PERSISTENCE AND MOVEMENT OF FUNGAL CONIDIA APPLIED TO SOIL FOR THE MANAGEMENT OF THE SUGARBEET ROOT MAGGOT, TETANOPS MYOPAEFORMIS (RODER).

Authors: Pingel, Randall; SMITH, GARRY - GM15 USDA - RETIRED; Campbell, Larry; Eide, John

Submitted to: American Society of Sugarbeet Technologists
Publication Type: Proceedings
Publication Acceptance Date: 3/22/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The fungus, Metarhizium anisopliae, has potential as an alternative to chemical soil insecticides for the management of the sugarbeet root maggot. For 3 years (1996-98) in the same field, soil applications of the fungus were made to evaluate the effectiveness of various management strategies. But, there is a need to better understand what happens to the fungus in the soil after applications, and critical questions need to be answered such as: 1) what concentration of conidia (the infective units of the fungus) is present after application, 2) does the fungus persist throughout the period during which the root maggot is active, 3) does the conidial concentration increase over time with repeated applications, 4) does timing of applications (fall vs spring) affect conidial concentration, and 5) do conidia move within the soil profile? From May 27 to Aug 19 of 1998, soil samples within the top 9 in. (in increments of 3 in.) of the soil profile were taken every 2 weeks and analyzed for the presence of conidia. There was no decease in conidial concentration throughout the sampling period. Most of the conidia were present in the top 3 in. of the soil profile, and there were fewer conidia present in the middle and bottom 3 in. of the soil profile when applications were made for only 2 years. The number of conidia did not increase with more applications, nor did timing of applications (fall vs. spring) affect the levels of conidia present in the soil. The data suggests the fungus persists overwinter and during the period of maggot activity with no appreciable reduction in conidial concentrations, there is minimal buildup of inoculum over the years or with timing of applications and there is more downward movement of conidia with more years of applications.

Technical Abstract: The fungus, Metarhizium anisopliae (Metschnikoff) Sorokin has potential as an alternative to chemical soil insecticides for the management of the sugarbeet root maggot. For 3 years (1996-98) in the same field, soil applications of an isolate of the fungus (ARS-T1) were made over rotations (wheat, barley, and sugarbeets) and seasons (fall and spring) to evaluate the effectiveness of management strategies. There is a need to better understand what happens to the fungus in the soil after applications (i.e., what concentration of conidia is present, do conidia persist throughout the season, does the fungal concentration build up with repeated applications or timing, and do conidia move within the soil profile?). From May 27 to Aug 19 of 1998, soil samples within the top 22.5 cm (in increments of 7.5 cm) of the soil profile were taken every 2 weeks and analyzed for the presence and quantity of conidia. Concentrations of conidia for the fungal treatments ranged from approximately 4E4 to 1.6E5 CFU/g of soil throughout the sampling period. The number of conidia did not increase with more applications, nor did timing of applications (fall vs. spring)affect the levels of conidia present in the soil. 57-89% of the conidia were present to the top 7.5 cm of the soil profile, and there were significantly fewer conidia present in the middle and bottom 7.5 cm of the soil profile when applications were made for only 2 years. The data suggests the fungus persists overwinter and during the period of maggot activity with no appreciable reduction in conidial concentration, there is minimal buildup of inoculum over the years or with timing of applications, and there is more downward movement of conidia with more years of applications.