Efficiency of insecticidal treatment of potato seed tubers against pests

Main potato pests and the scale of their threat

Potatoes are rich in nutrients, which is why they are affected by a wide range of harmful organisms. For many years, the Colorado potato beetle (Leptinotarsa decemlineata Say.) has remained the main phytophage during the growing season of potatoes. Among polyphagous pests, click beetle larvae (order Coleoptera, fam. Elateridae), or wireworms, are dominant, while in seed potato cultivation, the harmfulness of aphids (fam. Aphididae) — vectors of viral infection — increases.

Even when implementing protection measures in zones with consistently high numbers of Colorado potato beetles, harvest losses can reach 30.0%, and in their absence — up to 100%. Depending on the potato cultivar and the development stage of the plants at the time the pest’s harmful stage appears, losses can be up to 50%. If the Colorado potato beetle destroys 50% of the potato leaf surface before the flowering stage, the tuber harvest decreases by 2–3 times, and with 100% defoliation — by 6–8 times. An increase in the pest population density to over 40 larvae per plant completely prevents the obtaining of a harvest.

• 15 beetle larvae per plant — harvest losses of 15.0–20.0%
• 30 beetle larvae per plant — harvest losses up to 50.0%
• Tuber damage by wireworm at harvesting — up to 40–60%
• Time for Colorado potato beetle to develop resistance — 3–5 years

The harmfulness of wireworms is closely related to the hydrothermal regime of the soil. Under arid conditions, larvae begin to damage potato tubers more intensively to compensate for the moisture deficit. If the humidity level of the topsoil horizon drops below a critical point, the larvae move into deeper, moist layers. As the harvest forms, larvae of different ages concentrate near the potato plants and make tunnels in the tubers. This not only spoils the commercial appearance of the potatoes and suppresses the plants, but also opens the way for pathogens of fungal and bacterial diseases that cause dry or wet rot.

How to assess the wireworm infestation of potato batches

Reliable protection of plantings requires advanced insecticidal seed treatments with an expanded spectrum of action. It is important to remember that the uncontrolled use of chemical plant protection products allows the Colorado potato beetle to develop resistance to many active ingredients in an average of 3–5 years. To prevent this, it is necessary to search for and use products from new chemical classes.

To plan protection measures, it is important to accurately assess tuber damage by pests during the storage period in farms. For this purpose, tuber analysis is carried out according to a special methodology.

1. From each batch of potatoes weighing 10 tons, a sample of 200 tubers is taken from at least 10 different locations.
2. For every subsequent 10 tons, an additional 50 tubers are taken from at least 4 locations.
3. At a depth of 20–30 cm, tubers are taken consecutively, without selection, to ensure an equal number of tubers in the sample.
4. The selected samples are washed in the laboratory.
5. A visual inspection of each tuber is conducted for the presence of damage by click beetle larvae.

Assessment of the phytosanitary situation and experimental methodology

Phytosanitary examination of seed potatoes in storage facilities for 2021–2023 showed a high level of tuber damage by wireworms (click beetle larvae). The share of tubers with slight damage (up to 3 tunnels) reached 12.2%, and with severe damage (more than 3 tunnels) — 17.1%. During the growing season, there remains a high threat from the Colorado potato beetle: its population against the background of protective spraying fluctuates from 0.1 to 16.4 individuals per plant with maximum infestation of plantings up to 60.0%.

• Standard tolerance for wireworm for elite class — 5.0%
• Actual severe tuber damage — up to 17.1%
• Economic threshold of pest (ETP) for Colorado potato beetle on plantings — 8.0–16.0 individuals/plant
• Maximum potato infestation by the beetle — 60.0%

To assess the effectiveness of pre-planting tuber treatment, small-plot experiments were established. Trials were conducted in 2021 and 2022 on the mid-season cultivar Skarb, and in 2023 on the mid-early cultivar Manifest. The area of the experimental plot was 25 sq. m, the replication was fourfold, and the arrangement of treatments was randomized. Agricultural practices corresponded to those generally accepted for potato cultivation in the central agro-climatic zone.

Before planting, the soil infestation by wireworm was assessed by the excavation method to a depth of 30 cm. Samples were taken with a hand auger 11.3 cm in diameter with a working surface area of 0.01 sq. m in a checkerboard pattern to calculate the average number of pests per square meter. At harvesting, the proportion of slightly damaged (1 tunnel per tuber) and severely damaged (more than 1 tunnel per tuber) tubers was determined. Plant development dynamics were assessed by emergence, height, and number of stems on the 30th day (for the Manifest cultivar) and the 40th day (for the Skarb cultivar) after planting.

