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David Marburger

David Marburger

Since April 2016, I have served as the Small Grains Extension Specialist at Oklahoma State University. My research and extension efforts focus on delivering science-based recommendations in order to increase small grains production and profitability for stakeholders throughout Oklahoma and the southern Great Plains.

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First hollow stem update – Stillwater 2/21/17

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture (full explanation). Wheat growth at our Stillwater location has continued to progress rapidly. Listed below is the second set of FHS measurements from this location (Table 1). These measurements were collected from plots that were not grazed. The point of reference I gave the last post was approximately 50% of the varieties reach or pass FHS by March 1 at Stillwater under normal conditions. Of the 31 wheat varieties we took measurements on today, 20 of those have reached FHS. That brings the total to 51 out of 62 wheat varieties (82%) which have reached FHS. Keep in mind that the numbers reported from Stillwater are likely behind those being observed in southern Oklahoma and ahead of those observed in northern Oklahoma. The First Hollow Stem Advisor can provide an estimate of first hollow stem progress in your area.

 

 

Table 1. First hollow stem (FHS) results by variety collected at Stillwater on 2/17/17 and 2/21/17. Plots were sown on 9/13/16. The threshold target for FHS is 1.5 cm (approximately the diameter of a dime). The amount of hollow stem for each variety represents the average of ten measurements. Varieties that have reached FHS are highlighted in red.

Table 1 2.21 Stillwater.jpg

 

Wheat Disease Update – 21 February 2017

This article was written by Dr. Bob Hunger, Extension Wheat Pathologist

Department of Entomology & Plant Pathology

Oklahoma State University – 127 Noble Research Center

405-744-9958

     I indicated last November that leaf rust was severe in many wheat varieties that had been planted early (mid-September) in Dr. David Marburger’s variety demonstration strips here at Stillwater. As we moved into December and January, there were two severe cold spells along with drought that caused significant death of the rank foliage.  Many of the burned/dead leaves were infected with leaf rust, and killing of these infected leaves stopped the spread of leaf rust to new/young foliage.  The burning of the foliage in these plots was quite noticeable in mid-January (Figure 1A).  Last week I examined these plots to see if leaf rust had overwintered, and sure enough, viable leaf rust pustules were present on some of the newer/younger leaves (Figure 1B).

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Figure 1. (A) Severe leaf burn of wheat in mid-January, 2017.  (B)  Leaf rust pustules as observed on leaves in mid-February in the same plots in (A).

     Hence, leaf rust has overwintered in much of Oklahoma and inoculum to start this disease in the spring will come not only from within the state, but also from Texas where widespread, moderate levels of leaf rust have been reported (see report below from Texas).  The two recent widespread rain events also will support the further infection and spread of leaf rust in Oklahoma, but weather through March and April still will be the ultimate determiner as to how severe leaf rust becomes in Oklahoma in 2017.  However, be sure to start checking your wheat over the coming weeks for the presence of leaf rust (especially if you have a moderately susceptible to susceptible variety).  I can’t imagine any spraying is needed at this time for leaf rust, but you should stay alert for the presence of this disease as we proceed into March and April when conditions for leaf rust infection and spread typically become more favorable.

     The other rust that can greatly impact yield in Oklahoma is stripe rust (Figure 2). Typically if stripe rust is going to be a problem in Oklahoma we start to see “hot spots” in fields from late February into early March.  Note that often early season stripe rust infections do not typically show the striping pattern associated with stripe rust but rather pustules tend to occur more in clusters as depicted in Figure 3.  Reports of moderate to severe stripe rust also typically are coming in from Texas by this time in years when stripe rust is severe in Oklahoma.  However, no stripe rust has yet been reported in Oklahoma this year, and reports indicate stripe rust is sparse in Texas (see below).  This is good news in terms of the likelihood of stripe rust in Oklahoma, but continue to watch for stripe rust when looking for leaf rust.

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Figure 2.  Early season infection of stripe rust.  Note that in contrast to later season stripe rust infection, early season infections do not show the “striping” typically associated with stripe rust.

