This report presents information from a survey of pesticide use on stored potatoes harvested in Scotland in 2018. Data were collected from 57 growers, who collectively cultivated 29 per cent of the area of potatoes grown in Scotland. Pesticide use in potato stores was recorded for crops grown for seed production and for consumption (ware potatoes). Ratio raising was used to produce estimates of national pesticide usage from the sample data.
The overall estimated quantity of potatoes stored in 2018 was approximately 1,105,891 tonnes, a slight decrease of three per cent compared with the 2016 survey. Seed potato tonnage decreased by an estimated one per cent to ca. 408,870 tonnes and ware potatoes by four per cent to ca. 697,021.
Sixty-seven per cent of seed and 80 per cent of ware potatoes sampled in 2018 were stored in refrigerated stores. The majority of the remaining stores were ambient ventilated stores. All the potatoes surveyed were stored in boxes.
The proportion of stored seed potatoes treated in 2018 was 28 per cent, significantly lower than the 47 per cent treated in 2016 and 2014. The proportion of stored ware potatoes treated increased from 11 per cent in 2016 to 13 per cent in 2018.
The principal pesticide encountered on seed potatoes in 2018 was the fungicide imazalil, which was applied to an estimated 26 per cent of the stored crop for control of a range of tuber diseases. The only other pesticide encountered was the fungicide thiabendazole, which was applied to eight per cent. Imazalil and thiabendazole were also the only fungicides used on seed potatoes in the previous two surveys. As in 2016 and 2014, a small proportion of the seed crop was treated with ethylene (<0.5 per cent). Ethylene is approved as a commodity substance for plant growth regulation in post-harvest crops under the Control of Pesticide regulations (COPR).
The sprout suppressant chlorpropham (CIPC), remains the most commonly used formulation on ware potatoes However use has decreased, with 11 per cent of the stored crop treated compared to 17 per cent in 2016, but is similar to levels of use in 2014 (seven per cent treated). In contrast, the use of ethylene increased with eight per cent of the stored crop treated, compared to one per cent in the previous survey. Ethylene was not encountered on ware crops in 2014. The sprout suppressant spearmint oil was encountered for the first time, applied to two per cent of the stored ware crop. The increase in use of non-CIPC growth regulators may have been influenced by the impending loss of chlorpropham which may have encouraged growers to use other growth regulating active substances. Thiabendazole was the only fungicidal formulation recorded, applied to <0.05 per cent of the stored ware crop, the lowest level of fungicide use in stored ware potatoes since 2012.