# Effect of Early Foliar Disease Control on Wheat Scab Severity (Fusarium graminearum) in Argentina

Authors: Jorge David Mantecón
Journal: International Journal of Agronomy
 (2013)

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## Abstract

Wheat scab is common in Argentina mainly durum wheat and some bread varieties. The epidemics occur every 5 to 7 years. During the 2007, 2008, and 2009 growing seasons, three trials were conducted at the INTA Balcarce Experimental Station. Each plot had six rows of 5 m long, spaced 0.15 m apart and was set up in a randomized complete block design with four replications. Trifloxystrobin plus cyproconazole was sprayed at Z3.1 stage. Treatments were sprayed at Z6.1 stage with tebuconazole, prochloraz, and metconazole to improve scab control. Artificial inoculations were made in Z6.1. Severity ofSeptoria leaf bloth and leaf rust was assessed in boot stage (Z3.9). Scab severity was rated at early dough stage (Z8.3). Yields were recorded each year. Fungicide only applied at Z3.1 stage did not reduce field scab severity but reduced the seeds infection and increased the yields. Early fungicide spray produced yield increase at about 22% and a decrease in seed infection of up to 40%. Yields increased in a 55.3% and in a 19.6% when compared with the inoculated and not inoculated check, respectively. The purpose of this study was to evaluate the effect of foliar disease control on scab, crop yield, and seed health.


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## Body

## 1. Introduction

Head blight (scab) caused byFusarium graminearum Schwabe (teleomorphGibberella zeae (Schw.) Petch) occurs in humid wheat producing areas of the world [1, 2]. In Argentina, it is common in durum wheat and some bread wheat cultivars depending of susceptibility to the pathogen [3]. Very destructive outbreaks occurred in 1978, 1985, 1993, 2000, 2001, and 2002 growing seasons [4–6]. Damage has been significant in south east of Buenos Aires province. The disease attacks the heads and then seedling of small grains, but it is the most conspicuous and does the most damage when infecting the wheat heads.In Argentina, the use of foliar fungicides on wheat is common, and it has increased considerably [7]. Near 30% of the crop area in SE of Buenos Aires is sprayed to control of foliar disease like rust and leaf blotch [8]. The control of scab by fungicide applications should be a preventive action because if fungicide applications are done when the symptoms appear, the disease control efficiency would be extremely low. Therefore the use of fungicide to control wheat scab is low compared with the use of fungicide for controlling foliar disease.Yields can be improved with the use of fungicides, but yield increments vary extremely according to disease severity, fungicide efficiency, timing spray, and number of applications [9, 10]. Fungicide sprays reduce up to 70% head symptoms, and 80% yield increase can be obtained under the climatic conditions of Argentine [11, 12]. Sometimes early applications of fungicides in crop due to severe symptoms of leaf rust and leaf blotch are necessary.These sprayings produce healthy plants in advance crop stage, reducing the incidence or severity of wheat scab in the field. The objective of this work was to evaluate the effect of early and early plus flowering fungicide spray on the severity of scab in wheat field, as well as the disease’s yield and grain infection.


## 2. Materials and Methods

### 2.1. Research Sites

During the 2007, 2008, and 2009 growing seasons, three trials were conducted at the INTA Balcarce Experimental Station (Argentina) in a Brunizen soil with 3.9% of organic matter. ProInta Oasis wheat cultivar, bread type, susceptible to the foliar rust (Puccinia recondita), leaf blotch (Septoria tritici), and scab diseases (F. graminearum) were used. The trials were conducted under low mechanical system in a soil precultivated with wheat that was fertilized at sowing time and tillering stage with 100 kg·ha−1 diamonic fosfate. Weed and insect were controlled according to standard recommended practices for the region.


### 2.2. Fungicide Treatments and Spray Timing

In tillering stage Zadoks 3.1 [13] trifloxystrobin plus cyproconazole 276.5SC at 140+60 g·ha−1 was sprayed in certain plots to improve foliar rust and leaf blotch disease control and to reach the anthesis stage Zadoks 6.1 [13] with good healthy plants. Plots were sprayed at anthesis stage Zadoks 6.1 with tebuconazole 25EW at 187.5 g·ha−1, prochloraz 45EC at 450 g·ha−1, and metconazole 9 SL at 90 g·ha−1. All fungicide applications were sprayed mixed in water with a carbonic anhydride pressurized backpack sprayer equipped with a constant boom pressure of 40 lb pulg−2 and a boom length of 1.2 m with 0.3 m and four ceramic disc-type cone nozzles at a rate of 150 L ha−1.