     Other foliar disease to watch for include tan spot, Septoria leaf blotch, and powdery mildew (Figure 3A-C).  These diseases (especially tan spot and Septoria leaf blotch) are more likely to occur in no-till, continuous wheat fields.  If sufficiently severe in a no-till field, spraying for these in March may be beneficial but only if young wheat plants are severely spotted with one of these diseases.  For additional information regarding early season foliar wheat diseases and possible control with an early fungicide application, please see our fact sheet (PSS-2138) that discusses split application of fungicides by clicking here.

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Figure 3. Wheat diseases typically observed in no-till, continuous wheat fields include (A) Tan spot; (B) Septoria leaf blotch; (C) Early season powdery mildew.

Reports/excerpts of reports from other states:

TexasDr. Clark Neely; Assistant Professor & Extension Small Grains and Oilseed Specialist; Texas A&M University; Feb 14, 2017: Weather conditions have been drier this fall and winter than the previous two years, which is having a positive impact on wheat rust presence across the state. This time last year, producers were dealing with widespread reports of stripe rust in their wheat fields due to wet conditions. This year, stripe rust has been reported in a few locations throughout Central and South Texas, however, pressure appears lighter overall and observed mainly in highly susceptible border plots (‘TAM 111’) in research trials. A few reports of very light stripe rust in producer fields in the central Blacklands was reported also. Light pressure was reported in an Ellis County trial and trace amounts were found in trials near Thrall and College Station. No stripe rust has yet been found in South Texas (Uvalde, Castroville, Corpus Christi), Northeast Texas (Greenville), or the Rolling Plains. Though inoculum is currently low, forecasted weather conditions appear to be favorable for further development beginning this weekend through mid-week as a large percentage of the state is expected to receive an inch or more of precipitation and coincide with cooler temperatures. Therefore, producers in the Blacklands should keep an eye on wheat fields over the next couple of weeks to watch for further stripe rust development.

     Meanwhile, leaf rust is present in much of Southeast Texas. Research plots in Thrall, College Station and Wharton all show moderate leaf rust pressure so far. Light levels of leaf rust are also reported in producer fields in Hill and McLennan Counties with a single severe case reported in ‘TAM 304’ that was sprayed with a fungicide. With plenty of inoculum present, this disease is likely to spread once temperatures increase in the coming weeks, though moisture conditions throughout the spring will influence the degree and speed to which it will increase. As of two weeks ago, leaf rust was not observed at Uvalde or the Castroville nursery and recent reports indicate little to no leaf rust further north in Northeast Texas and the Rolling Plains.

Spring-planted oat for forage

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 may be the case in certain areas of Oklahoma 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 and grazing can be found by clicking here or going to www.wheat.okstate.edu under “Wheat Management” then “Seeding”. Some of the key points from that fact sheet are listed below:

Oat forage trial 2013

Spring oat can provide an alternate hay or forage source in the spring.

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 be better off 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. 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 to maximize yield and quality.

 

Stillwater First Hollow Stem Update 2/18/17

Yesterday, we posted our first hollow stem (FHS) results from Chickasha. None of the varieties had reached FHS, but as I cautioned in that post, those measurements were collected under a simulated grazing scenario based on the way forage data was collected from that trial.

 

Listed below is the first set of FHS measurements from our Stillwater location (Table 1). These measurements were collected from plots that were not grazed. The point of reference I gave yesterday was approximately 50% of the varieties reach or pass FHS by March 1 at Stillwater under normal conditions. From the results below, 30 of the 62 wheat varieties examined have just reached FHS. Compared to the point of reference, that is about 12 days ahead of schedule.

 

On February 10, we checked several of the known ‘early’ varieties (e.g., Billings, Gallagher) at Stillwater, and little to no hollow stem was present at the time. Therefore, we thought we would be safe with taking measurements in the middle to latter part of the week. Well, the warm temperatures over that weekend and the rainfall we received at Stillwater earlier this week provided great growing conditions. As a result, about half of the wheat varieties reached FHS. I suspect that we missed being on the front side of the 1.5 cm threshold by about a day or two for a lot of these varieties that have reached FHS. Our next round of measurements from Stillwater will come early next week.

