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,...
Each autumn since 1947, the Potato Marketing Board (Potato Division of the Ministry of Food before 1955) has carried out a survey of maincrop potato growers in order to obtain good, pre-harvest estimates of ware production. Fields surveyed were, in general, on the same farms each year, and the original farm sample was selected to be as representative as possible of potato crops in each region of Great Britain having regard to variety, soil type, and potato acreage. Growers of less than one acre of potatoes have not been fully represented in the annual samples since 1955 because the Marketing Board could only obtain information from registered producers and registration was not required of those who set less than one acre.Since 1952, advantage has been taken of the crop check-weighing scheme to obtain information on the incidence of Common Scab, and in the report on this work in 1952(Large and Honey, 1955 the standard yield sampling method is described. Latterly, the sampling rate has been varied such that 4 samples are taken on fields between 3 and 10 acres in size, whereas up to 8 are taken in fields of 30 acres or miore. In 1953, information was wanted on insect pest damage to the ware crop, and in 1954 and the two following years the crop check inspectors were asked to obtain supplementary information on wireworm and slug damage in each of the fields on the sample lists. In practice, nearly 3,000 ware crops, representing about 4 per cent of the national potato acreage, were inspected each season, and the sample tubers were graded as " sound " (those standing on a li-inch riddle which the trade would accept as ware), " wireworm damaged " (those with sufficient wireworm holing to render them unsaleable on the ware market), and " slug damaged ". In the rather rare cases where both types of damage occurred on the same tubers, grading was according to the pest responsible for the greater part of the damage. ACCURACY OF THE DAMAGE ESTIMATESThe accuracy of the crop check yield sampling method is known to be satisfactory. A standard error of rather less than ±0-2 tons per acre on an average yield of about 8-5 tons per acre was found by Dyke and Avis (1953) when a similar method was used on a sample of 1,000 fields in England and Wales. There remain, however, three sources of error in the detection of pest damage within the yield samples : first, tubers lifted from moist or wet ground are often covered with a thin layer of adherent soil which can obscure traces of insect damage ; second, the crop check survey work necessarily has to be carried out ten to thirty days before the crops are lifted and cannot therefore give a true picture of wireworm damage at the time of lifting ; and third, if, as Miles and Cohen (1937) have suggested, wireworm injury continues in clamped tubers, a further source of error is introduced in the assessment of national losses from crop check survey results.
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.
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