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Article

Effect of Fungicide Protection of Sugar Beet Leaves (Beta vulgaris L.): Results of Many Years Experiments

by
Iwona Jaskulska
1,
Dariusz Jaskulski
1,*,
Jarosław Kamieniarz
2,
Maja Radziemska
3,4,
Martin Brtnický
4 and
Emilian Różniak
5
1
Department of Agronomy, Faculty of Agriculture and Biotechnology, Bydgoszcz University of Science and Technology, 7 Prof. S. Kaliskiego St., 85-796 Bydgoszcz, Poland
2
Independent Researcher, 16 Skalista St., 62-080 Sierosław, Poland
3
Institute of Environmental Engineering, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776 Warsaw, Poland
4
Department of Agrochemistry, Soil Science, Microbiology and Plant Nutrition, Faculty of AgriSciences, Mendel University in Brno, Zemedelska 1, 61300 Brno, Czech Republic
5
Research & Development Centre Śmielin, 89-110 Sadki, Poland
*
Author to whom correspondence should be addressed.
Agronomy 2023, 13(2), 346; https://doi.org/10.3390/agronomy13020346
Submission received: 5 December 2022 / Revised: 15 January 2023 / Accepted: 23 January 2023 / Published: 25 January 2023
(This article belongs to the Section Pest and Disease Management)
Browse Figures
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Abstract

:
The rosette is the above-ground morphological part of sugar beet in the first year of its ontogenesis. The size and health of the leaves determine photosynthesis and the production of sugars and their redistribution throughout the plant and thus the yields and quality of individual organs. One means of protecting leaves is to apply fungicides. Their efficacy and effects of use depend on, among other things, the active ingredient and number of sprayings, as well as environmental conditions. The aim of the 11-year study was to evaluate the effect that the foliar application of fungicides in sugar beet cultivation had on leaf infestation and damage, the Leaf Area Index (LAI), leaf yield, and a plant foliage index (FI) expressed as the ratio of leaf mass to root mass. In field experiments, six treatments were compared: a control without fungicides; three sprayings with triazoles, benzimidazoles, and strobilurins as the active ingredients; and a single application of tebuconazole, epoxiconazole, strobilurin, and an epoxiconazole + thiophanate-methyl mixture. The efficacy and effects of the fungicide protection depended on its method of application and environmental conditions. Applying fungicides weakened the positive correlation of sugar beet leaf infestation and leaf damage to the sum of precipitation relative to the unprotected plants. In ten of the eleven years of the study, fungicide protection significantly increased leaf yields of plants and decreased their FI. In only three years did three sprayings increase leaf yield more than single sprayings, and, in six years, at least one of the active ingredients or the epoxiconazole + thiophanate-methyl mixture was as effective as triple sprayings. It is therefore warranted to permanently monitor the condition of plants and to select the fungicide application method depending on conditions.

1. Introduction

Sugar beet (Beta vulgaris L. subsp. Vulgaris var. Altissima Döll.) is the second most important plant after sugar cane (Saccharum officinarum L.) in sugar production. It is economically significant for its potential as an additional source of bioethanol, plastics, and pharmaceuticals production, and for the value of its roots and leaves as fodder [1,2,3]. Sugar beet cultivation is most heavily concentrated in Europe and North America. This crop currently accounts for over 4.5 million hectares of cultivated area. The largest producers of sugar beet are Russia, France, Germany, the United States of America, Turkey, Poland, China, Egypt, Ukraine, and Great Britain [4].
Sugar beet is a dicotyledonous plant with a two-year life cycle characterized by C3 photosynthesis. It belongs to the Chenopodiaceae family (now Amaranthaceae), and in its first year it forms a thickened storage root (which is the raw material of the sugar industry) and a rosette of leaves [5]. The morphology and use value of the root depend mainly on genotype [6]. The root of the sugar beet, weighing up to 2 kg, is buried in the soil and comprises about 70% of the plant’s mass. The dry matter content in the root is 15–25%, and sucrose can comprise over 20% [7,8,9]. Sugar is formed in the leaves by photosynthesis and is then transported to the roots and stored in the vascular tissues of the secondary cambium [10].
Sugar beet leaves comprise about 20–30% of the plant’s mass and are the basic organ in which photosynthesis takes place. The assimilates are then distributed to other organs, mainly the roots [11,12,13]. The optimal leaf area index (LAI) of a sugar beet canopy during the period of intense rosette formation and the formation of a dense canopy in the first year of development is approximately 3–4 m2 m−2 [14,15]. Although, according to Hoffmann et al. [16], the correlation between the yield of the roots and of the above-ground part is weak, the condition of the foliage, the intensity of photosynthesis, and the redistribution of assimilates nevertheless strongly determine the yield of roots and their technical quality [17,18]. Due to the relatively low nutritional value of sugar beet leaves and their saponin contents that limit their use as animal feed, the leaves can be used as a raw material in the chemical industry, e.g., for the production of furfurals [19] or protein extraction [20]. The above-ground part of the beet, as a waste product from the harvesting of the root, is a source of nutrients and organic matter for the soil [21].
Sugar beet foliage is determined by genotype and by environmental and agrotechnical conditions [22,23,24,25], including the occurrence of diseases and pests [26,27]. The leaves of sugar beet, including of that cultivated in Poland, are infected mainly by Cercospora beticola, Ramularia beticola, Erysiphe betae [28,29], and Alternaria tenuissima [30]. Beet susceptibility or resistance to diseases is genetically conditioned, although it also largely depends on environmental conditions and agrotechnical practices [31,32].
The principles of includentegrated production and integrated crop protection, includeding for sugar beet, emphasize the dominant roles of breeding, cultural, and biological methods in reducing the occurrence of pathogens. Protection measures, including fungicides, can be used if they serve to protect crops and their quality, but should only complement these methods [33,34,35]. To minimize the risks associated with using plant protection products, selective active ingredients should be used and changed for subsequent treatments, and doses and numbers of treatments should be kept to a minimum [36,37]. The efficacy of treatments limiting the occurrence of beet leaf diseases depends on the pathogen diagnosed and fungicide selected [38]. The key elements of a strategy to chemically control beet pathogens are type of active ingredient, number of treatments performed, and environmental and agrotechnical conditions [39,40,41].
Based on study of the literature and observations of production plantations, it was assumed that using fungicides during the sugar beet growing season improves leaf health, reduces pathogen damage, increases leaf weight and increases canopy LAI. However, the effects of fungicide protection depend on environmental conditions, including the course of the weather, the type of fungicide active ingredient used, and the number of applications.
The aim of the research was to determine the occurrence of symptoms of leaf infestation by pathogens, LAI (leaf area index), leaf yield, and leaf yield to root yield (FI index) as a result of the foliar application of fungicides in sugar beet cultivation, depending on the method of their application and various environmental conditions in 11 years of a field experiment.