 

Table 1. First hollow stem (FHS) results by variety collected on 2/17/17 at Stillwater. Plots were sown on 9/13/16. The threshold target for FHS is 1.5 cm (approximately the diameter of a dime). The amount of hollow stem for each variety represents the average of ten measurements. Varieties that have reached FHS are highlighted in red.

table1-5

First Hollow Stem Update 2/17/17

First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture (a more detailed explanation can be found by clicking here). Each year, we collect FHS measurements from the varieties in our forage variety trials. This year, we have two forage variety trial locations, Chickasha and Stillwater. Both locations were sown in mid-September. To give you a point of reference, under normal conditions approximately 50% of the varieties reach or pass FHS by March 1st at Stillwater. However, with the warmer than normal temperatures and estimates from the First Hollow Stem Advisor on the Oklahoma Mesonet, we have begun collecting our FHS measurements.

 

Listed below are the first set of FHS measurements from our Chickasha location (Table 1). A couple of the ‘early’ varieties are beginning to show hollow stem, but none of the varieties have reached FHS at this time. However, with the recent rainfall and warm forecasted temperatures, I suspect some of the early varieties will reach FHS very soon. I also need to provide you a word of caution with the Chickasha results. Based on how we collected our forage measurements this year, the FHS results at this location are coming from a simulated grazing situation. Grazing can delay the onset of FHS, which is why we recommend checking for FHS from a non-grazed area of the field (e.g., just outside the hot wire) to give a short buffer time for finalizing plans to remove the cattle. Because of this, there may be some varieties on this list if planted in the Chickasha area that may be closer to FHS than what is presented in the table. As always, keep in mind that wheat varieties in areas south of Chickasha may be further along, while varieties in areas further north may be a little behind yet. We are also taking measurements today from our trial at Stillwater, and I will get those results posted as soon as we get them summarized.

 

Table 1. First hollow stem (FHS) results by variety collected on 2/16/17 at Chickasha. Plots were sown on 9/15/16. The threshold target for FHS is 1.5 cm (approximately the diameter of a dime). The amount of hollow stem for each variety represents the average of ten measurements.

chick-fhs-2-17-17

*triticale variety

Time to start thinking about first hollow stem

First hollow stem (FHS) occurs just prior to the jointing growth stage and is the optimal time to remove cattle from wheat pasture. This is the optimal time because the added cattle weight gains associated with grazing past first hollow stem are not enough to offset the value of the reduced grain yield (1-5% loss every day past FHS). With the warmer than normal temperatures throughout the beginning of this year and the forecasted warm temperatures, it is likely we will start seeing FHS occur for some of our “early FHS” wheat varieties in Oklahoma in the next 7-14 days, especially towards the southern border.

 

One of the moving targets each year is determining when to start scouting for FHS. To help combat this, the First Hollow Stem Advisor was developed by researchers at Oklahoma State University. This is an online tool available on the Mesonet website, https://www.mesonet.org/index.php/agriculture/category/crop/wheat/hollow_stem_advisor. This tool uses soil temperature data to show the current probability of FHS occurrence, as well as 1-week and 2-week projections (detailed information on how this works can be found here). With this tool, producers can select their variety from a list of varieties that separates them into three FHS categories: early, middle, and late. Then, maps can be generated to provide the probability of FHS based on current conditions and the 1- and 2-week projections. Charts and tables can also be generated for individual Mesonet sites. Created maps have a color scheme to represent the probability of FHS occurrence. When using this tool, it is recommended to start scouting for FHS from a non-grazed part of the field once the 5% probability level is reached (green color). Because stem elongation will begin moving quickly as the temperature warms up, starting your scouting at the 5% level will help give you the time it takes for making the necessary preparations for removing the cattle by the time FHS occurs. Methods on how to scout for FHS are listed at the end of this post. For producers who do not scout, it is recommended to remove cattle when the 50% probability level is reached. A 50% probability level indicates that over a multi-year period (e.g., 10 years), FHS has occurred by that date in 50% of those evaluated years (e.g., 5 years). The same interpretation is used for other probability levels.

