Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: As indicated in the Texas reports below, both leaf rust and stripe rust are present across Texas with stripe rust appearing to be the most prevalent and severe. This also seems to be the case in Oklahoma – at least across central to southern Oklahoma. John Fenderson (Monsanto) indicated yesterday that on a recent trip he took across central to southern Oklahoma he saw “clean” wheat around Chickasha but along highway 70 going west to Frederick he saw lots of stripe rust and some leaf rust. In a few places he saw the ground colored orange from stripe rust spores indicating a stripe rust “hot spot.” In fields such as this (especially if there are many hot spots), application of a fungicide to control the stripe rust should be considered. In addition to helping to control the stripe rust, there could be the benefit of also limiting leaf rust, powdery mildew and possibly tan spot/septoria.
Around Stillwater, I have not seen much change since two weeks ago. I have not confirmed any stripe rust, but have seen leaf rust. However, we have been mostly quite cold with only slight moisture but stripe rust may also be starting. I will wait until it warms up a bit before I look again.
Reports/excerpts of reports from other states:
Dr. Amir Ibrahim (Prof, Small Grains Breeding and Genetics, Texas A&M AgriLife Research) 26-Feb-2015: The wheat crop in South Texas is at now at Feekes stages 5-6 [start of node elongation/first node detectable at base of tiller] depending on the line. Leaf Rust (P. triticina) is spreading in our trials at College station (Brazos County) and both ‘Baldwin’ catch plot and ‘TAM 110’ are 100S. As for stripe rust (P. striiformis), the ‘Sisson’ catch plot is 70S whereas the ‘Patton’ border is 100S. It is noteworthy that we reported stripe rust on Patton near Ennis (Ellis County) on January 29, 2015.
Leaf rust is easy to find, but severity is very low at Bushland (Potter County) in Texas High Plains and Chillicothe (Hardeman County) in Texas Rolling Plains. Unconfirmed reports also indicated spread of stripe rust in Brady (McCulloch County) in the heart of the state. Reports also indicated that ‘Redhawk’ was especially susceptible there and that some producers are already applying fungicides. Both leaf and stripe rusts are also present in Wharton County in South Texas.
If conditions continue to prevail, we can have significant leaf and stripe rust levels compared to last year, in my opinion.
Dr. Ron French (Ast Prof & Extn Plant Pathologist, Texas A&M AgriLife Extension Service, Amarillo) 25-Feb-2015: Update on wheat rust in Texas- some commercial fields. Leaf rust had been reported in Texas in fall 2014 as far north as Hansford County (Texas Panhandle, bordering the Oklahoma Panhandle) and throughout NW Texas, especially the Texas Panhandle. In early winter 2015, leaf rust was still found around the Amarillo area. This winter in Amarillo, we have had temperatures as low as 3°F and will still be as low as 12°F and not much higher than the mid- 50s F for the next week, including snow. In some cases when temperatures have dropped this much, some fields with trace levels of leaf rust no longer exhibited leaf rust for a while, whether that meant inoculum did not survive, was not active, or had new inoculum come in to that field. I visited some random fields today in the Amarillo area and was not able to find any leaf rust. This does not mean that leaf rust is not present but that it may be present at really low trace levels.
Last Wednesday, February 18, I did find leaf rust in one wheat field in Wichita County at trace levels in very few plants and only in the lowest two leaves. The biggest wheat in that field was at Feekes 4. Wichita County is in the Texas Rolling Plains and borders Clay, Wilbarger, and Archer Counties in Texas, and Tillman and Cotton Counties in SW Oklahoma. With high temperatures expected not to be higher than 63°F and as low as 25°F for the next seven days, could disappear, as observed in previous years when leaf rust was first observed in mid-to-late March.
Unlike 2014, no leaf rust has been observed so far in the lower Coastal Bend of Texas around Kingsville and Corpus Christi by this time. Some days have been cooler than normal and they have had more rain than in some previous years.
Stripe rust has been present as far west as Tom Green County in west Central Texas, where the city of San Angelo is located. Stripe rust was first observed at the very end of January and beginning of February. Stripe rust levels were significant in lower leaves only and the ground was covered in orange spores. A few fields that were sprayed with Tilt on February 16th had taken advantage of the fact that topdressing of nitrogen was being done on the wheat. Within a week, fields looked great and new growth looks “excellent” (probably a combination of topdressing, moisture from overhead pivot irrigation, root growth, and the fungicide application). At time of spraying, the wheat was fully tillered. Some varieties with some level of stripe rust include TAM 113, Coronado, Greer, Redhawk, Cedar, and TAM 304.