2. Materials and Methods

The field experiments were carried out in the Experimental Unit of Nordzucker Polska S.A. in Kuyavia-Pomerania Voivodeship of Poland. A single-factor, long-term (11-yr) field experiment was carried out in the years 2006–2016 on sugar beet plantations on the premises of the Chełmża sugar factory (18°37′ E, 53°11′ N, 91 m a.s.l.). The experimental factor was the method of sugar beet fungicidal protection. The investigated treatments were the active ingredients from different groups in the foliar fungicides and the number of sprayings during the sugar beet vegetation period. Active ingredients registered in Poland for the protection of sugar beet and used in scientific research to reduce the occurrence of diseases of this plant were applied:
  • no fungicide—control
  • three sprayings (active ingredients: triazoles, benzimidazoles, strobilurins)
  • one spraying (tebuconazole)
  • one spraying (epoxiconazole)
  • one spraying (epoxiconazole + thiophanate-methyl)
  • one spraying (strobilurins)
Each treatment was replicated four times in a randomized block design. The experimental units were plots of 10 m × 2.7 m. Sugar beet was sown in rows with a spacing of 45 cm, and seeds were sown every 7.7 cm along the row at a depth of 2–3 cm. The plant density in the plots was corrected manually in the BBCH 12–14 phase, leaving plants at every 18–21 cm in a row.
Each year, the field experiments were located in a different field of different texture and properties, but always on Cambisols (Table 1 and Table 2). For organic carbon content in the cultivated soil layer, the coefficient of variation (CV) was 17.5% over the 11-year study period, and for content of mineral nitrogen and available forms of macronutrients it was even greater, reaching as much as 35.5%.
The characteristics and variability of thermal and precipitation conditions during the beet vegetation period in the study years were presented alongside the long-term averages based on data from the meteorological station located at PW Farol Sp. z o.o. in Falęcin, in the vicinity of the Chełmża sugar factory (Table 3). In the study years, the air temperature was most variable at the beginning of the sugar beet vegetation period (April) and at its end (September and October). In terms of total rainfall, the most variable months were April, September, and October (CV 14.6–15.5%), while the most even were from May to August (CV 6.4–7.4%).
The previous crop for sugar beet in each study year was winter wheat. The soil was conventionally tilled, being ploughed with shallow stubble cultivation and deep pre-winter ploughing. Phosphorus–potassium fertilization was dosed according to the concentrations in the soils in the experimental fields on a year-by-year basis and averaged 70 kg P2O5 ha−1 and 140 K2O ha−1. Nitrogen fertilization was dosed the same each year, at 120 kg N ha−1 divided into two doses of 60 N ha−1 pre-sowing and a top dressing of 60 kg N ha−1 in the BBCH 35–39 phase.
The sowing date ranged, depending on the research year, between the earliest date of 3 April (in 2009) and the latest date of April 24 (in 2008 and 2013). Taking into account genetic gain over the research period, different varieties of sugar beet were sown. These were, chronologically: ‘Kujawska’—four years, ‘Jagoda’—one year, ‘Pewniak’—one year, ‘Schubert’—one year, ‘Socrates’—one year, ‘Sinan’—two years, ‘Janpol’—one year.
Weeds were eliminated by a split-dose method using herbicides of dicotyledonous and monocotyledonous species. Depending on the severity and species structure of weed infestation, the following active ingredients were used: chloridazon, lenacil, metamitron, desmediphane, ethofumesate, phenmediphan, triflusulfuron-methyl, and haloxyfop-P. These were applied in accordance with manufacturer recommendations and the principles of integrated plant protection. Pests were controlled only as interventions once harmfulness thresholds had been exceeded and using active ingredients admitted for use in a given period, e.g., deltamethrin, chlorpyrifos, and dimethoate.
The foliar fungicides were applied according to the experimental factor and treatments. The long period of study and the changes in the assortment of plant protection products on the market were the reason that various preparations containing a specific active ingredient were used. On the object, where three sprays were carried out (treatment 2), they were: Amistar Gold (1.0 L ha−1), Horizon 250 EW (0.8 L ha−1), Optan 183 SE (1.0 L ha−1), Sfera 267.5 EC (0.7 L ha−1), Tebu 250 EW (0.8 L ha−1), Topsin M 500 SC (1.2 L ha−1). In single treatments, the following were used: Amistar 250 SC (1.0 L ha−1), Duett Ultra 497 SC (0.6 L ha−1), Safir 125 SC (1.0 L ha−1), Safir 125 SC (1.0 L ha−1), Soprano 125 SC (1.0 L ha−1), and Tebu 250 EW (0.8 L ha−1). A single fungicidal spraying was applied after the appearance of the first symptoms of sugar beet leaf spot (Cercospora beticola). Depending on the year, this was between 27 July and 1 September. When three sprayings were used, the first was applied in mid-July, and the third 3–4 weeks after the single-dose spraying of fungicides had been applied to other plots. Spraying was carried out with an experimental trolley sprayer AP 1–5/w with nozzles with a capacity of 0.72 L min.−1 (APORO Sp. z o.o., Poznań, PL). The working pressure was 3.0 bar, the driving speed was 4.2 km h−1, and the amount of water used for spraying was 300 L ha−1.
Immediately before the first fungicide spraying, the leaf area index of the plant canopy was determined (LAI-1), and a second evaluation was made before harvest (LAI-2). A SunScan SS1-COM system probe (Delta-T Devices Ltd., Cambridge, UK) was used to evaluate the LAI index. Before the sugar beet harvest, the degree of pathogenic infection of leaf blade and leaf damage were also assessed and expressed on a nine-point bonitation scale. Every year, the assessment was performed by the same person in accordance with the methodology used at Nord Zucker Company (1°—no infection or damage to leaf blade, 9°—entire leaf blade infected). During root harvesting, the leaf yield was determined and the plant foliage index (FI) as the ratio of leaf yield to root yield was calculated.
The results were mathematically and statistically processed in Microsoft Excel 2016 [42] and Statistica 12 [43]. The normality of distribution of results for each feature was checked using the Shapiro-Wilk test. A single-factor (fungicide protection method) analysis of the variance of normally distributed results describing the LAI index, leaf yield, and FI index was performed. The significance of the influence of the experimental factor (F statistic) and the significance of the differentiation of the studied parameters’ mean values was assessed for each treatment using Tukey’s post-hoc test at p = 0.05. Standard deviation (SD) was calculated for the results of the assessment of leaf damage.
Skewness and kurtosis were used to evaluate the shape of the distributions in the data describing how sugar beet leaf infestation differed among the study years. The strength of the relationship between the infestation of beet leaves and sum of precipitation was determined by simple Pearson correlation. In addition to the statistical significance of the correlation coefficient (r) at p = 0.05, the following classification |r| was adopted to assess its strength: 0.0–0.3 weak correlation; 0.3–0.5 moderate correlation; 0.5–0.7 strong correlation; 0.7–1.0 very strong correlation. A simple correlation calculation was also made for individual characteristics of sugar beet foliage depending on the method of fungicidal protection.

