May 16, 2011 Pest and Disease Update

From Ned Tisserat, CSU Extension Specialist and Professor
Bioagricultural Sciences and Pest Management

The wheat disease situation in Colorado still remains very quiet.   I have had no reports of leaf or stripe rust.    Our neighboring states are also reporting very low levels of disease, especially the rusts.  That is good news for us because rust inoculum usually tracks up through Texas, Oklahoma and Kansas.    The biggest concern in regions adjacent to us is barley yellow dwarf virus.  This aphid transmitted virus will cause pockets of yellow, stunted wheat.  The leaf tips often have a purple or red tinge.  Also start looking for symptoms of viruses carried by the wheat curl mite.  These include wheat streak mosaic, high plains virus, and the more recently identified triticum mosaic.   Affected plants exhibit yellow mottled leaves and a stunted or splayed growth.   Remember, we are offering free virus testing, so if you have suspicious looking plants, please contact me for sampling and collecting information. (Contact information below.)

We did confirm (via K-State) a case of wheat soil borne mosaic virus in northeastern Colorado in an irrigated wheat field.  While this virus is common in central Kansas and Nebraska, it is a bit of a rarity for us.  The virus is transmitted by a water mold type organism and tends to occur in low, wet areas of the field.   Considering the dry fall we had, this was an unusual find (at least we hope so).

Here are some reports from other states.

Dr. Stephen Wegulo from U. Nebraska:

Yesterday (May 5) I surveyed wheat fields in southwest Nebraska (Chase, Furnas, Keith, Lincoln, Perkins, and Red Willow counties).  Growth stage was Feekes 6 in all fields surveyed.  I did not find any rust diseases.  The predominant disease was tan spot at trace to low levels in dryland fields.  However, in one irrigated field in which wheat was drilled into wheat stubble, tan spot was so severe that the entire field looked yellow due to extensive yellowing of lower leaves.  I also found wheat soilborne mosaic in a single low spot in a different irrigated field.

Oklahoma: Dr. Bob Hunger OSU.   A trip yesterday to central Oklahoma (El Reno area) then to Kingfisher and Marshal (west of Stillwater) confirmed that barley yellow dwarf is the most prevalent disease this year in Oklahoma.  I saw very little leaf rust at any of these locations.  Powdery mildew, although present, was definitely in the “shut-down” mode.  Some fields and trials had what appeared to be damage from freeze and/or drought.  At Lahoma (west of Enid), Dr. Brett Carver (OSU Wheat Breeder/Geneticist) reported seeing some leaf rust but still at low levels, and also found a few isolated pockets of stripe rust.  In these areas and at Stillwater, wheat is mostly at the milk to soft dough stage.
Around Stillwater where more moisture has been received, leaf rust is starting to increase (especially on susceptible varieties).  Dr. Art Klatt (OSU Wheat Breeder/Geneticist) reported seeing active and severe powdery mildew, and increasing levels of leaf rust (20-30S range) on his trial planted in a bottom area.  Similarly, leaf rust is increasing in the variety-demonstration trial planted at Stillwater, and in a fungicide trial.
Samples continue to come into the Diagnostic Lab that test positive for various combinations of wheat streak mosaic virus, high plains virus, Triticum mosaic virus, and BYDVs.  Nearly all of these samples are from northwestern OK or the panhandle.

Reports/excerpts of reports from other states:
Kansas (Dr. Erick De Wolf, Wheat Plant Pathologist, Kansas State University), 04-May:  Stripe rust was found in Labette county Southeast Kansas this week.  Doug Jardin describes finding a small “hot spot” in the variety Hitch, which is one of the Yr17 varieties that had a lot of problems last year.  The overall incidence of stripe rust was very low at this location, and it appears the stripe rust has not spread out of the hot spots yet. This area of the state has been cool and wet recently.  The wheat at this location ranged between boot and flowering.  A trace amount of leaf rust was observed in Reno county (central Kansas) May 4.  The wheat at this location was been under considerable drought stress and the plants were rolling their leaves in response the dry soil conditions.  The wheat at this location was heading.   Barley yellow dwarf appears to be very common this year in south central and southeastern Kansas. I have observed numerous fields with patches of BYD ranging in size from 1ft to 20ft in diameter.  Wheat streak mosaic is also being reported in more fields than we have seen in the last 4 years.  The disease is severe is some fields near volunteer wheat and at trace levels in other fields.

Ned Tisserat
Extension Specialist and Professor
Bioagricultural Sciences and Pest Management
Plant Sciences 1177
Ft. Collins CO 80523
Ned.Tisserat@colostate.edu
970-491-6527
970-491-3862 (FAX)

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