Four experiments in S.E. England (1960–1963) and one in N.E. England (1963) used different methods to expose selectively plants to swede midge infestations in the field. The two methods which were satisfactory in assessing yield losses were 1) marking naturally infested plants and 2) marking artificially infested plants with small temporary cages to confine the ovipositing midges over the plants and comparing the yields with those of nearby clean uninfested plants. The symptoms of attack were recorded and classified as either primary or secondary. The primary symptoms “swollen petiole” and “crumple leaf” were commoner and more reliable indicators of swede midge attack than the secondary symptoms “many neck” and “cabbage top” which could be caused in other ways. Yields of infested and uninfested plants were compared and it was found that the sowing date and tolerance to attack were related. Early sown plants yielded more and were more tolerant to midge attack than late sown plants even when heavily attacked. It seems that only in unfavourable growing seasons this pest would seriously affect yields of swedes. Résumé LES SYMPTÔMES DE L'ATTAQUE PAR LA CECIDOMYIE DU NAVET (CONTARINIA NASTURTII) ET L'EFFET SUR LA RÉCOLTE DES NAVETS Des expérimentations conduites en Angleterre, quatre dans le Sud‐Est (1960–1963) et une dans le Nord‐Est du pays (1963), ont utilisé différentes méthodes en vue d'exposer sélectivement des plantes de plein champ aux attaques de la Cecidomyie du navet. Les deux méthodes qui ont donné satisfaction pour l'évaluation des pertes dues à ces attaques furent: 1° — soit de marquer les plantes naturellement infestées 2° — soit d'utiliser des plantes artificiellement infestées, en les maintenant dans de petites cages temporaires avec des Cecidomyies afin de limiter la ponte à ces plantes, et de comparer ultérieurement les récoltes de ces plantes marquées avec celles de plantes à peu près saines. Les symptômes de l'attaque ont été classés en primaires ou secondaires. Les symptômes primaires «pétiole renflé» et «feuille frippée» étaient plus fréquents et représentent des indicateurs plus valables de l'attaque par la Cecidomyie que les symptômes secondaires: «many neck» et «cabbage top» qui pourraient avoir une autre origine. Les récoltes de plantes infestées et non‐infestées ont été comparées et il a été montré que ces récoltes dépendaient de la date du semis et de la tolérance aux attaques. Les plantes issues de semis précoces produisaient davantage et étaient plus tolérantes à l'égard des attaques de la Cecidomyie, même quand elles étaient fortement attaquées, que celles semées plus tard. Il semble que cet insecte ne puisse affecter de façon sérieuse les récoltes de navet que dans les années défavorables à la croissance de cette culture.

A SUMMARY of results from a survey of pest damage to the ware potato crop over the years 1954-56 has already been published (Baker and Waines, 1957). The present article covers the seven-year period 1954-60, and is restricted to a consideration of wireworm damage in England and Wales in relation to the use of soil insecticides. It includes a number of analyses that were not possible with the limited data available when the earlier paper was written.During the seven cropping seasons discussed here, 14,207 ware potato fields were visited by Potato Marketing Board field staff 2-3 weeks before the crops were lifted. The wireworm damage estimates given later in this paper therefore refer to the earliest date on which the crops might have been commercially lifted; in most cases a lifting delay of several weeks in September/October, coinciding with the peak autumnal feeding period of the wireworms, will result in something like a doubling in the amount of damage noted at crop check time. A more realistic picture of commercial wireworm damage can therefore be obtained by doubling the figures for average tuber damage, and their standard errors. While this correction is necessary for tuber damage we do not consider any appreciable correction to be needed for the proportions of crops damaged by wireworm: if enough wireworms are present in a field to do detectable damage it is almost certain that some of it at least will have been done by the time of the annual crop-check survey. ANALYTICAL APPROACHBaker and Waines emphasized that the crop-check survey fields were generally on the same farms from year to year. Over the years the sample has changed to some extent, and an independent check made by Rothamsted Statistical Department in 1958 (B. M. Church and Mary G. Hills, in lit.) indicated that growers whose crops were sampled every year tended to get somewhat higher yields than other registered potato producers. In other respects, however, the Rothamsted check suggested that substantially unbiased estimates were being obtained from the survey: thus, we calculated that 19 per cent of the ware potato growers used insecticides in 1958, compared with 20-3 per cent estimated from the independent Rothamsted sample. We have assumed that the pest damage and insecticide data from the crop-check work give a substantially correct picture of the overall position, while acknowledging that the information on tuber damage may be minimal because of the time lag between sampling and commercial lifting.It is well known that soil type, cultural treatments and other practices, can influence wireworm populations and the damage they do. Inspection of the crop-check results for each year separately showed that a three-way breakdown was possible. 94 Plant PathologyThe numbers of damaged, and the total number of inspected, Majestic and King Edward (including Red King), crops were classified as growmg on light soils (sand and gravel, silt, skirt, warp, peat, black, fen, moss, light loam, and red), on medium loams, or on heavy soils (heavy loam, clay,...

A SUMMARY of wirewomi and slug damage to ware potato crops in Great Britain for the years 1954to 1956(Baker and Waines, 1957) and a paper on wireworm damage to the ware potato crop in England and Wales, 1954 to 1960 (Strickland, Bardner and Waines, 1962 have already been published. In this paper, damage to potato crops in Scotland by wireworms and other soil pests (mainly slugs) is considered for the years 1954 to 1960. Data have been obtained from the Potato Marketing Board. Potato fields were visited two or three weeks before crops were lifted and tuber samples were examined, weighed and graded in the standard crop-check manner. In general, crop checks were made on the same farms each year.