During the growing season, the number of Colorado potato beetles (adults, eggs, larvae) was determined on plots of 10–20 adjacent plants after the pest appeared on the control plots. The number of aphids, which are vectors of viral diseases, was estimated based on the wingless population using the 100-leaf sampling method. The obtained data were processed using analysis of variance (ANOVA) with MS Excel statistical software.

Results of the use of plant protection products

To protect potatoes from harmful entomofauna, two groups of products for pre-planting tuber treatment were tested with a working solution application rate of 10–15 l/t. The first group included single-component insecticides based on various active ingredients. The second group included multi-component insectofungicides, combining insecticidal and fungicidal protection.

• Koyot, SC (imidacloprid, 600 g/l) at an application rate of 0.25 l/t;
• Imidor Pro, SC (imidacloprid, 200 g/l) — 0.7 l/t;
• Cruiser, SC (thiamethoxam, 350 g/l) — 0.22 l/t;
• Taker, SC (clothianidin, 600 g/l) — 0.1–0.15 l/t;
• Celest Top, SC (thiamethoxam, 262.5 g/l + difenoconazole, 25 g/l + fludioxonil, 25 g/l) — 0.4 l/t;
• Shansometox Trio, SC (thiamethoxam, 262.5 g/l + difenoconazole, 25 g/l + fludioxonil, 25 g/l) — 0.4 l/t.

In the control plots without treatment, 45–49 days after planting, the Colorado potato beetle infestation reached 30.7–52.8%, with a population of 9.7–37.7 larvae per plant. Without protection, pest damage to the bushes reached 62.1–72.1%, whereas in the treated plots, the leaf surface remained without visible damage. The biological efficacy of Imidor Pro, SC was 83.4–100%, Cruiser, SC — 89.1–96.6%, Koyot, SC — 94.2–99.4%, and Taker, SC — 93.2–100%. Celest Top, SC and Shansometox Trio, SC showed 100% efficacy throughout the entire observation period.

* Note. For the control without treatment, the number of pest larvae is given (individuals per counted plant). For the other variants, the biological efficacy (%) is indicated.
Date of appearance of Colorado potato beetle larvae in the control: in 2021 — 08.07 (9.7 individuals/plant), in 2022 — 04.07 (37.7 individuals/plant), in 2023 — 04.07 (26.0 individuals/plant).

Based on the assessment of the wingless aphid population, it was established that the biological efficacy of the studied products Imidor Pro, SC, Taker, SC, Koyot, SC, Cruiser, SC, Celest Top, SC, and Shansometox Trio, SC reached 100% on all count dates, with a population in the untreated variant ranging from 10 to 17.0 individuals/100 leaves (Economic Threshold of Harmfulness 5.0–10.0 individuals/100 leaves).

When assessing the harmfulness of click beetle larvae during the potato harvest, it was determined that when using the products Imidor Pro, SC, Taker, SC, Koyot, SC, Cruiser, SC, Celest Top, SC, and Shansometox Trio, SC, there was a trend towards reduced tuber damage by wireworms, against the background of their population before planting of 21.1–41.7 individuals/m², which significantly exceeded the threshold level of harmfulness (5.0–10.0 individuals/m²). The biological efficacy of the studied products reached 71.7–95.9% in reducing the number of tubers damaged by wireworms. Table 3 – Biological efficacy of products for pre-planting treatment of tubers against wireworms in potato plantings (small-plot experiment, RUE "Institute of Plant Protection")

Rate Tuber damage, % Biological

Variant of application, l/t total efficacy, %

1 passage more than 1 passage

2021 Without treatment – 7.1 5.7 1.4 – Imidor Pro, SC 0.7 1.5 0.7 0.7 79.6 Taker, SC 0.1 0.7 0.7 0.0 90.1

2022 Without treatment – 27.2 13.3 14.0 – Cruiser, SC 0.22 7.8 3.9 3.9 71.7 Taker, SC 0.1 7.2 3.6 3.6 73.5 Taker, SC 0.15 6.1 2.7 3.4 77.7

2023 Without treatment – 7.3 2.9 4.4 – Koyot, SC 0.25 2.0 1.4 0.6 72.6 Celest Top, SC 0.4 0.3 0.3 0.0 95.9 Shansometox Trio, SC 0.4 0.3 0.3 0.0 95.9 Note. The wireworm population before planting in 2021 was 23.7 specimens/m², in 2022 – 41.7, in 2023 – 21.1 specimens/m².

