## 1 Introduction  
One of the most devastating diseases of the sugar beet (_Beta vulgaris_ L) in the continental region is Cercospora leaf spot (CLS), caused by the fungus _Cercospora beticola Sacc_[1, 2]. It causes severe leaf necrosis, resulting in decreased root weight, yield, and reduced sugar production and quality [1, 3, 4], hence significant economic losses [2, 5]. Despite crop protection measures, sugar beet yield losses due to pests (such as wireworms, fam. Elateridae), and diseases (such as downy mildew (_Peronspora farinos_), powdery mildew (_Erysiple betae_), or Ramularia leaf spot (_Ramularia beticola_), are between 30.2% and 13.1% on sandy, and on average between 37.1% and 16.7% on clay soils, respectively [6]. The most common and effective control measure against this pathogen is the use of fungicides. Several studies report the use of synthetic fungicides in comparison to contact once. According to [7], synthetic compounds such as strobilurin and benomyl, as well as pyracolostrobin + boscalid,were the most effective active compounds for Cercospora sp. Control, followed by folpet, captan and maneb, and copper. The results shown by [8], indicate the high efficacy of strobilurin fungicides, while contact fungicides provided only poor disease control efficacy and also that the combination of systemic and contact fungicides provided significantly better control compared with that obtained by single applications of each mixture component. However, the use of systemic fungicides has several drawbacks, with pathogen resistance being the most significant. This is why the advantage is given to contact fungicides. According to [3], during the past 15 years in Minnesota and North Dakota, crop rotation and combinations of different fungicides have decreased CLS infection. Many sugar beet cooperatives support the use of forecasting models and decision-support tools to ensure that fungicides are only applied when they are needed. According to [9], the use of a model to determine the time of fungicide application can eliminate up to 50% of spraying compared to a calendar spray schedule. Recommended spray volume and full product label rates should be followed when applying fungicides to achieve good coverage, resulting in better disease management and reduced selection pressure for resistance traits [10]. It is very important to choose the appropriate fungicides, their application rates, and timing, because the treatment must provide a long-lasting fungicide deposit, which is usually achieved by adding an adjuvant or wetting agent. Additionally, for _C. beticola_, it is important to use fungicides as an efficient manner for disease control. For the control of CLS, the first efficient fungicide was copper-based Bordeaux, which has been the dominant fungicide for several decades. However, limited (low) efficacy in the first place [10] led to the development of other copper-based products, such as cooper oxychloride and copper hydroxide. The copper-based fungicides are usually combined with other active ingredients to obtain multi-site activity (for example, benalaxyl + copper oxichloride). Such mixtures are considered protective or preventive, and they should be applied preventively since they do not affect fungi once they have infected the plant [11]. Contact fungicides, including the copper-based one, have several disadvantages. They do not penetrate into the plant tissue and remain active only as long as the fungicide remains on the plant surface in a sufficient concentration to inhibit fungal growth, usually 7-14 days [12]. Additionally, protective fungicides are sensitive to environmental conditions such as rainfall and solar radiation, in contrast to systemic fungicides, which are absorbed into the leaf after application and are not affected by rain wash-off and solar radiation [12]. This is the main reason why it is important to prolong the biological efficacy of protective fungicide solutions and their resistance to rainfall.