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Control of Foliar Diseases of Field Pea in Southern Brazil

Gilberto Omar Tomm1, Hadley Randal Kutcher2, Edson Clodoveu Picinini1 and Beatriz Donida3

1EMBRAPA Trigo, Passo Fundo, RS, BRAZIL, www.cnpt.embrapa.br e-mail tomm@cnpt.embrapa.br
picinini@cnpt.embrapa.br

2
Agriculture and Agri-Food Canada, Melfort, SK, Canada, e-mail: kutcherr@agr.gc.ca.
3
COTREL, Erechim, beatriz@cotrel.com.br

Abstract

Field pea fits well in the grain production systems of southern Brazil, where two crops are produced annually, and has the potential to contribute to increased diversification and sustainability of the cropping systems. Foliar diseases are the main limiting factor to field pea production in this region and disease control is essential to maintain field pea productivity in this humid environment. The objective of this study was to search for suitable fungicides to reduce disease severity, particularly of Ascochyta blight and anthracnose.

Our study demonstrated that fungicide application effectively reduced disease severity and maintained yield and quality. A single application of a combination of active ingredients (pyraclostrobin and epoxiconazole) appeared to result in a synergy that proved to be the most effective treatment evaluated. Therefore, use of fungicides with other integrated disease management practices, such as early seeding and cultivar choice, should help to maintain yield and quality of field pea in southern Brazil.

Media summary

This study demonstrated that a fungicide not previously recommended for peas effectively reduced severity of symptoms and maintained yield and seed quality in high rainfall areas.

Key Words

Mycosphaerella pinodes, Phoma medicaginis, Ascochyta pisi, Colletotrichum pisi

Introduction

Field pea is susceptible to a number of fungal diseases, the most damaging of which is generally Ascochyta blight. This disease is usually a complex of two fungal species Mycosphaerella pinodes (Berk. & Blox.) and Phoma medicaginis var. pinodella (Jones) Boerema. Under some climatic conditions a third species Ascochyta pisi Lib., may also be involved (Hagedorn 1984). The disease complex is favored by moist conditions during plant development. In southern Brazil field pea is cultivated in a high rainfall environment and consequently suffers frequently from Ascochyta blight. Anthracnose, caused by Colletotrichum pisi Pat., is field pea disease which is considered of minor importance as it normally only occurs sporadically and in localized areas (Hagedorn 1984). However under climatic conditions like those of southern Brazil (frequent precipitation, high humidity, and warm temperatures) this disease may be severe. Wounding of pea plants, caused by infection by M. pinodes or P. medicaginis var. pinodella has been reported to facilitate infection of plants by C. pisi, especially on pea stems (Hagedorn 1984).

Work has been conducted at Embrapa Trigo to determine if foliar diseases of field pea can be managed by manipulating seeding date and choice of cultivar. Study of the effect of these factors on disease development will allow the development of an Integrated Disease Management (IDM) package for field pea production in southern Brazil. The objective of this study was to evaluate fungicides for their effectiveness to reduce the severity of pea diseases, particularly Ascochyta blight and anthracnose, in the humid environments of southern Brazil.

Methods

This study was conducted at sites located within 60 km distance of Passo Fundo, in the state of Rio Grande do Sul (RS) in southern Brazil (28015'S, 52024'W). Average annual rainfall is 1763 mm with 944 mm from June through November (pea growing season). The month with the lowest precipitation is usually May (~100 mm), while the highest is September (~200 mm). The highest mean monthly maximum temperature is 28.40C in January and the lowest mean minimum is 9.00C in July. Precipitation and temperature data for this study are summarized in Table 1. The soil at the experimental sites was a dystrophic dark red latosol (Haplorthox), mapping unit Passo Fundo, predominantly clay. Rolling topography combined with highly erosive rains is common in the state of Rio Grande do Sul (RS) and most of Southern Brazil. These environmental conditions favour many plant diseases.

