ISSUE 4    May 26, 2005

BLACKLEG ON CANOLA

Blackleg is a fungal disease of canola that can cause foliar and stem lesions. Spores of the blackleg pathogen are produced on canola stubble and discharged into the air in the early spring. These spores can land on cotyledons or leaves and cause infections on susceptible varieties. The infections on the cotyledons and leaves can spread to the vascular tissue in the plant causing cankers on the lower stem area later in season. Leaf infections appear as white to gray circular to oval lesions with tiny black dots inside of the lesion. Lower stem lesions can appear as cankers that are elongated, white to gray in color, with tiny black dots inside.
                  


Blackleg lesions on a canola leaf    
   

Blackleg canker on the lower stem area
of a canola plant.

Good crop rotation practices is the first line of defense against blackleg. Canola should not be planted in fields that had diseased canola in the previous three years. Many highly-resistant varieties are available as well. Unfortunately, two new pathogenicity groups (PG) of blackleg were recently discovered in North Dakota (PG 3 and PG 4). Although their prevalence throughout the state is very low, these new PGs may be able to cause severe disease on some resistant varieties. A blackleg nursery was established in Langdon last year to evaluate resistant varieties that were submitted by seed companies. The results from that trial are available on the NDSU Extension Plant Path. website under "Research trial data". That site is located at: http://www.ag.ndsu.nodak.edu/extplantpath/

Quadris fungicide is registered on canola for blackleg control. Quadris can be applied at 6.2 to 15.4 fl oz/A at the 2 to 4 leaf stage for blackleg control. Quadris was evaluated for blackleg control in Langdon in 2004 at the high rate (15.4 fl oz). Quadris significantly reduced disease levels and increased yield over the untreated check in this trial; however, at the high rate, Quadris would be too expensive to apply. More research is being conducted in 2005 to evaluate this fungicide at lower rates, which would be more economical.

 

SOYBEAN RUST FUNGICIDE MANUAL AVAILABLE

A new multi-state publication will soon be available through the NDSU Extension Service titled, "Using Foliar Fungicides to Manage Soybean Rust". This publication was prepared by plant pathologists, agronomists, and agricultural engineers from over twenty institutions. This 50 page manual contains different chapters that include information on fungicide and application basics. These publications were purchased through funds gratefully donated by the North Dakota Soybean Council, and will be available through your local NDSU Extension Service office or through the NDSU Distribution Center (701-231-7882). This publication is also available on-line at:

http://www.oardc.ohio_state.edu/SoyRust/index.htm  

Soybean rust was found in 9 states in the southern U.S. in November and December of 2004. It has been detected on kudzu (an alternative weed host) in four Florida counties and on volunteer soybean in one Georgia county this spring. The spread of disease within these confirmed areas has been extremely slow thus far. Occurrence of soybean rust throughout the U.S. can be monitored through the following USDA website:

http://www.sbrusa.net/

Carl Bradley
Extension Plant Pathologist
carl.bradley@ndsu.edu

 

WHEAT TAN SPOT DETECTED IN WINTER WHEAT AND SPRING WHEAT

NDSU area specialists reported seeing tan spot fungal infection in winter wheat across much of the state, during an extension conference call on May 24. I also observed it in two winter wheat fields in Cass Co. on May 23rd. The winter wheat I observed was planted into heavy wheat stubble and the tan spot was fairly severe on lower leaves, and with an average 10% severity on upper leaves. The winter wheat fields were in the second to third jointing stage.

I also observed very small tan spot infections on spring wheat field trials planted on light wheat stubble in Fargo. These tan spot infections didnít have the typical distinct tan center and yellow halo, but were more of a pale tan spot with a slightly purple ring, and were only about 1/8 inch wide. These were new infections resulting from recent rains and were slightly purple in color because of the cold temperatures at the time of infection. Similar tan spot lesions were observed by field scouts in the southwest portion of the state, as well. Because of the wet conditions across much of the state, interest is increasing in the early tan spot fungicide application. See Crop and Pest Report # 2, May 12, 2005 issue, for further information on early season fungicides.

 

WHEAT RUSTS IN SOUTHERN PLAINS

The latest issue of the USDA Cereal Rust Bulletin (May 19, 2005 issue) indicates that wheat leaf rust is increasing in the central Great Plains, while stripe rust is decreasing. Recent dry and warm weather in states such has Oklahoma reduced the development of stripe rust.

In Kansas, severities of leaf rust vary depending on the part of the state and varieties examined. Susceptible wheat cultivars in south central Kansas had 40% severities, while in central Kansas, only 5% severities were observed.

 

NDSU SMALL GRAIN DISEASE FORECASTING WEB SITE

The NDSU Small Grain Disease Forecasting web site shows that favorable weather for tan spot infection has occurred across many NDAWN weather sites in the state. Below is an example of information provided for Dazey, ND when the site was accessed on May 25.

That site can be found at the following web address:

http://www.ag.ndsu.nodak.edu/cropdisease/

Favorable infection periods for tan spot fungus - Dazey, ND

 

5/23

5/22

5/21

5/20

5/19

5/18

5/17

5/16

tan spot

Yes

Yes

Yes

Yes

Yes

Yes

No

No

Recent weather information provided for Dazey location

 

5/23

5/22

5/21

5/20

5/19

5/18

5/17

5/16

Rain (in.)

0

0

0.89

0

0

0.21

0

0

RH (%)

60

56

79

82

79

86

74

71

Temp avg.

62.5

63.9

67.4

63.7

63.5

60.9

57.9

46.9

Hrs wet

12

10

10

7

12

5

3

7

Marcia McMullen
Extension Plant Pathologist
Marcia.McMullen@ndsu.edu

 


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