Protection of Oats against Puccinia and Drechslera Fungi in Various Meteorological Conditions

Abstract

Due to their multi-purpose use and, in many cases, lower requirements and financial outlays for cultivation, oats are an interesting crop. However, fungal diseases may contribute to significant declines in grain yields and quality. The aspects that may potentially influence this matter of fact include weather conditions. The aim of the study was to determine the severity of diseases caused by fungi in oat cultivation during the vegetation season. The next goal was to assess the efficacy of the selected active ingredients (a.i.) of fungicides from the chemical groups of triazoles and strobilurins in selected diseases’ control under various meteorological conditions. All of the fungicides were applied in the form of a spray treatment to reduce the severity of the diseases in the cultivation of different oat varieties. Husked and naked oat varieties were used. The health status of the oat plants was determined on the basis of a macroscopic evaluation of plants performed in accordance with the proper methodology. Field experiments were carried out under different weather conditions, which varied over the years during which the trials were conducted. Statistically significant differences were found in the reduction in infection for F and F1 leaves with D. avenae and P. coronata in comparison to the control treatment, regardless of the a.i. used. The use of a.i. tebuconazole (250 g/L), a.i. epoxiconazole (125 g/L), a.i. azoxystrobin (250 g/L) and a.i. picoxystrobin (250 g/L) enabled a reduction in the severity of oat helmintosporiosis in all years of the study for all the varieties analyzed. The efficacy was 72.4%, 74.2%, 71.5%, and 73.1%, respectively. Higher efficacy in reducing P. coronata was found in comparison with D. avenae. The obtained research results confirm the satisfactory efficacy of the above-mentioned active substances in reducing the fungi D. avenae and P. coronata.

1. Introduction

Oat (Avena sativa L.) is an annual species from the Poaceae family, cultivated in the world on 10.2 million ha [1], which is only 4.7% of the area where wheat is sown (218 million ha). Due to the wide range of products obtained from processed grain and the favorable composition of macronutrients, including highly unsaturated lipids and high fiber content—glucans, in oat grain—this species an important element of the food chains of humans and animals [2,3,4,5]. Oat grain also contains other important bioactive compounds, such as polyphenols, which, together with fibers, protect against the development of chronic diseases, including cancer [6].

In Poland, oats are grown in all cultivated areas. This plant is characterized by low and moderate soil and thermal requirements, but to obtain high yields, in addition to proper agrotechnics, the availability of water is necessary—especially in the period from the stem elongation stage (BBCH 30) to the end of heading stage (BBCH 59). Currently, the area under oat cultivation is 0.47 million ha [7]. There are 38 varieties of spring oats registered in the Polish National Register of Oat Varieties, including 35 common oats and 3 varieties of naked oats.

Oats may be infected with pathogenic fungi; like other cereal species, they may occur on leaves, stems, and panicles, which may lead to lower and poorer-quality grain yields [8,9]. The most important diseases caused by fungi on oat plants include the following: oat crown rust (Puccinia coronata f. sp. avenae P. Syd & Syd) and oat leaf helmintosporiosis [Pyrenophora avenae Ito and Kurib (anamorpha of Drechslera avenae)]. Oat crown rust is considered an important and dangerous disease for oats [10]. The disease occurs in many regions of Europe, North America, South America, Africa, and Asia [11,12,13,14,15,16]. The optimal weather pattern for the development of oats is also the optimal condition for the development of oat crown rust; therefore, the greatest losses caused by the disease (10–50%) are observed in years when the oat yield should be the highest [17,18,19,20]. Helmintosporiosis of oats caused by the fungus [Pyrenophora avenae Ito and Kurib (anamorpha of Drechslera avenae)] is one of the most harmful and widespread oat diseases. In early-infected oat plantations, seedlings may be destroyed, and plants may die in the early stages of development [21], which consequently leads to a reduction in the plant density per square meter. The development of the pathogen takes place at a temperature of 6–8 °C, and in the event of drought in the initial period of plant development, it is inhibited [9,21]. A number of studies conducted around the world have concerned the harmfulness of the above-mentioned substances [22,23,24] and their molecular characteristics [25,26,27,28]; however, there is a lack of current scientific reports on the possibility of their chemical reduction using fungicides [20,29,30,31].

The aim of this study was to assess the effect of active substances of fungicides from the chemical group triazoles and strobilurins used via spraying to reduce the severity of oat helmintosporiosis and oat rust in oat cultivation under various meteorological conditions prevailing in the years of the study. The research hypothesis assumed that varied weather conditions do not affect the effectiveness of the fungicides used in protecting oat plants against oat helmintosporiosis and oat rust.

2. Materials and Methods

This research was carried out in the years 2012–2016 based on the experiment established at the Field Experimental Station (PSD) Winna Góra, belonging to the Institute of Plant Protection-National Research Institute in Poznań. The studies were designed as two-factor experiments, in a randomized block design, with four field replications. The size of the experimental plots was 15 m² (1.5 m × 10 m). The research was carried out on sandy clay soil, quality class III b, with a pH of 5.5.

The subject of the studies were four husked oat varieties, i.e., Arab (Poznańska Hodowla Roślin Ltd., Tulce, Poland), Bingo (Hodowla Roślin Strzelce, Sp. z o.o., Strzelce, Poland), Arden and Breton (DANKO Hodowla Roślin Sp. z o.o., Choryń, Poland), and Maczo, a naked variety of Hodowla Roślin Strzelce, Sp. z o.o. The Arden variety is characterized by good resistance to helmintosporiosis, high resistance to powdery mildew, septoria leaf blight and crown and stem rust. The Arab variety has quite a high resistance to oat crown rust, average to stem rust, and low to the powdery mildew of cereals and grasses. The Bingo variety has a high resistance to powdery mildew, stem and crown rust, and leaf septoria, and it has quite high resistance to helmintosporiosis. The Breton variety has high resistance to powdery mildew, as well as good resistance to leaf septoria and helmintosporiosis, and the Maczo variety has high resistance to crown rust for oats and powdery mildew for cereals and grasses, but quite low resistance to helmintosporiosis for oats.

