Advances of Fungicide Application for Winter Oilseed Rape

Abstract

The area of oilseed rape has increased dramatically during the last twelve years in Latvia: from 400 ha in 1997 to 93 900 ha in 2009. This is the reason why development of diseases has become one of the most important risk factors for oilseed rape cultivation under intensive management in Latvia. White stem rot (Sclerotinia stem rot) caused by Sclerotinia sclerotiorum, Phoma stem canker (blackleg, stem rot, Phoma leaf spot) caused by Leptosphaeria spp., and Alternaria spot caused by Alternaria spp. are the most important diseases of rape all over the world, including the Baltic region and Latvia (Brazauskiene & Petraitiene, 2004; Balodis et al., 2007). Downy mildew (caused by Peronospora parasitica) has been detected in Poland, Latvia and other regions where rape is cultivated (Sadowski et al., 2002; Bankina et al., 2008). Powdery mildew (caused by Erysiphe cruciferarum) is a significant disease in the warmer part of Europe (Mert-Turk et al., 2008), but in a temperate climate it is seldom observed, e.g., a high level of the infection was observed in Poland in the years 1998 and 1999 (Sadowski et al., 2002). Gray mould (caused by Botrytis cinerea) and wilt (caused by Verticillium dahliae) have been observed very sporadically (Sadowski et al., 2002). Clubrot (caused by Plasmodiophora brassicae) as an important disease and serious threat to oilseed rape production is recognized in many regions of Poland, especially if rape and other crucifers occupy a large part of the sowing structure (Korbas et al., 2009; Jedrycka et al., 2002). Snow mould (caused by Typhula spp.), the same as downy mildew, powdery mildew, gray mold, wilt, and clubrot, has been found also in Latvia; however, those diseases are recognized as economically unimportant in this country at present (Bankina et al., 2008). Sclerotinia stem rot has been reported as one of the most harmful diseases in many countries (United Kingdom, France, Germany, etc.). Different opinions exist regarding economic importance of the disease, as, in some cases, yield losses of up to 50% have been reported (Koch et al., 2007). However, there are data that at least half of fungicide applications have been unnecessary (Young et al., 2007). Analysis of the dataset from official field trials of the German state extension service during 1991–2003 has shown that only 33% of fungicide treatment had been economically effective (Dunker & Tiedemann, 2004). The development of Sclerotinia stem rot is dependent on meteorological conditions, therefore incidence of the disease differs greatly among the years. The first symptoms of disease are not visible at the time of fungicide application. Fungicides from different chemical groups are used to control Sclerotinia stem rot: metconazole, tebuconazole, boscalid, and others. Some differences in the efficacy of