### 2.3. Inoculation Method

Inoculations were made 2 days after fungicide sprayings in Z61. A mixture of isolates ofG. zeae from the culture collection at the Agricultural Regional Experimental Station INTA Balcarce was used. The inoculum was prepared by culturing F. graminearum in Petri dishes with APG (2%) + glucose potato agar plus cellulose (2%) at pH 5.5 and incubated at 24°C in darkness for 48 hours. Cultures were then exposed to daylight and ambient temperature to stimulate sporulation. A sterile paintbrush was used to transfer propagules of the fungus including ascospores to a glass bottle of sterile water. The suspension was homogenized and filtered with a cloth of fine mesh. Inoculum was diluted in 1.5 L of sterile water to achieve an inoculum density of 1×104 ascospores cc−1. Inoculum was applied on spikes of plants in the two central furrow of each plot with a manual-type sprayer.


### 2.4. Field Evaluation

Scab severity was rated at early dough stage [13] in relation to the percentage of heads showing symptoms according to Stack and Mcmullen scale [14].Severity ofSeptorialeaf blotch was assessed on James scale [15] that reflects the vertical progress of symptoms in the canopy and the overall proportion of leaf area affected. Leaf rust was rated on the same scale in relation to the percentage of the least leaf area covered with pustules. Both diseases were rated in boot stage at Zadoks 3.9 scale [13]. Yields were recorded each year, and samples of seeds were obtained for determination of 1000 kernel weight.


### 2.5. Laboratory Evaluation

The percentage of infected seeds was determined by placing 100 seed per replication in 2% sodium hypochlorite for 15 sec, rinsing in water for 2 min, and placing seed in containers with moist cotton covered with moist filter paper. The containers were incubated in polyethylene bags to maintain high relative humidity during 8 days. Records included the percentage of grains withFusarium mycelium after 7-day incubation.


### 2.6. Design and Statistical Analysis

Every year each experimental plot had six rows of 5 m long, spaced 0.15 m. Treatments were arranged in a randomized complete block design with four replicates. Data was subjected to analysis of variance, and means were compared by LSD atP=0.05.


## 2.1. Research Sites

During the 2007, 2008, and 2009 growing seasons, three trials were conducted at the INTA Balcarce Experimental Station (Argentina) in a Brunizen soil with 3.9% of organic matter. ProInta Oasis wheat cultivar, bread type, susceptible to the foliar rust (Puccinia recondita), leaf blotch (Septoria tritici), and scab diseases (F. graminearum) were used. The trials were conducted under low mechanical system in a soil precultivated with wheat that was fertilized at sowing time and tillering stage with 100 kg·ha−1 diamonic fosfate. Weed and insect were controlled according to standard recommended practices for the region.


## 2.2. Fungicide Treatments and Spray Timing

In tillering stage Zadoks 3.1 [13] trifloxystrobin plus cyproconazole 276.5SC at 140+60 g·ha−1 was sprayed in certain plots to improve foliar rust and leaf blotch disease control and to reach the anthesis stage Zadoks 6.1 [13] with good healthy plants. Plots were sprayed at anthesis stage Zadoks 6.1 with tebuconazole 25EW at 187.5 g·ha−1, prochloraz 45EC at 450 g·ha−1, and metconazole 9 SL at 90 g·ha−1. All fungicide applications were sprayed mixed in water with a carbonic anhydride pressurized backpack sprayer equipped with a constant boom pressure of 40 lb pulg−2 and a boom length of 1.2 m with 0.3 m and four ceramic disc-type cone nozzles at a rate of 150 L ha−1.


## 2.3. Inoculation Method

Inoculations were made 2 days after fungicide sprayings in Z61. A mixture of isolates ofG. zeae from the culture collection at the Agricultural Regional Experimental Station INTA Balcarce was used. The inoculum was prepared by culturing F. graminearum in Petri dishes with APG (2%) + glucose potato agar plus cellulose (2%) at pH 5.5 and incubated at 24°C in darkness for 48 hours. Cultures were then exposed to daylight and ambient temperature to stimulate sporulation. A sterile paintbrush was used to transfer propagules of the fungus including ascospores to a glass bottle of sterile water. The suspension was homogenized and filtered with a cloth of fine mesh. Inoculum was diluted in 1.5 L of sterile water to achieve an inoculum density of 1×104 ascospores cc−1. Inoculum was applied on spikes of plants in the two central furrow of each plot with a manual-type sprayer.