3. Results

Sugar beet foliage did not differ significantly between fungicidal protection methods in 7 out of 11 study years, and the LAI-1 index ranged from 4.95 m2 m−2 to 5.32 m2 m−2 (Figure 1). The lowest leaf area indices for the sugar beet were in 2009 (LAI-1 = 4.22 m2 m−2) and in 2008 (LAI-1 = 4.49 m2 m−2). Before harvest, after the application of fungicides in accordance with the research assumptions, the LAI-2 for individual years ranged from 3.29 m2 m−2 in 2009 to 4.0 m2 m−2 in 2013 (Figure 1). The LAI-2 in five other years (i.e., 2007, 2010, 2011, 2014, and 2016) was statistically the same as in 2013.
The fungicidal protection method significantly differentiated the pre-harvest leaf area index of the sugar beet field (Figure 2). On average, in the study years, LAI-2 was highest (3.95 m2 m−2) in the canopy where three fungicide sprayings were performed. After a single spraying of plants with epoxiconazole, epoxiconazole + thiophanate-methyl, and strobilurins, the LAI-2 index did not differ significantly from the LAI index of the beet after three sprayings, although it was 0.11–0.17 m2 m−2 lower. The LAI-2 index was lowest (3.28 m2 m−2) in plants not protected with fungicides.
Before harvesting, the sugar beet leaves were infected and had leaf blades that were damaged to degrees that varied depending on the plant protection method during the growing season. On the leaves, in different intensity in the following years, there were symptoms of the presence of cercospora leaf spot (Cercospora beticola), ramularia leaf spot (Ramularia beticola), powdery mildew (Erysiphe betae), and less beet rust (Uromyces beticola). Each year, the least infected and least damaged leaves were in the plots where fungicides were applied three times (Table 4). Only in 2006 and 2011 was the degree of infestation of beet leaves protected with epoxiconazole + thiophanate-methyl and strobilurins (and, in 2011, also with tebuconazole), the same as after three sprayings with fungicide. In each study year, the leaves of unprotected plants (in the control plot) were the most infected. Only in 2013 was the degree of infestation and damage to the leaves of unprotected plants the same as that of plants protected with the active ingredient tebuconazole.
In most years, infestation and leaf damage was greater than average (negative skewness), especially in unprotected plants. When fungicides were used, above-average infestation was also more frequent, but it was closer to average, as evidenced by the lower absolute value of the skewness index (Table 5). Protection by the triple application of fungicides resulted in leaf infection for individual years being closer to the average than single treatments, as shown by the differences in kurtosis coefficients.
The degree of infestation and damage to leaves of unprotected plants (i.e., the control) was significantly positively correlated with the sum of precipitation in April–July and in June–August. It was also strongly (r > 0.500) dependent on the sum of precipitation in the periods: May–June, June–July, June–August, June–September, and July–August (Table 6). The use of each active ingredient in a single spraying and especially three sprayings weakened the positive dependence of the degree of leaf infection on the amount of rainfall in these periods.
In ten out of eleven study years, fungicidal protection significantly influenced the yield of sugar beet leaves, and only in 2006 was no such effect found (Table 7). In each year, except 2006, the yield of leaves after three sprayings of fungicide was significantly higher than that of unprotected plants (i.e., the control), and in 2009, 2011, and 2015 it was also higher than after each single spraying. However, in 2013, the yield of leaves was highest after spraying with epoxiconazole. In 2007, leaf yields for all experimental treatments (all active ingredients and all methods of application) were significantly greater that for the unprotected control. Tebuconazole applied in one spraying increased leaf yield over unprotected plants in five years, epoxiconazole in six years, epoxiconazole + thiophanate-methyl in four years, and strobilurins in three years.
The yield of roots, similarly to the yield of leaves, varied in the study years and ranged from 58.4 t ha−1 to 89.2 t ha−1. On average, in the entire period, the highest yield of roots—80.1 t ha−1 was on the object where three sprayings were applied, and the lowest (71.9 t ha−1 on the object without fungicide protection) control was observed. The ratio of the yield of leaves to the yield of roots shaped the size of the FI index. In the first year of field experiment, fungicidal protection did not significantly differentiate the FI index (Table 8). In the following years, this index for unprotected plants (control treatment) was not significantly lower than for plants protected with all fungicides (other treatments). Three fungicidal sprayings significantly increased the FI index of plants relative to unprotected beet in 9 out of 11 years of the study, but relative to single sprayings only in 2009 and 2015. On the other hand, in each year of the study (except in 2006), at least two fungicide protection treatments used in the experiment allowed the same low or lower FI value in unprotected plants to be obtained. These were tebuconazole (7 years), epoxiconazole (8 years), epoxiconazole + thiophanate-methyl (8 years), and strobilurin (9 years).
The LAI-2 index was positively significantly correlated with the LAI-1 in sugar beet plants protected with fungicides, for single sprayings and for three sprayings. However, these indices were not significantly correlated in the canopy of unprotected control plants (Table 9). On these plots, LAI-2 was positively correlated with the degree of infection and damage to leaf blades. No such correlation was found in plants protected with fungicides; on the contrary, there was a clear, though statistically insignificant, tendency towards negative correlation. The yield of leaves from unprotected plants was correlated positively with the LAI-2 index and negatively with the degree of leaf infestation. On the other hand, in plants protected with fungicides, leaf yields were not significantly correlated with degree of infestation, and they rose as LAI-2 values increased. When sugar beet was protected with epoxiconazole + thiophanate-methyl and strobilurins, leaf yield was significantly positively correlated with both LAI-2 and LAI-1.

