Sustainable Agriculture Reviews 31 by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783319942322
Publisher: Springer International Publishing

After pesticide application, 20 3-instar larvae were placed in the soil. The flasks were sealed with voile fabric and incubated at 27 ± 0.5 °C for nine days, until adult emergence; incubation continued for four more days at room temperature . The total insect survival was significantly affected and pathogenic activity was detected from the pupa stage on. Pupa survival was reduced (P < 0.05); the same occurred during the adult phase. No effect was observed at the larval stage. The pesticides applied to the soil affected the activity of M. anisopliae slightly: Only in the dry conidia assay the fungicides chlorothalonyl and tebuconazole reduced (86.2 and 82.5%, respectively) the survival period of C. capitata compared to the control (95.0%). The techniques used for conidia application did not influence the total insect survival rate, but conidial suspension applied on soil surface reduced survival during the pupae and adult phases (Mochi et al. 2006). Weedicides also appeared to be toxic but level of toxicity was low as evidenced from inhibition of fungal growth from 10.26 to 26.07%. There was no significant variation between attrazin, nitrofen, glyphosate and pendimethalin (23.07%), but the toxicity was more than two times of 2,4-D and butachlor inhibited 10.26 and 12.39% respectively (Rachappa et al. 2007). Li and Holdom (1994) also reported absolute safety of 2,4-D. Chemical constituents of weedicides, mostly being selective to specific group of plants may not exert toxicity to fungal spores.

Moorhouse et al. (1992) also found little correlation between in vitro laboratory studies and in situ applications of fungicides and insecticides for M. anisopliae. In their studies, there were some indications that reduced germination in vitro may be linked to reduced infection rates in soil, but this relationship was not significant. This was not the case in the acaricide, insecticide and herbicide treatment (Mochi et al. 2006). Based on fungal respiratory activity, the toxic action of a range of pesticides (acaricides, fungicides, insecticides and herbicides) on M. anisopliae in the soil is small, suggesting little negative impact on the fungal activity resulting from their use (Mochi et al. 2005). In the rhizosphere soil, some fungicides tested in these studies significantly reduced the number of M. anisopliae CFU. To my knowledge, this is the first study to consider the impact of fungicides on entomopathogenic fungal populations in the rhizosphere. The biology of entomopathogenic fungi outside of their role as entomopathogens is becoming an increasingly important area of study. The potential of utilizing rhizosphere competent entomopathogenic fungi is great and any adverse effect that chemical fungicides have on the fungal population in the rhizosphere must be considered. If the fungus is not able to persist and proliferate in the rhizosphere it may not be present at levels adequate to control BVW larvae feeding on the roots. There was no significant increase in the M. anisopliae populations in the rhizosphere in this study relative to the bulk soil populations as was observed by Bruck (2005). It can take as long as 8–10 weeks for fungal populations to increase significantly in the rhizosphere (unpublished data).

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