ISSUE 1   May 5, 2005

SOYBEAN SEED TREATMENTS PAY OFF IN COOL, WET SPRINGS

Fungicide seed treatments on soybean have been shown to pay off in cool, wet springs. Seedling diseases caused by Rhizoctonia, Fusarium, Phytophthora, and especially Pythium can be prevalent depending on several factors. Fields with poor drainage, history of root rot, or with very tight rotations are those that may be more prone to have seedling disease pathogens present. A soybean seed treatment study conducted in Cass and Richland Counties in 2003 and 2004, shows how seed treatments can have a large effect in years with cool, wet springs (Table 1).

 

Cass Co. (Yield)

 

Richland Co. (Yield)

Treatment

2003

2004

2003

2004

Untreated

29

4

35

26

Warden

31

21

37

39

SoyGard

30

19

36

42

YieldShield

31

13

36

39

LSD 0.05

NS

4

NS

5

In 2003, minimal differences were observed among treatments, but in 2004, plots with fungicide seed treatments performed much better than the untreated checks. Looking back in the spring of 2004, soils remained cool and wet for an extended period of time. In these soils, unprotected seeds were at risk to infection by numerous seedling blight pathogens. If the choice to use a fungicide seed treatment on soybeans is made, be sure to use one with broad-spectrum control such as ApronMaxx RTA (Syngenta), SoyGard (Gustafson), Kodiak + Allegiance (Gustafson), or Warden RTA (Agriliance). Rhizobium inoculants can be used with treated seed; however, fungicides should be allowed to dry first and inoculants should be applied as close to planting as possible.

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

 

WHEAT STREAK MOSAIC VIRUS

Some winter wheat fields coming out of dormancy this spring are showing yellowing and mottling of leaves. Several things may be causing this yellowing of winter wheat:.

a) Recent freezing temperatures or nitrogen deficiency may be causing some of the yellowing, especially if leaves are uniformly golden yellow, or only older leaves are showing symptoms.

b) Or a virus infection called wheat streak mosaic virus (WSMV) may be causing some pale yellow streaking and mottling on individual leaves, symptoms typical of this virus infection (see Figures 1 and 2).


Figure 1.  Close up of WSMV symptoms.


Figure 2.  Field expression of WSMV.

 

Last fall, some winter wheat fields in Bottineau county, ND, showed these symptoms of pale yellow streaking and mottling, and were confirmed as positive for WSMV infection. A few fields had severe infection and it was recommended to destroy these fields last fall. Some additional winter wheat fields may be showing symptoms this spring.

The wheat curl mite that transmits this virus overwinters in ND on winter wheat, volunteer winter wheat and some perennial grasses - grass plants that stay alive over winter and start regrowth in early spring. The mites do not have to blow in from southern wheat areas, they readily overwinter here. However, recent cold temperatures will have inhibited or slowed down mite activity and reproduction. A return to warm spring temperatures will reactivate this mite and allow it to increase in population and subsequently transmit WSMV to new plants. WSMV is always most severe under warm, dry conditions.

For more information about the disease, see NDSU Ext. Circular PP-646 Wheat Streak Mosaic, available through the NDSU Extension Service web site at http://www.ag.ndsu.nodak.edu.

Growers who may wish to have a confirmation of WSMV infection in their wheat crops may send plant samples to the NDSU Diagnostic Lab, Dept. of Plant Pathology, Walster Hall, NDSU, Fargo, ND, 58105. The fee for the first sample tested is $25, but if several fields are included in the submitted samples, a $10 fee will be charged for each additional WSMV test for the grower. Growers should submit whole seedlings rather than just a few leaves.

 

REPORTS OF RUST IN WHEAT IN SOUTHERN PLAINS

An Oklahoma wheat disease update provided on April 29th to the USDA Cereal Disease Laboratory, St. Paul, indicated that much of the Oklahoma winter wheat crop is in the berry stages and some fields of susceptible cultivars are showing severe stripe rust.

In a May 3rd report, a Kansas State extension plant pathologist indicated that stripe rust is developing in susceptible cultivars, such as Jagger, especially in southern and western Kansas. The recent cool weather across the plains has favored development of stripe rust. Leaf rust is also present in some Kansas fields, but it is favored by warmer temperatures. The Kansas Ag. Statistical Service reports that the majority of the Kansas crop is now jointed and only 7% of the crop is showing moderate to severe disease.

Rust incidences in the southern plains are of interest to us, because these rust spores may move with prevailing winds to infect our crops. However, we have a ways to go before our crops are at risk.

 

NDSU SMALL GRAIN DISEASE FORECASTING WEB SITE

The NDSU Small Grain Disease Forecasting is now operable for 2005. The Internet location of this site is:

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

This site provides information to wheat producers on the risk of infection of tan spot, Septoria blotch, leaf rust and Fusarium head blight, based on weather information provided by 59 NDAWN weather stations. A grower or consultant may access the nearest NDAWN weather station, choose the growth stage of the crop, and determine risk of these four disease for that date. At this same site, a summary of weather conditions for the past 12 days also is provided. Information on disease risk is useful for making fungicide decisions during the growing season.

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

 

NDSU PLANT DIAGNOSTIC LAB GETTING READY FOR SOYBEAN RUST SAMPLES

This summer will likely be one of the busiest for the NDSU Plant Diagnostic Lab. In preparation for the volume of samples we expect to receive for soybean rust identification, the lab will hire an additional lab aide, and its clerical support will increase as well. Some of you may have had the opportunity to meet the labís returning summer clerical assistant, Ms. Miriam Tobola. She is a full-time high school art teacher during the school year, and the lab are fortunate to be the recipient of her talents during the summer months. The lab aide is yet to be determined, but some of the responsibilities will include data entry and sample preparation.

A third addition to the lab, specifically for soybean rust-related samples, will be Dr. Art Lamey, Professor Emeritus in the Department of Plant Pathology. He has agreed to assist in soybean rust identification, on a part-time basis, this summer. He has been a tremendous supporter of the diagnostic lab.

Due to available funding through the USDA and the Great Plains Diagnostic Network (a region of the National Plant Diagnostic Network), samples for soybean rust identification will be evaluated at no charge. However, this fee waiver only applies to samples that relate to soybean rust, not other diseases that can resemble soybean rust symptoms. If diagnoses other than soybean rust identification are requested, then the normal lab fees will apply. This fee is $15 for North Dakota residents with samples that require no special manipulation, $25 for samples that require special manipulation, or $25 for residents of states outside North Dakota.

Kasia Kinzer
Plant Diagnostician
diaglab@ndsu.edu


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