NDSU Crop and Pest Report
Plant Pathology


ISSUE 7  June 12, 2003

IPM SURVEY DISEASE UPDATE

NDSU IPM field scouts surveyed 138 wheat and 41 barley fields last week for diseases. No new observations of wheat leaf rust were made this past week. They observed tan spot in 66% of the wheat fields, with an average severity of leaf spotting at 3.2%. The highest incidences of plants infected and highest severities of tan spot were seen in wheat fields in the southwest part of the state, where over 50% of the fields are wheat planted into last year’s wheat ground.

The above map can be accessed at:

http://www.ag.ndsu.nodak.edu/aginfo/ndipm

The Small Grain Disease Forecasting models have indicated favorable infection periods for tan spot at most NDAWN locations this past week. These can be viewed at:

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

Of the barley fields surveyed, 35% showed some levels of spot blotch or net blotch. Net blotch was more commonly observed in the eastern part of the state, while spot blotch was more commonly observed in the western counties. A field agronomist from Dickinson reported severe spot blotch in one barley field at the boot stage. John Swenson, the Griggs Co. extension agent, reported net blotch as very noticeable in some barley fields in Griggs Co.

 

SMALL GRAIN FUNGICIDES

The early season for application of fungicides is past for most producers, and now many are thinking about boot or heading application. Barley is in the boot in some locations and some winter wheat is heading.

Excellent control of late season leaf disease on hard red spring wheat and barley has been achieved at Fargo by applying fungicides at heading or flowering. The following table shows the control levels achieved on Robust barley and Oxen spring wheat at Fargo in 2002 when various fungicides were applied at boot or at early heading or early flowering. All treatments gave control, but applications at early flowering or early heading resulted in more significantly lower leaf disease scores than did the boot application.

% Leaf disease on flag leaf as measured at soft dough stage, Oxen spring wheat and Robust barley, Fargo, 2002.

Product

*Fargo Barley

*Fargo Wheat1

*Fargo Wheat2

*Fargo Wheat3

**Fargo Wheat4

Untreated

12.9 b

19.9 b

25.5 b

18.3 b

18.7 b

Folicur

–

2.3 b

7.0 a

3.5 a

10.5 ab

Tilt

5.3 a

3.9 b

–

3.3 a

12.5 ab

Stratego

5.0 a

–

–

–

8.0 a

Headline

5.2 a

6.3 b

5.8 a

–

–

Quadris

5.7 a

–

–

–

–

* Fungicides applied at early flowering (Feekes 10.51) in wheat or early full head emergence (Feekes 10.5) in barley

** Fungicides applied at boot (Feekes 10)

Values in above table followed by a different letter are significantly different from each other at the 95% confidence level

If leaf diseases are very severe on the flag minus one and flag minus two leaves at boot, a grower may wish to apply a reduced rate of a strobilurin fungicide such as Headline, Stratego, or Quadris on wheat or Headline on barley, or apply a protectant mancozeb to protect the flag leaf , then consider late season application at heading or flowering to control scab and late season leaf diseases.

What about scab? The unanswered question now is the weather during flowering of wheat and full head emergence of barley. Will it be favorable for Fusarium head blight (FHB = scab)? The current weather pattern makes most of us nervous, as we know that this kind of weather with a little warmer temperatures during those growth stages would be favorable for FHB.

The two best choices for FHB control are the systemic triazole products Tilt and Folicur. Folicur has a Section 18 label for use for FHB control in wheat and barley, and Tilt has a 24C state label for heading application in wheat. The strobilurin fungicides, such as Headline, Quadris, and Stratego are not recommended for use for FHB control because they have increased the DON (vomitoxin) levels in some tests when applied at flowering.

The following table indicates % reduction in DON with fungicides in several trials at Fargo in 2002.

% Reduction in DON (vomitoxin) with fungicide application at flowering (wheat) or at early full head emergence (barley) Fargo, 2002

Product

*wheat1

*wheat2

*barley

Folicur 4 fl oz

34

15

11

Tilt 4 fl oz

---

18

1

Headline 6 fl oz

- 33

- 29

- 17

Headline 9 fl oz

0

---

—

*A negative number = an INCREASE in the DON level over the untreated check. A --- means that product wasn’t included in test.

The above two tables indicate that a grower will have to make a choice about late season disease control. If leaf diseases are the only concern, then data from the first table may be a guide to fungicide application. If FHB also is a concern because of continued favorable weather, growers who want to make only one fungicide application may want to wait and make a fungicide application of Folicur or Tilt for wheat or Folicur for barley that will control both leaf diseases and give the best reduction in DON.

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

 

SCLEROTINIA RISK MAPS POSTED ON THE WEB

Sclerotinia Risk Maps for canola in North Dakota and northwestern Minnesota are now being generated for the 2003 growing season. The maps are posted 2 times per week on the web at the Northern Canola Grower's website, which is:

http://www.northerncanola.com

The maps are also posted on a NDSU site, which is:

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

A sclerotinia risk map, a top zone soil moisture map, and a canola growing degree day map are available for each posting date.

The project collaborators are Dr. Art Lamey, NDSU professor emeritus, Dr. Carl Bradley, NDSU Extension plant pathologist, Dr. Luis del Rνo, NDSU plant pathologist, and Dr. Gary Platford and Jennifer Lamb of P&D Agro Consulting Inc.

Sponsors are the Northern Canola Growers Association, Minnesota Canola Council, North Dakota State Board of Agricultural Research and Education, the USDA-ARS Sclerotinia Initiative, and North Dakota State University.

Weather data and technical information is contributed by Environment Canada Meteorology Service Commercial Weather Services Division, North Dakota Agricultural Weather Network (NDAWN), and Dr. John Enz, NDSU climatologist.

 

DISEASES THAT PREFER WET SOILS

With all of the rain hitting several locations in North Dakota the past week, much of the soil is saturated. Plant pathogens that belong to a group known as water molds or oomycetes require saturated soil to infect plant roots and cause disease. These oomycetes produce spores that actually swim (thus the need for saturated soil) to plant roots and cause infections. The three main oomycete pathogens that can cause problems on some of the broadleaf crops in North Dakota are Aphanomyces, Phytophthora, and Pythium. Diseased plants infected by these three pathogens tend to be observed in the field in patches.

Aphanomyces cochlioides causes damping-off and root rot of sugarbeet. This disease tends to show up more often in warmer soil (68 to 86 degrees). Infected roots may turn black and shrink to a dark, slender thread. Sugarbeet is the only crop affected by Aphanomyces cochlioides, but some weed species are also hosts.

Aphanomyces euteiches can cause a root rot of pea, lentil, alfalfa, dry bean, and different weed species. This pathogen has not been verified in North Dakota, but symptoms resembling Aphanomyces root rot have been observed on dry pea. Disease symptoms include sloughing off of the root cortex (leaving a central strand of root vascular tissue attached), and dark, shrunken roots.

Phytophthora sojae can cause damping-off and root rot of soybean. Phytophthora root rot is the most damaging disease of soybean present in North Dakota. Root infection can occur anytime throughout the growing season. Symptoms appear as rotted roots with dark lesions progressing up the stem from the soil.

Several Pythium species are able to cause damping-off and root rot on several crops grown in North Dakota. Symptoms on the root may appear as sloughing off of the cortex, leaving the central vascular tissue attached. Pythium ultimum, one of the most common species, can be most damaging when soil temperatures are below 60 degrees.

Management of diseases caused by oomycetes generally require an integrated approach. Management tools available for oomycete disease management include crop rotation, fungicide seed treatments, and resistant varieties.

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


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