Improved Strategies for Controlling Sclerotinia blight of Peanut: Site-specific Disease Models and Advisory, Fungicide Timing, and Pathogen Detection.

Abstract

Regression strategies were used to describe the relationships between modeled environmental variables and increase of Sclerotinia blight. Changes in incremental disease incidence were described with 5-day moving averages of modeled site-specific weather variables. The model explained approximately 50% of the variability in Sclerotinia blight index in eight environments from 2002 to 2005. Linear regression was used to describe progress of Sclerotinia blight on peanut lines with varying levels of partial resistance. These models were used to develop a site- and cultivar-specific fungicide spray advisory for Sclerotinia blight. The advisory was tested at two locations in 2006. The advisory performed nearly as well as the calendar-based applications of fungicide, while saving one to two fungicide sprays depending on the level of host resistance.

Field and greenhouse experiments were conducted to investigate the timing of application and comparative efficacy of the fungicides fluazinam and boscalid. In field studies from 2004-2006, applications of fungicide that preceded the largest incremental increase in disease incidence provided the best control of disease or increased yield. Reductions in infections in the greenhouse occurred when fungicide was applied before, or up to 2 days after inoculation. Fungicide applied 4 days after inoculation did not reduce the number of infections compared to no fungicide application.

The intergenic spacer (IGS) region of the nuclear ribosomal DNA (rDNA) and a portion of the large subunit of the mitochondrial (mt) rDNA were used to design species-specific primers for S. minor. PCR protocols using primer Sm-F resulted in amplification of all S. minor isolates tested. DNA from 15 of 16 S. minor isolates were amplified with primers MtSm-F and MtSm-R. Both primer sets amplified only S. minor DNA from mixtures that also contained DNA from other soil fungi or peanut. PCR protocols with primers targeting the IGS region were more sensitive in detection of S. minor from infected peanut plant parts than primers targeting the mt region.