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Novo Mesto, Slovenia

The in vitro effect of five commonly used herbicides viz., pyridate, fluazifop-P-butyl, foramsulfuron, tembotrione and S-metolachlor on mycelial growth of entomopathogenic fungus Beauveria bassiana (ATCC 74040) was evaluated each at different concentrations: 100, 75, 50, 25, 12.5, 6.25 and 0% of recommended field application rate on PDA agar plates at 15 and 25°C. The herbicides tested were classified in 1-4 scoring categories based on reduction in mycelial growth: 1 = harmless (<25% reduction), 2 = slightly harmful (25-50%), 3 = moderately harmful (51-75%), harmful (>75%) in toxicity tests. All the five herbicides had fungistatic effect to B. bassiana at varying intensities depending on their concentrations in medium. The present study showed that B. bassiana is very sensitive to the herbicides tested, particularly at recommended as well as lower field dosage. The selected herbicides foramsulfuron, tembotrione and S-metolachlor have strong fungistatic effect on mycelial growth (> 75% inhibition) at 15 °C and concentrations from 50 to 100%. Foramsulfuron has fungicidal effect at 100 % concentration. Foramsulfuron, tembotrione and S-metolachlor were less inhibitory at 25 than at 15 °C, but the temperature had no influence on reduction of mycelial growth at pyridate and fluazifop-P-butyl. Of the herbicides tested, pyridate and fluazifop-P-butyl showed less adverse effects and are probably compatible with B. bassiana in the field. However, extensive field studies complemented by parallel laboratory experiments should consider assessing the interaction between selected herbicides and B. bassiana isolates to evaluate their ecological impact in cropped environments.

Tomato leaf miner (Tuta absoluta) is a major pest on tomatoes worldwide. It can spread very easily with plantings and contaminated packaging, it can attack all aboveground parts of tomato, it is hidden from contact insecticides and has adaptive life-cycle with several secondary host plants. Because of these advantages of the pest, biological control is considered as one of the most efficient methods to control the pest, because natural enemies are active in finding host and they develop with it. According to the researches single products are not as efficient as combinations of biological control agents, biological agents and chemical insecticides, and appropriate phytosanitary measures in greenhouses, monitoring with sex pheromones and mass trapping, if necessary. In Europe, we are looking for indigenous natural enemies that could adapt to the new host and could be therefore used in biological control of tomato leaf miner. We have the same goal in Slovenia, though the damage of T. absoluta still does not have economic impact.

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