4. Discussion

The area in which the field experiments were performed is under a continental climate, defined as Dfb [44]. The Kuyavia-Pomerania region has one of the greatest precipitation deficits in Poland. In this region, average annual precipitation is around 500 mm or even less, and the average air temperature is around 8 °C. Meteorological conditions in this region are highly variable, both spatially and temporally, especially in the summer months [45]. Although most rainfall occurs from June to August, the risk of meteorological droughts in July–August is 26.7–40.0%. The estimated precipitation deficit in the area of the field experiments relative to sugar beet requirements is 32–49 mm, and a maximum of nearly 200 mm [46,47,48].
A detailed analysis of precipitation and thermal conditions is justified, as these strongly influence the occurrence of sugar beet diseases, including one of the most dangerous pathogens that causes heavy damage, i.e., Cercospora beticola. The conditions that are conducive to infection by and development of this pathogen are temperatures between 15 °C and 35 °C, and high air and leaf humidity [49,50]. In the authors’ own research, the degree of infestation and damage to sugar beet leaves was determined without identification of pathogens. Although changes (chlorosis, necrosis) caused by Cercospora beticola Sacc. were predominant, there were also symptoms of the presence of other pathogens, including Ramularia beticola. These pathogens differ in their optimal temperatures for development. This may, along with the low precipitation in the region, have resulted in the relatively low variability in occurrence of leaf damage in the study years, even in the absence of fungicide protection (i.e., infection from 2.3 to 5.5 on the 9-point scale); this combination of environmental factors may also account for the lack of significant dependence of leaf infestation on air temperature. Due to the lack of such a relationship, the assessment of correlation between air temperature and beet foliage was omitted in this study. However, there was a strong positive correlation between leaf infestation and rainfall conditions in some parts of the beet vegetation period, as infection by and development of many pathogenic fungi is favored by high humidity [51,52]. Higher rainfall, both in the first part of the beet vegetation period (April–June) and in the second (June–October), caused greater leaf blade infestation in plants not protected with fungicides. In most years of unprotected plants, the infestation was above average and greater than in protected plants, which indicates the widespread occurrence of leaf diseases. On the other hand, healthy, undamaged, properly developing leaves are an important assimilation organ of beet in terms of both root yield and its quality for the sugar industry [53,54,55], as well as for other uses of the leaves [56,57,58].
An effective way to protect sugar beet leaves is to apply fungicides. In using such products, it is very important to select an active ingredient and method of application appropriate to the specific production conditions, taking into account the effects of genetic gain and technological progress [59,60,61,62]. In our study, leaf infestation was effectively limited by all the active ingredients used, i.e., tebuconazole, epoxiconazole, strobilurin, and the epoxiconazole + thiophanate-methyl mixture, though to differing extents in different years. Even more effective was the extension of the protection period by the application of three fungicidal sprayings. In this case, the plants were provided with protection for about 6–8 weeks during the phases of intensive leaf and root growth, and high probability of infection. The long protection period and the use of three different active ingredients increased the probability of protection against many pathogens developing under various habitat conditions. Similar research results are presented by Kristek et al. [63]. The authors, who also used one or three fungicide sprayings against sugar beet leaf spot in the agricultural habitat conditions of Croatia, found them to have high efficacy. In the case of three treatments and the use of active ingredients from different groups, i.e., triazoles and strobilurins (as in our own study), the reduction in pathogen occurrence was significantly greater than after a single application. In turn, the high efficacy of epoxiconazole against the sugar beet leaf disease complex has been confirmed in Lithuania. One treatment reduced the occurrence of Cercospora beticola and Ramularia beticola by as much as 90% [64]. Currently, according to the principles of integrated plant protection, it is considered appropriate to use fungicides from different groups, with different active ingredients or highly effective mixtures thereof [65]. Such a procedure is dictated by, among other things, the limited risk of fungicide-resistant pathogens [66].
