ISSUE 12    July 26, 2007

SMALL GRAIN SURVEY RESULTS - JULY 16-20

NDSU IPM field scouts surveyed 45 wheat fields and 19 barley fields during the third week of July. For wheat, the average growth stage was late milk; and for barley, the average growth stage was early dough.

Wheat: Wheat stem maggot was reported from 80% of the surveyed fields, with an average of 6.6% tillers affected. Grain aphids were reported observed in 24.4% of surveyed fields. Leaf rust was reported in 28.9% of surveyed fields, with average leaf rust severity in infected fields at 9%. All areas of the state had leaf rust, except for the far northwest counties. Durum wheat varieties are resistant to leaf rust, having a "slow rusting" reaction; durum is a prominent crop in Burke and Divide counties of NW North Dakota.

Tan spot and/or Septoria fungal leaf spots were observed in all fields surveyed. Following the high temperatures of this week, it will be more difficult for scouts to determine leaf disease severities, as many leaves may turn brown.

Barley yellow dwarf observations were made in 26.7% of surveyed fields, and bacterial leaf blight in 35.6% of surveyed fields, with a wide range of severity in symptomatic fields.

Fusarium head blight, or scab was reported almost exclusively from the NE region, but from a few fields in the EC region, too. The highest field severity reported was 4%, with an average in infected fields of 1.2%, or very low loss potential. Loose smut was observed in 24% of surveyed fields, but % tillers showing symptoms was generally 2%.

As evidenced above, a combination of insect and disease problems are nibbling away at wheat yields this year. In fields treated with fungicides, leaf rust, tan spot, Septoria and scab should be adequately controlled, but the virus and bacterial diseases were not controlled with fungicides, and grain aphids may have not been controlled with insecticide, and wheat stem maggot does not have a control recommendation at this time. Yields in most areas will still be very good, but some % of the yield potential will have been lost due to the above problems, as well as from heat stress and possibly root rot.

Barley: Barley leaf rust was found in 31% of fields surveyed, at severities ranging from 1-5%. Barley stem rust was observed in 1 field. Barley yellow dwarf and bacterial leaf blight were both observed in 36.8% of surveyed barley fields. Low levels of loose smut were observed in 26.3% of surveyed fields, and Fusarium head blight was observed only in 3 fields, with field severity less than 1%.

 

CEREAL RUST BULLETIN REPORT, July 17, 2007

The newest edition of the Cereal Rust Bulletin from the USDA Cereal Disease Lab in St. Paul indicates that wheat leaf rust is present in low to high severity levels on spring wheat cultivars in the northern plains, with some cultivars showing rust (Knudson and Ada) that have been previously rated as resistant to moderately resistant.

The Bulletin also indicates that stem rust was found on some susceptible spring wheat cultivars (cultivars not commonly grown in ND) in plots in Minnesota and South Dakota. We found low levels of stem rust on a susceptible winter wheat cultivar (Radiant) in winter wheat plots in Ransom County on July 10.

 

POTENTIAL EFFECT OF LATE LEAF RUST DEVELOPMENT IN WHEAT

Flowering time applications of triazole fungicides, such as tebuconazole (Folicur and generic products), propiconazole (Tilt and generics), or prothioconazole (Proline), have been shown to provide wheat leaves protection from leaf rust infections for a solid three weeks, when applied at the full label rate. Thus, application at flowering should provide protection until soft dough stage. As the crop progresses into mid and hard dough, leaf rust infections may occur, but yield losses with these late infections generally are not high. Late infections may cause some test weight reductions.

The following table, based on data developed by Kansas State University plant pathologists, describes possible % yield reductions with light to heavy flag leaf rust infections, depending on flowering or kernel stages when these infections occur. Similar information was not available for late rust impacts on test weights.

Estimated Yield Losses in Wheat Due to Leaf Rust - according to Severity on the Flag Leaf and Growth Stage
(From Kansas State University wheat pathologist)

Growth stage

% Rust Severity on Flag Leaf

10%

25%

40%

65%

100%

 

.......estimated % Yield Loss.......

Flowering

10

15

20

30

35

Milk

2

5

8

15

20

Soft dough

1

3

4

7

10

Hard dough

1

2

2

3

6

Marcia McMullen
Ext. Plant Pathologist
marcia.mcmullen@ndsu.edu

 

SOYBEAN RUST SPREADS TO NORTH TEXAS/ARKANSAS

In the last 10 days soybean rust was found in Northeast Texas north of Dallas, and near the Red River of the south (on the Texas/Arkansas border) north of Texarkana. The disease was found in low levels. The map below is from the IPM-PIPE website, available at http://www.sbrusa.net/. The movement of soybean rust should not alarm growers in our region, but it is best to be aware of the disease development to our south. In the event that soybean rust moves close to North Dakota, we will make growers aware of the situation as it develops.

Soybean rust map
Map of sentinel plots in U.S. scouted for soybean rust as of July 25, 2007.
Soybean rust is absent in counties colored green and present in counties
colored red. Map available at www.sbrusa.net.

 

SOYBEAN RUST BROCHURE BEING DISTRIBUTED

Included in the upcoming mailing from the North Dakota soybean council will be a soybean rust brochure. The soybean rust brochure discusses the biology of the disease, the sensitive growth stages of soybeans, and the national program (IPM-PIPE) that I am involved with which that keeps track of soybean rust movement and disease development, and develops control strategies. The brochure also provides internet links to up-to-date disease information.

We are very appreciative of the North Dakota soybean councilís willingness to distribute this brochure. If you have any questions regarding information on the brochure please let me know, my contact information is on the back. If soybean rust becomes a threat, we will let you know.

 

SOYBEANS AND SUNBURN

I have recently received phone calls concerning some ugly looking soybean leaves. This caught me a bit by surprise; I used to see this while I was in graduate school in Arkansas, but didnít really think I would see it here. It turns out, that this is most likely soybean sun scorch/sunburn. There isnít much you can do about sunburn, it happens once in a while. Minor sunburn shows up as small burnt red spots. Severe sunburn scorches the whole leaf, and tends to follow the leaf veins. After a while, the leaf dries and cracks. Sunburn can occur on both sides of the leaf, but I have seen it more commonly on the underside of the leaf when the leaf is flipped up. The picture is courtesy of Lowell Wyun at Gwinner Farms Elevator.

Sunburn on soybeans
Sunburn/Sun scorch on soybean leaves (Photo by L. Wyum)

Sam Markell
Ext. Plant Pathologist
samuel.markell@ndsu.edu


NDSU Crop and Pest Report Home buttonTop of Page buttonTable of Contents buttonPrevious buttonNext button