2013 ASHS Annual Conference

The goals of this project were to 1) determine whether Contans  (Coniothyrium minitans, Cm) applications to flailed diseased crop residues left on the soil surface generate a “biocontrol epidemic” under western Oregon conditions and 2) evaluate efficacy of low rate (1-1.5lbs/A) at-bloom and after harvest Contans applications on white mold (Sclerotinia sclerotiorum/Ss) sclerotial survival in western Oregon.

Exp. 1.  A commercial fall cauliflower crop infested with white mold was flailed in November 2007; Contans (2 lbs/A) was applied to the decomposing residues. Sterile sclerotia were placed in bags on 4 dates then removed and evaluated for viability and Cm colonization.

Exp. 2.  Eight snap bean fields were planted, inoculated with Ss and flailed at maturity,  Sclerotia were collected, bagged and replaced in each field. Contans (1.5 lbs/A) was applied to 4 of the fields.  Bags were removed on 6 dates over 2 years and evaluated for viability and Cm colonization.

Exp. 3. Four treatments were applied at bloom to 2 bean fields (one with and one without a history of Contans): 1) water, 2) 1 lb/A Contans, 2) Contans/low rate Topsin, and 4) high rate Topsin.  White mold sclerotia were collected at harvest and evaluated for Cm colonization.

Results: Low rate Contans applications created an ongoing “biocontrol epidemic” in the field in western OR environmental conditions. Sclerotia died more rapidly in Cm+ fields than in Cm- fields. At bean planting in the second summer after fall Contans application there were still sufficient sclerotia in the Cm+ fields to generate white mold development. However, it is likely that by the following June, sclerotial populations in the Cm+ fields would be near zero. Sclerotia that developed on beans grown in fields treated the previous year with Contans died as rapidly as sclerotia treated with Contans after bean harvest. At-bloom Contans application resulted in 70-80% Cm colonication of sclerotia; high rate Topsin application resulted in the lowest colonization (15-21%), and the Contans/half rate Topsin tank mix resulted in an intermediate level of colonization (45-50%). Applying Contans to snap beans at bloom is effective but is not currently a registered use. Contans treatment may make it possible under western OR conditions to reduce white mold rotation length from 5 to 4 or 3 years. Contans should be used as one tool in a diverse white mold management toolbox including rotation, row spacing and orientation, nitrogen and irrigation management, resistant varieties, and fungicides.