In the following years, oats were sown with a Unia row seeder (Grudziądz, Poland) in rows with a spacing of 12.5 cm to a depth of 3.5 cm at a density of 550 grains × m⁻², and they were harvested with an experimental plot combine harvester, the Wintersteiger Classic (Ried im Innkreis, Austria), at the full maturity stage (BBCH 89). After harvest, the grain yield (dt × ha⁻¹) at 14% humidity and the weight of 1000 grains were determined.

In the conducted studies, fungicides containing active substances from the chemical group of strobilurins (azoxystrobin and picoxystrobin) and triazoles (epoxiconazole and tebuconazole) were used. Azoxystrobin was used at a dose of 250 g × ha⁻¹ (Amistar 250 SC, 1.0 l × ha⁻¹, Syngenta Poland, Warsaw, Poland), picoxystrobin at a dose of 250 g × ha⁻¹ (Acanto 250 SC, 1.0 l × ha⁻¹, DuPont Poland, Warsaw, Poland), epoxiconazole at 125 g × ha⁻¹ (Rubric 125 SC, 1.0 l × ha⁻¹, Cheminova A/S, Harboøre, Denmark), and tebuconazole at 250 g − ha⁻¹ (Sparta 250 EW, 1.0 l × ha⁻¹, Cheminova A/S, Lemvig, Denmark). The spraying treatments that were the subject of the research were carried out in the BBCH oat stage of 59–63, using a Wachowiak backpack sprayer (Poznań, Poland) equipped with a compressed air cylinder and a spray boom with 4 nozzles (DG TeeJet 110-02 VS, TeeJet, Glendale Heights, IL, USA), which were placed at a distance of 25 cm from each other. The spray’s liquid flow rate was set to 200 l × ha⁻¹, and the working pressure was 2.5 bars. The distance between the spray boom and the plant surface was 50 cm.

The assessment of oat leaf infection with pathogenic fungi was carried out in BBCH stages 71–75, 10–14 days after treatment, on subflag and flag leaves marked as F and F1. The occurrence of P. coronata and D. avenae was assessed on the leaves. The determination of plant infection with leaf pathogens was performed according to the EPPO 2012 (European and Mediterranean Plant Protection Organization) disease determination key, in which it is expressed as a percentage of the infected leaf area with visible etiological symptoms, in accordance with the EPPO PP 1/26 methodology (4). For each disease, the percentage of plants with symptoms, regardless of their severity, and the infection index were calculated. The effectiveness of the fungicide was calculated according to Abbott’s formula:

$${\displaystyle \frac{\mathrm{a}-\mathrm{b}}{\mathrm{a}}}\times 100[\%]$$

where a = the percentage of infection in the control, and b = the percentage of infection in combination with the assessed fungicide.

The analysis of meteorological data was based on the readings of the meteorological stations of the Institute of Plant Protection-National Research Institute in Poznań, located at the Field Experimental Station (PSD) Winna Góra (52°12′36″ N, 17°26′4″ E). To determine water relations in the environment, Sielianinow’s hydrothermal index (

Table 1. Classes of Sielianinow’s hydrothermal index.

K-Index Classes	Values	Color Marking
Extremely dry	k ≤ 0.4
Very dry	0.4 < k ≤ 0.7
Dry	0.7 < k ≤ 1.0
Slightly dry	1.0 < k ≤ 1.3
Optimum	1.3 < k ≤ 1.6
Slightly humid	1.6 < k ≤ 2.0
Humid	2.0 < k ≤ 2.5
Very humid	2.5 < k ≤ 3.0
Extremely humid	k > 3.0

) [32] was used, and it was calculated according to the formula [33]:

$$k={\displaystyle \frac{P}{0.1\times \mathit{\Sigma }t}}$$

where K denotes the value of the hydrothermal index, P—the monthly sum of precipitation, and t—the sum of the average daily air temperatures for a given month.

The humidity characteristics of the months were determined according to the value of the K index [34] (

Table 2. Values of Sielianinow’s hydrothermal index and characteristics of thermo-humidity conditions in individual months of 2012–2016.

Month	Year
	2012	2013	2014	2015	2016
January	0.0	0.0	3.7	5.8	0.0
February	0.0	0.0	0.5	1.8	3.2
March	0.5	0.0	2.2	2.8	1.8
April	0.9	0.8	1.2	0.8	0.0
May	0.9	1.9	2.8	0.7	0.5
June	0.7	1.5	0.8	1.1	0.6
July	1.1	0.7	1.1	1.6	1.8
August	1.9	0.2	1.1	0.3	0.5
September	1.6	2.7	1.7	0.4	0.0
October	1.2	0.5	0.8	1.2	1.7
November	0.8	2.9	0.8	2.7	2.3
December	2.2	2.0	4.9	1.4	6.9

).

Table 3. Weather conditions during field study in Winna Góra.

Month	Average Temperature [°C]						Precipitation [mm]
	2012	2013	2014	2015	2016	1960–2016	2012	2013	2014	2015	2016	1960–2016
March	6.2	–2.1	7.4	6.0	4.0	3.2	10.6	23.0	22.4	33.4	55.0	29.5
April	9.3	8.2	11.3	9.2	9.1	8.2	22.4	23.6	28.2	26.2	39.8	31.2
May	15.1	14.1	14.1	13.4	15.2	13.4	54.4	79.0	43.2	23.0	35.4	47.4
June	16.7	18.6	17.3	16.1	18.1	16.7	109.2	17.0	25.3	50.6	105.4	62.8
July	19.1	20.1	22.4	20.0	19.3	18.2	75.8	40.0	57.8	54.2	145.6	76.9
August	19.4	19.2	17.5	22.1	18.2	17.8	59.8	35.8	56.8	60.6	31.6	63.7
March–August	14.3	13.0	15.0	14.5	14.0	12.9	332.2	218.4	233.7	248.0	412.8	311.5

presents the average temperature and total precipitation in the years of the study, from the beginning of spring vegetation until the harvest of crops. The aforementioned data for the multi-year period (1960–2016) are also included. In most cases, the average temperature for the multi-year period was lower for individual months than in the years of the study. In the case of the March–August periods, in the years 2012–2016, the average temperature was higher than for the multi-year period. Precipitation in the individual years of the study was not evenly distributed, but there was no month in which the total precipitation was lower than 10 mm.

