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Agricultural News

No Problems Yet- Wheat Disease Update with Dr. Bob Hunger of OSU

Sat, 07 Apr 2012 21:30:24 CDT

No Problems Yet- Wheat Disease Update with Dr. Bob Hunger of OSU Disease pressure continues to be very low in Oklahoma wheat fields, even as the weather has swung around and become milder as we go through Easter weekend, with the prospect that this coming week will bring more of the same type of weather. OSU Extension Plant Pathologist Dr. Bob Hunger provides us his latest wheat disease report as of Saturday morning, April 7- it follows- by the way, the picture here is from Canadian County where we found this single instance of some light rust on a wheat stalk- this on Saturday morning, April 7. You can see a bunch of pictures we took on Saturday the 7th in northeastern Canadian County- and every field we saw, had wheat fully headed or at least fully in the process of being headed. Click here for our WheatWatch 2012 set of photos, which has shots all the way back to last fall. Scroll to the bottom of the set to see the most rece

Oklahoma: Thursday and Friday (05-06 Apr) I visited variety trials/demos or fields at Kingfisher (50 miles west and 20 miles south of Stillwater), Minco (40 miles south of Kingfisher), Apache (25 miles north of Lawton), Lawton, Snyder (35 miles west of Lawton), multiple fields east and west of Frederick/Manitou area (20 miles south of Snyder), Altus, Granite (30 miles north of Altus), and multiple fields located 20 miles north of Clinton. Wheat was mostly in the heading to flowering range with the exception of the fields north of Clinton, which were in the boot to just heading range (mostly later planted). Below are observations by disease.

Leaf rust was at a very low incidence along the entire route with only widely scattered pustules observed.
Barley yellow dwarf spots were seen occasionally at nearly every stop, but BYD was not as widespread or severe as I have seen it in trials here at Stillwater.
Powdery mildew was not found at any stop - I just realized that I really wasn't looking for PM, but if it had been heavy I can't imagine I would have missed it.
Stripe rust could be found at nearly every location as widely scattered short stripes. I found one large (5 ft X 10 ft) "hot spot" at Kingfisher, but didn't find any at Minco and very little north of Clinton. In most cases where stripe rust was found, sporulation also was found. However, in southwestern OK, it was apparent that in many of the stripes the pustules had "deactivated" or "shut off" due to the hot temperatures two weeks ago, but were starting to activate (sporulate) again since the start of the wet and cool weather this past week. At no location did I see heavy, widespread stripe rust. Mark Gregory (Southwest OK Area Extension Agronomist) visited most of the southwestern fields with me and afterwards traveled east on highway 70. Mark reported some heavy stripe rust on flag leaves in a trial close to I-40 along with some leaf rust.
Tan spot (TS), Septoria leaf blotch (SLB), physiological leaf spot (PLS): Several fields I visited exhibited symptoms of TS, SLB and/or PLS. Most of these were no-till fields with varying amounts of residue present. In some fields, numerous pseudothecia (resting bodies) of the tan spot fungus were found on that straw residue. In others, few (if any) pseudothecia could be found. Symptoms on leaves were most severe in the lower canopy where large blotches of dead leaf tissue, yellowing, and some spotting were observed. In the upper canopy, smaller spots could be observed that ranged from small dark black lesions with white centers to those more typical of tan spot (brownish centers surrounded by yellowish halos). Most of these fields where I observed this were the variety Duster.
In some of these fields, I believe that TS and or SLB are occurring, but there also is a greater incidence this year of PLS, which we have seen in previous years. PLS is not well understood, and can range from the look of the flecking caused by the onset of rust pustules to those as described in the previous paragraph. These types of PLS have been seen in isolated incidence over the years, particularly in Duster and Doans. However, over this past trip I observed PLS also in Billings, Jackpot, Fuller, Endurance, and Gallagher. Unfortunately, I am not having much success in identifying common factors. For example, I did not see any PLS at Kingfisher, saw mild flecking (the pseudo-leaf rust flecking type) on Billings, Duster, and Jackpot at Minco, saw the "leaf rust-type" PLS on Duster at Apache, and then saw some severe fields with the tan spot/SLB/PLS combination is several fields in southwestern OK. However, not all fields of Duster or other varieties showed this PLS or had it severely. For example, a field of Duster near Granite was outstanding with no (or very little) appearance of TS, SLB, or PLS. Why the difference?