Field experiments were established as randomized complete block design in solid blocks of field pea cv. Dileta (in 2001) and cv. Marjoret (in 2002) seeded under no-tillage during late June with a commercial seed drill adjusted for a target plant population of 80 plants/m2. Fertilizer, including 20 kg of N/ha, was applied at seeding according to soil test. At each site the seeded area was divided into 4 replicates of 2.4 x 5 m plots in 2001, and 5 replicates of 3 x 5 m plots in 2002. In 2001, fungicide applications on the three experiments (Table 2) were made on August 21-23, (first disease symptoms, at flowering onset) followed by an identical application on September 14-17. In 2002, fungicides were applied on the two experiments either singly or in combination once at the early flowering stage of plant development and for some treatments a second fungicide application was made 19 days after the first application (Tables 3 and 4). One treatment consisted of three fungicides (mancozeb, chlorothalonil, pyraclostrobin) applied on September 26, October 3 and October 15.

Table 1. Precipitation (mm) and temperature (oC ) at Passo Fundo, RS, Long term average (LTA. 30 year mean) and during 2001 and 2002.

 

Monthly precipitation

Mean monthly temperature

LTA

2001

2002

LTA

2001

2002

June

129

106

242

12.7

13.5

13.2

July

153

104

146

12.8

13.3

12.4

August

166

28

234

14.0

16.6

15.2

September

207

240

254

14.8

15.5

14.1

October

167

276

372

17.7

18.6

18.8

November

141

117

205

19.8

20.9

20.1

Total/year

963

871

1453

15.3

16.4

15.6

Source of information: http://www.cnpt.embrapa.br/agromet.htm

In 2002, ten plants per plot were evaluated at BBCH (BASF, Bayer, Ciba-Geigy and Hoechst) decimal growth stage 75 (50% of pods have reached final length, Lancashire et al. 1991). Two disease assessment were made, the first assessed the amount of leaf and stem tissue with disease symptoms on a 0-9 scale (0 = no symptoms, 9 = all leaves and stems covered with symptoms and necrotic tissue, Xue et al.1997), and a second assessed the amount of damage only on the lower stem of each plant, again using a 0-9 scale with 0=no symptoms (Wang 1998). Experiments were hand harvested on October 23, 2001 at Quatro Irmos (low and higher laying areas), November 19, 2001 at Coxilha, and November 5- 6, 2002, and threshed after drying.

Results

Precipitation during the growing season was 92 mm below and 490 mm above long term average in 2001 and 2002 respectively, while monthly temperatures were 1.1 and 0.3 above the long term average respectively (Table 1). These data suggests that environmental conditions were more favorable for disease development and therefore for fungicide response in 2002 than in 2001.

Hail damage at Coxilha in 2001 reduced yields (Table 2) and increased variation leading to non significant yield and thousand seed weight (TSW) differences among treatments. No clear differences due to treatments were visible in any of the foliage and stem visual assessments in any of the three 2001 trials.

In 2002 both experiments only showed trace levels of Ascochyta blight at time of first fungicide application (early flower, decimal growth stage 61) on September 25, 2002. However, at the time of disease evaluation (October 18, 2002) Ascochyta blight infection was very high and symptoms of anthracnose were also readily observed.

Visual assessment of field plots on October 17th indicated that only one treatment at either experimental site had a consistent and marked effect on the diseases. This treatment consisted of a single application of the combined active ingredients pyraclostrobin and epoxiconazole. The application of pyraclostrobin or epoxiconazole singly did not appear to be as effective at reducing disease symptoms as the combined use of the chemicals. In Brazil, the trade name of this product is Opera (BASF), and is registered for control of foliar diseases of wheat and soybean. Active ingredients registered for use on field pea or used experimentally in the Canadian prairies (mancozeb, chlorothalonil and azoxystrobin) appeared to have limited impact on Ascochyta blight or anthracnose under the experimental conditions near Passo Fundo during 2002. However, in 2001 at the low lying area of Quatro Irmos azoxystrobin led to the highest absolute yield, which was statistically similar to pyraclostrobin + epoxiconazole. Statistical analyses of 2002 data confirmed most of the visual field observations. At Coxilha the combined single application of pyraclostrobin + epoxiconazole dramatically reduced the symptoms of disease on both the foliage and the lower stem of each plant compared to the check or any other treatment (Table 3). None of the other treatments by either assessment method were different from the check. Results at the Passo Fundo site were not quite as dramatic but again the pyraclostrobin + epoxiconazole treatments were less severely diseased than the check (Table 4). At Passo Fundo the single application of pyraclostrobin alone was similar to the combined pyraclostrobin + epoxiconazole treatment.

