Crops & Conservation

When to Use Fungicide for Winter Wheat Disease Management

There are a number of factors that determine whether a fungicide application will return a profit.

Should we use fungicide to assist in winter wheat disease management?  The answer is, it depends.

There are three things necessary for disease infection to occur. Disease infection requires a host (wheat plant), disease source (prior crop residue containing disease or other sources), and the proper environment (generally wet conditions and appropriate temperatures).

The following are some questions or points to ask when trying to determine whether a fungicide application to winter wheat may return a profit:

• Geography – do you farm in an area that is more at risk to disease potential
• Is the winter wheat planted in wheat, barley, or corn stubble
• Is there disease present on the lower leaves or the flag leaf
• Is the yield potential 45, 60 bushel, or greater
• What variety is planted
• What are the weather conditions or pattern (e.g. extended period of wet weather...)
• What is your yield goal and fertility program

Answering no to one of these questions does not suggest that you should not apply a fungicide. If yield potential is high, producers in the western Dakotas would likely benefit from a flag leaf or early flower fungicide application as they did in western N.D. in 2005 (see Kadrmas 2005 yield monitor map).  Likewise, winter wheat planted in canola, pea, or flax stubble may still benefit from an early fungicide application if the environment is dictating heavy disease pressure. Observation and information gathering or a good crop consultant are important for making good decisions.

An understanding of the environmental conditions favoring various diseases can also be beneficial.  Martin Draper, former extension plant pathologist at SDSU, developed the table at the bottom of this page comparing the environmental conditions favored by the three types of rust impacting wheat.

Fungicide Timing: NDSU, SDSU and DU winter wheat fungicide timing trials conducted since 2000 indicate that a combination treatment that applies fungicide at a one-half rate with the herbicide, followed by a fungicide application at the early flower stage of winter wheat, has provided the most consistent return on investment when winter wheat is planted in spring wheat or barley stubble.

This yield map courtesy of Ryan Kadrmas, who farms near Dickinson, N.D., graphically illustrates the effect of a foliar fungicide when warranted in winter wheat. He seeded Jagalene in this field on Sept 27, 2004. On May 24, 2005, herbicide was applied along with Stratego at 4.5 oz/A, water volume 5 gpa. On June 18, 2005, he applied Headline at 6.0 oz/A, water volume 15 gpa, at the flag leaf stage. The vertical check strip where no Headline was applied is visibly apparent. Kadrmas observes that scab losses were at least 5 bu/A in this field, although average yield still ran 74.5 bu/A. The darkest green areas of the yield map indicate where yield ran above 85.7 bu/A, and the red where yield was below 64.8 bu/A.

	Stripe Rust	Leaf Rust	Stem Rust
Day temps	60 – 70	68 – 77	77 – 86
Night temps	50 – 60	59 – 68	59 – 68
Dew	yes	yes	yes

Winter wheat was planted in spring wheat stubble at the SDSU/DU fungicide time of application study at Andover, S.D. in 2006 (Figure 1). Headline was applied at the 5 to 6 leaf growth stage, Quilt at flag leaf, and Prosaro at the early flower growth stage of winter wheat.  Combinations of these treatments were then applied with each of the fungicides applied at the same growth stage as the individual products.

All treatments yielded more than the untreated check and returned a profit.  The Prosaro treatment at early flower yielded less than the combination treatment of Headline and Prosaro. If you recall, the weather in the summer of 2006 turned very dry and warm shortly after the winter wheat finished flowering, which was not conducive to further disease development. That is why the earlier fungicide treatments at the 5 to 6 leaf and flag leaf stages of growth have slightly higher yields.  There was considerable mildew and leaf spot disease pressure during the earlier growth stages. But it is interesting, despite the heat and lack of disease pressure following flowering, that the combination treatment once again had the highest yield.

Varieties & Yield Potential: Figures 2, 3, and 4 contain the winter wheat variety response to fungicide for the Ellendale, N.D. trial from 2004 to 2006, respectively. There was a very significant yield increase to fungicide application for all varieties in 2004 when the yield environment was very high, and there was significant leaf spot disease pressure and some leaf rust.  Both the early and late applications were required to protect the early growth and the flag leaf. 

