Fungicide spray programs to manage downy mildew (dryberry) of blackberry caused by Peronospora sparsa

Abstract

Downy mildew (dryberry) of blackberry, caused by Peronospora sparsa, is a major disease of blackberry in Michoacán, México. The objective of this research was to evaluate different fungicide spray programs to manage systemic infections of downy mildew and dryberry disease in two different regions of Michoacan, Mexico in the 2007 and 2008 growing seasons. The presence of asymptomatic infections of P. sparsa in experimental plots was confirmed by nested PCR using published primers amplifying a fragment of 477 bp of the ITS region of ribosomal DNA. In 2007, the experiment was conducted in an 8-year-old commercial planting in Tangancicuaro. Fungicide applications began early in the growing season approximately 10 days after bud brake (July 10). In 2008, the experiment was conducted at the same location, but treatments began later (August 4) approximately 21 days after bud break at which time plants had fully expanded leaves. An additional plot was established in Atapan in 2008. Seven fungicide programs using commercial formulations and recommended rates of mefenoxam, potassium phosphite, azoxystrobin, captan, mancozeb, copper sulfate, Bacillus subtilis, and a sanitizing agent were tested at both locations. Results from both years and locations indicated that all programs beginning with potassium phosphite (3–4 applications) on a 10–14 day schedule after bud brake, significantly reduced the severity and incidence of downy mildew on leaves, and dryberry on fruits compared to the untreated control, regardless of the fungicide (either biological or chemical) that was applied later in the season. Programs that included 1 or 2 applications of mefenoxam, the first application in drench, early in the season also provided good control. Fungicide programs that were initiated with protectant fungicides or used protectant materials only did not provide a satisfactory level of control. Early detection of systemic infections of P. sparsa through the use of PCR and the use of fungicide spray programs based on early season applications of systemic fungicides such as potassium phosphite and mefenoxam provided good to excellent control of foliar downy mildew and dryberry of blackberry in Michoacán, México.