ISSUE 10   July 7, 2005

NDSU IPM SURVEY, June 27_July 1

Wheat: NDSU IPM field scouts examined 89 wheat fields for diseases and insects the last week of June. Tan spot and leaf rust continued to be the most common diseases observed, but additional detections of Septoria leaf spot complex were observed, and a smattering of head diseases were seen. Wheat leaf rust was observed in 28% of fields surveyed, with severity ranging from 1 - 20% (see wheat leaf rust severity map). The Septoria leaf rust complex was observed in 24% of wheat fields surveyed, with severity as high as 40% in one field in the southwest that was in early dough stages. Septoria leaf diseases are often commonly seen once head emergence has occurred. A smattering of head diseases also are being observed now, with glume blotch and loose smut being reported. Grain aphids were observed in 24% of the wheat fields surveyed, with threshold numbers being approached in a field in Sheridan and Eddy counties.

Barley: Of the 29 barley fields scouted the last week of June, all but five had high incidences of spot blotch or net blotch. Two barley fields also showed leaf rust, and 34% of the barley fields showed high numbers of grain aphids.

Sunflower: The field scouts checked 42 sunflower fields the last week of June and about half had some level of downy mildew present. Low levels of sunflower beetle larvae were detected in 5 of the 42 fields.

Soybean: Initial scouting in 24 soybean fields in the east central and central region of the state the last week of June revealed no disease problems. A very low population of soybean aphid was observed in 4 fields, one field in Cass county and three in Barnes.

 

FUSARIUM HEAD BLIGHT AND SPORE COUNTS

A smattering of individual kernel infections of Fusarium head blight have been observed in wheat plots in Fargo, as of July 5th. Reeder spring wheat is the variety in these plots, and Reeder is a susceptible variety. The plots flowered on June 28th and are in the kernel watery ripe stage now. These plots also were inoculated about three weeks ago with infected corn kernels distributed on the soil surface. Scab infections have been observed in winter wheat in plots in counties bordering South Dakota. Levels of infection vary with susceptibility of the winter wheat cultivars.

Dr. Shaukat Ali reports that low spore counts of Fusarium graminearum were observed in Fargo spore traps from July 3 to July 5th in uninoculated plots, while high numbers of spores were observed in plots that had been inoculated with the fungus.

The small grain disease forecasting site predicts moderate to high risk of scab infection for flowering wheat across the state, as of July 5th. Risk may go down considerably if the predicted weather for the week holds true, hot and no rain.

 

QUILT AND TILT FUNGICIDES GET NEW SUPPLEMENTAL LABELS

Syngenta recently received supplemental labels for Quilt and Tilt fungicides. Both products can now be applied to wheat until full head emergence (Feekes growth stage 10.5). Previously, Quilt had a full federal label only for application up through early flag leaf emergence. Previously, late application of Tilt to wheat was covered through a state 24C label. These full head emergence labels are for wheat only. The application window for barley with Quilt and Tilt is still through Feekes growth stage 8.

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

 

SOYBEAN RUST IN ALABAMA

Soybean rust was found in Baldwin County, Alabama last week in a soybean rust sentinel plot. Florida also detected soybean rust in a soybean rust sentinel plot in Marion County, a county that had already reported having soybean rust in the weedy host kudzu earlier this year. An additional find on kudzu in Leon County, Florida was also reported last week. The total number of counties with confirmed soybean rust to date is eight (1 in Alabama, 6 in Florida, and 1 in Georgia. Spraying a fungicide to control soybean rust is still not warranted for North Dakota. To track the spread of soybean rust in the United States, go to the following website: http://www.sbrusa.net/

 

SOYBEAN FUNGICIDES WITHOUT RUST?

Three foliar diseases of soybean that can commonly be found in North Dakota are bacterial blight, downy mildew, and Septoria brown spot. These diseases either cannot be controlled with a fungicide and/or do not cause enough yield reduction to warrant a fungicide application. Applying a fungicide for purposes other than controlling a disease should be reconsidered. Many of the fungicides registered on soybean have a high risk of pathogens developing resistance to them. Many of the same or similar fungicides are applied to several crops grown in North Dakota including potato, sugarbeet, wheat, and barley. The more times a pathogen population is exposed to a fungicide, the greater pressure is placed on that population to select out individuals with reduced sensitivity to the fungicide. A trial conducted at Fargo in 2004 showed no significant yield benefit with the use of foliar fungicides applied at the R3 growth stage (see below).

Fungicide

Rate/A

Yield (bu/A)

Untreated control

 

37

Tilt

8 fl oz

38

Folicur

4 fl oz

38

Laredo EC

8 fl oz

38

Stratego

10 fl oz

40

Headline

12 fl oz

38

Quadris

15.4 fl oz

36

Bravo Weatherstick

2.25 pt

37

LSD 0.05

 

NS*

*No statistically significant differences.

 

HIGH SCLEROTINIA RISK FOR CANOLA

Most of North Dakota is under high risk of Sclerotinia for canola that is blooming according to the July 3rd Sclerotinia risk map. The risk map is available on-line at:

http://www.ag.ndsu.nodak.edu/aginfo/sclerotinia/risk070405.htm

or

http://www.northerncanola.com/.

See Issue no. 8 (June 23, 2005) of the Crop and Pest Report for more information regarding Sclerotinia and fungicides registered on canola.

 

SCOUT DRY PEA FOR ASCOCHYTA / MYCOSPHAERELLA

Due to wet weather, scouting of dry pea fields for Mycosphaerella blight and Ascochyta foot rot of dry pea may be warranted. These are two separate diseases caused by two separate fungal pathogens. However, the symptoms of these two diseases are very similar and both diseases may be present in the same field. Symptoms of these diseases can be observed as small, purple to black lesions on the leaves, pods, and stem. The fungicides Amistar, Quadris, and Headline are available for control of these diseases. According to recommendations by Agriculture and Agri-Food Canada in Saskatchewan (http://paridss.usask.ca/specialcrop/pulse_diseases/index.html), fungicide applications should be made at early flowering before lesions cover 50% of the leaf area in the bottom 1/3 of the canopy. A fungicide decision support system for pea is available at the Agriculture and Agri-Food Canada Website listed above. Other methods used to control these diseases include crop rotation, planting disease-free seed, and variety selection. Complete variety resistance is not available; however, varieties differ in their level of susceptibility.

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


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