Other measures of the efficacy of protection of sugar beet leaves against pathogenic fungi, in addition to reduced infestation, are the pre-harvest LAI index value and leaf yield. The LAI index before the application of fungicides (LAI-1) differed over the years due to the influence of variable habitat conditions, especially soil properties and the course of the weather. According to Choluj et al. [67] and many research results presented by Varg et al. [68], the LAI of spring-sown sugar beet peaks at the transition of July to August and then falls off towards the end of the first vegetative period. In the geographical, environmental, and agrotechnical conditions of central and southern Europe, the optimal LAI index is about 3–4 m2 m−2, although it may exceed 5 m2 m−2 or even 9 m2 m−2 [69]. In the present study, depending on the year of the study, the LAI determined in July before the application of fungicides ranged from 4.22 m2 m−2 to 5.32 m2 m−2. The LAI value before harvest was 3.29–4.00 m2 m−2 and was significantly higher in plants protected with fungicides than in unprotected plants. In unprotected plants, no significant correlation was found in the level of the leaf area indices either pre-harvest (LAI-2) or before the application of fungicides (LAI-1). This indicates the dominant role that habitat conditions in the second part of the beet vegetative period have in shaping the foliage. On the other hand, there was a significant positive correlation between these indicators after fungicide use, which may have been due to the lower impact that the environment has on changes in foliage before harvest. This conclusion is also confirmed by LAI-2’s significant negative correlation with a degree of infestation and leaf damage in unprotected plants compared against the lack of such correlation in plants protected with fungicides.
The strong dependence of the state of plant foliage on environmental conditions, especially at the end of vegetation, indicates the need for plant protection. However, the use of fungicides should precede the diagnosis of disease risk, preferably using the most advanced methods and techniques [70,71,72,73]. Further to this point, in one year, the fungicide protection method was not found to have a significant effect on leaf yields or the FI index (ratio of leaf mass to root mass). Moreover, in only one of the eleven years of the study did all four active ingredients and the mixture epoxiconazole + thiophanate-methyl have the same effect on leaf yields. Meanwhile, in six of the eleven study years, at least one of the active ingredients or the epoxiconazole + thiophanate-methyl mixture was as effective as triple treatment. This indicates a need to select the optimal fungicide and the number of treatments for the given environmental and agrotechnical conditions.

5. Conclusions

The results of the study show that protecting sugar beet leaves using fungicides not only reduces infestation by fungal pathogens but also increases the LAI of the canopy (especially in the second half of the growing season), leaf yields, and the value of the FI index expressed as the ratio of the leaf mass to root mass. However, the need for and effects of foliar application of fungicides vary significantly by year and depend on the habitat and agrotechnical conditions on which the sugar beet is cultivated. In periods of high rainfall that are conducive to plant infection, fungicides have a lower positive correlation with the degree of infestation and leaf damage. However, the efficacy and efficiency of fungicide protection differs depending on its method of use. The extent to which leaf damage decreases and canopy LAI and yield increase is influenced by, among other things, the choice of active ingredient in the fungicide or mixture thereof, and by the number of sprayings. The results of the long-term study confirm the need for careful monitoring of the condition of plants before making decisions on the use of fungicides. Of the 11 years of field experiments, in one year, the fungicide protection did not significantly affect the yield of leaves or the FI index. In only three years, three sprayings increased the leaf yield more than did one spraying. The beneficial effect of each active ingredient and the epoxiconazole + thiophanate-methyl mixture on the leaf yield and FI index in all years was not confirmed. Depending on the active ingredient, a significant increase in leaf yield occurred in three to six of the eleven years of the study. Based on these experimental studies conducted in the environmental and agrotechnical conditions of Poland, one of Europe’s largest sugar producers, it was concluded that the need for permanent observation of plants in sugar beet plantations and the application of integrated protection principles to ensure the condition of their foliage has been confirmed.