 

To give an example of what the tool provides and show some of the FHS conditions around OK, I have generated some statewide maps below. For producers in areas of southeastern and south central OK who planted an “early” wheat variety (e.g., Gallagher), now would be the time to go out and start scouting for FHS (Figure 1).

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Figure 1. Current FHS probabilities for “early” wheat varieties.

 

Looking at the 1-week projection for “early” varieties, you can see how the probabilities have increased, and producers in areas further north should begin scouting (Figure 2).

Figure 2.png

Figure 2. One-week FHS projection (i.e., through February 8) for “early” wheat varieties.

 

For producers who planted “middle” or “late” FHS varieties, the 1-week projections indicate producers across much of the state still have a little bit of time yet before beginning to scout. However, producers along the southern border will need to begin scouting (Figure 3).

Figure 3.png

Figure 4.png

Figure 3. One-week FHS projections (i.e., through February 8) for “middle” (top) and “late” (bottom) wheat varieties.

 

Methods for scouting for FHS:

  • Check for FHS in a non-grazed area of the same variety and planting date. Variety can affect FHS date 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 the developing grain head may still be below the soil surface at this stage.
  • 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.
  • More detailed information on FHS can be found at wheat.okstate.edu under ‘wheat management’ then ‘grazing’ or by clicking here.

fhs 077

The first hollow stem growth stage is reached when there is 1.5 cm of hollow stem (about the diameter of a dime) below the grain head. Photo by Dr. Jeff Edwards.

 

Similar to previous years, we will monitor occurrence of FHS in our wheat plots at Stillwater and Chickasha and report the findings on this blog.

Time to topdress wheat?

By David Marburger and Brian Arnall

There are few crop inputs for winter wheat that deliver as much return on investment as nitrogen fertilizer. It takes approximately two pounds of nitrogen to produce one bushel of grain. This year that will cost approximately $0.80-$1.00 to produce a bushel of grain worth about $3.25. Of course, nitrogen is not the only yield determining factor in a wheat crop, but it does represent a significant investment in a year that will have very tight margins. Also, the law of diminishing marginal returns eventually kicks in, but nitrogen fertilizer is still one of the safest bets for wheat inputs.

Topdress nitrogen fertilizer is especially important because it is applied and utilized at a time when the plant is transitioning from vegetative to reproductive growth. Several things, including the number of potential grain sites, are determined just prior to jointing, and it is imperative that the plant has the fuel it needs to complete these tasks. Jointing occurs around the end of February in southern OK and around the second week of March in northern OK. Jointing also marks the beginning of rapid nitrogen uptake by the plant which is used to build new leaves, stem, and the developing grain head. The nitrogen stored in these plant parts will be used to fill the grain later in the season, and the plant is dependent on this stored nitrogen to complete grain fill.

Early January is our normal time for beginning to topdress nitrogen fertilizer in winter wheat in Oklahoma. However, the lack of significant rainfall in many areas during November through December has presented some interesting and frustrating challenges regarding topdress nitrogen fertilizer. The biggest of these is deciding when and how much to apply. Listed below are some considerations for topdressing nitrogen this year.

When to apply

  • In order to have full benefit, nitrogen must be in the rooting zone by the time wheat is jointing, and moisture is required to move nitrogen into the rooting zone. Since precipitation is usually very limited in January and February in Oklahoma, we need the nitrogen out on the field when the precipitation hopefully arrives back.
    • If you applied nitrogen pre-plant, consider waiting until closer to jointing for a topdress application. By being patient in this situation, we are hoping for a rainfall that will not only provide soil moisture to move that topdress N down into the root zone but also provide enough N for a higher yield potential. Otherwise, if we stay dry through jointing, you will likely have enough nitrogen present to compensate for a lower yield potential.
    • If you decided not apply any nitrogen prior to planting, due to residual soil nitrogen amounts or simply did not want to invest the money into the crop at the time for example, did you happen to use a N-rich strip?