The farthest north I have seen stripe rust is in Wichita County at low trace levels, on February 18th. The biggest wheat in that field was at Feekes 4. Although normally dry, this area may be getting some snow and rain in the next week or so, so there could be an increase in inoculum. But since temperatures are expected to range from 25° to 41°F on the low side, and between 32-63°F on the high side for the next seven days, this may not be conducive to stripe rust increase or establishment. Time will tell. Other fields in that area have not had stripe rust so far from what I gathered today.
Other locations with stripe rust include fields around De Leon, in Comanche County, located in Central Texas. The application Tilt in February is not uncommon in some locations in southern Texas as powdery mildew can be an issue. This year, applications of Tilt have occurred due to stripe rust concerns and in many cases, taking advantage of top dressing of nitrogen on wheat.
First hollow stem is the optimal time to remove cattle from wheat pasture (full explanation). To monitor first hollow stem, we measure hollow stem for the 56 lines in our September-sown wheat forage plots at Stillwater each year. In spite of the recent cold snap many varieties are progressing towards first hollow stem. The small grains extension crew split ten stems from lines tested in our program today and Gallagher, Everest, Jackpot, Winterhawk, T153, T154, LCS Pistol, and TAM 112 join the list of varieties at or past first hollow stem. Full results are posted in the table below. We will take another set of measurements the first of next week and report the results on this blog.
The numbers reported from Stillwater are likely behind those being observed in southern Oklahoma and ahead of those observed in northern Oklahoma. You can check progression of first hollow stem around the state by using the First Hollow Stem Advisor on the Oklahoma Mesonet site.
|First hollow stem measured in wheat sown 09/16/2014 at Stillwater, OK. Varieties in red are at or past first hollow stem.|
|Variety||cm of hollow stem 02/26/15|
|Doublestop CL Plus||0.0|
|Brawl CL Plus||0.9|
Spring-planted oat has been a “go to” forage crop for southern Great Plains beef producers for years. It is a good option when winter wheat was not planted in the fall due to wet conditions, or, as is the case this year, when wheat failed to emerge due to drought. Forage production potential for spring-planted oat is around 1,500 to 2,00 lb/ac, but you will need about 60 – 75 lb/ac of nitrogen to make this type of yield. A fact sheet detailing spring oat production for hay can be found at www.wheat.okstate.edu. I will provide the Cliff’s Notes version below.
Seed — Plant 80 – 100 lb/ac of good quality seed that has a germination of no less than 85%. There aren’t many options regarding varieties, so you will likely be limited to whatever seed is available in your area. The key is not to cut back on seeding rate, regardless of variety.
Seedbed — Sow oat seed at approximately 1/2 to 3/4 inches deep. Most producers will fare better with a conventionally-tilled seedbed. You are planting seed at a time of year when the ground is already marginal regarding temperature. Conventionally-tilled seedbeds warm more quickly, which should speed germination. There is one exception to the conventional till recommendation. If you are sowing into a stale seedbed or a failed wheat crop that is very thin, no-till should be okay. Just avoid situations where excessive residue will keep the soil cold.
Grazing — Oat plants should have a minimum of six inches of growth prior to grazing. Unlike fall-seeded cereals, you should not expect a large amount of tillering. Dr. Redfearn indicates a good stand of spring oat can provide a 750 lb animal approximately 60 days of grazing when stocked at 1.5 animals per acre
Hay — Oat should be cut for hay at early heading.
Wheat lodging is not generally a widespread problem in Oklahoma, but it does occur. Lodging occurs due to a variety of factors, and as shown in the figure below, the timing of lodging will determine the final impact on grain yield. Lodging at head emergence, for example, can cause as little as 30 or as much as 80% yield reduction. The numbers in the figure do not account for harvest losses, which can exceed losses associated with lower photosynthetic capacity shown in the figure.
