University of Illinois

No. 7/May 8, 1998

Wheat Fungicides: To Spray or Not to Spray

I have received a number of calls requesting information on the effectivenessof foliar fungicides for wheat. This question is difficult to answer directlybecause effectiveness depends upon a number of factors, including the farmer'slevel of risk, varietal differences, weather patterns, and wheat prices.

 Are foliar fungicides effective in controlling diseases?This is the easy one: definitely. The choice of product and the timingof application may vary from product to product, but they generally canimprove yield. Data from the 1997 Fungicide and Nematicide Tests from theAmerican Phytopathological Society on a wheat fungicide trial at Purdueare summarized in Table 4.

 Table 4. Wheat yields as affected by fungicide application,Purdue, 1997
FungicideRate/acreGrowth stage
at application1
Penncozeb 75W2 lbGS 3166.8 a
Tilt 3.6E4 fl ozGS 3176.7 b
Penncozeb 75W2 lbGS 3176.1 b
Tilt 3.6E4 fl ozGS 3776.1 b
Tilt 3.6E4 fl oz GS 31, GS 3775.5 b
Penncozeb 75W2 lbGS 3177.5 b
Tilt 3.6E4 fl oz GS 3777.5 b
Bayleton 50 DF2 fl oz
+ Penncozeb 75W2 lbGS 5877.5 b
Tilt 3.6E4 fl oz GS 31, GS 3777.4 b
Bayleton 50 DF2 fl oz
+ Penncozeb 75W2 lbGS 5877.4 b
Penncozeb 75W2 lbGS 3173.8 ab
Bayleton 50 DF1 fl oz
+ Penncozeb 75W2 lbGS 5873.8 ab
Tilt 3.6E4 fl ozGS 3175.2 b
Bayleton 50 DF2 fl oz
+ Penncozeb 75W2 lbGS 5875.2 b
Folicur 3.6F6 fl oz GS 3173.8 ab
Folicur 3.6F6 fl ozGS 3775.4 b
Folicur 3.6F6 fl oz GS 5879.0 b
Bayleton 50 DF2 fl oz
+ Penncozeb 75W2 lbGS 5875.2 b
Tilt 3.6E4 fl ozGS 3777.8 b
Untreated control67.0 a
NOTE: Means within a column followed by a letter in common are not significantlydifferent at P = 0.05.
1Growth stage 31 = one node detectable, 37 = flag leaf emerging,58 = spike emerged.

Although almost all products improved yields, was this improvementenough to actually justify the fungicide application? This, again,depends on other factors. If the weather patterns were continually favorablefor foliar diseases, then simply protecting your yield with the fungicideis usually economical when compared to not treating. If you apply a fungicideand maintain your 70-bushel yield and your neighbor does not and has a10 to 15 percent yield loss (7 to 11 bushels) due to diseases, then youhave justified the application by maintaining your yields.

 If, however, weather patterns do not favor diseases and you applya fungicide, then you and your neighbor may have similar yields; and youwill receive no benefits from the fungicide (unless you consider the peaceof mind from not worrying about diseases). So, monitoring the weather isan important component of disease management. Wheat diseases are alwaysmore damaging in wet periods with mild to warm temperatures.

 What are the economics of applying a fungicide to wheat?Plant pathologists generally agree that a fungicide application on a fieldcrop should have at least a 2:1 return on investment. That means for every$15 spent on a fungicide, you should return a minimum of $30. Less thanthat may mean no economic benefits. Recent wheat prices from the CBOT,May '98 wheat to May '99 futures, were $2.98 to $3.50 per bushel, dependingon delivery date. At these prices, you would need to gain 9 to 10 bushelsper acre to return the $30. Can that be done? In some years, the answeris yes. From the Purdue data in Table 4, returns varied from noneto a maximum of 12 bushels per acre. The average gain from a fungicidein this trial was 8 bushels per acre, not really enough to return the expected$30 per acre ($24 to $28 returned for 8 bu at the prices mentioned). Ifdisease pressures were higher, then a greater return could be expected.

 When should a fungicide be applied? With the Section 24(c)label for Tilt this year, farmers have more flexibility in fungicide-applicationtiming. Fungicide programs should be directed toward maintaining the healthof the flag leaf and flag-1 (the leaf directly below the flag). Flag-leaflosses can reduce yield, as well as test weights. Scouting and identifyingdiseases should always precede any fungicide or other pesticide application.Consideration of the effects of the environment on disease progress isalso important. Most foliar diseases and head diseases of wheat are favoredby high moisture and mild to warm temperatures. Thus, if forecasts arefor continued dry conditions, diseases will not be as important as if therewere frequent rains. Fungicides will typically provide no economic returnunless conditions favor disease.

 In summary, the decision to apply a fungicide to wheat shouldbe based upon proper identification of the disease or diseases present.Once the disease has been identified, then its location on the plant shouldalso be noted. The Septoria diseases (leaf blight, glume blotch), tan spot,and scab all overwinter in debris and are splashed or windblown on theplants. The Septoria diseases and tan spot begin on the lower leaves andmove upward as the season progresses. Scab spores are windblown into theopen flowers, so it's a different situation.

 A consideration of the use of a fungicide this year may be anapplication of Tilt to early flowering varieties (Clark, Ernie) becausethe continued rainy weather and mild temperatures will favor infectionby the scab fungus. This fungus infects only open flowers, although themajor damage appears much later. Tilt is labeled for scab suppression andcan reduce the damage caused by this fungus, as well as the others listedabove. With the 24(c) label, producers can wait well past the flag leafstage and receive benefits from controlling late season diseases.

 H. Walker Kirby (, Extension Plant Pathology, (217)333-8414