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Wheat Disease Update – 21 February 2018

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

 

Foliar diseases such as leaf rust and stripe rust were scarce across Oklahoma last fall and into 2018 because of the drought. I have seen a few leaf rust pustules on wheat plants in trials around Stillwater and have heard of leaf and stripe rust as well as powdery mildew from growers across the state. However, my observations and these reports all indicate extremely light levels. More importantly, reports of foliar diseases from Texas were lacking until recently. These reports are critical because areas in Texas provide the inoculum for Oklahoma. On February 9th, Dr. Clark Neely (Small Grains/Oilseed Extension Specialist; Texas A&M AgriLife Extension) reported seeing stripe rust on the susceptible variety ‘Patton’ in trials near Uvalde, TX (Fig 1). Here is Dr. Neely’s report: “I wanted to notify everyone that we have our first stripe rust siting in Uvalde, TX as of last Friday (02/9/18). At the time, it was mainly limited to the susceptible border rows (‘Patton’). A few leaf rust pustules were present as well, but very few. Growth stage is around Feekes’ 5 with some already initiating jointing at Feekes’ 6. Central and South Texas has been experiencing very damp, overcast conditions for the past week and are expecting more of the same for the foreseeable future, so I would expect to see further development. Variety trials at Castroville, College Station, Thrall, Hillsboro, McGregor, and Muenster, TX have all appeared clean so far over the past couple of weeks while topdressing nitrogen.”

 

Figure 1. Stripe rust on wheat near Uvalde, TX observed on 2/9/18 by Dr. Clark Neely (Small Grains/Oilseed Extension Specialist – Texas A&M AgriLife Extension).

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Remember, stripe rust typically forms stripes in older plants (Fig 2A), but early infections have pustules not typically in stripes (Fig 2B). In contrast, pustules of leaf rust are not formed in stripes and are more of a brownish-rust color as compared to the yellowish-golden rust color of stripe rust (Fig 2C).

 

Figure 2. Wheat stripe rust on adult plant (2A), an initial stripe rust infection in February (2B), and a wheat leaf with both stripe and leaf rust pustules (2C).

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Other foliar diseases 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. Regarding leaf and stripe rust, there was not much rust overwintering in Oklahoma, and inoculum to start this disease in the spring will mostly come from Texas.

 

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.

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Finally, the recent rain events in Oklahoma will revive the wheat in the state, but also will provide conditions favorable for foliar diseases (especially as temperatures become more moderate). Hence, I recommend scouting fields for the foliar diseases discussed above during the coming weeks and paying attention to what is happening to the south of us in Texas. 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 at www.wheat.okstate.edu.

Determining the optimal time to remove cattle from wheat pasture (if you still have pasture to graze…)

The wheat growing season up to this point has been extremely tough to say the least. The forage situation has been a kick-in-the-knees in addition to taking it on the chin with the grain prices. Trying to get wheat pasture established was hard enough between fighting off the fall armyworm and working around the rain. Then on top of all that after getting a stand established, it has not rained since. As a result, many producers have already grazed as much as they could and have removed their cattle, or they have not even had the chance to graze. For the few producers who still have pasture to graze, leaving some leaf material out there after grazing will be important for having any chance of a decent grain crop. Ideally, there should be a minimum of 60% canopy coverage left. It also does not look like we will have cool and wet conditions after cattle removal to allow the plants more time to recover from the grazing injury. This situation is shaping up to be similar to last year, and that puts even more emphasis on removing cattle from wheat pasture at the right time.

 

The optimal time to remove cattle from wheat pasture is at a growth stage called first hollow stem (FHS, between Feekes 5 and 6). 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% every day past FHS). The wheat variety, amount of grazing, time when cattle are removed, and weather conditions after cattle removal determine how much total grain yield potential might be reduced.

 

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. 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 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 preparations for cattle removal 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 an evaluated period (e.g., 10 years), FHS would have occurred by that date in 50% of those 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 Oklahoma, I have generated some statewide maps below. For producers along the southern Oklahoma border 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 areas further north should begin scouting (Figure 2).

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Figure 2. One-week FHS projection (i.e., through February 22) for “early” wheat varieties.

 

For producers who planted “middle” (e.g., Duster) or “late”  (e.g., Doublestop) 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 should begin scouting (Figure 3).

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Figure 3. One-week FHS projections (i.e., through February 22) for “middle” (top) and “late” (bottom) wheat varieties.

 

Remember that this tool should be used as a proxy to begin scouting for FHS. The best estimate of FHS is still to split stems from plants in each field to determine where they are developmentally. Another word of caution I want to mention when using the tool for this year especially is to consider when you were finally able to get stand establishment. If this did not occur until the end of September to the beginning of October, this tool may be a little ahead of where your plants are developmentally. In this case, the tool can still give you the cue to start scouting, but checking for FHS in each field will let you know if you do have some grazing time left.

 

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 (~5/8″) of hollow stem present, it is time to remove cattle. 1.5 cm is about the same as the diameter of a dime (see picture below).
  • More detailed information on FHS can be found at wheat.okstate.edu under ‘Wheat Management’ then ‘Grazing’ or by clicking here.

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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. 

 

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.

Spring-planted Oat for Forage

When wheat pasture fails due to drought, there are limited opportunities to recover lost forage production. Spring-planted oat is the best option to offset forage losses from wheat pasture and has been a “go to” forage crop in this case for southern Great Plains beef producers for years. The window for spring-planted oat is between February 15 and March 10. Forage production potential is around 1,500 to 2,00 lbs/acre, but you will need about 40 – 60 lbs/acre 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 by going to www.wheat.okstate.edu under “Wheat Management” then “Seeding”. Some of the key points from that fact sheet are listed below.

oat

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

 

Seed — Plant 80 – 100 lbs/acre 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.

 

Dicamba Restricted Use Required Applicator Training Locations and Dates

In response to an elevated number of off-target movement claims in many states in 2017, this training has been mandated by the EPA for application of newly formulated dicamba products. The following formulations of dicamba are approved for use in the Roundup Ready® Xtend Crop System as of November, 2017 and are covered by these trainings:

 

  • XtendiMax® herbicide with VaporGrip® Technology (Monsanto)
  • DuPont® FeXapan® herbicide Plus VaporGrip® Technology
  • Engenia® Herbicide (BASF)

 

The application requirements in these trainings apply to all labeled uses of these products in Oklahoma. These trainings are designed to satisfy the federal requirement for mandatory dicamba applicator training and to satisfy the Oklahoma Department of Agriculture, Food & Forestry requirement for dicamba specific training. This training is not a substitute for the state-specific Certified Applicator training which is required to purchase and use Restricted Use Pesticides.

 

For more information contact the Oklahoma Department of Agriculture, Food & Forestry (Debbie Mandrell – 405.522.5949 – Debbie.Mandrell@ag.ok.gov) or your local Oklahoma Cooperative Extension Service county office.

 

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