Neem and karanja oil are the most promising botanical insecticides in crop protection nowadays. Given that information about the insecticidal abilities of these oils is lacking, the aim was to explore the effects of neem and karanja oil binary mixtures. The insecticidal activity of NeemAzal T/S (Trifolio-M GmbH, Lahnau, Germany) (neem oil), Rock Effect (Agro CS a.s., Česká Skalice, Czech Republic) (karanja oil), and their binary mixes (at 1:1, 1:2, and 2:1 volume ratios) against the larvae of the Colorado potato beetle (CPB; Leptinotarsa decemlineata) was studied. In our bioassays, a synergistic effect of the mixtures, which was dose-dependent, was observed for the first time against this pest. The most effective blend was the 1:1 ratio. Its efficacy was more or less the same as, or even greater than, the neem oil alone. The LC50 of neem oil two days after application was (0.075 g·L−1) and the LC50 of the mixture was (0.065 g·L−1). The LC50 of karanja oil was (0.582 g·L−1), which was much higher than the LC50 of neem oil. The LC90 of neem oil five days after application was (0.105 g·L−1) and the LC90 of the mixture was (0.037 g·L−1). The LC90 of karanja oil was (1.032 g·L−1). The results demonstrate that it is possible to lower the doses of both oils and get improved efficacy against CPB larvae; nevertheless, further verification of the results in field conditions is necessary.

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The antifungal and insecticidal effect of the essential oil from Ocimum sanctum L. was evaluated using a model set of harmful organisms hazardous for health and the economy. Toxigenic and plant pathogenic filamentous fungi, including causal agents of human infections, were chosen as exemplary fungal groups—Fusarium verticillioides, Penicillium expansum and Aspergillus flavus. Spodoptera littoralis (African cotton leafworm), Culex quinquefasciatus (Southern house mosquito), the lymphatic filariasis vector and potential Zika virus vector, and the common housefly, Musca domestica were chosen as model insects. Major and minor active substances were detected and quantified using GC/MS analysis. Environmental safety was verified using the non-target useful organism Eisenia fetida. Significant antifungal and insecticidal activity, as well as environmental safety, were confirmed. The essential oil showed the highest efficacy against A. flavus according to MIC50/90, and against S. littoralis larvae according to LD50/90. The monoterpenoid alcohol linalool, t-methyl cinnamate, and estragole as phenylpropanoids were detected as effective major components (85.4%). The essential oil from Ocimum sanctum L. was evaluated as universal and significantly efficient, providing a high potential for use in environmentally safe botanical pesticides.

The increasing scarcity of active substances approved for use in plant protection is reflected in the growing effort to find suitable plant protection alternatives. Products based on plant oils could provide a promising environmentally friendly solution. In previous research in laboratory conditions, the synergistic effect of neem and karanja oils on Leptinotarsa decemlineata (CPB) larvae was observed. The aim of this current study was to verify whether the synergistic effect would also be observed in field conditions. The active substances used included azadirachtin A (NeemAzal® T/S); in both a reduced dose of 10.6 g/ha and a normal dose of 26.5 g/ha (Neem1, Neem2), Pongamia pinnata oil (Rock Effect New–REN); in a reduced dose of 1987.6 g/ha, and a mixture of both reduced doses (MIX). The protective effect was expressed by a visual estimation of the damaged leaf area on the potato plant. The MIX variant was always among the least damaged variants throughout the experiments, while the control was always the most damaged variant. A synergistic effect was observed at site I in 2021 when the MIX variant was more than 10 times less damaged than the control; in other cases, it was around 3 times less damaged. Treatment with MIX provided a protective effect comparable to NeemAzal® T/S in the full dose. This mixture can therefore be used to expand the portfolio of suitable preparations against CPB larvae in potato production.

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