A process for choosing wheat varieties to manage disease in 2023

by Dr. Terry Spurlock, Extension and Research Plant Pathologist and Dr. Jason Kelley, Extension Feed Grains Agronomist - August 28, 2023

Key Points 

• Commonly occurring diseases of wheat can be managed with an integrated approach.
• Choosing wheat varieties that demonstrate genetic resistance to diseases of concern should be the primary focus of an integrated approach.
• Between flag leaf emergence and full flowering, the weather in Arkansas is often conducive for disease development.
• Using the data from variety testing program trials, this article demonstrates a strategy for choosing varieties that will likely aid in management of economically important wheat diseases.

Economically Important Wheat Diseases in Arkansas (The Big Three)

Wheat disease management in Arkansas typically deals with three diseases, Fusarium head blight (scab), stripe rust (Figure 1), and Septoria tritici blotch (Figure 2).  That’s not to suggest that other diseases such as bacterial streak and leaf rust aren’t important or can’t be damaging given a susceptible variety and the right environment, but those three seem to occur more often and are more often severe.  Recently, meaning the last two seasons, Arkansas has experienced low pressure from scab and stripe rust, which is likely due to the environment.  This could all change next year.  Because disease severity is driven by weather, and weather can’t be reliably predicted months in advance, disease severity is never really known until we are in the crop year itself.  For this reason, we want to do as much as we can to prepare for these ‘big three’ prior to putting a seed in the ground this fall. This becomes much easier for any crop once we have identified the diseases that should scare us.  In wheat, we will begin our variety selection process with these big three.

Figure 1. Fusarium head blight (scab) symptoms on a wheat head (left).  The image demonstrates typical scab symptoms where the wheat kernels become light tan to almost white. There are often pink to orange colored spore masses around infected kernels.  The image at right demonstrates stripe rust pustules on a susceptible wheat variety oriented in a linear or ‘striped’ fashion.

Figure 2. Foliar symptoms of Septoria tritici blotch on wheat (left) and pycnidia produced by the fungus that causes Septoria tritici blotch on a wheat leaf(right).  Pycnidia contain spores.  These pycnidia can be seen under magnification with a handheld lens and help to confirm the presence of the disease.

Variety Selection Process

Each year the University of Arkansas System Division of Agriculture Variety Testing Program places official variety trials on research stations in Arkansas.  For our process, we will use the last two years of disease and yield data from five trials planted at Rohwer, Pine Tree, Marianna, Kibler, and Keiser.  Each one of these locations had all the same varieties planted each year but not both years.  Some varieties were planted in 2023 but not 2022, and some in 2022 but not 2023.  Ideally, we would like to look at three or four years of variety testing data that includes multiple disease evaluations and recorded yields.  However, that would significantly reduce our options.  More good data is always better, and two years data should be considered the minimum.  No decisions on variety selection should be made with only a single year’s data. 

For the selection process, let’s consider what would be important and how those characteristics might be prioritized in the list below.

1. Included in the last two years of the variety testing program.
2. In the ‘higher yielding’ group across all locations for both years.
3. Low Fusarium head blight.
4. Low stripe rust.
5. Lower levels of Septoria.

Data from wheat variety trials have been summarized in Table 1.  If we explicitly follow those five criteria, then we’ve got some issues to negotiate before we can be comfortable with a list of variety options.  For those varieties listed in Table 1, we satisfy the initial requirement as all are included in 2022 and 2023.  However, the second is a bit less clear.  We will come back to this one as it can be best explained by disease severity of Septoria in 2023.

Moving to our third and fourth criteria, the predominant disease rated in 2022 was scab.  Overall, the scab pressure in 2022 was relatively moderate to low and there was very little pressure from other foliar diseases like stripe rust or Septoria.  Typically, scab is not a yield reducing disease unless moderate to severe.  However, scab can negatively impact quality resulting in dockage at the point of sale when a toxin that is produced by the fungus, deoxynivalenol (DON), is measured in high enough concentrations (around 2 parts per billion).  Therefore, it makes sense to pick varieties with the lowest scab levels from the higher yielding group to minimize the likelihood of scab.  Since there was very little stripe rust in 2022 or 2023, we can’t use variety trial data to further adjust our group of varieties.  However, disease data from some of these varieties were included in past variety trials and inoculated nurseries. These are summarized in the Wheat Update 2022 located here:  https://www.uaex.uada.edu/farm-ranch/crops-commercial-horticulture/wheat/  and help to reinforce our confidence in the working group of varieties.  

Lastly, we can consider our Septoria evaluations from 2023.  As mentioned earlier, the varieties we are putting in the higher yielding group for two years are less clear.  Two varieties in the current group, Dyna-Gro 9120 and Delta Grow 1800, had yields move from above the yield average in 2022 to below it in 2023.  Also, the yield average of Progeny Turbo was reduced by about 5 bushels per acre from 2022 to 2023.  Since these yield averages are across all locations, it is a strong indication of the yield potentials of these varieties where Septoria pressure was relatively high as these three varieties had more severe Septoria in 2023 (by simple average) than others in the selected ‘higher yielding’ group.  The other varieties also had ‘some’ Septoria.  Here, we must decide to either remove them from our working group of varieties or consider that we may need a fungicide application in 2024 to control Septoria should the environment be conducive for it to readily develop.

Conservatively, our process has allowed us to choose seven varieties to plant in Fall of 2023 that offer high yield potential and reduced likelihood of severe scab, stripe rust, and Septoria in 2024.  Three others may get a little more Septoria but may also be good options if time and budget allow for increased scouting and fungicide application.  For fungicide treatment options see either the current MP154 (https://www.uaex.uada.edu/publications/mp-154.aspx) or 2022 Wheat Quick Facts ( https://www.uaex.uada.edu/farm-ranch/crops-commercial-horticulture/wheat/).

As always, one can grow a productive wheat crop with varieties that are not on this working list example.  Still, planning for the ‘Big Three’ in advance of planting can help increase the likelihood of a more profitable one.   

Table 1.  A group of varieties selected using disease severity ratings from official variety trials in 2022 and 2023 by location and combined yields from all locations in 2022 and 2023. 

Disease data were collected using a scale of 0-9 where 9 indicated the most severe disease.

FHB - Fusarium head blight, SEP - Septoria tritici blotch, BLS – Bacterial leaf streak