Table 2 . Effect of fungicides on grain yield and thousand seed weight (TSW) of pea (cv. Dileta) at a low laying area of Quatro Irmos, at a higer laying area of Quatro Irmos, and at Coxilha, RS, Brazil, 2001.

Treatment

Rate
(g a.i./ha)

Quatro Irmos (Low)

Quatro Irmos (High)

Coxilha

Yield
(kg/ha)

TSW
(g)

Yield
(kg/ha)

TSW
(g)

Yield
(kg/ha)

TSW
(g)

Azoxystrobin

25

2,647ab

193bc

2,683

216ab

1,848

133

Azoxystrobin

50

2,383b

198abc

2,350

196bc

1,714

133

Tebuconazole+Tryfloxystrobin

125+75

2,338b

203abc

2,466

222a

1,373

129

Propiconazole+Azoxystrobin

125+25

2,534ab

205abc

2,326

201bc

1,888

130

Piraclostrobin+Epoxiconazole

133+50

3,670a

226a

2,645

216ab

1,817

132

Propiconazole

125

1,893b

194bc

1,977

195c

1,515

127

Tebuconazole

125

1,818b

193bc

2,070

205abc

2,154

130

Epoxiconazole

125

2,420b

211ab

2,301

215abc

1,907

130

Chlorothalonil

1125

1,735b

178c

2,059

194c

1,991

131

Check

0

2,127b

197abc

2,297

206abc

1,595

127

Means followed by the same letters within columns are not significantly different at P=0.05 by Tukey's test.

Table 3. Effect of fungicide treatments on foliar disease symptoms, yield, and thousand seed weight (TSW) of field pea (cv. Marjoret) , 2002, at Coxilha, RS, Brazil. Data are means of 5 replicates.

First fungicide application

Second fungicide application1

Disease assessment of

Yield
(kg/ha)

TSW
(g)

Fungicide

Rate
(g a.i./ha)

Fungicide

Rate
(g a.i./ha)

Foliage
(0-9)

Lower stems
(0-9)

Azoxystrobin

100

-

 

8.2 a

7.3 a

 

571 a b

149 a b

Pyraclostrobin

100

-

 

6.8 a b

5.4 a b

 

661 a b

168 a b

Tryfloxystrobin

100

-

 

7.2 a

5.9 a b

 

701 a b

158 a b

Tryfloxystrobin +
Propiconazole

62.5
+ 62.5

-

 

8.3 a

7.8 a

 

288 b

137 b

Mancozeb

1875

Pyraclostrobin

100

7.4 a

6.4 a b

 

778 a b

169 a b

Difenconazole

75

Azoxystrobin

100

7.0 a b

6.2 a b

 

653 a b

160 a b

Tebuconazole

125

Tryfloxystrobin

100

7.3 a

6.0 a b

 

709 a b

171 a b

Epoxiconazole

94

-

 

7.5 a

6.4 a b

 

760 a b

165 a b

Chlorothalonil

1126

Pyraclostrobin

100

7.1 a

5.9 a b

 

721 a b

167 a b

Pyraclostrobin
+ Epoxiconazole

100
+ 37.5

-

 

4.5 b

3.0 b

 

1028 a

191 a

Mancozeb /
Chlorothalonil2

1875 /
1126

Pyraclostrobin

100

7.3 a

6.7 a b

 

639 a b

163 a b

Check

 

-

 

8.3 a

7.3 a

 

650 a b

161 a b

1At 19 days after the first application. 2Chlorothalonil was applied 8 days after mancozeb for this treatment.

Means followed by the same letters within columns are not significantly different at P=0.05 by Tukey's test.

In terms of yield and thousand seed weight (TSW) analysis of variance revealed a high degree of variation in the data of the 5 site-years but a trend was present for greater yield and TSW with the pyraclostrobin + epoxiconazole treatment compared to other single application treatments (Tables 2, 3, and 4).