## 2.4. Field Evaluation

Scab severity was rated at early dough stage [13] in relation to the percentage of heads showing symptoms according to Stack and Mcmullen scale [14].Severity ofSeptorialeaf blotch was assessed on James scale [15] that reflects the vertical progress of symptoms in the canopy and the overall proportion of leaf area affected. Leaf rust was rated on the same scale in relation to the percentage of the least leaf area covered with pustules. Both diseases were rated in boot stage at Zadoks 3.9 scale [13]. Yields were recorded each year, and samples of seeds were obtained for determination of 1000 kernel weight.


## 2.5. Laboratory Evaluation

The percentage of infected seeds was determined by placing 100 seed per replication in 2% sodium hypochlorite for 15 sec, rinsing in water for 2 min, and placing seed in containers with moist cotton covered with moist filter paper. The containers were incubated in polyethylene bags to maintain high relative humidity during 8 days. Records included the percentage of grains withFusarium mycelium after 7-day incubation.


## 2.6. Design and Statistical Analysis

Every year each experimental plot had six rows of 5 m long, spaced 0.15 m. Treatments were arranged in a randomized complete block design with four replicates. Data was subjected to analysis of variance, and means were compared by LSD atP=0.05.


## 3. Results and Discussion

During the evaluation years, significant differences were found between the control check in regards to scab severity, yield, infected kernels, and kernels weight variables. The rates of said variables in the untreated check show the levels of natural infection during test trials, but significant differences were detected between inoculation and no inoculation in the checks and show the efficiency of the artificial inoculation.Leaf blotch and rust control by trifloxystrobin plus cyproconazolesprayed at Z3.1 stage were very good and show lower infection level than the checks (Tables1, 2, and 3). In every season the checks that were sprayed with trifloxystrobin plus cyproconazole at Z3.1 stage and that were artificially inoculated did not reduce significantly head blight infection, nor did they increase grain weight. They did, however, heavily reduce the percentage of infected kernels, improving yields compared with inoculated check. In the absence of artificial inoculations on natural infections there was no difference between spray and not spray at Z3.1 stage for all scab parameters analyzed. Similar results were obtained in previous works [10, 11] with fungicide sprays in Z6.1 stage on aestivum wheat. Given the results, early sprayings cause healthy plants with a lower level of foliar diseases, which improves the physiological state of the crops, producing a higher amount of kernels with a lower level of infection caused by the pathogen.Table 1
Effect of early fungicides sprays on scab severity, yield, infected kernel, and weight grains in 2007 season.
Treatments
Dose (g·ha−1)
Rust severity1
Leaf bloth severity2
Scab severity3
Yield (t/ha−1)
Infected kernel (%)
Weight 1000 seeds (g)
Check
—
8/25
6/50
15bc
3.35cde
5cd
32.3a
Check + inoculation
—
8/25
6/50
80a
2.32f
48a
25.6b
Z31 trifloxystrobin + cyproconazole 267.5SC
140
+
60
5/1
4/25
12bcd
3.34cde
6cd
33.2a
Z31 trifloxystrobin + cyproconazole 267.5SC + inoculation
140
+
60
5/1
4/25
76a
3.10de
26b
31.6a
Z61 tebuconazole 25EW
187.5
5/1
6/50
5cd
3.82abc
2cd
34.3a
Z61 prochloraz 45EC
450
8/15
6/50
2d
3.88ab
0d
33.9a
Z61 metconazole 9SL
90
8/15
6/50
6bcd
3.94a
3cd
33.8a
Z61 tebuconazole 25EW + inoculation
187.5
8/15
6/50
18b
3.66abc
5cd
34.5a
Z61 prochloraz 45EC + inoculation
450
8/15
6/50
10bc
3.72abc
5cd
33.7a
Z61 metconazole 9SL + inoculation
90
8/15
6/50
12bcd
3.76abc
4cd
32.9a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 tebuconazole 25EW
140
+
60