The compliance of the empirical distribution of the observed features with a normal distribution was tested using the Shapiro–Wilk normality test [35]. An analysis of variance (ANOVA) was performed to verify the null hypotheses about the lack of influence of individual factors on the variability of the observed features. Depending on the experiment, the following were used: a three-way ANOVA (years, varieties, and fungicides); a two-factor ANOVA (years and means); a two-factor ANOVA (years and varieties); and a one-factor ANOVA (pure substances and agents separately). For each combination of levels of the studied factors, mean values and deviations were calculated for the observed features. The least significant differences (LSDs) were calculated. Homogeneous groups were created based on the smallest significant differences. The density distribution of the observed features, determined according to individual differentiating factors, is presented in the form of density charts. The correlation of the observed features was determined on the basis of Pearson’s linear correlation indexes. The significance of the correlation indexes was tested at the following significance levels: 0.05, 0.01, and 0.001. The correlation index is presented in the appropriate tables. The relationship between the yield and individual quantitative characteristics was analyzed using regression analysis. The power of individual trend equations was characterized using the R2 index of determination.

3. Results

The occurrence of oat helmintosporiosis depended on the active substance used and the variety and varied between years (

Table 4. Efficiency of Drechslera avenae control [%] in years 2012–2016 in Winna Góra.

Variety	Treatments	2012		2013		2014		2015		2016
		Inf. 1	Efficacy	Inf. 1	Efficacy	Inf. 1	Efficacy	Inf. 1	Efficacy	Inf. 1	Efficacy
Arab	Untreated check	13.38 a	0.0	9.10 b	0.0	11.31 a	0.0	8.00 ab	0.0	5.13 bcd	0.0
	Azoxystrobin 2	3.00 b	77.6	0.43 e	95.3	4.81 defg	57.5	0.94 h	88.3	0.69 ef	86.6
	Epoxiconazole	4.50 b	66.4	1.53 cde	83.2	4.50 defgh	60.2	2.19 fgh	72.7	0.94 ef	81.7
	Picoxystrobin	2.50 b	81.3	1.31 de	85.6	5.00 def	55.8	2.69 efgh	66.4	2.31 def	54.9
	Tebuconazole	3.75 b	72.0	2.03 cde	77.8	4.88 defg	56.9	2.63 efgh	67.2	0.25 f	95.1
Arden	Untreated check	11.75 a	0.0	11.6 b	0.0	9.50 ab	0.0	7.50 abc	0.0	6.00 abc	0.0
	Azoxystrobin	3.25 b	72.3	0.78 de	93.3	4.56 defgh	52.0	5.63 bcde	25.0	1.00 ef	83.3
	Epoxiconazole	3.25 b	72.3	0.68 de	94.2	4.31 defgh	54.6	3.56 defgh	52.5	1.00 ef	83.3
	Picoxytrobin	2.25 b	80.9	1.90 cde	83.6	2.38 efghi	75.0	4.94 bcdef	34.2	1.13 ef	81.3
	Tebuconazole	2.25 b	80.9	3.73 cd	67.9	5.44 cdef	42.8	3.06 defgh	59.2	2.00 def	66.7
Bingo	Untreated check	11.25 a	0.0	4.60 c	0.0	6.7 bcd	0.0	4.63 cdefg	0.0	8.50 a	0.0
	Azoxystrobin	2.50 b	77.8	0.98 de	78.8	3.44 efghi	49.1	1.50 gh	67.6	0.88 ef	89.7
	Epoxiconazole	2.50 b	77.8	0.48 e	89.7	1.44 hi	78.7	1.00 h	78.4	1.81 ef	78.7
	Picoxytrobin	2.00 b	82.2	0.78 de	83.2	2.25 fghi	66.7	0.63 h	86.5	1.13 ef	86.8
	Tebuconazole	3.50 b	68.9	0.49 de	89.4	1.06 i	84.3	1.31 h	71.6	1.00 ef	88.2
Breton	Untreated check	12.50 a	0.0	9.10 b	0.0	5.56 cde	0.0	6.25 bcd	0.0	6.88 ab	0.0
	Azoxystrobin	2.00 b	84.0	0.43 e	95.3	3.69 defghi	33.7	2.88 efgh	54.0	2.25 def	67.3
	Epoxiconazole	2.50 b	80.0	1.53 cde	83.2	1.38 hi	75.3	3.69 defgh	41.0	2.81 cdef	59.1
	Picoxytrobin	1.75 b	86.0	1.31 de	85.6	1.69 ghi	69.7	2.69 efgh	57.0	3.75 bcde	45.5
	Tebuconazole	2.80 b	77.6	2.03 cde	77.8	1.56 hi	71.9	3.50 defgh	44.0	0.88 ef	87.3
Maczo 3	Untreated check	13.75 a	0.0	17.25 a	0.0	8.31 abc	0.0	10.00 a	0.0	6.63 ab	0.0
	Azoxystrobin	3.50 b	74.6	2.40 cde	86.1	4.94 def	40.6	1.44 gh	85.6	1.88 ef	71.7
	Epoxiconazole	2.50 b	81.8	1.65 cde	90.4	3.19 efghi	61.7	3.38 defgh	66.3	0.63 ef	90.6
	Picoxytrobin	3.50 b	74.6	0.58 de	96.7	3.00 efghi	63.9	2.94 efgh	70.6	1.81 ef	72.7
	Tebuconazole	2.75 b	80.00	2.50 cde	85.5	4.00 defghi	51.9	3.25 defgh	67.5	1.50 ef	77.4
LSD (0.05)		Variety: 0.647; fungicide: 0.647; years: 0.647; V × F: 1.447; V × Y: 1.447; F × Y: 1.447; V × F × Y: 3.235

¹ average % of infested area of leaf blades of F and F1 leaves; ² rates: azoxystrobin, 250 g × ha⁻¹, epoxiconazole, 125 g × ha⁻¹, picoxystrobin, 250 g × ha⁻¹, and tebuconazole, 250 g × ha⁻¹; ³ naked variety. Different letters (a–i) indicate statistically different mean values (α = 0.05).

). The average infection of the F and F1 leaves of plants from untreated objects of the examined varieties ranged from 4.60 to 17.25%. In 2012, the most severely infected variety was Maczo—on average, 13.8% of the area of its leaf blades was infected. In the case of other varieties, the infection ranged from 11.25% to 13.38%. The tested fungicides reduced the severity of the disease in all varieties by 66.4-86.0%. The disease was most effectively reduced via the use of a fungicide containing picoxystrobin; in the Arab, Arden, Bingo, and Breton cultivars, this reduction was over 80.9–86.0%, and in Maczo, it was 74.54%. The lowest effectiveness in reducing oat helmintosporiosis was obtained in the Arab variety after the application of epoxiconazole and in the Bingo variety after the application of tebuconazole, at 66.36% and 68.89%, respectively.