Author Contributions

Conceptualization, I.J., D.J. and J.K.; methodology, I.J., J.K. and D.J.; investigation, J.K., D.J. and I.J.; resources, J.K., M.R. and M.B.; data curation, J.K., D.J., I.J., M.R., M.B. and E.R.; Formal analysis, I.J., D.J., J.K. and E.R.; writing—original draft preparation, I.J., D.J., J.K., M.R. and M.B.; writing—review and editing, I.J., D.J., J.K., M.R., M.B. and E.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors thank the company Nordzucker Polska S.A. for the possibility of performing field experiments.

Conflicts of Interest

The authors declare no conflict of interest.

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Agronomy 13 00346 g001 550
Figure 1. Leaf Area Index (±SD) of sugar beet before first fungicide spraying (LAI-1) and before harvest (LAI-2) in the study years; a–f—the same letters indicate no significant differentiation.
Figure 1. Leaf Area Index (±SD) of sugar beet before first fungicide spraying (LAI-1) and before harvest (LAI-2) in the study years; a–f—the same letters indicate no significant differentiation.
Agronomy 13 00346 g001
Agronomy 13 00346 g002 550
Figure 2. Leaf Area Index—LAI-2 (±SD) for sugar beet depending on fungicidal protection method, averaged for the study years; a, b, c—the same letters indicate no significant differentiation.
Figure 2. Leaf Area Index—LAI-2 (±SD) for sugar beet depending on fungicidal protection method, averaged for the study years; a, b, c—the same letters indicate no significant differentiation.
Agronomy 13 00346 g002
Table
Table 1. Characteristics of organic carbon content (g kg−1 soil) and soil grain size (% share of each fraction) in experimental fields.
Table 1. Characteristics of organic carbon content (g kg−1 soil) and soil grain size (% share of each fraction) in experimental fields.
CharacteristicOrganic CarbonSoil Fraction
SandSilt 0.05–0.02 mmSilt 0.02–0.002 mmClay
Minimum7.454.116.614.22.3
Maximum11.765.324.124.94.4
Mean9.357.119.520.03.3
Standard deviation1.63.22.22.60.5
Coefficient of variation CV (%)17.55.511.212.815.0
Table
Table 2. Description of soil agrochemical properties.
Table 2. Description of soil agrochemical properties.
CharacteristicpHContent
Mineral Nitrogen (kg ha−1) in the Soil Layer (cm)Available Forms *
(mg P, K, Mg kg−1 Soil)
0–3030–6060–900–90PKMg
Minimum5.831.028.815.987.369.0145.837.0
Maximum6.981.786.062.4191.2138.1266.7100.0
Mean6.452.850.541.9145.2104.0197.452.3
Standard deviation0.414.314.914.930.720.243.217.6
Coefficient of variation CV (%)6.627.029.635.521.219.521.933.7
*—P—Phosphorus, K—Potassium, Mg—Magnesium.
Table
Table 3. Characteristics of meteorological conditions during the 2006–2016 sugar beet growing seasons and in the long term.
Table 3. Characteristics of meteorological conditions during the 2006–2016 sugar beet growing seasons and in the long term.
CharacteristicMonth
AprilMayJuneJulyAugustSeptemberOctober
air temperature (°C)
Minimum7.712.715.018.317.38.86.6
Maximum11.215.618.922.121.716.111.0
Mean9.214.016.919.618.613.78.6
Standard deviation1.31.01.21.51.22.11.3
Coefficient of variation CV (%)14.67.37.37.46.415.315.5
Long-term mean8.914.116.719.118.613.68.7
precipitation (mm)
Minimum1.216.923.434.87.50.15.3
Maximum57.0159.7140.6198.1161.778.6139.0
Mean27.666.762.3114.787.635.340.0
Standard deviation17.037.035.450.848.424.440.2
Coefficient of variation CV (%)61.655.456.844.355.269.1100.4
Long-term mean29.067.059.3121.874.940.941.5
Table
Table 4. Degree (±SD) of leaf infestation by diseases (9-point scale evaluation * before harvest).
Table 4. Degree (±SD) of leaf infestation by diseases (9-point scale evaluation * before harvest).
YearTreatments
ControlThree SprayingsTebuconazoleEpoxiconazoleEpoxiconazole + Thiophanate-MethylStrobilurins