+
187.5
5/1
4/5
2d
3.95a
4cd
33.9a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 prochloraz 45EC
140
+
60
+
450
5/1
4/5
0d
3.92a
3cd
34.6a
Z31 trifloxystrobin + cyproconazole 267.5SC +  Z61 metconazole 9SL
140
+
60
+
90
5/1
4/5
1d
4.02a
2cd
34.9a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 tebuconazole 25EW + inoculation
140
+
60
+
187.5
5/1
4/5
12bcd
3.68abc
6cd
33.2a
Z31 trifloxystrobin + cyproconazole  267.5SC + Z61 prochloraz 45EC + inoculation
140
+
60
+
450
5/1
4/5
10bcd
3.75abc
6cd
33.2a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 metconazole 9SL + inoculation
140
+
60
+
90
5/1
4/5
10bcd
3.79abc
4cd
32.7a
LSD (P=0.05)
10
0.55
6.5
3.8
1 and 2[15]. Where 1st digit = foliar number and 2nd digit = % severity. 3[14].
Within a column, means followed by the same letter are not significantly different (P=0.05).Table 2
Effect of early fungicides sprays on scab severity, yield, infected kernel, and weight grains in 2008 season.
Treatments
Dose (g·ha−1)
Rust severity1
Leaf bloth severity2
Scab severity3
Yield (t/ha)
Infected kernel (%)
Weight 1000 seeds (g)
Check
—
7/5
4/5
10bc
3.50abc
2cd
34.5a
Check + inoculation
—
7/5
4/5
50a
3.05c
25a
29.6b
Z31 trifloxystrobin + cyproconazole 267.5SC
140
+
60
4/1
3/5
14b
3.50abc
2cd
34.5a
Z31 trifloxystrobin + cyproconazole 267.5SC + inoculation
140
+
60
4/1
3/5
50a
3.15bc
14b
29.8b
Z61 tebuconazole 25EW
187.5
4/1
3/5
2d
3.90a
0d
35.5a
Z61 prochloraz 45EC
450
7/5
4/5
4bcd
3.78a
0d
35.9a
Z61 metconazole 9SL
90
7/5
4/5
5bcd
3.96a
0d
34.7a
Z61 tebuconazole 25EW + inoculation
187.5
7/5
4/5
15b
3.86a
6c
35.5a
Z61 prochloraz 45EC + inoculation
450
7/5
4/5
15b
3.92a
6c
34.9a
Z61 metconazole 9SL + inoculation
90
7/5
4/5
15b
3.86a
4cd
34.1a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 tebuconazole 25EW
140
+
60
+
187.5
4/1
3/5
0d
3.99a
1d
36.9a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 prochloraz 45EC
140
+
60
+
450
4/1
3/5
0d
3.85a
1d
35.5a
Z31 trifloxystrobin + cyproconazole 267.5SC +  Z61 metconazole 9SL
140
+
60
+
90
4/1
3/5
0d
3.97a
0d
36.1a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 tebuconazole 25EW + inoculation
140
+
60
+
187.5
4/1
3/5
14b
3.78a
4cd
34.7a
Z31 trifloxystrobin + cyproconazole  267.5SC + Z61 prochloraz 45EC + inoculation
140
+
60
+
450
4/1
3/5
9bc
3.93a
4cd
36.6a
Z31 trifloxystrobin + cyproconazole  267.5SC + Z61 metconazole 9SL + inoculation
140
+
60
+
90
4/1
3/5
9bc
3.84a
3cd
36.7a
LSD (P=0.05)
6
0.55
6
3.9
1 and 2[15]. Where 1st digit = foliar number and 2nd digit = % severity. 3[14].
Within a column, means followed by the same letter are not significantly different (P=0.05).Table 3
Effect of early fungicides sprays on scab severity, yield, infected kernel, and weight grains in 2009 season.
Treatments
Dose (L/ha−1)
Rust severity1
Leaf bloth severity2
Scab severity3
Yield (t/ha)
Infected kernel (%)
Weight 1000 seeds (g)
Check
—
8/5
7/20
29b
3.35bc
16c
32.3ab
Check + inoculation
—
8/5
7/20
75a
2.59e
62a
29.6b
Z31 trifloxystrobin + cyproconazole 267.5SC
140
+
60
5/15
4/25
25b
3.33bc
14c
35.5a
Z31 trifloxystrobin + cyproconazole 267.5SC + inoculation
140
+
60
5/15
4/25
69a
3.20c
36b
29.5b
Z61 tebuconazole 25EW
187.5
5/15
7/20
1c
3.98a
0d
35.4a
Z61 prochloraz 45EC
450
8/5
7/20
1c
3.90ab
0d
34.9a
Z61 metconazole 9SL
90
8/5
7/20
2c
4.10a
2d
36.1a
Z61 tebuconazole 25EW + inoculation
187.5
8/5
7/20
8c
3.86ab
4d
35.0a
Z61 prochloraz 45EC + inoculation
450
8/5
7/20
8c
3.79abc
0d
34.9a
Z61 metconazole 9SL + inoculation
90
8/5
7/20
10c
3.91ab
2d
35.2a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 tebuconazole 25EW
140
+
60
+
187.5
5/15
4/25
5c
4.12a
2d
35.9a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 prochloraz 45EC
140
+
60
+
450
5/15
4/25
5c
4.15a
1d
36.1a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 metconazole 9SL
140
+
60
+
90
5/15
4/25
1c
4.20a
0d
35.8a