In the course of the research, in addition to determining the biological efficacy of the studied products for pre-planting tuber treatment, an assessment was made of their effect on the biometric parameters of potato plants during the growing season and on crop yield.

Field trials showed that the use of such products as Taker, SC, Cruiser, SC, Koyot, SC, Celest Top, SC, and Shansometox Trio, SC did not have a significant effect on potato emergence: deviations from the untreated variant were insignificant and ranged from -5.2% to -1.1%. However, tuber treatment at planting with the insecticide Imidor Pro, SC had a negative effect on plant emergence, which decreased by 28.2% compared to the untreated variant. Table 4 – Effect of products for pre-planting treatment of potato tubers on plant biometric parameters and their productivity (small-plot experiments, RUE "Institute of Plant Protection")

Seedling emergence rate, yield, cultivar,

Treatment variant, application rate, %, pcs/plant, ± to variant without treatment

± to control, c/ha %

2021 Imidor Pro, SC 0.7 -28.2 -1.2 -1.5 69.0 27.8 Tucker, SC 0.1 -4.9 -0.4 1.0 99.9 40.2 LSD05 7.6 0.8 3.2 52.2

2022 Cruiser, SC 0.22 -5.1 0.1 0.9 139.0 57.3 Tucker, SC 0.1 -4.4 0.2 -0.3 135.9 56.1 Tucker, SC 0.15 -5.4 0.2 -0.6 148.0 61.1 LSD05 5.5 0.3 1.5 33.8

2023 Coyot, SC 0.25 -1.1 -0.3 3.9 83.2 27.7 Celest Top, SC 0.4 -1.1 -0.6 5.2 110.4 36.8 Shansometox Trio, SC 0.4 -5.2 -0.8 2.8 107.2 35.7 LSD05 6.9 0.9 4.0 59.4

Analysis of biometric indicators during the initial period growing season of potato plants (full emergence) grown from tubers treated before planting showed no negative effect of the investigated preparations on plant development. The number of productive stems per bush in the studied variants varied compared to the variant without treatment from -0.8 to 0.3 pcs/plant. However, when testing the insecticide Imidor Pro, SC, a decrease in the number of productive stems by 1.2 pcs/plant was noted, which was statistically significant.

When assessing the influence of the studied preparations (Tucker, SC; Cruiser, SC; Coyot, SC; Shansometox Trio, SC; Imidor Pro, SC) on the height of the crop, no significant change in plant growth was noted. In the experimental plots, deviations in plant height proved to be statistically insignificant and varied from 0.3 to 3.9 cm. However, when using the insectofungicide Celest Top, SC under the conditions of 2023, a significant increase in plant height by 5.2 cm was observed compared to the variant without treatment.

Comparison of yield data established that pre-planting treatment of tubers with insecticidal preparations to protect potatoes from phytophages contributes to the formation of an additional crop harvest. The preserved potato harvest when using all studied seed treatments ranged from 69.0 to 148.0 c/ha with maximum indicators when treating tubers before planting with the insecticide Tucker, SC in 2022 at an application rate of 0.15 l/t (61.1 %).

The biological efficiency of the studied insecticidal preparations (Cruiser, SC; Tucker, SC; Coyot, SC; Imidor Pro, SC; Celest Top, SC and Shansometox Trio, SC) for pre-planting treatment of tubers in protecting potatoes from harmful entomofauna on the 14th day after the appearance of pests in the variant without treatment is presented below:

By evaluating biometric indicators during the potato growing season, it was determined that the preparation Imidor Pro, SC had a phytotoxic effect on potato plants in the form of a decrease in emergence by 28.2 % and the number of productive stems by 1.2 pcs/plant relative to the variant without treatment during the initial development phases of the crop.

However, further observations showed that the use of both single-component and multi-component preparations for pre-planting treatment of potatoes contributed to the preservation of 27.8–61.1 % of the tuber harvest.

All studied preparations for pre-planting treatment of potatoes for crop protection against major pests are registered plant protection products and can be used as insecticides against the following pests:

• Colorado potato beetle;
• aphids;
• wireworms.

This application allows for expanding the range of available insecticidal preparations.

Brechko, E. V. Biological justification and improvement of the potato protection system against the Colorado potato beetle in Belarus: abstract of thesis … candidate of agricultural sciences: 06.01.07 / E. V. Brechko; National Academy of Sciences of Belarus, RUE "Institute of Plant Protection". – Priluki, 2010. – 23 p.

Brechko, E. V. Economic justification of the feasibility of conducting protective measures to reduce the population and harmfulness of the Colorado potato beetle / E.V.