Freeze injury or disease can cause lodging due to stem failure, which is characterized by plant stems breaking near the base. I the absence of weakened stems due to freeze or disease, most lodging in wheat is caused by failure of the root anchorage system (root lodging). Root lodging occurs when the anchorage system of a top-heavy wheat plant is weakened due to moist soil and wind provides sufficient force to overcome the rotational stiffness of the root/soil complex. Research has shown that increasing the soil water content from 17 to 26% reduced the force required for anchorage failure by 33%, and as little as 0.25 inches of water plus 11 mph winds were enough to cause lodging. The thicker the wheat crop and/or the taller the wheat crop, the more force that winds exert on the root anchorage system and the greater the likelihood of lodging.
In 2013 and 2014 we evaluated the plant growth regulator trinexapac-ethyl, which is sold under the trade name Palisade®. Palisade is a giberellic acid inhibitor and works primarily by reducing plant height. In our study we evaluated 12 oz/ac of Palisade with and without 4 oz/ac of Tilt (propiconazole) applied at Feekes GS 7 (two nodes visible above the soil surface). We included an untreated check and ALL plots, including the check, received 10.5 oz/ac of Quilt Xcel at Feekes GS 10.5 (heading). We conducted the trial at Stillwater (Irr), Perkins (Irr), and Chickasha (Non-Irr).
I provided 2013 results in a blog post last year, and this post provides an update including our 2014 findings. While application of Palisade resulted in numeric reductions in plant height at Chickasha and Stillwater in 2013, differences among treatments were not statistically significant. In 2014 application of Palisade or Palisade plus Tilt significantly reduced plant height at Chickasha and Perkins.
We rated plots for lodging at harvest using a 1 – 10 scale with 0 equaling no lodging and 10 equaling complete lodging. Application of Palisade plus Tilt reduced lodging over Palisade alone at Chickasha. Application of Palidsade or Palisade plus Tilt resulted in numeric reductions in lodging scores at Stillwater in 2013, but the result were too variable to result in statistical significance. Palisade did not affect lodging at Perkins in 2013. There was no lodging for any site or treatment in 2014.
Application of Palisade or Palisade plus Tilt increased grain yield at Chickasha and had no effect on grain yield at Stillwater or Perkins in 2013. It is interesting to note that the Palisade treatment increased grain yield at Perkins in 2013 even though the plots lodged at comparable levels as the non treated check. My best hypothesis is that the treated plots lodged later than the non treated plots, as all plots were standing at anthesis (see picture below). Application of Palisade or Palisade plus Tilt increased grain yield at Perkins in 2014 even though there was no lodging. There were no differences in grain yield at Stillwater or Chickasha in 2014.
To summarize our work, we found a trend for one to two inch reductions in plant height when Palisade or Palisade plus Tilt were applied, but this did not consistently translate to increased grain yield. Our results are consistent with other wheat plant growth regulator research, which has reported similar variation in response among sites and years. The literature also shows that reduction in lodging is relative to the straw strength of the variety. That is, a plant growth regulator will not make a lodging prone variety stand like one with excellent straw strength, rather they will make it less prone to lodging relative to the same variety non treated.
Based on current evidence, plant growth regulators in Oklahoma are best kept on acres with high (> 80 bu/ac) yield potential that may have greater propensity for lodging due to variety or fertility. If these high yield potential acres are being sprayed with a growth regulator at GS 7, the addition of a foliar fungicide might be prudent if it can be included at a relatively low cost. This early-season fungicide application will not, however, substitute for a fungicide application at flag leaf.
Full disclosure: Syngenta donated the product for this trial, but the only funding for the research was provided by the Oklahoma Agricultural Experiment Station and the Oklahoma Cooperative Extension Service. We conducted a separate trial evaluating Palisade in drought stress environments that was partially funded by Syngenta. The analysis and recommendations made in this blog post are based on research findings from 2013 and 2014 production years. Recommendations may change as further research is conducted and new information is obtained.
First hollow stem is the optimal time to remove cattle from wheat pasture (full explanation). We measure first hollow in our September-sown wheat forage plots at Stillwater each year, and the warm temperatures have caused first hollow stem to advance ahead of schedule this year. The small grains extension crew split ten stems from each of the 56 lines tested in our program yesterday and Sy Llano, WB-Cedar, WB-Redhawk, and a few experimental lines were all at first hollow stem. Early varieties such as Gallagher, Greer, Everest, WB4458, TAM 114, and Brawl CL Plus are not far behind. A full listing of first hollow stem measurements are included in the table at the end of this blog. We will take another set of measurements the first of next week and report the results on this blog.
