Sensitivity of the entomopathogenic fungus Beauveria bassiana (Bals.-Criv.) Vuill. to selected herbicides.

BACKGROUND

The in vitro effect of six commonly used herbicides viz., amidosulfuron, dicamba, metribuzin, pyridate, S-metolachlor and tembotrione on mycelial growth of entomopathogenic fungus Beauveriabassiana (ATCC 74040) was investigated. Mycelial growthrates at 15 and 25°C were evaluated on PDA plates containing 100, 75, 50, 25, 12.5, 6.25 and 0% of the recommended application rate of each selected herbicide. The tested herbicides were classified in 4 scoring categories based on reduction of mycelial growth in toxicity tests.

RESULTS

All six herbicides had a fungistatic effect of varying intensities, dependent on their rate in medium, on B. bassiana. The present study showed that B. bassiana is sensitive to all tested herbicides, particularly at recommended as well as lower field rates. Metribuzin, S-metolachlor and tembotrione had a strong fungistatic effect on mycelial growth even at rates 25 and 12.5%.Pyridate was slightly harmful, depending on the rate and temperature. Dicamba and amidosulfuron had slight effect on mycelial growth. Sporulation and conidial germination of B. bassiana were significantly inhibited by all tested herbicides. Amidosulfuron and dicamba, both at 100% rate, had the lowest inhibitory effect on sporulation, i.e. 24% and 44%, respectively. Other herbicides in test showed much higher inhibitory effect on sporulation (69-95%). With exception of dicamba with 33% of conidial germination inhibition all other herbicides in test inhibited conidial germination for 70-100%. At 200% dosage, inhibition rates even increased.

CONCLUSION

Of all tested herbicides, amidosulfuron and dicamba showed the least adverse effects and are therefore probably compatible with B. bassiana in the field.