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Thursday, November 6, 2014

Novermber, 2014 Wheat Status and Questions



Wheat Status November, 2014

The following is a re-print of an e-mailed update regarding some of the things we (Texas A&M AgriLife Personnel) have been seeing in wheat this fall.  It is written by Dr. Ron French, Extension Plant Pathologist Amarillo, and sums a few things up very well.

Leaf rust of wheat in the Texas Panhandle (26 counties) area during fall 2014.

I have received phone calls regarding leaf rust, samples have been submitted, and I have visited fields that have had leaf rust (no stripe rust, no stem rust).  Leaf rust is as far north as Hansford County and as far south as Hale County, so far. Leaf rust has been present since at least October 14.   This is very similar to what occurred in fall 2007 and fall 2008.  

Here is a link to a factsheet that was done in fall 2008 titled “Leaf Rust of Wheat in the Texas Panhandle, Texas South Plains, and Texas Rolling Plains (Fall 2008)”. http://amarillo.tamu.edu/files/2010/11/LeafRustFall2008PSR.pdf

I was not able to find any leaf rust in parts of the Rolling Plains (Wichita Falls, Elektra) during a drive back from Wichita Falls that I did last week on Wednesday, October 29, 2014. I have made some calls and there are no reports yet. (NOTE: the wheat was recently planted)

In summary, a warm and wet year (plus dew) for the Texas Panhandle (based on the 26 counties) will allow for leaf rust to be present as late as the end of November.  In 2008, we were as high as the low 80s Fahrenheit  during some days in November and as late as Thanksgiving week for Amarillo (week of November 23). We also had snow as well during late November that year.  In 2007, leaf rust of wheat was present through early December in the Rolling Plains.

Although theoretically inoculum could potentially survive a mild winter, a normal winter will not allow for that.  Since spring 2008, I have been monitoring a few fields and I have not been able to track any survival of inoculum. From the Texas High Plains to Wichita Falls. In fact, one year, there were trace levels of leaf rust in mid-March, but after a cold spell and snow, that field was clean for the rest of the season.

Wheat rusts (Puccinia spp.) are not good soil and leaf survivors (dry out, freeze dry, loose viability quickly, can be microbially degraded) but there “edge” comes from producing billions of small spores.  Although most desiccate while wind-blown, it only takes a viable spore to initiate infection. The spore inoculum follows the so-called “Puccinia pathway” from South to North (i.e. warmer areas such as South Texas, Louisiana, and Mexico may/will send spores to northern locations.

If the pathogen produced a hard tissue survival structures like sclerotia or chlamydospores,  survival would take place. Or if there was vascular infection in the stem.  Or if it infected roots (like Fusarium spp.)

Therefore, there is no need to spray and any leaf loss is nowhere near that to a field being grazed.

Fields with leaf rust are showing new leaf growth with minimal or no leaf rust present. And with low temperatures between 28° and 46° F in the Texas High Plains in the next few days, leaf rust activity will keep on decreasing as the pathogen is most active between 59°-72°F. Currently, only certain hours of the day are still providing ideal conditions for leaf rust development.



Wheat viruses:

Blayne has been recommending samples be sent to the Texas Plant Diagnostic Clinic in Amarillo (http://plantdiagnostics.tamu.edu) lab by consultants, producers, and others for diagnosis of diseases, including those caused by viruses.  Wheat viruses such Wheat streak mosaic virus and/or Triticum mosaic virus have been found in some samples from Swisher County as well as other counties.

Most samples brought in due to yellowing of the leaves, are found to be infected with Fusarium sp., especially if the seed was not treated with a fungicide.  Some yellowing of the leaves are due to leaves touching the soil, getting wet, not drying as fast, and therefore are attacked by secondary fungi such as Alternaria sp.). These are samples that my group (French lab) processes for all disease except for viruses. Virus diagnosis is done by the Rush lab via Jacob Price.

For more information, go to: http://sickcrops.tamu.edu

Best regards

Ron French

Ronald D. French, Ph.D.
Assistant Professor and Extension Plant Pathologist
Coordinator, Texas Plant Diagnostic Clinic
Department of Plant Pathology & Microbiology
Texas A&M AgriLife Extension Service
6500 Amarillo Blvd. W.
Amarillo, TX 79106

Main Office: 806-677-5600
Office Phone: 806-677-5616


Thank You Dr. French.  I would like to add that our usual wheat pest populations have been running fairly low, but we are finding several arthropod species that are known to be vectors of wheat diseases. The recent rains were just the fuel this wheat needed to recover from these noted ailments and carry it down the road a bit.

Blayne

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