ISSUE 11   July 23, 2009

NDSU IPM FIELD SURVEY UPDATE - JULY 22

NDSU IPM field scouts surveyed 119 wheat fields and 22 barley fields across the state for the week ending July 17th. Average growth stage over all wheat fields surveyed was "head half emerged" and for barley, "full head emergence".

Wheat: Tan spot was observed in 83% of the surveyed fields, and average severity was 16.2% of the leaf area covered by tan spot. The previous week, tan spot severity averaged about 12%. Only trace levels of leaf rust were observed, in two winter wheat fields, one in Bowman county in the southwest and one in Nelson county, in the northeast. Head scab was observed in only five fields, with an average field severity of 1.7%. Loose smut was observed in 10% of the surveyed wheat fields this past week, similar to last week.

Wheat streak mosaic virus (WSMV) symptoms were observed in 10% of the wheat fields surveyed, similar to the previous week. Barley yellow dwarf virus symptoms were easily observed along field edges in some areas. A golden yellow flag leaf, with the yellowing beginning at the leaf tip, is characteristic of barley yellow dwarf virus infection. This virus is transmitted by grain aphids. Our survey scouts found grain aphids in 36% of the wheat fields surveyed, with an average of 13% of the tillers in these fields having at least one grain aphid.

Barley: As in wheat, along with fungal leaf spot infections, symptoms of barley yellow dwarf virus were observed in some barley fields. (See picture).

In barley, 41% of the surveyed fields this past week had grain aphids observed, with an average of 35% of the tillers in these fields having at least one grain aphid. Head scab has not been reported yet from barley.


Barley yellow dwarf virus symptoms in barley
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WHITE-TIPPED AWNS IN WHEAT

Iíve observed some white tipped awns of wheat this week, in plots that were planted on May 13th (see picture). Iíve also heard of similar observations in commercial wheat fields. White tipped awns may be more visible in certain varieties or be associated with specific planting dates. These white awn tips are NOT due to a disease, but are most likely associated with the sunny days and high winds that have recently occurred - the plants couldnít translocate moisture fast enough to the awns, and the tips dried out.


White-tipped awns in wheat.

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

 

SOYBEAN LEAF BLEMISHES

In the last week, I have received numerous calls about soybean leaf blemishes. Many have been related to sunscald, but some due to low levels of disease. This article is intended to provide a few photos and brief information about some common ailments people are starting to see on their soybeans. I would encourage anyone interested in additional information and photographs of regionally important soybean diseases to visit the website of University of MN Extension Plant Pathologist Dr. Dean Malvick at

www.extension.umn.edu/cropdiseases/soybean/index.html

Sun Scald. Often observed on leaves after sunny days, and more frequent on the undersides when leaves are turned upwards.


Sun scald.
Photo courtesy of L. Wyum.

Septoria Brown Spot. Caused by a fungal pathogen. Often occurs on the lower leaves, and symptoms are small brown spots with a general yellowing of leaf tissue. Septoria brown spot is favored by warm and wet conditions and very unlikely to be economic in North Dakota.


Septoria Brown Spot.
Photo courtesy of D. Malvick.

Bacterial Blight. Caused by a bacterial pathogen. Bacterial blight is the most common disease on soybean leaves in North Dakota, and favored by cool and wet weather. A yellow-green halo will be present around small necrotic lesions. It most commonly appears after rain, high winds, or hail. In some fields, minor economic losses may be possible, but in most situations it is unlikely. Fungicides will not control bacteria.


Bacterial Blight.
Photo courtesy of D. Malvick.

Physiological / Unknown. Last year we saw tremendous amounts of this symptom. After numerous discussions last year, we are still unclear. Ozone, physiological spoting, hot winds, etc. were considered.

The disease Cercospora leaf blight resembles sunscald or this unknown ailment. However, this disease is rarely found outside of the southern U.S., and is favored by hot humid conditions, something we have definitely not had in North Dakota. In over 25 years of research in the state, soybean pathologist Dr. Berlin Nelson has never identified Cercospora leaf blight in North Dakota.


Photo courtesy of Hans Kandel.

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


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