The data suggests a synergistic effect between the combined active ingredients pyraclostrobin + epoxiconazole when applied in a single application. The trend in both experiments was for less disease development, increased yield and higher TSW in the combined treatment compared to the check or to application of either product alone. This synergistic effect has also been noted in the control of leaf spot diseases of wheat at Passo Fundo.

Table 4. Effect of fungicide treatments on foliar disease symptoms, yield, and thousand seed weight (TSW) of field pea (cv. Marjoret) at Passo Fundo, RS BRAZIL. Data are means of 5 replicates.

First fungicide application

Second fungicide application1

Disease assessment of

Yield
(kg/ha)

TKW
(g)

Fungicide

Rate
(ga.i./ha)

Fungicide

Rate
(ga.i./ha)

Foliage
(0-9)

Lowerstems
(0-9)

Azoxystrobin

100

-

 

7.3abc

6.1abc

824ab

157c

Pyraclostrobin

100

-

 

5.8bc

4.4c

948ab

175ab

Tryfloxystrobin

100

-

 

7.2abc

6.2abc

952ab

166abc

Tryfloxystrobin+
propiconazole

62.5
+62.5

-

 

7.7a

6.9a

919ab

157c

Mancozeb

1875

Pyraclostrobin

100

7.4ab

6.7ab

703b

155c

Difenconazole

75

Azoxystrobin

100

6.3abc

5.1abc

1004ab

176a

Tebuconazole

125

Tryfloxystrobin

100

7.1abc

6.0abc

880ab

168abc

Epoxiconazole

94

-

 

7.0abc

5.8abc

1014ab

168abc

Chlorothalonil

1126

Pyraclostrobin

100

7.8a

6.6abc

743b

159bc

Pyraclostrobin+
epoxiconazole

100
+37.5

-

 

5.6c

4.6bc

1147a

180a

Mancozeb/
chlorothalonil2

1875/
1126

Pyraclostrobin

100

7.4abc

6.3abc

1029ab

166abc

Check

     

7.9a

7.0a

724b

152c

1At 19 days after the first application. 2Chlorothalonil was applied 8 days after mancozeb for this treatment.

Means followed by the same letters within columns are not significantly different at P=0.05 by Tukey's test.

The use of the contact fungicide chlorothalonil as a first fungicide application, followed by a second application with a partially systemic product such as pyraclostrobin was not effective in reducing disease symptoms or increasing yield or quality compared to the untreated check in either experiment (Tables 3 and 4). Similarly, the application of 3 different fungicides in 3 applications, using contact fungicides as the first two applications (mancozeb and chlorothalonil) and pyraclostrobin as the third did not reduce disease symptoms or improve yield or quality. Use of a semi-systemic product (pyraclostrobin or pyraclostrobin + epoxiconazole) before significant disease development appeared to be the best strategy under the experimental conditions in this study. Application of semi-systemic products as a second fungicide application appeared too late to control disease progression.

Conclusion

This study demonstrated that fungicide application to field pea in southern Brazil is effective for reduction of foliar diseases and for maintenance of yield and seed quality. The use of fungicides with other integrated pest management practices such as early seeding and choice of a disease tolerant or less susceptible cultivar should help to maintain yield and quality of field pea in southern Brazil.

References

Hagedorn, D.J. 1984. Compendium of Pea Diseases. American Phytopathology Society 57 pp.

Lancashire, P.D., H. Bleiholder, T.van den Boom, P. Langeluddeke, R. Stauss, E. Weber and A. Witzenberger. 1991. A uniform decimal code for growth stages of crops and weeds. Annals of Applied Biology 119: 561-601.

Wang, T.F. 1998. Evaluation of mycosphaerella blight resistance in pea. M.Sc. Thesis. University of Saskatchewan, Saskatoon. 129 pp.

Xue, A., T.D. Warkentin, M.T. Greeniaus and R.C Zimmer. 1997. Genotypic variation in seedborne infection of field pea by Mycosphaerella pinodes and its relation to foliar disease severity. Canadian Journal of Plant Pathology 18:370-374.

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