In 2012, the weather conditions for the development of oat plants were unfavorable (IV–VII months). The value of the Sielianinow coefficient ranged from 0.7 to 1.1 (very dry–slightly dry). The stress conditions that occurred allowed the pathogen to develop intensively. The average level of infection of the control objects of the analyzed varieties was measured at 12.52%. In 2013, the highest infection with D. avenae was recorded in plants of the Maczo variety from the control site, at 17.25% of the leaf blade area (Table 4). In the case of the other varieties, the infection ranged from 4.6 to 11.6%. The obtained values of infection with D. avenae differed statistically significantly between the varieties. The disease was most effectively controlled via the use of fungicides from the strobilurins chemical group. In the Maczo variety, picoxystrobin reduced the infection by 96.7%; in the remaining varieties, it did so by 83.2–85.6%. Azoxystrobin used in the Arab, Arden, and Breton varieties reduced the infection by 95.3%, 93.3%, and 95.3%, respectively. The lowest effectiveness in reducing paralysis after the use of tebuconazole was in the Arab and Arden varieties, at 77.8%, 67.9%, and 77.8%, respectively.

In 2013, the weather conditions for the development of oats plants were moderately optimal (IV–VII months). The value of the Sielianinow coefficient ranged from 0.7 to 1.9 (very dry–slightly humid). The conditions prevailing in the critical developmental stages of oats were favorable for their development and also for the development of D. avenae. The average level of infection of the control objects for the analyzed varieties was measured at 10.33%.

In 2014, symptoms of helmintosporiosis were found in 5.56–11.31% of the infected leaf blade area in plants growing in the control plots. The highest effectiveness in reducing oat helmintosporiosis was achieved with the Bingo variety and tebuconazole—84.3%. In the case of other varieties, the effectiveness ranged from 42.8 to 71.9%. The use of picoxystrobin reduced leaf infection in the Arab, Arden, Bingo, Breton, and Maczo cultivars by 55.8%, 75.0%, 66.7%, 69.7%, and 63.9%, respectively. The lowest effectiveness was obtained after the use of azoxystrobin in the Bingo variety, at 33.7%.

In 2014, the weather conditions for the development of oats plants were unusual (IV–VII months). The value of the Sielianinow coefficient ranged from 0.8 to 2.8 (dry–very humid). Weather conditions during the season were characterized by a lack of humidity, except for May, when a high amount of precipitation was recorded, which was reflected in a high value of the Sielianinow coefficient (2.8). During the development of the oat flag leaf, conditions were favorable for the development of the pathogen. The average level of infection of the control objects for the analyzed varieties was measured at 8.27%.

In 2015, the infection of the leaf surface in control plants with D. avenae ranged from 4.63 to 10.0%. The lowest infection was recorded in the Bingo variety, and the highest, as in 2012–2013, was in the Maczo variety. The use of fungicides from the triazole and strobilurin groups reduced the infection by 41.0–78.4% and 25.0–86.5%. The highest effectiveness was obtained after the use of azoxystrobin in the Arab and Maczo varieties, at 88.3% and 85.6%, versus the Arden, Bingo, and Breton at 25.0–67.6%. The application of azoxystrobin and picoxystrobin in the Arden oat variety reduced the severity of helmintosporiosis less compared to the other substances (25.0% and 34.2%). A similar tendency was found after the use of azoxystrobin in the Bingo variety (67.6%). Epoxiconazole and tebuconazole in the Bingo variety inhibited the development of the disease in leaves less strongly.

In 2015, the weather conditions for the development of oats plants were moderately unfavorable (IV–VII months). The value of the Sielianinow coefficient ranged from 0.7 to 1.6 (dry–slightly humid). The weather conditions during the season were characterized by a high amount of rainfall during the sowing period—a Sielianinow coefficient of 2.8. The rainfall deficiency occurring in the period from April to June was unfavorable for the development of the pathogen. The average level of infection of the control objects for the analyzed varieties was measured at 7.27%.

The amount of infection on the leaves of oat plants from control objects in 2016 was 5.13–8.50%. The highest control efficiency was achieved after the use of tebuconazole and epoxiconazole, at 95.1% in the Arab variety and 90.6% in the Maczo variety, respectively. The use of triazoles reduced paralysis by 59.1–95.1%, while strobilurins did so by 45.5–86.8%. In the Arab and Breton cultivars, after the application of picoxystrobin, no statistically significant differences were found compared to the control objects. The highest effectiveness was recorded in the case of the Bingo variety, which, after all fungicides were applied, ranged from 78.7 to 89.7%.

In 2016, the weather conditions for the development of oats plants were extremely unfavorable (IV–VII months). The value of the Sielianinow coefficient ranged from 0.0 to 1.8 (extremely dry–slightly humid). The extremely unfavorable weather conditions during the development of the oats affected the limited development of the pathogen D. avenae. The rainfall occurring in July did not affect the intensity of the occurrence of oat helminthosis. The average level of infection of the control objects for the analyzed varieties was measured at 6.62%.

The infection of oat varieties with P. coronata was recorded in 2013, 2014, and 2016 (

Table 5. Efficiency of Puccinia coronata control [%] in years 2012–2016 in Winna Góra.

