The Grain Growers Classroom

What Happened To Wheat In 2005?

And what can we learn from the various challenges?

By David Boehm

Sixty bushel straw and a 30 bushel wheat crop. This scenario occurred for many spring and winter wheat producers in 2005. What happened to all that potential we were expecting, and what can we learn from the various challenges of the past year?

Most of our limitations of this year’s crop start with water.  Much of the eastern spring wheat region received 15-30+ inches of spring and summer rains, some occurring 3-5” at a time.  This left drowned-out areas in many fields.

Because of this moisture, the environment was ideal for leaf and head diseases.  High levels of tan spot were noted early in the season for both winter and spring wheat. Tan spot is active in wet and moderate temperatures of about 65-75°.  We generally see these conditions from germination to approximately the boot stage.  For winter wheat, tan spot was found across the entire plant, including the flag leaf.  Uncontrolled tan spot can cause severe reduction in plant health and yield losses since it infects early.  Once the temps warm up, tan spot generally shuts down.

Leaf rust and septoria like warmer temps, around 75-85°, so we see these later in the season.  Periods of wet weather or morning dew that lasts until late morning can help leaf rust spread very quickly if fungicides are not applied and varieties are susceptible.

Some areas in western ND and eastern MT received 15-20” of rain, which brought on fungal leaf diseases most producers there have little experience with and do not control with fungicides.  Many producers here grow varieties with little or no disease resistance and believe the phrase, “it’s too dry here for any disease.”  While they normally get by without problems, this was not the case in 2005. Reduced yield and test weight were common in the west because of the diseases, even with the great rainfall and early yield potential.

A less common, yet very threatening foliar problem is that from bacterial blight.  While fungicides control leaf diseases such as tan spot, rusts, and septoria, they have no control over bacterial diseases which came on very strong in eastern wheat fields around mid-July. You may have noticed necrotic lesions on the leaves that have a water-soaked appearance followed by a white, powdery look from the dried out bacterial cells. Bacterial blights are generally not this much of an issue.

Another bout with scab
The biggest disease story in the region was the return of fusarium head blight, or scab. Much of the eastern region suffered levels not seen since 1997 or earlier. The spring and winter wheat crop in SD was devastated for many producers with yield reports of 18-30 bu/ac.

Winter wheat varieties have little or no tolerance to scab as they normally flower before it is warm enough for scab infection.  Scab requires 75-85° at flowering time with adequate moisture.  In 2004, it was generally too cold at this time for scab infection.  We may not see scab in winter wheat like this for many years. Field levels of scab across the region varied from 5-80% if left untreated. 

Remember that Folicur fungicide is labeled for suppression only, not control of scab.  This level of suppression is usually enough. Folicur did reduce scab levels by 20-50%.  While there is varietal difference for scab tolerance, remember that no varieties are resistant under high scab pressure.  Even more scab-tolerant varieties like Alsen and Freyr are vulnerable to infection under high scab pressure, and infection may occur even if a fungicide is applied. 

Beat by the heat
Warm temperatures also played an important role in wheat development.  Although the warmer temps in July generally dried out wet fields, slowed down diseases, and helped push along harvest maturity, the extreme warm temps also led to yield reductions, especially in later maturing varieties. Temps of 95-105° in the west and south were common for long periods of time.  If the crop was flowering at this time, as for late-seeded wheat, it is quite possible that these flowers and subsequent florets were aborted, causing empty portions of heads that looked good from a distance.  Also, any plant that is in the grain fill stage will suffer from high temps, specifically with lower test weights.

Other issues such as root rots from water-logged fields, higher than average levels of wheat stem maggot, reduced weed control in wet fields, and frost damage for some winter wheat fields may have all played a role in skimming wheat production potential in 2005.

Wheat Management Lessons
It was a good wheat harvest for many in 2004, and a not-so-good row crop harvest. It was a good row crop harvest for many in 2005, and not so good for wheat. What will happen in 2006?  Of course, we don’t know what the weather will have in store for us.   That’s why we need to have a good crop rotation, and not put all of the proverbial eggs in one basket.

Risk management considerations specific to wheat:

1. Always spread your risk by growing as many varieties as feasible, given the acres of wheat planted.  Each variety will give you different tolerances to leaf diseases and scab.  Plus, spreading out maturities will not only spread out harvest but will help reduce scab infection with different flowering stages, and the timing of heat damage. In 2004, a long and cool season, later maturing varieties performed very well, opposite from hot and dry years where early varieties finish with less heat damage. Normally, earlier maturity helps escape scab infection, not the case in 2005 where winter wheat and early maturing spring wheat showed more scab, regardless of genetic scab tolerance. More varieties spread risk of lodging, and manage the balance between more yield potential versus higher protein potential.
2. For disease management, try to use varieties that offer better disease tolerance.  Built-in tolerance is a better option than fungicides where timing and cost can be critical.  Remember, no variety is resistant, so scouting fields were the environment is conducive gives you the best chance of making the right fungicide decisions. If you are in a drier area and/or use varieties with little or no disease tolerance, pay attention to wet spring seasons like 2005. 
3. For scab management, try to include one variety with better tolerance and pay attention to extension bulletins and disease forecasts. Apply fungicides when the majority of your field is prior to or at flowering, preferring ground application where better head coverage and more water are used.  If you plan on saving grain for seed, you should strongly consider a germination test to determine if you should buy new certified seed.

A great rule of thumb for variety selection is to grow three or more varieties.  One for disease tolerance (scab in the east), one for higher yield potential, and one for more protein potential, will help insure that one variety will be the best choice for what Mother Nature throws at you and what the market will pay you for.

Septoria Tan Spot Bacterial Blight Susceptible Reaction of Leaf Rust

Boehm is regional manager for AgriPro Wheat. He is a member of the Minnesota wheat checkoff-funded Minnesota Small Grains Research and Communications Committee, with a master’s degree in plant breeding from NDSU. He can be reached by email at david.boehm@agripro.com.