Transactions of RHASS Volume 1940 - Page 053
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| Year | 1940 |
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94 INSECT AND OTHER PESTS or 1939. three or four weeks there hatch minute whitish Wireworms, which grow slowly and gradually assume the yellow-brown, glossy appearance that distinguishes the full-grown larva (Fig, 4). The latter is g in. long, thin and cylindrical, with a, pair of strong jaws and three pairs of short legs just behind the head. During the five years of their underground existence they moult eight or nine times at the rate of twice a year, in spring and autumn. For two periods each year, when they feed actively, first from March to May and again in September- October, Wireworms are abundant in the root zone near the surface. At other times they are more sparsely represented at the surface than they are at deeper levels up to 8 to 10 inches. When they have completed their growth in late summer Wireworms burrow to a depth of 6 to 8 inches, and make for themselves a small cavity in the soil, in which they change to a pupa. About a month later the pupa turns into the Click Beetle, which, however, remains dormant below ground until May of the following year. Wircworm Damage—So far as arable crops are concerned VVireworms are practically omnivorous, but some crops appear to be more susceptible to attack than others. Among those that are specially prone to injury are wheat, oatS, barley, and potatoes. Cereal crops suffer greatest damage in spring and early summer when the plants are young and the wireworm population is actively feeding near the surface. The first sign of attack is the appearance of gaps in the rows, where one plant after another has been destroyed by itinerant Wireworms which bite through the underground stem of one plant before proceeding to the next. In potatoes Wireworms may not only riddle the setts, but also disfigure the tubers with deep pits that render them unmarketable. In some recent experiments at Warburton, Cheshire, Miles and Cohen1 showed that about 25 to 55 per cent of the tubers of twelve varieties from first and second earlies and maincrops, in equal numbers of four each, were damaged by Wireworms. In each of the three groups, Sharpe’s Express, Great Scot and Arran Banner were respectively least injured, whilst Ninety-fold, Catriona and Majestic, in the corresponding groups, were badly damaged. Further trials may serve either to corroborate or contro- vert the results, which were based on trials too small to be significant. Among root crops swedes and turnips are considered to be fairly safe so far as wireworm injury is concerned, provided they escape the spring attack. Autumn attack is likely to result in nothing more serious than a slight loss in 1 Miles, H. “K, and Cohen, M., 1938. “ Investigations on \Vireworms and their Control.” Jour. Roy. Lanes. Agrie. Soc.,.repr., 31 pp. INSECT AND OTHER PESTS OF 1939. 95 yield. According to Petherbridge1 sugar-beet following grass is considerably damaged by Wireworms, but where the beets are intersown with wheat the damage is materially reduced. Of crops that are partly resistant to Wirewerm attack there are field beans and peas. Rye is less susceptible than wheat or cats, and of the Brassicas marrow-stem kale and. rape, because of their strong growth, are rarely troubled. Linseed and mustard are practically immune. Wireworm Control.—-In controlling the VVireworms of field crops after grass land there are certain cons1derations which require careful attention. The most important of these are time of ploughing, type of cultivation, ch01ce of crop, tune of sowing relative to wireworm actiVity, and system of manuring. These various questions have been recently; discussed by Miles,2 and are also emphasised in a leaflet published by the Ministry of Agriculture and Fisheries, and will be briefly reviewed here. 1. Time of Ploughing.—After a pasture or ley has been broken, VVireworins continue to subsist on the buried turf, and it is only after the turf has decayed that they turn their attention to the crop. Damage to the crop, therefore, Will depend 011 the rate of decay of the tllI'f,'11./1110h Will vary according to the kind of turf and compos1tioii of the soil. Thus a crop sown in autumn on land broken from grass .the previous summer will probably be attacked in the spring, whilst one that is sown in spring after the land has been ploughed in late winter or early spring will probably escape, and it will then be the second crop of the rotation which will suffer. But the time of ploughing is not only important in regard to the later onset of wireworm attack; it has also a direct bearing on the mass of the wireworm population. Dhus ploughing grass land in spring and autumn exposes the \Vire- worms, which are then at the surface in greater numbers than at other seasons, to the attack of msectivorous birds. It is well to remember, too, that late summer is the season when eggs, newly hatched larvae, and the inert, delicate pupae are to be found, and these are all susceptible to the disturbance of the soil by tillage operations. 2. Cultivation.—~For the control of both pests and diseases authorities are agreed that grass land should be deeply ploughed with the furrow slice completely inverted and'the sod buried to a depth of eight inches or more. Experience, too, has ‘ Petherbridge, F. R., 1938. “ \Vircworins and Sugar-Beet.” Jour. Min. A' '-., V l. XLV., ) . 23-27. h ‘ n ' g‘nlililesffl. VV., “ Wireworms and the Breaking-up of Grassland. Agri- - lt ,v l. XLVI., n. 480-488. ' . h “13 1‘l‘nzz‘vrox‘ijmiore ” chilei, No. 11, 1939. Ministry of Agriculture and Fisheries. |
| Title | Transactions of RHASS Volume 1940 - Page 053 |
