ISSUE 9   June 29, 2006

FOLIAR FUNGICIDES FOR SOYBEAN

Several foliar fungicides are now available for use on soybean in North Dakota as either a fully registered product or through a Section 18 emergency-use exemption for soybean rust. In the absence of soybean rust, foliar diseases present in North Dakota on soybean (such as Septoria brown spot and downy mildew) generally do not require management through the use of fungicides because these diseases generally do not cause economic losses. Foliar fungicides evaluated in NDSU trials on soybean at Fargo from 2004 to 2005 have not resulted in an economic benefit (see table). In other northern states, similar trends have also been observed with few to no economic benefits being gained from foliar fungicide applications on soybean. Dr. Marty Draper (South Dakota State Univ.) summarized results of soybean fungicide trials conducted throughout the northern U.S. (ND, MN, SD, NE, MO, KS, IL, OH, and DE) at the 2005 National Soybean Rust Symposium in Nashville, TN. He reported that an economic benefit with the use of Quadris or Headline fungicide was realized only 40% (10/25) and 25% (8/32) of the time, respectively in these trials (presentation available at: http://www.plantmanagementnetwork.org/). Trials conducted at NDSU have used only one soybean variety each year and have followed spring wheat in rotation. Different varieties may respond in different ways to fungicides, and soybean following soybean in rotation will generally have greater foliar disease pressure. More research is probably needed to evaluate fungicide use on different soybean varieties under tight rotations to see when or if an economic benefit may occur.

Year

Fungicide

Rate/A

Timing

Yield (bu/A)

2004

Untreated control

   

37

 

Tilt

8 fl oz

R3

38

 

Folicur

4 fl oz

R3

38

 

Laredo EC

8 fl oz

R3

38

 

Stratego

10 fl oz

R3

40

 

Headline

12 fl oz

R3

38

 

Quadris

15.4 fl oz

R3

36

 

Bravo Weatherstick

36 fl oz

R3

37

     

LSD 0.05

NS*

         

2005

Untreated control

   

40

 

Stratego / Folicur

7 fl oz / 4 fl oz

R1 / R3

40

 

Laredo EC/Laredo EC

7 fl oz / 7 fl oz

R1 / R3

43

 

Echo 720 / Echo 720

20 fl oz / 20 fl oz

V5 / R3

40

 

Folicur / Folicur

4 fl oz / 4 fl oz

R3 / R5

41

 

Headline

6 fl oz

R1

42

 

Headline

6 fl oz

R3

39

 

Headline

9 fl oz

R1

41

 

Quilt

14 fl oz

R1

44

 

Quadris

6.2 fl oz

R1

41

 

Tilt

4 fl oz

R1

42

 

Domark

4 fl oz

R1

39

     

LSD 0.05

NS*

*No statistically significant differences among treatments.

 

SOYBEAN RUST UPDATE

Soybean rust sentinel plots are being monitored this year in North Dakota and several other soybean-producing states. So far, soybean rust has been observed on kudzu in Alabama, Florida, Georgia, and Texas. The first and only find on soybean in 2006 came recently in Florida, which was found in a soybean rust sentinel plot. Information from the soybean rust monitoring efforts from all of the participating states is available on-line at: http://www.sbrusa.net/. Maps of where soybean rust has been found and commentaries from each state specialist is available at the site. New additions to the site include soybean aphid information and a Good Farming Practice Tool that can be used by growers to document their good farming practices when managing soybean rust for crop insurance purposes.

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

 

WHEAT AND BARLEY DISEASE OBSERVATIONS, June 19-23

Wheat: NDSU IPM summer field scouts surveyed 165 wheat fields and 11 barley fields during the week of June 19-23. The average growth stage of these crops during that week was Zadoks 40 = the boot stage, with a wide range of growth stages, from 2-leaf to soft dough. The most common leaf disease in wheat was still tan spot, with 83% of fields showing symptoms; however, the average severity was less than 5%. Leaf rust was observed in 10% of the surveyed fields, and average severity of leaf rust in infected fields was 6%. Leaf rust was scattered across the state with no apparent hot spots. Septoria leaf spot was observed in 15% of wheat fields surveyed, primarily in the NE area. Loose smut was found in 38% of post-heading wheat fields, with an average incidence of infected tillers in these fields at 3%. Other diseases were observed very infrequently.

Barley: Leaf spots were commonly found by field scouts, but were not severe. Barley growth stage averaged Zadoks 40 (boot stage) at the time. Two of the four headed barley fields had loose smut at 4 and 10% incidence of infected tillers, respectively.

 

WHEAT LEAF DISEASE AND FUSARIUM HEAD BLIGHT UPDATE FROM NDSU DISEASE FORECASTING SITE

Tan spot: On June 28, the NDSU forecasting site (http://www.ag.ndsu.nodak.edu/cropdisease/)

indicated that many NDAWN stations reported favorable weather for tan spot infection anywhere from three to seven days of the past week. Recent cooler night temperatures are resulting in extended dew periods now, and many NDAWN sites reported 8- to 12-hour dew periods in recent days. Tan spot and other leaf diseases may become more abundant with these conditions. Growers should assess individual fields for moisture availability and yield potential for fungicide decisions. However, wheat prices are going up and fungicide prices going down, making an economic return more likely if disease is a risk.

Fusarium head blight: Some NDAWN stations in the state indicated that weather had been favorable for moderate risk of Fusarium head blight on very susceptible or susceptible spring wheat varieties. The area of risk, which is primarily in the north central tier of ND counties, is small and is similar to last week’s areas of risk. Dr. Shaukat Ali is reading spore counts from the Minot area today, but values weren’t available at the time this pest report was due. Interested readers should check the above-mentioned web site for the latest spore findings. Dr. Ali’s spore trap numbers were low at Fargo June 26-27, and were high from Langdon for June 23-26. Spore counts tend to fluctuate in a particular site due to either the occurrence or lack of rain showers.

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


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