Efficacy of Certain Pesticides Against Potato Tuber Moth, Phthorimaea operculella (Zeller), Under Field Conditions

MATERIALS AND METHODS

Experimental area: Field experiments were conducted at the Department of Plant Protection, Faculty of Agriculture, Assiut University, Assiut, Egypt.

Selected pesticides: The recommended concentrations of three commercial pesticides, which were obtained from the Central Agricultural Pesticide Laboratory (CAPL), Dokki, Egypt, belonging to different chemical groups were used in this study (Table 1).

Used cultivars: The potato that was tested (The Netherlands variety spunta) was brought from Seed Stock Exchange, Beheira Governorate, Egypt.

Assessment protocols of pesticides against Phthorimaea operculella: Field trials were carried out in the form of the Department of Plant Protection, Faculty of Agriculture, Assiut University, Assiut Governorate, during two successive summer seasons, 2021 and 2022.

The potato cultivar used is Sponta. At room temperature, the tubers were placed for two weeks while the modern growths reached 1 cm with a medium size 50-60 g weight.

The Complete Block Design (RCBD) experiments were done. The t-test distribution outline with six treatments including control and replicated three times. An experiment was conducted to evaluate the efficiency of three products against Phthorimaea operculella under field conditions, an area of 300 m² was divided into 7 plots. Spunta was cultivated on the 1st and 3rd February, 2021 and 2022, respectively. The normal agriculture treatments such as, land preparation, irrigation, mechanical weed control and fertilization were followed according to the Ministry of Agriculture recommendations and weeds were controlled using different agricultural practices. The temperature during the experimental seasons ranged between 8-25°C (from 15th January to 30th May, 2021) and from 9-30°C (from 15th January to 20th May, 2022).

A month after planting, the insects were counted and recorded every week from five randomly selected plants from each plot or 20 tubers near the surface of the soil until Phthorimaea operculella numbers reached the economic threshold level (5% live larvae for checked plants). The applications of the chemical were applied for all treatments twice with an interval of 15 days, the first was 75 days after sowing during the 2021 and 2022 seasons. The application was made using a knapsack sprayer loaded with up to 15 L. Samples of 10 leaves were seized randomly from each plot before the first spray directly and after 15 days for each spray. The individual-evaluated pesticides including indoxacarb, emamectin benzoate and sulfoxaflor were sprayed based on the recommendation of the Egyptian Ministry of Agriculture. Simultaneously, the mixtures emamectin benzoate+ indoxacarb and emamectin benzoate+sulfoxaflor were applied at the rate of half recommended dose of each pesticide within the tested mixture. The harvesting time of the yield began after 115 days according to the maturing of the potato cultivar.

Statistical analysis: Reduction percent was calculated according to Henderson and Tilton equation²⁹ and subjected to Analysis of Variance (ANOVA) using CoStat Statistical software (Microcomputer program analysis version 6.400, CoHort Software, Berkeley, California, USA) as follows:

However, the least significant difference (LSD at 5%) was used to compare the treatments.

RESULTS

The effect of two sprays of selected pesticide applications (alone and mixture) on Phthorimaea operculella larval infestation and reduction percent during the 2021 and 2022 seasons were presented in Table 2-3 and Fig. 1-2. The mean population of Phthorimaea operculella larvae that infested before spray for the two seasons ranged from 2.67 to 7.33 in all treatments and control. After spray, the percentage of mean reduction in infestation differed significantly. For all the two sprays, emamectin benzoate+sulfoxaflor treatment (70.5 and 72.5%, respectively) was the superior, followed by emamectin benzoate+indoxacarb (64.5 and 67%, respectively) and sulfoxaflor alone (51.2 and 64.2%, respectively) during 2021 and 2022 seasons. However, the treatments of emamectin benzoate and indoxacarb demonstrated the lowest mean reduction percent among the tested treatments (for emamectin benzoate was 46.5 and 53.5% and for indoxacarb was 44.3 and 44.8%, respectively) during the two seasons. In general, the mixture of emamectin benzoate and sulfoxaflor was considered the best mixture and treatment in reducing the infestation in potato potatoes.

Fig. 1:

Reduction percent of certain pesticides against potato tuber moth after the second application from the transplantation in the potato field during the 2021 season

Fig. 2:

Reduction percent of certain pesticides against potato tuber moth after the second application from the transplantation in the potato field during the 2022 season

DISCUSSION

In general, all treatments have reduced the infestation of Phthorimaea operculella during the 2021 and 2022 seasons. However, the combination of emamectin benzoate and sulfoxaflor was a powerful treatment with a reduction percent 70.5 and 72.5% during the 2021 and 2022 seasons, respectively, followed by the mixture of emamectin benzoate with indoxacarb with a reduction percent 64.5 and 67%, respectively. Further, indoxacarb alone was considered the least treatment with a reduction percent 44.3 and 44.8% during the 2021 and 2022 seasons, respectively. In this regard, seven compounds on the Phthorimaea operculella larvae under field conditions in Kafr El-Sheikh and, Egypt, emamectin benzoate (proclaim 5% WG), indoxacarb (deltarab 15% SC) and emamectin benzoate 1.5%+indoxacarb 7.5% (penny 9% SC) were effective in reduction percent (79.06, 77.83 and 75.70%, respectively) in 2014 season. However, at Al-Gharbiya Governorate, the reduction percentages were 82.48, 79.36 and 78.11%, respectively³⁰. Furthermore, another study which conducted in Sharkia Governorate, Egypt on potato plants (Kara variety) stated that emamectin benzoate (proclaim 5% WG) and emamectin benzoate+indoxacarb (penny 1.5+7.5% SC) were the most potent selected pesticides on Phthorimaea operculella larvae and the general mean reduction percentage during 2014/2015 seasons were 85.04% and 84.80%, respectively when diluted in Nile water³¹. Xentari, profenofos and abamectin were the most toxic to 1st instar larvae of Phthorimaea operculella³².

CONCLUSION

Emamectin benzoate in combination with sulfoxaflor and indoxacarb is considered the most powerful treatment against Phthorimaea operculella larvae as compared to other treatments under field conditions. These two mixtures going to be recognizable as an alternative to other pesticides in the control of potato chewing pests. However, it is necessary to perform more studies to determine the mechanisms and justifications for how molecular genetics and biochemical interactions can increase the efficacy of pesticide mixtures. Emamectin benzoate must also be combined with other pesticides in trials and the findings must be compared to those obtained, to determine the most effective mixtures for controlling Phthorimaea operculella in the field in Egypt.

SIGNIFICANCE STATEMENT

The potato crop is one of the most significant strategic and export crops in Egypt, yet it is plagued by numerous destructive pests, such as Phthorimaea operculella, which reduce crop yield significantly. Given that, this study assessed certain pesticides on Phthorimaea operculella under field conditions. The results suggested that the selected pesticides evaluated in this study can be used effectively in IPM programs under field conditions in Egypt.