Variety	Treatments	2013		2014		2016
		Inf. 1	Efficacy	Inf. 1	Efficacy	Inf. 1	Efficacy
Arab	Untreated check	11.75 a	0.0	7.31 ab	0.0	8.75 bc	0.0
	Azoxystrobin 2	1.15 b	90.2	3.69 cdef	49.6	0.06 d	99.3
	Epoxiconazole	0.48 b	96.0	1.81 defg	75.2	0.25 d	97.1
	Picoxytrobin	0.43 b	96.4	1.00 efg	86.3	0.13 d	98.6
	Tebuconazole	0.73 b	93.8	1.00 efg	86.3	1.38 d	84.3
Arden	Untreated check	13.05 a	0.0	5.69 abc	0.0	9.29 bc	0.0
	Azoxystrobin	0.23 b	98.3	2.13 defg	62.6	1.00 d	89.2
	Epoxiconazole	0.90 b	93.1	0.81 fg	85.7	1.25 d	86.5
	Picoxytrobin	0.43 b	96.7	0.94 efg	83.5	1.00 d	89.2
	Tebuconazole	0.40 b	96.9	0.31 g	94.5	0.50 d	94.6
Bingo	Untreated check	11.35 a	0.0	4.19 bcde	0.0	13.50 a	0.0
	Azoxystrobin	0.50 b	95.6	3.06 cdefg	26.9	0.75 d	94.4
	Epoxiconazole	0.38 b	96.7	1.50 defg	64.2	0.50 d	96.3
	Picoxytrobin	0.10 b	99.1	1.38 defg	97.2	0.13 d	99.1
	Tebuconazole	0.05 b	99.6	0.25 g	94.0	0.00 d	100.0
Breton	Untreated check	2.45 b	0.0	7.81 a	0.0	7.13 c	0.0
	Azoxystrobin	0.05 b	98.0	4.38 bcd	44.0	0.50 d	92.9
	Epoxiconazole	0.05 b	98.0	1.56 defg	80.0	0.50 d	92.9
	Picoxytrobin	0.11 b	95.4	1.94 defg	75.2	0.50 d	92.9
	Tebuconazole	0.15 b	93.9	0.56 fg	92.8	0.50 d	92.9
Maczo 3	Untreated check	1.40 b	0.0	3.19 cdefg	0.0	11.25 ab	0.0
	Azoxystrobin	0.25 b	82.1	2.94 cdefg	7.8	0.25 d	97.8
	Epoxiconazole	0.00 b	100.0	1.25 defg	60.8	0.38 d	96.7
	Picoxytrobin	0.05 b	96.4	0.38 g	88.2	0.31 d	97.2
	Tebuconazole	0.00 b	100.0	0.38 g	88.2	3.00 d	73.3
LSD (0.05)		Variety: 0.653; Fungicide: 0.653; Year: 0.653; V × F: 1.46; V × Y: v; F × Y: 1.46; V × F × Y: 3.264

¹ average % of infested area of leaf blades of F and F1 leaves; ² rates: azoxystrobin, 250 g × ha⁻¹, epoxiconazole, 125 g × ha⁻¹, picoxystrobin, 250 g × ha⁻¹, and tebuconazole, 250 g × ha⁻¹; ³ naked variety. Different letters (a–g) indicate statistically different mean values (α = 0.05).

). During the years of observation, the average infection of the flag and sub-flag leaves was recorded in the control objects of the examined varieties at the level of 1.40–13.50%. In 2013, the highest infection of plants from control objects was recorded in the Arden (an average of 13.05% of the infected leaf blade area), Arab (11.75%), and Bingo (11.35%) varieties. The effectiveness of triazoles and strobilurins in reducing P. coronata ranged from 82.1 to 100.0%. The highest effectiveness was achieved with epoxiconazole and tebuconazole in the Maczo variety, at 100%. The effectiveness of azoxystrobin ranged from 82.1 to 98.3% in all cultivars. In the case of picoxystrobin, the effectiveness of controlling crown rust was 95.4–99.1% in all varieties.

In 2013, the weather conditions for the development of oats plants were moderately optimal (IV–VII months). The value of the Sielianinow coefficient ranged from 0.7 to 1.9 (very dry–slightly humid). The conditions prevailing during the development of the flag and sub-flag leaves allowed the causal agent of oat crown rust to develop undisturbed. The average level of infection of the control objects for the analyzed varieties was measured at 8.00%.

In 2014, the infection of control plants amounted to 3.19–7.81% of infected leaf blades. The Maczo variety was the least infected, and Breton was the most infected. Statistically significant differences between the values of leaf blade infection were found between the Arab and Breton cultivars and the Maczo cultivar. In the Arab, Arden, and Breton varieties, statistical differences were proven between the amount of control infection and the combinations in which triazoles and strobilurins were used. In the Bingo variant, significant differences occurred in the case of the combination in which tebuconazole was used. No significant differences were noted in the Maczo variety. The highest effectiveness in reducing the disease was achieved after the use of tebuconazole, at 86.3–94.5%, depending on the variety cultivated, and after epoxiconazole, 60.8–85.7%. The lowest effectiveness was obtained after the use of azoxystrobin in the Arab, Bingo, and Maczo varieties, at 7.8–49.6%. The use of picoxystrobin reduced the incidence of the disease by 67.2–88.2%.

In 2014, the weather conditions for the development of oats plants were unusual (IV–VII months). The value of the Sielianinow coefficient ranged from 0.8 to 2.8 (dry–very humid). Diverse weather conditions during the oat development period resulted in the slower development of the pathogen compared to the remaining years of the study. The average level of infection of the control objects for the analyzed varieties was measured at 5.63%.

In 2016, plants from control plots were found to be infected with leaf blades at a level of 7.13–13.50%. The Bingo variety was the most infected, clearly more severely than the Arab, Arden, and Breton varieties. The highest effectiveness in reducing the disease was achieved through the use of tebuconazole (100%) in the Bingo variety. The use of epoxiconazole allowed effectiveness of 86.5–97.1% to be achieved, versus 89.2–99.1% for picoxystrobin and 89.2–99.3% for azoxystrobin.

In 2016, the weather conditions for the development of oats plants were extremely unfavorable (IV–VII months). The value of the Sielianinow coefficient ranged from 0.0 to 1.8 (extremely dry–slightly humid). The extremely unfavorable weather conditions during the development of oats affected the limited development of the pathogen P. coronata. The average level of infection of the control objects for the analyzed varieties was measured at 9.98%, and it was the highest in comparison to the other years of the study.

When the average percentage of oat F and F1 leaf area infected with D. avenae across the years was analyzed, statistically significant differences were found between the control objects and the active substances tested in the experiment (Figure 1). The use of fungicides resulted in a reduction in plant leaf infection with D. avenae by 71.48–74.15%. The infection of the F and F1 oat leaf surfaces with P. coronata over the years differed statistically significantly between the control objects and the research combinations. However, there were no differences in leaf infection between the combinations treated with fungicides (0.4–1.1% infection). The severity of the fungus P. coronata was most effectively reduced through the use of tebuconazole (92.4%), picoxystrobin (90.8%), and epoxiconazole (88%). Azoxystrobin had the weakest effect, with effectiveness of 75.3%.