The numbers reported from Stillwater are likely behind those being observed in southern Oklahoma and ahead of those observed in northern Oklahoma. Jim Johnson with the Noble Foundation reported seeing quite a bit of first hollow stem in early varieties last week.
The First Hollow Stem Advisor on the Oklahoma Mesonet indicates that early varieties in southern Oklahoma are likely past first hollow stem and that early varieties in central Oklahoma will reach this point within a week.
Keep in mind the one week projection uses historical weather conditions which are slightly above our current forecast. Cooler than normal conditions will not last long and wheat can grow anytime average daily temperature is above 32F. So, my advice is to move cattle off of wheat pasture in southern Oklahoma yesterday, start moving them off of wheat pasture in central Oklahoma today, and move cattle off wheat pasture in northern Oklahoma next week.
|First hollow stem measured in wheat sown 09/16/2014 at Stillwater, OK. Varieties at or past first hollow stem (>1.5 cm of hollow stem) are shaded in red.|
|Variety||cm of hollow stem 02/18/14|
|Doublestop CL Plus||0.0|
|Brawl CL Plus||1.2|
First hollow stem occurs just prior to jointing and is the optimal time to remove cattle from wheat pasture. First hollow stem usually occurs in mid to late February in southern Oklahoma and early March in northern Oklahoma. Grazing past first hollow stem can reduce wheat grain yield by as much as 5% per day and the added cattle gains are not enough to offset the value of the reduced wheat yield.
Similar to previous years, we will monitor occurrence of first hollow stem in our wheat plots at Stillwater and report the findings on this blog. There is also a new first hollow stem advisor available on the Oklahoma Mesonet that can assist in determining when to start scouting.
Checking for first hollow stem is fairly easy.
- You must check first hollow stem in a nongrazed area of the same variety and planting date. Variety can affect date of first hollow stem by as much as three weeks and planting date can affect it even more.
- Dig or pull up a few plants and split the largest tiller longitudinally (lengthways) and measure the amount of hollow stem present below the developing grain head. You must dig plants because at this stage the developing grain head may still be below the soil surface.
- If there is 1.5 cm of hollow stem present (see picture below), it is time to remove cattle. 1.5 cm is about the same as the diameter of a dime.
- Detailed information on first hollow stem can be found at www.wheat.okstate.edu under ‘wheat management’ then ‘grazing’
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: Reports of diseases in Oklahoma have been sparse (as expected for this time of year) but certainly more numerous than last year when drought curtailed foliar diseases. Yesterday (10-Feb) I found wheat leaf rust at a low, but consistent level in guard strips of Jagalene planted around a large wheat breeder nursery here in Stillwater. Susceptible-type pustules were on lower leaves at 15-25%. As temperature increases and with moisture this rust will increase and spread.
Gary Strickland (Extension Educator – southwest Oklahoma) indicated to me that he had heard reports of some leaf rust in Tillman County and also has seen a few pustules here and there on wheat in Jackson County, but nothing severe. He has seen no powdery mildew and no root rots to speak of. He also indicated there were a lot of acres of “little wheat” with some looking good if moisture had been received but that the southwest OK was quickly drying out.
Symptoms of wheat soilborne mosaic/wheat spindle streak mosaic (SB/SS) have shown up in Dr. Edward’s variety demonstration as well as in my SB/SS evaluation nursery, but symptoms are not yet striking as the flush of spring growth has not yet started.
Reports/excerpts of reports from other states:
Louisiana; Dr. Stephen Harrison (Professor; Wheat & Oat Breeder, LSU AGCenter) 3-Feb-2015: “Stripe rust has been reported in several commercial fields and nurseries around central and northeast Louisiana.”
Texas Dr. Amir Ibrahim (Prof, Small Grains Breeding and Genetics, Texas A&M AgriLife Research) 3-Feb-2015: “Wheat stripe rust found in Texas Blacklands area: On January 29th, Russell Sutton, Assistant Research Scientist with the Small Grains program at Texas A&M University and our anchor in the northern Blacklands area and northeast Texas, visited our research plots near Ennis Texas. Russell found a small hot spot of stripe rust on the susceptible variety ‘Patton’ that we use as a spreader. The spot was about three feet in diameter and the lower leaves where heavily infected. The wheat appears to have completed the tillering stage and ready to begin jointing. Russell will return in two weeks and collect some spores and look for more infection sites.