Pesticide usage in Scotland: Arable Crops and Potato Stores 2024

Data and methodology

Sampling and data collection

Using the June 2024 Agricultural Census [10], a sample was drawn representing arable cultivation in Scotland.

The country was divided into 11 land-use regions (Figure 31). Each sample was stratified by these land-use regions and according to holding size. The holding size groups were based on the total area of arable crops grown. The sampling fractions used within both regions and size groups were based on the areas of relevant crops grown rather than number of holdings, so that smaller holdings would not dominate the sample.

The survey covered pesticide applications to arable crops where all or the majority of the growing season was in 2024. As well as recording treatments applied directly to the crop, data was also collected on land preparation treatments prior to sowing or planting the crop.

Following an introductory letter and phone call, data was collected during a phone interview or by email. Where necessary, information was also collected from agronomists and contractors. In total, information was collected from 313 holdings growing arable crops (Tables 12). These 313 holdings represent 9% of the total crop area grown.

Raising factors

National pesticide use was estimated by ratio raising. This is a standard statistical technique for producing estimates from a sample. It is the same methodology used by the other UK survey teams and has been used for all historical datasets produced by the Pesticide Survey Unit, allowing comparability over time. The sample data were multiplied by raising factors (Table 15). These factors were calculated by comparing the sampled area to the areas recorded in the Agricultural Census within each region and size group. An adjustment (Tables 16) was made for each crop within each region by applying the raising factors to the sample area of each crop grown and comparing this with the census area. This adjustment modifies the estimate to take into account differences in composition of crops encountered in the sample and those present in the population. A second adjustment was necessary for some crops which were present in the population but were not encountered in the sample in some strata.

Detailed data tables and data used to create the charts in this report are available in Excel format in the supporting document published separately.

Changes from previous years

There are changes which should be noted when comparing the 2024 data with the previous survey.

The 2024 report follows a different structure to earlier survey reports. Previously full data tables were included in survey reports. This report only includes short summary data tables for each of the crops but references full data tables published in Excel format in a supporting document. This is a similar format used in other Scottish Government accredited publications. Figures have also been improved to meet accessibility criteria.

For this report and other reports prior to 2022, the June Agricultural Census was used to draw a sample of farmers growing relevant crops to participate in the survey. National pesticide use was then estimated by ratio raising, by comparing the sample area to the areas recorded in the June Agricultural Census data. However, there was no June Agricultural Census in 2022. Instead the May 2022 Single Application Form data was used to draw the sample and estimate national pesticide use (see the 2022 report for full details). This should be taken into account when comparing 2024 data with the previous survey in 2022.

Integrated Pest Management (IPM) data was not collected during the 2024 survey. It is anticipated that IPM data will be collected during the 2026 survey and subsequently published.

Data quality assurance

The dataset underwent several validation processes as follows; (i) checking for any obvious errors upon data receipt (ii) checking and identifying inconsistencies with use and pesticide approval conditions once entered into the database (iii) checking of data held in the database against the raw data. Where inconsistencies are found these are checked against the records and with the grower if necessary. Additional quality assurance is provided by sending reports for review to members of the Working Party on Pesticide Usage Surveys and other agricultural experts. In addition, the Scottish Pesticide Survey Unit is accredited to ISO 9001:2015. All survey related processes are documented in Standard Operating Procedures (SOPs) and our output is audited against these SOPs by internal auditors annually and by external auditors every three years.

Main sources of bias

The use of a random stratified sample is an appropriate survey methodology. A stratified random sample, grouped by farm size and region, is used to select holdings used in this survey. Sampling within size groups is based on area rather than numbers of holdings, so that smaller size groups are not over-represented in the sample. The pesticide survey may be subject to measurement bias as it is reliant on farmers/growers recording data accurately. As this survey is not compulsory it may also subject to non-response bias, as growers on certain farm/holding types may be more likely to respond to the survey than others. Reserve lists of holdings are held for each stratum to allow non-responding holdings to be replaced with similar holdings.

Experience indicates that stratified random sampling, including reserves, coupled with personal interview technique, delivers the highest quality data and minimises non-response bias.

Standard errors

The figures presented in this report are produced from surveying a sample of holdings rather than a census of all the holdings in Scotland. Therefore, the figures are estimates of the total pesticide use for Scotland and should not be interpreted as exact. To give an idea of the precision of estimates, relative standard errors (RSE) for total pesticide use on arable crops for both area and weight have been calculated. Standard errors are produced using the raising factors. An overall variance is calculated by summing the variance estimates for individual strata (region and size group) multiplied by the square of their raising factors. These variance estimates include a finite population correction. The overall standard error is calculated from the overall variance by taking its square root. This method of standard estimation was implemented as it is both relatively straightforward and has advantages over ratio estimator methods when within-strata sample sizes are small.

Standard errors are expressed as percentage relative standard errors for both total pesticide use by area treated and for weight applied. Larger relative standard errors mean that the estimates are less precise. A relative standard error of 0% would be achieved by a census. A relative standard error of 100% indicates that the error in the survey is of the same order as the measurement. Relative standard errors may be reduced with larger sample sizes. However, larger relative standard errors can also result from greater variability in pesticide use among holdings.

The RSE for estimates of total pesticide use on arable crops in 2024 was 3% for area and 4% for weight, the same as in 2022. For constituent crop groups, the RSE varied from 3% to 43% for area and 5% to 57% for weight, varying with sample size and uniformity of pesticide regime encountered (Table 18). High standard errors mean that there is more uncertainty associated with estimates of pesticide use.

Response rates

See supporting document (Table 17) which summarises the number of holdings contacted during the survey.

Financial burden to farmers

In order to minimise the burden on farmers, the survey team used non-visit methods of collection such as email, post or telephone call.

To determine the total burden that the 2024 arable crop survey placed on those providing the information, the surveyors recorded the time that 313 respondents spent providing the data during the surveys. This sample represents 100% of growers surveyed. The median time taken to provide the information was 18 minutes.

The following formula was used to estimate the total cost of participating:

Burden (£) = No. surveyed x median time taken (hours) x typical hourly rate* (* using median “Full Time Gross” hourly pay for Scotland of £19.26) [12]

The total financial burden to all growers resulting from participation in the 2024 arable crop survey was calculated to be £1,809.