second leaf as to bo able to with stand attack. Since the beetle’s most destructive period its dui;ing November and tho first* three weeks of'December, crops sown in October aro sufficiently advanced to bo free from serious injury later. Sowings made during November and tho first half of December are likely to be most seriously damaged and often destroyed. From tho last week in December onwards crops can be started with safety, though minor attacks occur by late-fiy-ing beetles.