20065.0 * (±0.21)4.0 (±0.24)4.2 (±0.15)4.2 (±0.22)4.0 (±0.22)4.0 (±0.21)
20075.3 (±0.24)3.0 (±0.17)4.3 (±0.16)4.0 (±0.10)4.0 (±0.14)3.8 (±0.10)
20084.8 (±0.18)2.5 (±0.08)2.7 (±0.15)3.0 (±0.22)2.7 (±0.18)2.7 (±0.10)
20094.5 (±0.32)3.5 (±0.18)4.2 (±0.21)3.6 (±0.16)3.8 (±0.15)3.9 (±0.13)
20105.0 (±0.26)2.3 (±0.22)3.0 (±0.12)3.0 (±0.15)3.0 (±0.14)3.5 (±0.15)
20113.8 (±0.21)3.0 (±0.22)3.0 (±0.14)3.3 (±0.22)3.0 (±0.22)3.0 (±0.13)
20125.5 (±0.31)2.6 (±0.22)4.5 (±0.10)4.3 (±0.17)3.5 (±0.14)3.6 (±0.14)
20132.3 (±0.17)1.3 (±0.15)2.3 (±0.18)2.0 (±0.14)2.3 (±0.08)2.0 (±0.10)
20144.0 (±0.24)2.8 (±0.15)3.4 (±0.15)3.0 (±0.15)3.2 (±0.17)3.0 (±0.22)
20154.2 (±0.17)2.8 (±0.12)3.4 (±0.22)3.3 (±0.17)3.3 (±0.15)3.2 (±0.18)
20165.0 (±0.29)2.5 (±0.20)4.2 (±0.15)3.8 (±0.18)3.8 (±0.18)4.0 (±0.20)
*—(1—no infection and no damage to leaf blade; 9—entire leaf blade infected).
Table
Table 5. Asymmetry of degree of leaf infestation in the study years, by fungicidal protection method.
Table 5. Asymmetry of degree of leaf infestation in the study years, by fungicidal protection method.
TreatmentsSkewnessKurtosis
Control −1.5072.803
Three sprayings−0.2851.602
Tebuconazole −0.302−1.37
Epoxiconazole −0.6260.601
Epoxiconazole + thiophanate-methyl−0.417−0.643
Strobilurin−0.9090.494
Table
Table 6. Correlation coefficients * of degree of leaf infestation and sum of precipitation in different periods of sugar beet vegetation, by fungicidal protection method.
Table 6. Correlation coefficients * of degree of leaf infestation and sum of precipitation in different periods of sugar beet vegetation, by fungicidal protection method.
Period (Months)Treatments
ControlThree SprayingsTebuconazoleEpoxiconazoleEpoxiconazole + Thiophanate-MethylStrobilurins
IV–V−0.006−0.1060.1120.089−0.120−0.084
IV–VI0.3610.2170.4190.4750.3960.405
IV–VII0.693 *0.1230.4170.4830.4150.389
IV–VIII0.4800.1800.3470.3800.3160.358
IV–IX0.366−0.0910.1110.2640.3020.260
IV–X0.315−0.1140.2410.2700.1980.266
V–VI0.5240.1270.3190.2890.3360.368
V–VII0.4370.0770.3450.3000.3610.322
V–VIII0.4520.1160.3950.4060.3210.360
V–IX 0.3500.0880.2900.2230.3010.231
V–X0.313−0.1080.2470.1980.2280.214
VI–VII0.5470.1410.3900.3380.3500.382
VI–VIII0.5300.0880.4060.3800.3470.405
VI–IX0.5130.2060.3910.4000.3580.350
VI–X0.612 *0.1790.4170.3650.3130.348
VII–VIII0.5280.2280.3950.4010.3560.374
VII–IX0.3950.2050.2700.3010.2540.283
VII–X0.3880.0930.2070.2260.2680.267
VIII–IX0.4090.1260.2660.3080.2510.280
VIII–X0.3590.2130.2940.3300.2440.272
IX–X0.308−0.0850.2610.2550.2680.301
*—correlation coefficient statistically significant at p = 0.05.
Table
Table 7. Yield of sugar beet leaves (t ha−1) in the study years (±SD), by fungicidal protection method.
Table 7. Yield of sugar beet leaves (t ha−1) in the study years (±SD), by fungicidal protection method.
YearTreatments
ControlThree SprayingsTebuconazoleEpoxiconazoleEpoxiconazole + Thiophanate-MethylStrobilurins
200640.7 (±3.8) a42.0 (±2.8) a40.6 (±3.3) a40.8 (±2.6) a42.1 (±3.4) a41.8 (±2.7) a
200737.3 (±2.5) d49.8 (±2.3) a44.5 (±2.6) bc44.5 (±2.4) bc48.0 (±2.3) ab42.6 (±2.8) c
200837.6 (±2.5) e50.3 (±2.4) a46.8 (±2.4) abc47.6 (±1.9) ab41.4 (±2.0) de43.7 (±2.2) cd
200939.5 (±2.5) b48.7 (±2.7) a36.8 (±2.1) bc35.1 (±1.7) c35.9 (±1.5) c34.1 (±2.3) c
201040.7 (±3.6) c52.6 (±2.6) a44.8 (±2.3) bc45.3 (±2.6) b50.3 (±2.1) a41.2 (±2.3) bc
201140.3 (±2.8) d48.9 (±2.3) a43.5 (±2.0) bc40.6 (±1.8) cd42.1 (±2.0) bcd44.0 (±2.1) b
201237.2 (±3.2) d47.3 (±2.3) a40.3 (±2.5) bcd43.9 (±2.2) abc44.3 (±2.4) ab39.8 (±2.0) cd
201344.1 (±2.9) c50.6 (±1.8) b50.4 (±1.8) b56.0 (±2.0) a50.7 (±1.7) b46.7 (±1.9) bc
201443.5 (±2.6) c55.7 (±2.0) a52.2 (±2.1) ab44.6 (±2.3) c45.3 (±1.6) c48.0 (±2.1) bc
201541.7 (±3.1) bc48.5 (±2.2) a38.6 (±2.5) c42.5 (±2.6) b40.3 (±2.4) bc44.0 (±2.4) b