In 2012, the oat grain yield from the control plots of the tested varieties ranged from 6.10 (Maczo) to 8.13 t × ha⁻¹ (Bingo) (

Table 6. Impact of triazole and strobilurin fungicides on oat grain yield.

Variety	Treatments	2012		2013		2014		2015		2016
		Yield [t × ha−1]	Rel 1	Yield [t × ha−1]	Rel	Yield [t × ha−1]	Rel	Yield [t × ha−1]	Rel	Yield [t × ha−1]	Rel
Arab	Untreated check	6.47 ij	100	7.03 bcdef	100	6.38 c	100	6.20 bcd	100	4.88 abcd	100
	Azoxystrobin 2	6.83 hi	106	7.74 ab	110	6.70 bc	105	7.12 a	115	5.06 ab	104
	Epoxiconazole	6.68 hij	103	7.74 ab	111	6.92 abc	109	6.84 ab	110	4.97 abc	102
	Picoxytrobin	7.21 fgh	112	7.77 a	111	6.42 c	101	7.29 a	118	5.08 ab	104
	Tebuconazole	7.04 ghi	109	7.05 abcde	100	7.06 abc	111	6.72 abc	109	4.97 abc	102
Arden	Untreated check	7.71 defg	100	6.54 ef	100	6.97 abc	100	5.79 de	100	4.47 abcd	100
	Azoxystrobin	7.93 bcdef	103	6.76 def	103	6.99 abc	100	5.79 de	100	4.46 abcd	100
	Epoxiconazole	7.82 cdef	101	6.68 ef	102	7.49 a	108	6.21 bcd	107	4.66 abcd	104
	Picoxytrobin	7.60 efg	99	6.65 ef	102	7.05 abc	101	6.24 bcd	108	4.59 abcd	103
	Tebuconazole	7.78 def	101	6.65 ef	102	7.37 ab	106	6.10 cd	105	4.71 abcd	105
Bingo	Untreated check	8.13 abcde	100	6.80 def	100	6.75 bc	100	3.55 k	100	4.16 d	100
	Azoxystrobin	8.44 abcd	104	6.77 def	100	7.02 abc	104	3.60 jk	101	4.44 bcd	109
	Epoxiconazole	8.52 abc	104.8	6.31 f	93	6.98 abc	104	3.60 jk	102	4.39 bcd	106
	Picoxytrobin	8.50 abc	105	6.80 def	100	6.45 c	96	3.82 ijk	108	4.25 cd	102
	Tebuconazole	8.56 ab	105	6.87 cdef	101	6.97 abc	103	3.37 k	95	4.31 cd	104
Breton	Untreated check	8.06 abcde	100	7.53 abc	100	6.72 bc	100	5.22 efg	100	4.93 abc	100
	Azoxystrobin	8.32 abcd	103	7.54 abc	100	6.37 c	95	5.22 efg	100	5.18 a	105
	Epoxiconazole	8.23 abcde	102	6.84 cdef	91	6.67 bc	99	5.66 de	108	4.92 abc	100
	Picoxytrobin	8.71 a	108	7.46 abcd	99	6.62 c	98	5.53 def	106	5.10 ab	104
	Tebuconazole	8.27 abcde	103	7.04 bcdef	94	6.94 abc	103	5.59 de	107	5.08 ab	103
Maczo 3	Untreated check	6.10 j	100	4.15 g	100	4.54 d	100	4.41 hi	100	2.96 ef	100
	Azoxystrobin	6.09 j	100	4.80 g	116	5.05 d	111	4.62 gh	105	3.13 ef	106
	Epoxiconazole	6.05 j	99	4.18 g	101	4.79 d	105	4.81 fgh	109	3.34 e	113
	Picoxytrobin	6.68 hij	110	4.59 g	111	4.65 d	102	4.32 hij	98	2.97 ef	101
	Tebuconazole	6.51 hij	107	4.25 g	103	4.61 d	102	4.44 hi	101	2.52 f	85
LSD (0.05)		Variety: 0.145; fungicide: 0.145; year: 0.145; V × F: 0.324; V × Y: 0.324; F × V: 0.324; V × F × Y: 0.724

¹ Rel—% in relation to untreated check; ² rates: azoxystrobin, 250 g × ha⁻¹, epoxiconazole, 125 g × ha⁻¹, picoxystrobin, 250 g × ha⁻¹, tebuconazole, 250 g × ha⁻¹; ³ naked variety. Different letters (a–k) indicate statistically different mean values (α = 0.05)

). The use of fungicides from the chemical groups for triazoles and strobilurins allowed yields of 6.09 (azoxystrobin, Maczo variety)—8.71 t × ha⁻¹ (picoxystrobin, Breton) to be obtained. The grain yield of the varieties compared to the control (100%) varied, and in the case of the Arab variety, it was 103–112%, versus the following: Arden, 99–103%; Bingo, 104–105%; Breton, 102–108%; and Maczo, 99–110%.

In 2013, the oat grain yield from control plots of the tested varieties ranged from 6.54 (Bingo) to 7.53 t × ha⁻¹ (Arab) (Table 6). The use of fungicides from the chemical groups of triazoles and strobilurins allowed yields of 6.31 (apoxiconazole, Bingo)—7.77 t × ha⁻¹ (picoxystrobin, Arab) to be obtained. The grain yield of the Maczo variety was clearly lower, ranging from 4.15 to 4.80 t × ha⁻¹. The grain yield of the varieties compared to the control (100%) varied, and in the case of the Arab variety, it was 100–111%, versus the following: Arden, 102–103%; Bingo, 93–101%; Breton 91–100%; and Maczo, 101–116%.

In 2014, the oat grain yield from control plots of the tested varieties ranged from 6.38 (Arab) to 6.97 t × ha⁻¹ (Arden) (Table 6). The use of fungicides from the chemical groups of triazoles and strobilurins allowed yields of 6.37 (azoxystrobin, Arden)—7.49 t × ha⁻¹ (apoxiconazole, Arden) to be obtained. The grain yield of the Maczo variety was clearly lower, ranging from 4.54 to 5.05 t × ha⁻¹. The grain yield of the varieties compared to the control (100%) varied, and in the case of the Arab variety, it was 101–111%, versus the following: Arden, 101–108%; Bingo, 96–104%; Breton, 95–103%; and Maczo, 102–111%.

