What Happened to Wheat in 2007 and What Did We Learn?

By David Boehm

This is the 3rd year I’ve been asked to write about what happened to the past season’s wheat crop and what management lessons we can learn from it. It appears I never have to worry about topics because there is always something to learn.

Moisture Conditions
As is the case nearly every year, wheat progress and conditions revolve around water; either how much or when.  Some areas received continuous and heavy rainfall in late April that caused crusting and emergence problems or outright flooding.

In areas with excess water, cereal grain plants generally got off to a poor start. Water-logged soils cause reduced root development and increased root fungal diseases. I’ve heard many an “old-timer” say that it is better for wheat to be dry early and wet in-season.  The thought is that wheat plants get “lazy.”  In fact, wheat root development continues, but slows down in saturated soils until oxygen levels are increased. When conditions do dry out, the plant has less overall vigor.  Even in areas that didn’t get excessive early season rains, grain yields in much of the central and eastern region were better following the dryer conditions in 2006.

Tan Spot
Next, let’s look at disease development. With good moisture, the presence of early season tan spot was common. Much of the region applies fungicides early with the herbicide application and this controls tan spot.  Even in western areas, this is important due to no-till and more wheat-on-wheat rotations.

Bacterial Blight
Bacterial blights were also present in wet areas.  Unfortunately, bacterial diseases are not controlled with fungicides.  Bacterial problems were common in areas that received heavy rainfall when the plants were still 6 leaves or smaller. Naturally-occurring bacteria in the soil splash up on leaves and enter the plant. This is more problematic when there is less soil surface residue in well-tilled fields. Then, as plants rub up against each other during wind events, the bacteria moves to new plants.  You’ll notice spots in fields with bacterial symptoms such as brown-streaking on leaves that develops within the leaf.  Symptoms are a water-marked or translucent appearance on the flag leaf.   If aphids are early, they can also move bacteria to new plants. Early and heavy infection will move to the wheat head and cause dark colored glumes, or symptoms known as black chaff. There is no chemical control for bacterial blight and since it is strongly dependent on heavy rain, there really is little control. Though there are probably some minor differences between varieties in their response to bacterial blight, none of the currently available varieties can be considered resistant. Generally it is not thought to be a large yield reducer, but early and severe infection will reduce the plant’s green surface and photosynthetic ability that will reduce plant health and productivity. I’ve had more than a few growers tell me their wheat yields were disappointing and pointed to heavy early rains and “sick-looking” plants even after fungicide applications.

Scab and Leaf Rust
Next, let’s move to the later season diseases of scab and leaf rust. Scab-prone areas in the central and east had sufficient moisture during flag leaf and heading so the scab risk was very high.  Scab forecast models during this time were positive.  But for most, it quit raining around mid-June, temperatures increased, and we experienced increased winds.  This probably had a big effect on scab development.  With the change in environmental conditions and the large percentage of producers applying scab fungicides like the Proline+Folicur mix or tebuconazole, it’s likely scab was controlled quite well.  In fact, so much fungicide was sold due to the weather conditions some fungicide was short or delayed in other areas of the region.  Whether fungicides were even necessary is a good and common question. I’d presume that with the mid-season moisture (and grain prices), making the decision to spray was accurate, but mother-nature still had final control.

What the scab fungicides had a big impact on was leaf rust control.  We watched high levels of leaf rust develop in the U.S. central plains, South Dakota and even into the  winter wheat in these regions. North Dakota had alarming levels as well. This gave us warning that leaf rust was available to infect spring wheat.  Aside from scab, tebuconizole is outstanding against leaf rust.  So the producers who questioned the economics of scab control got paid back with late season fungal disease management, especially if applied to a variety that lacked genetic resistance.  There were still areas in the region that experienced high leaf rust infection. Scab fungicides, along with Tilt or propiconazole, showed very good control and yield responses.

Wheat Stem Maggot
Another topic from 2007 was all the white heads in wheat fields. We initially assume this is insect damage caused by wheat stem maggot (WSM). WSM causes white and sterile heads, but the rest of the plant is still alive.  Gently pulling up on the head causes the stem to pull out from the plant.  WSM levels are generally low, around 1-5%.  It just looks heavier because it’s so noticeable.  If you count heads from a shoulders-width of plants, you generally find a smaller percentage than you might originally think.  However, over the past few years, there has been increasing levels of WSM throughout the region, as much as 25%.

Root Diseases
 If the entire wheat plant is white, the cause might be from root diseases.  This was higher this year when no seed treatment was used.  Plants that have weak root development are adequately healthy until the soil dries out. At that point, there aren’t enough roots to feed the plant, and the entire plant dies.  Sometime referred to as “dry-rot”, plants that look healthy early on die off in mid-summer. 

Applying What We Learned
So how can we apply what we learned? I could copy this section from past wheat management articles. Wheat management is always based on what could happen next year, not only what we saw in the previous summer. We learn from experience, but know that next year will most likely be different.

1. Apply fungicide seed treatments in wet soils and cool-dry soils.
2. Pay attention to early season water as it relates to tanspot.  This is especially pertinent in any no-till or wheat-on-wheat acres.
3. Early planting is always an advantage, provided the fields don’t drown-out.  There were late planted fields in western ND that were too immature to handle late season heat and drought stress. Significant yield responses were seen based on planting date. 
4. Always plant multiple varieties with different maturities as a management for disease risk and an adverse weather event such as heavy rains or high temperatures.  This also gives better control of fungicide timing and harvest.
5. Continue to use disease forecast models for foliar disease and scab but realize that environmental conditions can change in short order.
6. Pay attention to leaf rust levels in the central plains and South Dakota as an indication of what is moving north.

Boehm is regional business 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.