NDSU Crop and Pest Report
Plant Pathology


ISSUE 8   June 24, 2004

NDSU EXTENSION PLANT PATHOLOGY WEBSITE
Extension Plant Pathology now has a website where fungicide trial data, plant disease information, and on-line Extension publications can be found. Some pages are still under construction, but we will be continually updating and adding to the site. The website can be found at:

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

 

QUADRIS FUNGICIDE ON SAFFLOWER
The EPA recently granted a section 18 emergency exemption for use of Quadris fungicide on safflower for control of Alternaria leaf spot. The exemption is effective from July 1 to August 15, 2004. A single application of Quadris may be made by air or ground equipment at a rate of 6.2 to 9.3 fl. oz/A. The emergency exemption label can be found on the web at:

http://www.ag.ndsu.nodak.edu/aginfo/pesticid/sec18_2004.htm

 

FUNGICIDES FOR CANOLA
As a few canola fields are beginning to bloom in parts of the state, the time to make decisions on applying fungicides for protection against Sclerotinia stem rot draws closer. Canola plants become susceptible to Sclerotinia after they begin to cast their flowers, as the cast flowers are the primary sites of infection. Keeping an eye on the crop stage, the Sclerotinia Risk Map (see last week’s Crop & Pest Report), and scouting for apothecia (mushroom-like structures in the soil that produce spores) may help with spraying decisions.


Sclerotinia apothecia emerging from a sclerotium.
(Courtesy J.R. Venette)

The four fungicides registered for use on canola for Sclerotinia control are Topsin M (and generics), Ronilan, Endura, and Quadris. Data from 2003 research trials at Langdon, Carrington, and Minot are shown below (data courtesy G. Endres, B. Henson, B. Hanson, K. McKay, and M. Halvorson).

Carrington, 2003.

Product

% bloom

% Disease

Yield (lb/A)

Endura 5.8 oz

30

24*

1593

Endura 5.8 oz

50

17*

1695

Ronilan 12 oz

30

38

1576

Ronilan 12 oz

50

27

1664

Topsin 16 oz

30

33

1581

Topsin 16 oz

50

31

1527

Untreated

 

32

1534

Minot, 2003.

Product

% bloom

% Disease

Yield (lb/A)

Endura 5.8 oz

30

1*

2630

Endura 5.8 oz

50

1*

2835

Ronilan 12 oz

30

1*

2849

Ronilan 12 oz

50

1*

2943

Topsin 16 oz

30

1*

2944

Topsin 16 oz

50

1*

2925

Untreated

 

6

2669

Langdon, 2003.

Product

% bloom

% Disease

Yield (lb/A)

Endura 5.8 oz

30

56*

1978*

Endura 5.8 oz

50

40*

2191*

Ronilan 12 oz

30

78

1952

Ronilan 12 oz

50

67

2081*

Topsin 16 oz

30

74

1911

Topsin 16 oz

50

79

1706

Untreated

 

82

1516

*Statistically different than the untreated control.

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

 

WHEAT LEAF RUST ALERT

NDSU IPM scouts have found trace levels of wheat leaf rust now throughout much of the state, including in the north central counties. Greg LaPlante, private crop consultant, reported on June 23 some extensive leaf rust in the lower canopy of a field of ‘Ingot’ spring wheat in Richland Co. ‘Ingot’ is a cultivar with considerable susceptibility to leaf rust. This disease always bears close watching, especially in susceptible cultivars.

The USDA’s Cereal Rust Bulletin #7 (June 23, 2004) reports that "wheat leaf rust is widespread and more severe than last year throughout the central U.S." Severities of 10-20% have been reported on flag leaves of winter wheat in southeastern South Dakota and high levels were observed on very susceptible spring wheat varieties in a nursery in east central SD.

 

SMALL GRAIN DISEASE SURVEY, 614-6/18

NDSU IPM field scouts found little increase in disease development in wheat and barley this past week. Cold night temperatures have inhibited fungal growth and crop growth. Wheat and barley fields surveyed last week and their growth stage at the time of survey are below.

Figure of wheat surveyed:

Figure of barley surveyed:

Tan spot was the most common and widespread wheat disease observed (see figure). Although incidences of plants infected were high in some fields, severities generally averaged between 1 and 15%.

In barley, the most common diseases observed were net blotch in the northern counties and spot blotch in the western counties. The net blotch fungus likes cool temperatures, so may remain activity during this latest cool weather.

 

DISEASE FORECASTING MODELS - UPDATE

Prior to the latest cold snap, the Fusarium head blight model (FHB = scab) indicated many areas in the east were at risk of infection, although not many fields were flowering at the time. With the cold night temperatures recently, the FHB risk models indicate that the whole state of ND and western MN now (June 22) are at low risk for this disease. Risk of leaf spot infections also diminished over the past week because of cold temperatures. These risks change on a daily basis depending on weather conditions.

Many crops in the southern part of the state are in the boot stage to early heading. As control of FHB is optimum at early flowering for wheat and early full head emergence in barley, many growers still have some time yet to make a fungicide decision. If favorable weather (warmer temperatures and high relative humidities and dew) return, then growers may use the fungicide at these heading growth stages to control FHB and the leaf diseases. Application of the fungicides at heading stages has given excellent control of leaf diseases, under ND conditions.

Marcia McMullen
Extension Plant Pathologist
mmcmulle@ndsuext.nodak.edu


NDSU Crop and Pest ReportTop of PageTable of ContentsPrevious pageNext page