In 2015, the oat grain yield from control plots of the tested varieties ranged from 6.38 (Arab) to 6.97 t × ha⁻¹ (Arden) (Table 6). The use of fungicides from the chemical groups of triazoles and strobilurins allowed yields of 6.37 (azoxystrobin, Arden) −7.49 t × ha⁻¹ (apoxiconazole, Arden) to be obtained. The grain yield of the Maczo variety was clearly lower, ranging from 4.54 to 5.05 t × ha⁻¹. The grain yield of the varieties compared to the control (100%) varied, and in the case of the Arab variety, it was 101–111%, versus the following; Arden, 101–108%; Bingo, 96–104%: Breton, 95–103% and Maczo, 102–111%.

In 2016, the oat grain yield from control plots of the tested varieties ranged from 4.16 (Bingo) to 4.93 t × ha⁻¹ (Breton) (Table 6). The use of fungicides from the chemical groups of triazoles and strobilurins allowed yields of 4.31 (tebuconazole, Bingo) −5.18 t × ha⁻¹ (azoxystrobin, Breton) to be obtained. The grain yield of the Maczo variety was much lower, ranging from 2.52 to 3.34 t × ha⁻¹. The grain yield of the varieties compared to the control (100%) varied, and in the case of the Arab variety, it was 102–104%, versus the following: Arden, 100–105%; Bingo, 102–109%; Breton, 100–105%; and Maczo, 85–113%.

Table 7. Linear correlation coefficients between observed test characteristics—r-Pearson test and coefficients of determination (R²).

Feature		Drechslera avenae (Da)					Puccinia coronata (Pc)			Hydrothermal index (H)
		2012	2013	2014	2015	2016	2013	2014	2016	2012	2013	2014	2015	2016
Da	2012	1	-	-	-	-	-	-	-	0.009 (0.000)	-	-	-	-
	2013	-	1	-	-	-	0.486 3 (0.236)	-	-	-	0.028 (0.001)	-	-	-
	2014	-	-	1	-	-	-	0.634 1 (0.402)	-	-	-	−0.155 (0.024)	-	-
	2015	-	-	-	1	-	-	-	-	-	-	-	0.115 (0.024)	-
	2016	-	-	-	-	1	-	-	0.777 3 (0.604)	-	-	-	-	−0.093 (0.009)
Pc	2013	-	0.486 1 (0.236)	-	-	-	1	-	-	-	−0.080 (0.006)	-	-	-
	2014	-	-	0.634 1 (0.402)	-	-	-	1	-	-	-	−0.068 (0.005)	-	-
	2016	-	-	-	-	0.777 3 (0.604)	-	-	1	-	-	-	-	−0.043 (0.002)
H	2012	0.009	-	-	-	-	-	-	-	1	-	-	-	-
	2013	-	0.028 (0.001)	-	-	-	−0.080 (0.006)	-	-	-	1	-	-	-
	2014	-	-	−0.155 (0.024)	-	-	-	−0.068 (0.005)	-	-	-	1	-	-
	2015	-	-	-	0.115 (0.024)	-	-	-	-	-	-	-	1	-
	2016	-	-	-	-	−0.093 (0.009)	-	-	−0.043 (0.002)	-	-	-	-	1
Y	2012	−0.209 1 (0.044)	-	-	-	-	-	-	-	−0.499 3 (0.249)	-	-	-	-
	2013	-	−0.214 1 (0.046)	-	-	-	0.115 (0.024)	-	-	-	0.022 (0.000)	-	-	-
	2014	-	-	−0.078 (0.006)	-	-	-	-	-	-	-	0.115 (0.024)	-	-
	2015	-	-	-	0.134 (0.018)	-	-	-	-	-	-	-	−0.511 3 (0.261)	-
	2016	-	-	-	-	−0.040 (0.002)	-	-	−0.131 (0.017)	-	-	-	-	−0.687 3 (0.472)

Statistical significance at ¹ p = 0.05, ² p = 0.01, and ³ p = 0.001; Y—yield.

shows the strength of the relationships between plant infection with the fungi D. avenae, P. coronata and humidity and oat yield. Statistical analysis indicates a sufficient correlation between infection with the fungus D. avenae and P. coronata (r = 0.486) in 2013 and a moderate correlation in 2014 and 2016 (r = 0.684; 0.777). The results also indicate a weak negative correlation between D. avenae and the yield in 2012 and 2013. A sufficient-to-moderate negative correlation was also found between humidity and the oat yield (r = −0.499; −0.511; −0.687). The R² values indicate that the combined variability of the dependent variables can be explained to a maximum of 60% (in most cases, much lower) by the variability of the independent variables.

4. Discussion

In the conducted experiment, the use of fungicides from the chemical group of triazoles and strobilurins made it possible to reduce the severity of diseases, depending on the active substance and the year of testing. The assessment of the impact of the applied fungicide protection on reducing the severity of D. avenae was carried out in all years of the study, while, in the case of the fungus P. coronata, no infection was found in 2012 and 2015 due to frequent dry periods, which are not favorable for the occurrence of the disease. Reports from the literature [20] indicate the influence of weather conditions on the development of causal agents of diseases in oat cultivation and higher infection rates for varieties at low temperatures and wet weather.

