05-12-16 CSU Ext ALERT: Wheat Disease Update – Kirk Broders, Plant Pathologist…

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Wheat Disease Update – May 12, 2016

Written by: Kirk Broders, Plant Pathologist; Department of Bioagricultural Sciences and Pest Management, Colorado State University; C030 Plant Science Bldg., 1177 Campus Delivery, Fort Collins, CO, 80523-1177; 970-491-0850 (work);  kirk.broders@colostate.edu 

There has been good precipitation around the state this spring which has led to a good wheat crop, but also provides the potential for more foliar diseases than we usually see. Most of the wheat in the southeast has already headed out and there are low levels of stripe rust present, but likely will not impact yield especially where the wheat is further along. Wheat in the rest of the state ranges from booting to heading (Feekes 10 – 10.1). It is at this point that the flag leaf will also become fully emerged, and it will be important to ensure the flag leaf is protected in order to protect yield. I have received reports of stripe rust from multiple locations in eastern Colorado from Prowers County in the southeast and further north in Cheyenne, Kit Carson, Yuma, Washington and Arapahoe counties. Scott Haley mentioned he saw bacterial streak in the northeast part of Colorado and I have also received a couple reports and confirmed one report of Stagonosopora blotch on wheat in Washington County. Both reports were from wheat planted after a previous wheat crop. There were several reports of Stagonospora blotch in the state last year likely due to the significant amount of precipitation. This fungus is capable of surviving on wheat stubble and then infecting the successive crop given ample rainfall. Both Stagonospora blotch and stripe rust remain sporadically distributed and at low levels in most regions in the state, but with more predicted rain in the forecast growers may want to consider applying a fungicide once the flag leaf is fully emerged in order to ensure it is protected and the head is able to yield to potential. Certainly, they should take into consideration whether there is any foliar disease currently in the field or in their region, the potential yield of the crop and the cost of the fungicide to be applied, as well as the probability of cool, rainy weather in the forecast.

I am also including the message below from Bob Hammon for an update on the status of wheat disease on the western slope.

Bob Hammon, Area Extension Agent (Entomology/Agronomy),Tri River Area Extension

Grand Junction CO

I visited several wheat fields in the Fruita/Loma/Mack area on Tuesday and would like to update everyone on the present status of stripe rust in the area.

Most of the wheat is in boot stage, with flag leaves present on primary tillers  or just emerging from secondary tillers.

Stripe rust appears to be limited to several 2nd year wheat fields north of Fruita, although it is spreading slowly within those fields.  A fungicide application done a couple of weeks ago has certainly limited the spread within those fields.

We found a small patch of volunteer wheat with stripe rust located about three miles east of Fruita.  I have no doubt that there are other isolated pockets of active rust in the wheat growing area of the lower Grand Valley.

Stripe rust was first reported in the Grand Valley on May 27 last year.  It was present at low levels in several fields at that time. Wheat was flowering at the time.  It spread quickly in the first couple of weeks of June, and impacted many growers.  We are set up in a very similar situation this year.

The next month is a critical time for wheat growth.  The grain forms and fills in the next 5 to 6 weeks.  The flag leaf on the plant does 80% of the work in filling the grain.  If you lose the flag leaf, you lose your yield and grain quality.  It must be protected.

The decision to whether to spray or not can be difficult.  Some factors to consider are weather forecast, crop growth stage, presence of rust in the field, application methods, fungicide availability, and cost.

I consider all wheat in the Grand Valley to be at risk with weather being the great unknown factor.  The wetter the weather in the next month, the greater the risk.

Most fungicides have to go on in a preventative mode.  Once rust has developed within a field, control is significantly more difficult.  It is important to rotate fungicide classes over time to prevent development of resistance.  Tilt was the primary fungicide in use last year.  It was effective and remains a viable option.  Beware of using it repeatedly within a season.

I attached a picture taken Tuesday east of Fruita.  Note the rust symptoms on the upper part of the plant.  The infected leaf emerged in the past 10 days, showing that rust is actively spreading in the area.

I will be out of town for the next couple of weeks, but will be in contact via.  If you have questions, I will get back with a reply as soon as I can.

Reports from other states: 

Erick Dewolf, Extension Plant Pathologist, Kansas State University: Stripe rust continues to be the primary disease concern of wheat growers in Kansas.  Key changes for this week include additional detections in western Kansas and further disease development in central Kansas.  The disease has spread to the upper leaves of many susceptible varieties just as the crop begins to head and flower.  This is important because the upper leaves are critical to grain development. Damage to these leaves greatly increases the risk of yield loss.  Many growers are using fungicides to suppress the disease.

The attached map shows the current status of stripe rust in the state.
Erick De Wolf
Extension Plant Pathologist
Kansas State University
(785) 532-3968

Kansas Stripe Rust April 29_2016.png

Oklahoma:

Wheat Disease Update – 07 May 2016

Bob Hunger, Extension Wheat Pathologist

Department of Entomology & Plant Pathology – 127 Noble Research Center – Oklahoma State University – Stillwater, OK

405-744-9958 (work) – bob.hunger@okstate.edu

I was in the field this past week around Stillwater and up into northern OK around Lahoma (10 miles west of Enid), Cherokee (20 miles east of Alva) and just west of Alva.  Wheat around Stillwater is at milk to soft dough, with wheat in northern Oklahoma more in the full kernel to milk stage.  On susceptible varieties that were not sprayed, the effects of stripe rust were striking.  Although only little active sporulation of the stripe rust fungus can be seen at Stillwater, quite active sporulation was apparent at Lahoma.  Stripe rust also was found at Alva, but at a much lower incidence.

Finally, I have observed increasing and severe leaf rust around Stillwater, but not nearly as much in other locations.  This next week I will be going to several field days in central and northern OK and will report again next weekend.

Severe leaf rust on wheat near Stillwater

As a continuation from last week, wheat streak mosaic (WSM) is more common this year across northern and northwestern OK.  This past week I again visited an area where several fields of commercial wheat were significantly impacted by an adjacent field in which volunteer wheat and/or weeds were not controlled following the 2015 harvest.  This situation can result in devastation of wheat in surrounding fields.  The Plant Disease and Insect Diagnostic Lab also continued to receive samples testing positive for the presence of the viruses that cause WSM, high plains disease, and barley yellow dwarf.  For more information, see Fact Sheet EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic:  Three Virus Diseases of Wheat in Oklahoma) at http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-8987/EPP-7328.pdf

Wheat streak mosaic in wheat growing next to a field in which volunteer wheat had not been controlled in the fall or through the winter

Kirk  D. Broders, PhD
Assistant Professor
Department of Bioagricultural Sciences and Pest Management
Colorado State University
kirk.broders@colostate.edu

www.broderslab.com
Office: 970-491-0850

Submitted to BARN Media by:

Dr. Wilma Trujillo

Area Agronomist
Logan and Morgan Counties
Colorado State University Extension
Cell: (719) 688 – 9168