Although I do not have a full explanation for these occurrences, there are a couple factors that need emphasis.

1. First, much of the PLS that appears as small chlorotic (yellowish) circles that is being attributed to on-coming leaf rust, is not accurate. The best example of this was at the Apache trial, where there was this type of flecking on Duster, but no leaf rust or leaf rust-like flecks on Jagger or other leaf rust susceptible varieties. IF this was "on-coming leaf rust," Jagger and other leaf rust susceptible varieties would show severe leaf rust and/or leaf rust type flecking. In these cases, if a fungicide is applied, it is not being applied to protect against immediately imminent leaf rust.

2. The more severe PLS that is TS/SLB-like is more severe in no-till fields with high residue. It can also be found in fields with less residue and even conventionally tilled fields, but seems to not be as severe in those fields.

3. The PLS that is TS/SLB-like also seems to be associate more so with lower fertility, although in some cases this was difficult to determine.
I collected foliar and soil samples from many of the fields I visited the last two days and will make isolations to help determine the involvement of the pathogens causing TS/SLB, and, to see if any anomalies in the soil nutrition, especially as related to pH, salinity, and micronutrients such as chloride, are associated with the PLS fields.

Other reports from Oklahoma:

Gary Strickland (Jackson (southwester) County Extension Educator) 01-Apr: "I visited over 40 fields on Thursday and Friday of last week on the west side of the county and found no rust (leaf or stripe). Found some powdery mildew but very low in the canopy, minor in frequency and pressure. However, I did see several fields with barley yellow dwarf symptoms now appearing. Frequency within the fields is low to moderate but again found it in several fields. So far the only rust I have found is on the station (both leaf and stripe) in the wheat demo plots and on one farmer's field in the north central part of the county. However I just found a few spots low on the plant."

Reports/excerpts of reports from other states:

Kansas: Dr. Erick De Wolf (Wheat Extension Pathologist, Kansas State University): 04-Apr: I continue to get reports of low levels of stripe and leaf rust in Kansas. Reports to date have come from primarily south central and central regions of the state. Counties where stripe rust has been reported include: Harper, Kingman, Sedgwick, Pratt, Reno (south central); McPherson, Saline (Central). The wheat in these areas of the state ranges from flag leaf emergence to heading, which is approximately 2-3 weeks ahead of normal crop development. Weather conditions this week have been favorable for continued spread and development of rust diseases.
        Tan spot is also being reported in fields with considerable wheat residue left on the soil surface.
Wheat streak mosaic and barley yellow dwarf are also being reported in some fields. The reports of wheat streak to date have come primarily from central and a few from eastern KS. This viral disease is historically less common in these portions of the state.

Nebraska: Dr. Stephen Wegulo (Extension Plant Pathologist, Univ of Nebraska) 04-Apr: "I was at the UNL Havelock Farm here in Lincoln this morning. Some plots with thick stands had powdery mildew up to 70% severity in the mid canopy with many leaves in the lower canopy completely yellowed by the powdery mildew. I saw aphids and a few symptoms of barley yellow dwarf. I also saw symptoms of other viruses - soilborne mosaic, wheat streak mosaic. Samples recently submitted to the Plant and Pest Diagnostic Clinic from southeast Nebraska tested positive of soilborne mosaic, wheat streak mosaic, and Triticum mosaic viruses. I did not find any rust diseases. Growth stage was mostly Feekes 6 with some plants at Feekes 7."



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