Yes I did: If you currently see a difference between the N-rich strip and the rest of the field, then now would be time to begin making applications. For those producers who are using the Sensor Based Nitrogen Recommendation (SBNRC) system, your yield predictions and nitrogen recommendations generally become more accurate as the season progresses; however, growers wishing to hedge their nitrogen bet could apply a partial topdress now and supplement with a second top dress just prior to jointing if SBNRC recommendations call for additional nitrogen. If you cannot see a difference, then wait until closer to jointing to make the call.  https://osunpk.com/2014/02/24/sensing-the-n-rich-strip-and-using-the-sbnrc/

No I did not: Now would probably be ideal to start making those applications depending on fall growth and soil moisture levels. If soil moisture is present, considering apply enough N to reach the farms break-even yield goal. At minimum, 30-40 lbs of N should be applied. The rate ultimately depends on comfortability with putting more money into this crop. Also, it is not late to apply a N-rich strip:  https://osunpk.com/2013/09/19/nitrogen-rich-strips/

  • Do not apply nitrogen to frozen ground with a layer of ice or thick snow layer. Nitrogen will move with water. If melting snow or frozen rain is moving to the ditch, so will nitrogen applied to the soil surface.
  • Consider splitting or delaying top dress nitrogen applications to sandy soils until closer to jointing, as leaching can occur.

How much to apply

  • On average it takes about 2 lbs/ac of N for every bushel of wheat yield. In addition, dual-purpose wheat requires 30 lbs/ac of N for every 100 lbs/ac of beef or 1,000 lbs/ac of forage removed. You can subtract your soil test NO3-N from these total requirements.
  • Did you soil test? It is okay to adjust topdress N plans based on your current yield potential. When you submitted your soil test, you might have stated a 50 bu/ac yield goal which would require 100 lbs/ac of nitrogen; however, it is important to take a hard look and determine if this yield goal is still realistic based on your current crop status. This does not suggest to adjust based on what you think the weather might do, but it is okay to take inventory and adjust your topdress N up or down based on current field conditions.
  • Don’t have an N-rich strip? Many more producers are trying it this year simply due the fact that producers did not want to spend much money up front on wheat inputs. An N-rich strip helps take the guess work out of adjusting your topdress N up or down based on your current crop conditions. Your county extension educator can provide more information on N-rich strips and you can find more information on the web at npk.okstate.edu

What source to use

  • The plant does not care about the nitrogen source. A pound of nitrogen is a pound of nitrogen. Focus on getting the correct amount applied at the correct time, and choose your product based on price and application uniformity.
  • Use a source that can be applied uniformly. Spinner trucks or buggies work but are generally the least uniform. Air trucks or streamers are the most uniform.
  • Streamer nozzles almost eliminate leaf burn from UAN; however, leaf burn is generally not an issue until temperatures warm and/or you are applying fairly large amounts of UAN. Stream nozzles are also not affected much by wind and deliver a uniform pattern in a variety of conditions. There are also some studies that indicate banding of UAN through the use of stream nozzles will reduce nitrogen immobilization on crop residue. Keep in mind that you cannot tank mix herbicides when using streamer nozzles.
  • One pass herbicide/topdress applications are very efficient in terms of time and input costs, but in some scenarios, it can end up costing you more money. Consider two-pass applications when dealing with no-till fields, especially when canopy coverage is below 70%. This is due to the high probability that the nitrogen will be tied up when it hits the residue and will not be available for the current wheat crop. For a more in-depth discussion on tank mixing herbicides and UAN for top-dress see
    https://osunpk.com/2016/02/07/herbicide-and-uan-tank-mixed-for-top-dress

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Streamer nozzles provide uniform application of UAN in a wide variety of environmental conditions. 