The yield environment was also very high in 2005, but scab had the greatest impact on yield.  The greatest response to fungicide timing in 2005 was obviously from the early flower application for scab suppression. 

The yield increase to fungicide application at Ellendale in 2006 was limited by moisture stress and very hot temperatures following the flowering stage of winter wheat. Fungicide application costs were not recovered for the varieties Harding, Jerry and Millennium, which have better leaf disease tolerance. It should also be noted that Harding and Jerry have not yielded quite as well as the other varieties in this area. Fungicide application was basically a breakeven to a small profit for the other varieties with the good winter wheat prices.

It should also be noted that the 2005 and 2006 trials show how varieties respond in different environments based on their disease resistance. Wesley and Jagalene, two very scab susceptible varieties, could not recapture the top yields in 2005 even when they received the early flower fungicide treatment. However, in 2006, when there was less disease pressure, they performed at the top of the pack.

These trials point out the importance of knowing the environment (weather) and the diseases those environments favor, yield potential, diseases present, and variety characteristics.

Fungicide and Nitrogen Interaction: Nitrogen application and timing were discussed in the last issue.  There can be interactions between fungicide and nitrogen when winter wheat yield potential is high. 

Figure 5 (Ellendale – 2004) shows the average yield for seven winter wheat varieties with and without fungicide for each of the spring nitrogen timing treatments. There is no difference in yield for the nitrogen timing treatments when they have been treated with fungicide. However, the split nitrogen treatment yielded more than the early and late nitrogen treatments when no fungicide was applied.

Figure 6 is the yield difference between the fungicide treated and untreated yields from figure 5.  Yield response to fungicide treatment was greatest in the late nitrogen treatment (application at the 5 leaf stage) in two of the three years at Ellendale and a close second in the third year. The fungicide application to the late nitrogen treatment shows a 3-year average yield increase of 13 bu/A. The two years with the greatest yield increase also corresponded to the two years with lowest fall nitrogen soil tests.  I believe the greater response to fungicide application may be due to reduced early plant health because of lower available soil nitrogen.

Figure 7 indicates that nitrogen and fungicide can limit each other’s effectiveness. All eight treatments or bars in figure 7 received nitrogen in a deep band at seeding for an 80 bu/A yield goal.  The early, late and split N treatments received an additional stream bar application providing for a total yield goal of 135 bu/A.  The yellow bars did not receive the two fungicide treatments while the green bars did.

The fungicide treatment (in the check column - yellow bar vs. green bar) added 4.4 bu/A.  The extra N (average of yellow bars in the early, late and split N columns) increased yield over the check (yellow bar) by approximately 5.8 bu/A.  However, when you average the treatments (the three green bars in the early, late and split N columns) receiving both the extra nitrogen and fungicide treatment, and subtract that result from the yellow bar in the check column that did not receive the extra nitrogen or fungicide, the yield increase was 23.6 bu/A.

So many things can influence winter wheat’s yield response to applications of nitrogen, fungicide, or both.  However, some observations become clear after we review this data:

• Use a fungicide with the herbicide when winter wheat is planted in wheat or barley stubble.
• Consider applying a fungicide at the early flower stage of growth when winter wheat yield potential exceeds 50 to 60 bu/A.
• Two fungicide treatments, one with the herbicide and one at the early flower stage of winter wheat growth, have provided the best return when winter wheat is planted in wheat or barley stubble.
• All varieties respond to fungicide treatment, regardless of disease ratings, when yield potential is high (70 bu/A +).
• If your first nitrogen application is delayed until the 5 to 6 leaf stage, the odds appear to be greater to increase winter wheat yield from a fungicide application.
• Yield increases from fungicide application can be reduced if nitrogen is limiting yield.

Vander Vorst is regional agronomist with Ducks Unlimited, Inc., Bismarck, N.D. Find more information about DU’s agronomy program, including winter wheat performance data and production information, online at www.ducks.org/agronomy