Pesticide usage in Scotland: Arable Crops and Potato Stores 2024

General trends

Scottish potato storage

In 2024, the estimated quantity of potatoes stored in Scotland was 948,136 tonnes. This is very similar to the 951,194 tonnes reported in 2022 [1] and 4% less than that reported in 2020 [2] (987,615 tonnes) (Figure 1).

The quantity of seed potatoes stored in 2024 was estimated to be 313,206 tonnes, a reduction of 6% on the 2022 total of 332,745 tonnes. There has been a further reduction of 20% since 2020 when 391,208 tonnes of seed were recorded as stored.

In 2024, the estimated quantity of ware potatoes stored was 634,930 tonnes representing a 3% increase from 2022 and a 6% increase from 2020.

All potatoes surveyed were stored in boxes. Over half of seed crops were stored in refrigerated facilities (58%) with the remainder housed in ambient ventilated stores (42%). The majority of seed crops were also stored in refrigerated stores in 2022 (78%) and 2020 (60%).

Most ware potatoes in 2024 were refrigerated (88%), with the balance stored in ambient stores (12%). No unventilated stores were encountered in the survey. The proportion of ware potatoes refrigerated is comparable to 2022 (82%) and 2020 (86%).

Pesticide usage

Seed potatoes

In 2024 the estimated proportion of seed potatoes treated with a pesticide was 26%. This is similar to the 25% treated in 2022 but lower that in 2020 (39%) (Figure 2). Despite a challenging year for potato growers with wet weather delaying planting, increasing blight risk and producing variable yields, quality in store was good [3]. Therefore, pesticide use in stores remained similar to the previous survey in 2022.

In 2024 two active substances were encountered in seed potato stores. These were both fungicides with imazalil applied to 26% of the seed crop and thiabendazole applied to 3% (Figure 3, supporting document Table 2). The most used fungicide in 2022 and 2020 was also imazalil which was applied to 25% and 38% respectively. Thiabendazole use has declined in recent years. This may be linked to some storage diseases exhibiting resistance to this active substance [4]. There was no use recorded in 2022, 4% in 2020 and 8% in 2018.

Prior to 2018 the most used fungicide was a formulation of imazalil/thiabendazole applied to 27% of stored seed in 2016 and 40% in 2014. This formulation was withdrawn in 2015 and had a final use date of June 2017. Since then imazalil and thiabendazole have been applied as single active substance products in seed stores.

No ethylene has been recorded on stored seed potatoes in any survey since 2018.

Ware potatoes

In 2024 the proportion of stored ware potatoes treated with a pesticide was 9%, similar to the 8% in 2022 and 6% in 2020 (Figure 2). The proportion of ware potatoes treated with a pesticide has slowly increased since 2020, though still below the proportion treated prior to the loss of the growth regulator active substance chlorpropham (final use October 2020) (Figure 4).

Fungicide was applied to less than 0.5% of the stored ware crop in 2024. Less than 5% of stored ware potatoes have received a fungicide treatment over the last decade. Imazalil, one of only two fungicides encountered in ware potato stores in 2024, is not authorised as a plant protection product for stored ware potatoes. As noted in the 2022 potato stores report it was applied to seed crops which were later reclassified as ware.

The majority of pesticide used on stored ware potatoes were growth regulators (>99% Figure 4). Ethylene applications on stored ware potatoes increased slightly from 4% in 2022 to 6% in 2024. Spearmint oil decreased from 3% in 2022 to 1% in 2024. First approved for use in 2022, 1,4-dimethylnaphthalene increased from 1% in 2022, to 2% in 2024. This active is a naturally occurring compound found in potatoes that inhibits sprouting. Since the loss of chlorpropham in 2020, there has not been a significant increase in the use of other growth regulators in store. However, as noted in the previous report, use of maleic hydrazide has increased since the withdrawal of chlorpropham. The product is applied to the growing crop to prevent sprouting in storage. Maleic hydrazide was applied at 2% in 2018, 8% in 2020 and 12% in both 2022 [1] and 2024. Growing conditions can also influence applications of growth regulators.