201642.8 (±2.9) c54.2 (±2.4) a46.6 (±3.1) bc50.1 (±2.7) ab47.0 (±2.5) bc45.7 (±2.6) bc
a–e—the same letters in a row indicate no significant differentiation.
Table
Table 8. Foliage index (FI) of sugar beet plants in the study years (±SD), by fungicidal protection method.
Table 8. Foliage index (FI) of sugar beet plants in the study years (±SD), by fungicidal protection method.
YearTreatments
ControlThree SprayingsTebuconazoleEpoxiconazoleEpoxiconazole + Thiophanate-MethylStrobilurins
20060.58 (±0.07) a0.60 (±0.05) a0.57 (±0.05) a0.59 (±0.05) a0.60 (±0.04) a0.60 (±0.05) a
20070.54 (±0.04) c0.59 (±0.02) ab0.57 (±0.03) bc0.56 (±0.03) bc0.61 (±0.02) a0.56 (±0.03) bc
20080.52 (±0.05) c0.61 (±0.03) a0.57 (±0.04) ab0.60 (±0.04) a0.54 (±0.03) bc0.53 (±0.03) bc
20090.71 (±0.06) b0.78 (±0.04) a0.60 (±0.05) d0.58 (±0.04) d0.61 (±0.04) cd0.65 (±0.05) c
20100.54 (±0.04) cd0.59 (±0.02) ab0.56 (±0.03) bcd0.57 (±0.03) bc0.62 (±0.02) a0.53 (±0.03) d
20110.60 (±0.03) bc0.67 (±0.02) a0.61 (±0.03) bc0.57 (±0.03) c0.61 (±0.02) bc0.63 (±0.03) ab
20120.61 (±0.05) bc0.65 (±0.04) a0.60 (±0.05) c0.64 (±0.04) ab0.62 (±0.04) abc0.54 (±0.04) d
20130.52 (±0.03) bc0.55 (±0.02) b0.60 (±0.03) a0.64 (±0.03) a0.55 (±0.02) b0.50 (±0.03) c
20140.51 (±0.04) b0.63 (±0.02) a0.61 (±0.03) a0.55 (±0.02) b0.54 (±0.02) b0.60 (±0.03) a
20150.62 (±0.04) b0.67 (±0.03) a0.57 (±0.03) cd0.61 (±0.04) bc0.55 (±0.03) d0.61 (±0.04) bc
20160.52 (±0.02) b0.59 (±0.03) a0.56 (±0.04) ab0.55 (±0.03) ab0.54 (±0.02) b0.56 (±0.03) ab
a–d—the same letters in a row indicate no significant differentiation.
Table
Table 9. Correlation of foliage characteristics of sugar beet averaged for the study years by fungicidal protection method.
Table 9. Correlation of foliage characteristics of sugar beet averaged for the study years by fungicidal protection method.
Treatments
control
FeatureLAI-1LAI-2InfestationYieldIF
LAI-11.0000.3050.2290.050−0.455
LAI-2 1.000−0.650 *0.673 *−0.592
Infestation 1.000−0.683 *0.133
Yield 1.000−0.319
FI 1.000
three sprayings
LAI-11.0000.723 *−0.2480.195−0.468
LAI-2 1.000−0.4500.620 *−0.492
Infestation 1.000−0.5520.540
Yield 1.000−0.212
FI 1.000
tebuconazole
LAI-11.0000.697 *−0.0630.441−0.190
LAI-2 1.000−0.5740.801*−0.128
Infestation 1.000−0.535−0.136
Yield 1.0000.128
FI 1.000
epoxiconazole
LAI-11.0000.621 *0.2300.342−0.202
LAI-2 1.000−0.2440.711 *−0.267
Infestation 1.000−0.558−0.189
Yield 1.0000.267
FI 1.000
epoxiconazole + thiophanate-methyl
LAI-11.0000.766 *0.0910.794 *0.179
LAI-2 1.000−0.1530.886 *−0.179
Infestation 1.000−0.3090.376
Yield 1.000−0.071
FI 1.000
strobilurins
LAI-11.0000.713 *−0.0990.603 *−0.424
LAI-2 1.000−0.3860.642 *−0.247
Infestation 1.000−0.5430.406
Yield 1.000−0.362
FI 1.000
*—correlation coefficient statistically significant at p = 0.05.
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MDPI and ACS Style

Jaskulska, I.; Jaskulski, D.; Kamieniarz, J.; Radziemska, M.; Brtnický, M.; Różniak, E. Effect of Fungicide Protection of Sugar Beet Leaves (Beta vulgaris L.): Results of Many Years Experiments. Agronomy 2023, 13, 346. https://doi.org/10.3390/agronomy13020346

AMA Style

Jaskulska I, Jaskulski D, Kamieniarz J, Radziemska M, Brtnický M, Różniak E. Effect of Fungicide Protection of Sugar Beet Leaves (Beta vulgaris L.): Results of Many Years Experiments. Agronomy. 2023; 13(2):346. https://doi.org/10.3390/agronomy13020346

Chicago/Turabian Style

Jaskulska, Iwona, Dariusz Jaskulski, Jarosław Kamieniarz, Maja Radziemska, Martin Brtnický, and Emilian Różniak. 2023. "Effect of Fungicide Protection of Sugar Beet Leaves (Beta vulgaris L.): Results of Many Years Experiments" Agronomy 13, no. 2: 346. https://doi.org/10.3390/agronomy13020346

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