Wet conditions may favor early season crown and root rot in sugar beet

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

Rhizoctonia root and crown rot caused by Rhizoctonia solani Kuhn AG2-2 is the most common and serious soil-borne disease of sugar beet. R. solani survives as mycelium or sclerotia in the soil in organic debris and is thought to be most active at soil temperatures between 77 to 92 oF. However, we have found that the pathogen is active at lower soil temperatures and serious losses have occurred in areas with a history of Rhizoctonia especially after wet and cool springs. Over the past few years effective fungicides for control of Rhizoctonia have been successfully used in Michigan. For this season, after the wet, cool spring, we are recommending that growers apply Quadris 2.08SC as soon as they are able to re-enter fields. Application rates of 7 to 10.5 fl. Oz/A have proved effective in years when conditions have been particularly conducive for disease development. Results form trials exposed to natural incoulum are shown below and of course the more resistant varieties have relatively less yield loss due to Rhizoctonia, but even resistant varieties responded positively to the application of Quadris (In these trials the application to the resistant cultivar was in-furrow.).

Table 1. Effect of fungicide application on plant stand and yield in sugarbeet exposed to natural inoculum of Rhizoctonia solani AG 2-2. Linwood, MI, 2003.

Cultivar/rate of application of Quadris (fl oz/A) and date of application

Stand count (days after planting)

RAUPSC b

Yield

10

20

30

122

ton/A

E17

10.5 a

Apr 26

0

0

10.5

May 26

71.4

a c

85.9

ab

87.6

60.1

a

60.4

a

17.4

ab

E17

10.5

Apr 26

0

0

0

0

27.2

b

78.3

b

78.7

55.1

a

53.7

ab

16.7

ab

E17

0

0

5.3

May 16

5.3

May 26

35.8

b

82.0

ab

84.8

49.7

a

53.0

ab

15.2

ab

E17

untreated

0

0

0

0

58.6

a

84.8

ab

80.8

18.9

b

42.5

b

6.4

c

E17

0

0

10.5

May 16

0

0

25.3

b

78.3

b

79.5

49.0

a

51.0

ab

14.8

ab

E17

0

0

0

0

10.5

May 26

60.0

a

89.5

a

86.0

46.8

ab

55.9

ab

13.4

b

RH5

untreated

0

0

0

0

66.6

a

85.8

ab

84.2

56.3

a

58.6

a

13.5

b

RH5

10.5

Apr 26

0

0

0

0

60.8

a

78.6

b

78.9

72.3

a

62.3

a

21.4

a

LSD P = 0.05

16.9

0

10.7

0

10.6

28.6

0

13.4

0

6.73

0

a Rate of application of Quadris 2.08SC (fl oz/A).
b Relative area under the plant stand curve from planting to 122 days after planting. Indicates combined effect of damping-off and crown and root rot (R. solani) on plant stand.
c Means followed by same letter are not significantly different at P = 0.05 (Tukey test).

Table 2. Effect of fungicide application on mortality of sugarbeet plants exposed to natural inoculum of Rhizoctonia solani AG 2-2. Linwood, MI, 2003.

Cultivar/rate of application of Quadris (fl oz/A) and date of application

Dead or dying plants (%)

14 dap

28 dap

Total

AG2-2

E17

10.5 a

Apr 26

0

0

10.5

May 26

0.6

ab b

0.7

b

10.9

bc

9.5

bc

E17

10.5

Apr 26

0

0

0

0

1.1

ab

1.0

b

16.7

bc

14.3

abc

E17

0

0

5.3

May 16

5.3

May 26

0.6

ab

1.3

b

17.0

bc

12.5

bc

E17

untreated

0

0

0

0

1.0

ab

5.5

a

44.9

a

27.7

a

E17

0

0

10.5

May 16

0

0

1.4

a

1.7

b

19.5

bc

14.5

abc

E17

0

0

0

0

10.5

May 26

0.8

ab

3.9

a

20.1

b

9.8

bc

RH5

untreated

0

0

0

0

0.5

ab

0.6

b

19.7

bc

18.6

ab

RH5

10.5

Apr 26

0

0

0

0

0.3

b

0.4

b

4.6

c

3.7

c

LSD P = 0.05

1.1

0

1.82

0

15.15

0

14.44

0

a Application dates and days after planting.
b Means followed by same letter are not significantly different at P = 0.05 (Tukey test).

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