Z31 trifloxystrobin + cyproconazole 267.5SC + Z61 tebuconazole 25EW + inoculation
140
+
60
+
187.5
5/15
4/25
9c
3.88ab
1d
36.2a
Z31 trifloxystrobin + cyproconazole  267.5SC + Z61 prochloraz 45EC + inoculation
140
+
60
+
450
5/15
4/25
9c
3.93ab
1d
36.7a
Z31 trifloxystrobin + cyproconazole  267.5SC + Z61 metconazole 9SL + inoculation
140
+
60
+
90
5/15
4/25
10c
3.99a
2d
35.9a
LSD (P=0.05)
12
0.56
8
5.4
1 and 2[15]. Where 1st digit = foliar number and 2nd digit = % severity. 3[14].
Within a column, means followed by the same letter are not significantly different (P=0.05).During 2007 and 2009 seasons, scab severity was high (Tables1–3). Early fungicide sprayings at Z3.1 stage plus inoculations improved an increase in yields of an average of 22%, but a decrease infection in seeds of 40% compared with the check plus inoculations.The combined effects of a high level of foliar diseases infection and scab caused significant yield decrease, high infection in kernels, and noticeable reduction in weight. Nevertheless, spraying in full flowering stage with tebuconazole, prochloraz, or metconazole gives high head protection againstFusarium infection, reducing head blight severity and the percentage of infected kernels, thus increasing yields. These results agree with those obtained previously on durum wheat [12].Fungicide sprayings at Z3.1 and Z6.1 stages reduced foliar disease and scab severity to the minimum and show the best results in yields. Higher yields and lower infection in kernels were found in laboratory tests, although these results did not significantly surpassed the sprayed treated checks at Z6.1. The additive effect of foliar diseases (P. recondita and S. tritici) and scab (F. graminearum) can be measured through yield increases on fungicide sprayings at Z3.1 plus Z6.1, reaching average values of 55.3%, in comparison with the inoculated check and a 19.6% with the uninoculated check.During the 2008 season, scab severity was light due to less favorable environmental conditions. In this season scab infections that observed any inoculated and uninoculated control were lower than the 2007 and 2009 seasons. Treatments with fungicides sprayed in Z3.1 plus Z6.1 stages showed no symptoms of the disease in the field. No significant differences were registered in performance between treatments inoculated or not with fungicides sprayed on any Z3.1 and Z6.1 stages. All these treatments overcome the yields observed with fungicide sprayed at Z3.1 stage and the checks with or without inoculations. A similar relationship was observed when analyzed % infected kernels and weight of the seeds.


## 4. Conclusions

Based on field trials carried out over three consecutive years, fungicide spray at Z3.1 stage did not reduce significantly head blight infection and grain weight however heavily reduce the percentage of infected kernels.On natural infections there was no difference between spray and not spray with fungicide at Z3.1 stage for all scab parameters analyzed.When scab was severity in 2007 and 2009 seasons, early fungicide spray at Z3.1 stage improved an increase in yields of an average of 22%, while a decrease kernel infection of an average of 40% compared with the inoculated check.Twice fungicide applications at Z3.1 and Z6.1 stages reduced foliar disease and scab severity to the minimum and show that yields increase reaching average values of 55.3%, in comparison with the inoculated check and 19.6% with the uninoculated check.When scab was light in 2008 season, no significant differences were registered in performance between treatments inoculated or not with fungicides sprayed on any Z3.1 and Z6.1 stages. These treatments overcome the yields registered with fungicide sprayed at Z3.1 stage and the checks with or without inoculations.



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*Source: 956862-2013-10-28.xml*