Statistically significant differences were found in reducing the infection of F and F1 leaves of D. avenae and P. coronata compared to the untreated treatment, regardless of the active substance used. The use of tebuconazole, epoxiconazole, azoxystrobin, and picoxystrobin allowed for a reduction in the severity of oat helmintosporiosis in all years of the study for all analyzed varieties (71.5–74.2%). Our own research showed higher effectiveness in reducing P. coronata compared to D. avenae. It was 92.4% for tebuconazole, 88.0% for epoxiconazole, 74.1% for azoxystrobin, and 90.8% for picoxystrobin. The efficacy of azoxystrobin in reducing oat crown rust in 2014 was related to the occurrence of unfavorable weather conditions (Table 2). The plants developed under stressful conditions. The infection of the plants in 2014 occurred earlier, and the use of fungicides in accordance with the adopted methodology made it impossible to obtain full efficacy of the active substance. The obtained test results confirm the satisfactory efficacy of the above-mentioned active substances in reducing fungi of the types D. avenae and P. coronata, which other researchers recommend for use in cereal cultivation to control many economically important species of pathogenic fungi [9,19,21,36,37]. Observations [19] confirmed the effectiveness of the fungicide protection used in oat cultivation, which, similarly to our own research, varied over the years of the study. The active substance tebuconazole used in the studies, at the same time as in our own research, allowed the cultivation of the Belinda variety to reduce infection with D. avenae by 62%. The use of tebuconazole-based fungicides in the studies also showed significant differences in limiting the infection of leaf blades of the Villu variety with P. coronata compared to objects with which no fungicides were used. The results of our own research are also consistent with the recommendation of [38], who recommend the use of fungicides containing azoxystrobin, picoxystrobin, and triazoles to reduce oat crown rust. Research [20] confirms the usefulness of strobilurin-based fungicides in reducing oat crown rust and leahelminthosporiosis. The cited authors also noted that, in the cultivation of varieties characterized by lower resistance to infection with P. coronata and D. avenae, the effect of fungicide use is more visible than in the cultivation of resistant varieties. Our own research did not confirm this relationship. Despite differences in the genotypes of the tested oat varieties in terms of susceptibility to pathogens, no statistically significant differences between the varieties were found in the described research.

In our own studies, fungicides were used once, at a date referred to in the literature as late [19,39]. According to research [19], there is no clear answer to the question regarding the appropriate date of application of fungicides in oat cultivation. It is always necessary to know the resistance of varieties and to take into account the weather conditions prevailing at the protected oat plantation. The relationship between the date of application of fungicides containing tebuconazole and the date of infection of leaf blades with the fungus causing oat helmintosporiosis (D. avenae) and oat crown rust (P. coronata) was also observed. If the infection occurred at the stage when the panicle was already visible, the use of tebuconazole at the BBCH 59–63 stage achieved better results and higher control efficiency compared to the treatment performed at BBCH 40–44. In the study conducted by [40], the use of fungicides was effective when the level of infection in leaf blades during the macroscopic assessment was over 5%. The use of fungicides in our own research confirmed the above-mentioned observation for D. avenae and P. coronata. The study results obtained in the experiment carried out in the years 2012–2016 in Winna Góra made it possible to confirm the hypothesis about the influence of the applied fungicides from the chemical group of triazoles and strobilurins on reducing the infection of oats with fungi occurring during the growing season.

The use of fungicides from the chemical group of triazoles and strobilurins in our own experiments allowed a higher yield to be obtained than that from the control treatments. However, these differences, regardless of the active ingredient used, were statistically insignificant. The lowest yield was obtained in 2016 with the maximum value for the yield obtained in the 2012 experiment being 9.25 t × ha⁻¹. This was confirmed by the analysis of the density distribution of yield values per hectare for 2016 (1.76–5.82 t × ha⁻¹). The highest average yield value in the years 2012–2016 was obtained for combinations in which picoxystrobin was used (average 6.09 t × ha⁻¹). The difference in the amount of yield in the combinations in which fungicides from the chemical group of triazoles and strobilurin were used was, on average, 3.4% over the years (a yield increase of 0.20 t × ha⁻¹). In studies [20], the use of fungicides from the chemical group of strobilurins allowed 5% to 11% higher yields to be obtained. In combinations in which a high level of leaf infection with P. coronata was recorded after the application of s.c. from the chemical group of strobilurins, an increase in the yield from 17 to 27% was obtained (yield increase from 0.69 to 0.78 t × ha⁻¹), depending on the sowing date and variety. According to research [19], in conditions of weak infection with pathogenic fungi in the cultivation of the Belinda variety, in which treatments with active ingredients from the chemical group of triazoles were applied, analogously to our own research, near the BBCH 63 stage, the yield increased by 5.9% (yield increased by 0.3 t × ha⁻¹). The author also observed that the application of fungicides from the triazole chemical group in the above-mentioned stage resulted in statistically higher yields compared to treatments performed in stage BBCH 40–44.

The conditions occurring in the temperate climate zone (cool temperatures and high moisture) are suitable for the development of the fungi D. avenae. The occurrence of the pathogen was confirmed in regions where rainy and cool weather conditions occurred during sowing and the initial stages of development [41]. The optimum temperature for the pathogen’s development is approximately 20 °C, with a minimum temperature of 2–3 °C, while the mycelium can survive at 14 °C for at least 56 days under lab conditions [42]. The authors noted that climatic conditions unfavorable for the development of oats may affect the limitations in the development of the pathogen D. avenae. In years that are characterized by a moderate occurrence of climatic anomalies, the development of the pathogen seems to be undisturbed. Stress conditions for plant development may affect the variable level of intensity of the pathogen occurrence. Extremely unfavorable conditions for the development of oats (2016) were reflected in the low intensity of the pathogen’s occurrence. However, this did not affect the efficacy of the fungicides used in the field experiments. In relation to the causal agents of P. coronata, unfavorable climatic conditions for the development of oat plants (low Sielianinow coefficient) influenced the intensity of oat crown rust. In other research [43], the author suggested that the occurrence of rust was preceded by the occurrence of dry and warm weather. In our own research, the highest level of infection with P. coronata was observed in the season of 2016 (extremely unfavorable conditions for oat plants). These observations indicate that oat rust’s incidence is potentially linked to climate instability. This is also reflected in studies that have investigated the impact of climate on the occurrence of diseases in agricultural crops [44,45].

5. Conclusions

One of the most important aspects determining the yield and quality of grain is the use of appropriate protection against fungal diseases. Active substances from the chemical group of triazoles and strobilurins have shown medium and high effectiveness in controlling pathogenic fungi occurring in oat cultivation. The occurrence of the pathogenic fungi D. avenae and P. coronata on oat leaves in the years of the study showed variation in relation to the climatic conditions (different Sielianinow coefficients). Weather anomalies related to the lack of humidity and periodically stressful conditions could have had an impact on the occurrence and development of the above-mentioned pathogens. The effectiveness of the fungicides used did not deteriorate in years with different weather conditions. If fungicides are used at the right time, they allow for adequate protection of a plantation, even in years with more favorable weather conditions for plant pathogens.