NDSU Crop and Pest Report
Plant Pathology


ISSUE 8  June 19, 2003

SMALL GRAIN DISEASE FORECASTING UPDATE, 6/17/03

Fusarium graminearum spores are now being detected in spore traps in the Fargo vicinity.

The detection of these spores of the scab fungus indicate an increasing risk of Fusarium head blight as the crop is fast approaching flowering stage. The risk map of June 17th indicates a moderate risk (37 - 57%) in areas along the Red River Valley for that date.

Risk may go up or down depending on future weather conditions. High humidity and moderate temperatures will increase the risk, while low humidity and/or very hot temperatures will reduce the risk. Fusarium head blight risk map on June 17, 2003

Spore and Risk maps may be found at:

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

 

IPM DISEASE SURVEY RESULTS, 6/13/03

NDSUís IPM field scouts surveyed 127 wheat and 20 barley fields last week for leaf diseases. Tan spot was found in 67% of the wheat fields surveyed, similar to the previous week. Severity and incidence had increased slightly over the previous week.

Low levels of wheat leaf rust were found in fields in Emmons, Lamoure, McIntosh, Ransom, Sargent and Richland counties in the SE and SC districts of the state. Wheat leaf rust is reported to be fairly severe on flag leaves of non-fungicide treated winter wheat in some South Dakota fields and it is increasing in ND fields.

The scouts continue to find spot blotch and net blotch on barley leaves, plus some herbicide injury was observed in some fields.

 

SMALL GRAINS PROGRESSING FAST; FUNGICIDES NEED TO BE TIMELY

The small grain crops are rapidly growing because of recent warmer temperatures and ample moisture. Keeping ahead of the crop and the disease development can be difficult at this stage of the growing season. Growers need to be alert and be timely! Frequent field scouting, checking of accumulated growing degree days (NDAWN site at http://ndawn.ndsu.nodak.edu; click on applications) and using decision aid tools such as found on the small grain disease forecasting site, are critical for timely and appropriate fungicide use, when needed.

Barley needs to be sprayed for leaf and head diseases by early full head emergence. If Fusarium head blight is the target, then barley should be sprayed at early head emergence, after the heads are out of the boot. Spraying barley heads while they are still protected by the leaf sheath will NOT allow coverage of the critical infection sites, the grain head!

Wheat needs to be sprayed at early anthesis or flowering for Fusarium head blight control. This is generally when 10-25% of the main stems have started to flower, NOT when 10-25% of the crop has just headed. Like barley, protection for wheat heads can only be achieved when the fungicides are applied to the exposed grain head. Optimum results have been obtained when fungicides were applied during flowering. Folicur fungicide has a 30 day PHI for wheat and barley, while Tilt has a 40 day PHI for wheat.

 

SPRING WHEAT RESPONSE TO WHEAT LEAF RUST IN 2002

Wheat leaf rust severities were recorded on spring wheat cultivars at three locations, Prosper, Carrington, and Langdon, ND in 2002. The following charts indicate spring wheat leaf rust responses averaged over these 3 sites.

Of the over 100 North Dakota wheat leaf rust samples sent to the USDA Cereal Disease Lab in 2002, 59% were T races, 30% were M races, and 11% were K races. The K races are relatively recent to ND. Many of the wheat cultivars showing susceptibility above do NOT have wheat leaf rust resistant genes that confer resistance against the predominate T races. The same is true for the K races.

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

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ASCOCHYTA BLIGHT OF CHICKPEA

Ascochyta blight is a serious disease in chickpea, especially with the large kabuli varieties. Ascochyta blight lesions have been found on large kabuli type chickpeas in Beach and Minot, North Dakota as of June 11, and growers need to be monitoring closely for symptoms. Small kabuli and desi chickpeas are more tolerant to Ascochyta, however, with the continued wet, humid weather all chickpea types and fields need to be monitored closely. The disease can be first identified as light to dark brown spots that occur on leaflets or stems. Lesions will expand rapidly under wet, humid conditions (Fig. 1).

Figure 1. Asochyta blight of chickpea.

Fruiting bodies, called pycnidia, will develop in the center of the lesion. The fruiting bodies are small, round, and are black in color. Often, a hand lens is needed to observe the fruiting bodies. Severely infected leaves will yellow, wilt, and then die. Stem lesions will often be dark brown in color and may cause the stem to break.

It is very important to scout fields for the first incidence of the disease and spray chlorothalonil fungicide as soon as the first lesion is detected with the large kabuli types. Chlorothalonil products (Bravo Ultrex, Bravo Weatherstick Zn, others) are labeled in chickpea for early season Ascochyta control. Most chickpeas are small, only 6 to 8 inches high, and are two weeks from flowering. Fungicide trials at Minot and Williston indicate that chlorothalonil will effectively control Ascochyta when sprayed in the early vegetative stages, prior to the onset of the disease. If the disease is already present and stem lesions have occurred, then chlorothalonil will not be as effective in controlling the disease. If wet weather delays the application and/or stem lesions can be found, then an application of Quadris or Headline would be warranted. Headline (BASF) and Quadris (Syngenta) are both registered for use in chickpea in North Dakota. Once all chickpea types reach the flowering to pod filling stages, then Quadris or Headline would be the preferred fungicides to use to control Ascochyta blight in chickpea.

Kent McKay
Area Extension Specialist
NorthCentral Research Extension Center
kmckay@ndsuext.nodak.edu

 

CANOLA FUNGICIDES FOR SCLEROTINIA CONTROL

Canola in parts of North Dakota and western Minnesota are under moderate to high risk of Sclerotinia infection according to the June 15 Sclerotinia risk map. The risk map predicts when the spore-producing mushroom-like structures known as apothecia (Fig. 2) appear on the ground. Canola is only under risk while it is flowering. Three fungicides are registered for Sclerotinia control or suppression on canola. Topsin M or T-methyl (thiophanate methyl) and Ronilan (vinclozolin) may be applied when canola is between 20 and 50% flowering. Quadris (azoxystrobin) may be applied when canola is between 10 and 25% flowering. NDSU fungicide tests indicate that Topsin M and Ronilan are more effective than Quadris for Sclerotinia control in canola (Table 1).

The current Canola Sclerotinia Risk Map can be viewed at:

http://www.northerncanola.com

or

http://www.ag.ndsu.nodak.edu/aginfo/sclerotinia/sclerotinia.htm

Table 1. Efficacy of canola fungicides for control of Sclerotinia stem rot (Langdon REC, 2001 - data courtesy Bryan Hanson)

Fungicide

Rate/acre

Timing
(% bloom)

Disease incidence (%)

Yield (lb/A)

Topsin M

16 oz

30-40

6 a

2035 a

Ronilan

12 oz

30-40

12 a

1955 a

Quadris

9.6 fl oz

10-20

44 b

1556 b

Untreated

---------

--------

59 b

1303 b

Disease incidence or yield data followed by the same letter are not significantly different from one another.

Figure 2.  Apothecia of the Sclerotinia fungus.
(Photo courtesy J. Venette, NDSU)

Carl A. Bradley
Extension Plant Pathologist
cbradley@ndsuext.nodak.edu


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