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Poor nitrogen application can result in a streaked field. Some of the areas in this field were over fertilized while some where under fertilized, resulting in wasted nitrogen and less than optimal crop yield. 

Hessian fly showing up in SW OK

Gary Strickland, Jackson and Greer Co. Ag Extension Educator, has indicated a number of wheat fields in that area of SW OK are showing signs of Hessian fly. Most of these fields are no-till and planted with a susceptible wheat variety such as Fuller. Plant symptoms may go unnoticed until you start to see tillers dying, a good indication of an infestation. Further investigation by removing the plant and examining the stems at the base near the crown will help identify any larvae or pupae present. Dr. Tom Royer, Extension entomologist, recently wrote a nice article depicting how and what to look for: Plan to Manage Hessian Fly.

img_6299-cropped

Full-grown Hessian fly larvae form rice-like puparia that are shiny and dark brown. The puparium is commonly referred to as a “flaxseed.” Photo courtesy of Dr. Jeff Edwards.

Now would be a good time to scout your fields for this pest, especially if you have fields which are planted with a non-treated susceptible wheat variety, are in a continuous wheat rotation, use no-till or minimum tillage, were planted early (September into early October), or is a conventional tilled field next or near to a no-till wheat field. If you are unsure whether your wheat variety is resistant to Hessian fly, you can use this OSU fact sheet: Wheat Variety Comparison ChartUnfortunately, not much can be done to control this insect right now. However, we can learn from this year and make some management adjustments to control this pest next year.

For more information on Hessian fly and its management, consult fact sheet EPP-7086, Hessian Fly Management in Oklahoma Winter Wheat.

Wheat Disease Update – 30-November-2016

This post was written by Dr. Bob Hunger

Extension Wheat Pathologist

Department of Entomology & Plant Pathology

Oklahoma State University

During the first week of November 2016, I reported observing fairly severe leaf rust in rows of Jagalene wheat in Dr. Brett Carver’s breeder nurseries here at Stillwater.  About that time, leaf rust also was observed in the early planted variety-demonstration nursery planted in Stillwater by Dr. David Marburger.  The early planted plots were planted 13-Sep-2016.  For this variety-demonstration, Dr. Marburger plants a duplicate, later planted (26-Oct-2016) plot of each variety immediately in front of the early-planted plot.  This variety-demonstration nursery has provided an interesting observation of the effect of planting date on leaf rust as can be seen in Figure 1.

With cooler temperatures and light frosts we finally have received over the last 7-10 days, the older leaves infected with leaf rust in the early planted plots have mostly turned yellow.  Rust pustules are evident, but chlorosis (yellowing) is the predominate symptom.  Across all the varieties (>60), there is a range from nearly all yellow except the youngest leaves, to nearly all green (there is some tip yellowing/burning from the frosts).

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figure 1.jpg

By comparison, look at the photo below (Figure 2) showing early planted plots (background) and late planted plots in the foreground.  Leaf rust is not found in the late planted plots (foreground).  If early planted wheat had been grazed, which would be more typical with a mid-September planting date, much of the rank foliage would have been removed and rust would not be nearly as severe as in this variety-demonstration.  This is a good example of how planting date can effect disease incidence and severity given an environment favorable for disease such as we have had this fall with mild temperature and occasional rain and dews.

