Stability of Hybrid Response to Fungicide “Plant Health” Effect

By Paul Vincelli

Headline® is a very effective fungicide for control of certain corn diseases, especially gray leaf spot and northern leaf blight. It is also being marketed as a growth regulator, with claims of yield increases even in the absence of significant disease pressure.

Yield increases are, in fact, possible under low disease-pressure conditions. But few university scientists recommended fungicides in the absence of significant disease pressure since these yield increases don’t seem to happen often enough or predictable enough to rely on as a crop management strategy.

But maybe it isn’t that simple.

It seems well-established scientifically that corn hybrids differ in how they react to fungicides under low disease pressure. In some experiments, certain hybrids show a “growth-regulator yield boost” from fungicide; others don’t. But can growers count on it, year after year, in field after field?

The publically available, validly conducted research thus far indicates that this effect may not be very stable in most corn hybrids. In other words, it seems that few corn hybrids consistently provide a significant yield benefit from one year to the next when disease pressure is low.

I risk sounding like a “broken record”, repeating the same thing over and over, but the research keeps pointing to the same conclusion: The best reason to apply a corn fungicide is when pressure from foliar diseases is moderate to high on a susceptible hybrid. Any other reason for applying a fungicide—more stress tolerance, improved growth efficiency, stronger stalks—runs a significant risk of unnecessarily increasing production costs, environmental contamination, and pesticide residues in the kernels. It may happen, but it is more likely that it won’t.

Wheat Rusts are a “No Show” So Far

By Don Hershman

Over the past couple of years, wheat scientists, crop consultants, and wheat producers have heard a lot about the new races of wheat stem rust, loosely referred to as UG99 (Figure 6), that have the potential to greatly impact the world’s wheat supply. The big “hubbub” is due to the fact that most of the wheat varieties grown throughout the world, including many in the U.S., are fully susceptible to the disease. This is big change in the status of stem rust because, prior to finding UG99 (named for being found in Uganda in 1999), stem rust was adequately controlled using resistant varieties.

Because of the potential importance of UG99 to the U.S. wheat crop, new monitoring and communication activities targeting wheat stem rust have recently been initiated. This has resulted in a lot more people looking harder than ever before for wheat stem rust in most states east of the Rocky Mountains. In the process of looking for stem rust, other rusts--leaf rust (Figure 7) and stripe rust (Figure 8)--are also being monitored and survey results are being reported to stakeholders.

Increased rust monitoring and reporting activities have greatly increased our awareness of where rust diseases are at present and to what extent.

Based on all of this activity, there have been numerous reports from the South indicating that leaf rust, stripe rust and stem rust (not UG99) are all present. Many growers in Kentucky have heard these reports and this has generated some concern that our risk for one or more rust disease is higher than normal. I do not think this is the case. Personally, I see no evidence that rust diseases in the South are more widespread or severe for this time of the year than usual. And to date, no rusts (leaf, stripe, or stem) have been observed in Kentucky. My guess is that our rust risk is normal to below-normal based on the general lack of rainy weather since the wheat crop has greened up. Things could change if conditions turn wet, but for now we are in good shape. I am quite certain we will see one or more rust diseases in Kentucky –we always do. But for the most part, they are held in check by resistant varieties here and elsewhere.

We have stepped up monitoring activities for UG99 and are part of the national UG99 monitoring effort. All evidence suggests that UG99 will not arrive in the U.S. by natural means. By that I mean it will not likely enter the U.S. via a hurricane, as was the case with soybean rust. There are numerous rational reasons for this which I cannot go into with this article. Suffice it to say that all evidence suggests that when we find UG99 in the U.S., the origin will be associated with human activity (commerce related, or by researchers, terrorists, hobbyists, or tourists).