Your corn was planted late and has weathered the spring storms, but those delays will challenge the yield. But you have nothing to worry about because you plan to spray your corn with a foliar fungicide and another 25 bushels per acre will magically appear. Foliar fungicides have become a popular use of money and time the past several years, but is there any profitability in it?

The profitability question is quickly answered “no” by University of Illinois plant pathologist Carl Bradley in his July 3 newsletter. “Data summaries from both university and commercial sources all agree on this point--that foliar fungicides did not provide a benefit on corn every single time they were applied in 2007.” Will your field be one that did benefit, or will you field be one that did not benefit? Instead of a dice roll, Bradley suggests answering the question, “Under what circumstances a foliar fungicide applied to corn will be profitable?”

You can always spray a fungicide whether the corn needs it or not, and other than a guaranteed expense, there may have been a remote chance that you did the right thing. But what are those risk factors that you might want to consider, just in case you want to improve your management ability?
1) Since many corn pathogens survive in corn debris, planting corn after corn, and especially in no-till, will increase the chance that you made the right decision to spray. In other words, rotation and tillage are important.
2) If your planting date was late, your corn is more susceptible to gray leaf spot, so a late planting date is a high risk. So the calendar is important
3) Some hybrids carry susceptibility to such pathogens as gray leaf spot, and unless you are planting corn that has a high tolerance, spraying a foliar fungicide without knowing could be the right thing to do. But knowing your seed is the important factor.
4) Thorough scouting will give you an advantage because many pathogens begin to show up before tasseling. Fungicide applications are not recommended on resistant hybrids. For susceptible hybrids, location of the pathogen and its timing will be the determinant for spray.
5) Just like corn, foliar diseases like humidity and moisture also, and the greatest yield increases occurred in areas with high rainfall during recent university fungicide tests.

Bradley’s Iowa State colleague Alison Robertson says in a July 3 fact sheet that common rust is the first to appear, but it has not yet been seen. Next is gray leaf spot and northern corn leaf blight which appear at the end of July with hot and humid conditions. Robertson notes the timing could be critical because the delayed corn crop will just be starting to fill at that point, “Research has shown that the earlier in the grain-fill process that disease develops, the greater the impact on grain yield. This year, because tasseling and silking are delayed, grain filling will occur in late July through August, and may coincide with increased disease pressure.” She says with the more valuable crop, the use of a fungicide to protect every bushel may be appealing, but she tells corn growers to consider Bradley’s checklist.

Bradley and his colleagues at many Cornbelt universities and in Canada last year tested various foliar fungicide treatments. He says, “Results from university trials conducted in 2007 in 12 different states and Ontario indicated that hybrids with a "fair to poor" rating for gray leaf spot resistance had a 6 bu/A increase when a foliar fungicide was applied, compared to a 4 bu/A increase when a foliar fungicide was applied to hybrids with a "good to excellent" rating for gray leaf spot resistance.”

An important point made by Nebraska plant pathologist Tamra Jackson can be found in the latest Nebraska Crop Watch. She says most fungicides provide only 14-21 days of protection and in recent years, the appearance of fungal problems have spread throughout July and August. That means corn growers typically using foliar fungicides may need to schedule a second application. She also says it is going to take a two to three bushel response to pay for the cost of the spray.

When hail strikes, lesions are created on the corn stalk and on leaves that may provide an opening for pathogens. However, a simulated hailstorm, followed by the application of a variety of fungicides resulted in data that the fungicides did not significantly improve yield compared to the untreated check. The “hail” reduced the yield, but the fungicides did not help the yield recover.

If some of your neighbors insist a foliar fungicide makes the corn look healthier and yield more, Bradley says they are seeing the “greening” effect of some of the active ingredients in the fungicides. It does not automatically add yield to the plants, says Bradley after testing for that specific effect. He says fungicides are designed to kill pathogens, and that is the reason for their application, not a cosmetic reason. He says they will help increase production and profits, if use for their designed purpose.

Summary:
Fungal problems can reduce corn yields substantially, but can be expensive. There has been an increasing trend toward foliar fungicide applications, whether or not any pathogen has been detected in a corn field, with producers claiming that the yield was boosted as a result. While no research can confirm any yield increase due to a foliar fungicide, plant pathologists are saying that farmers whose corn is susceptible to fungal problems, may have reason for applications.

Have you applied a foliar fungicide hoping to increase yield, and if so, what happened? Are you concerned that corn pathogens may become immune to fungicides if they are over used?