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figure 2.jpg

There are a couple of additional points I should make with the photos above.  First, not many would plant wheat in early to mid-September for the purpose of grain only.  Hence, wheat in the early planted plots would most likely be grazed, which would remove much of the rank foliage and also the rust, and thereby the rust incidence would not be nearly as severe.  Wheat in a grain-only mode would look more like the wheat in the late planted plots (foreground plots in Figure 2).  Second, we normally would have colder weather earlier than we had this year that would have arrested rust development.  Then, newly emerging leaves would be healthy and green.  As I have said previously, I am not a proponent of spraying in the fall to control fall foliar diseases such as leaf rust because leaf rust development typically slows and stops once we get to colder temperatures in November-January (basically <60 F with frosts at night).  And remember, the primary concern with fall leaf rust is that with a mild winter and sufficient moisture, the rust will survive through the winter and inoculum will be present in fields to start the disease early in the spring.  Hence, monitoring of fields through the late winter and early next spring is recommended to see if application of a fungicide to control rust is indicated in the early spring.  For all the foliar wheat diseases (leaf rust, stripe rust, powdery mildew, tan spot, and septoria leaf blotch), control in the spring is more critical then control in the fall.  I have heard of fungicide being added in with a fall herbicide application to limit disease, but such an application would have needed to have been applied 3-4 weeks ago to prevent the situation as depicted in the photos above.  However, I can see where in a year such as this one with a fully susceptible variety that was planted early and not grazed there may be value to an early fungicide application.  BUT ESPECIALLY, watch these fields starting in late February to see if an application is merited because control of foliar diseases in the spring is much more critical than control in the fall.

Wheat Disease Update – 08-November-2016

This post is written by Dr. Bob Hunger

Extension Wheat Pathologist

Department of Entomology & Plant Pathology

Oklahoma State University

Fall 2016 has been mild/warm and relatively dry. Because of the dryness, fall foliar diseases should be relatively sparse, but some areas have received sufficient rain or had sufficient dews to favor development of wheat foliar diseases. That is the case around Stillwater as you can see in the photo below. This picture, which was taken November 5th in one of Dr. Brett Carver’s wheat breeding nurseries at Stillwater, was planted September 14th. The variety is Jagalene, which is highly susceptible to both leaf and stripe rust (I could find no stripe rust).

leaf-rust-1

Wheat foliage (‘Jagalene’) showing a highly susceptible reaction to leaf rust with an intermediate severity level. Note younger leaves show no leaf rust. This nursery is located in Stillwater, OK, and was planted 9-14-2016 with this photo taken on 11-5-2016.

 

I am not a proponent of spraying in the fall to control fall foliar diseases such as leaf rust because leaf rust development slows and stops once we get to winter temperatures in late November-January (basically <60 F). Typically the lower/older leaves with leaf rust pustules die, but the youngest leaves are green and healthy. Grazing helps to remove leaf rust infections, is not harmful to cattle, and also “opens” the canopy so there is increased air circulation and drying that are less favorable to development of leaf rust. Given these considerations, spraying to control leaf rust in the fall typically is not necessary.  The primary concern with fall leaf rust is that with a mild winter and sufficient moisture, the rust will survive through the winter and inoculum will be present in fields to start the disease early in the spring.  Hence, monitoring of fields through the late winter and early next spring is recommended to see if application of a fungicide to control rust is indicated in the early spring.

 

Other samples that have come to the lab for diagnosis appear to be related to abiotic conditions such as dryness or low fertility.  Some leaf spots have been observed on these samples, but they are either secondary or of low incidence and not a cause of major concern. Dr. Misha Manuchehri (OSU Weed Specialist) sent the following photo showing leaf spots she observed on plants in a trial located near Perkins, OK. Dr. Manuchehri is bringing a sample for us to isolate from, but this appears to be tan spot. Leaf spotting diseases such as tan spot and Septoria leaf blotch typically do not appear until late February or March.

leaf-spot

Leaf spots (most likely tan spot) on wheat foliage (variety not known). This nursery is located near Perkins, OK. Photo taken the first week of November 2016 by Dr. Misha Manuchehri.

 

For all the foliar wheat diseases (leaf rust, stripe rust, powdery mildew, tan spot, and Septoria leaf blotch), control in the spring is more critical then control in the fall. I have heard of growers adding a shot of fungicide with a fall herbicide application to limit disease present. I have no data to support the value of such an application, but there may be some value to it because plants are smaller and not growing as actively so limiting the amount of foliage loss due to a disease such as tan spot will contribute to the overall health of the wheat going into winter.  BUT ESPECIALLY, watch these fields starting in late February to see if an application is merited because control of foliar diseases is much more critical in the spring than in the fall.