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2018 delivered many DON lessons for corn

Last fall’s weather was partly to blame, but so too were the lack of management options and strategies

There can be little doubt that 2018 will go down in the record books as the worst year in Ontario for dealing with ear mould in corn and contamination by deoxynivalenol (DON). Wet weather through silking and then again in much of October and November challenged growers getting into their fields for timely harvesting of their corn crops, and what followed only added to their frustrations: waiting in line at the elevator to see whether their loads would be acceptable.

Now, the outcome is well known and most growers are just glad to see 2018 in their rear-view mirrors.

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What’s unsettling is that last fall wasn’t a case of a perfect storm of weather conditions and disease inoculum. Worse, there are indications the problem has yet to peak.

It’s what many had feared. The corn sector has fallen behind in dealing with ear rot diseases at that same time those outbreaks have worsened.

The numbers are obvious

Looking at the figures compiled by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), there is little doubt about 2018 and DON concentrations (see Table 1 below). At the 2019 FarmSmart conference in Guelph, Albert Tenuta and Dr. David Hooker made a presentation that included 2018 OMAFRA survey data.

On their own, the numbers are disturbing, particularly the double-digit figures on DON concentrations of greater than 5.0 parts per million (ppm), which makes the grain unsuitable for use in diets for cattle and poultry (see Table 2 below). When the data are compared with the seven previous years, however, the message is clear: 2018 really was the worst year to date for ear mould and subsequent DON concentrations.

One added revelation is that a pattern is beginning to emerge from the past eight years. Yes, 2018 was bad, but 2017, 2016 and 2011 were also tough years when looking at DON concentrations greater than five ppm. And 2006 had approached the severity of last year.

According to Tenuta, growers might consider the impact of 2018 and relax, believing 2019 can’t possibly see a repeat of the conditions that caused so much grief for farmers and the industry. But with four of the past eight years having DON issues, it’s a growing problem. Tenuta notes there are hot spots each year in parts of Ontario: the difference between 2018 and other problem years is that these areas have a larger geographical footprint.

“Whenever we have these big epidemic years, it is always centred around southwestern Ontario,” says Tenuta, field crops pathologist with OMAFRA. “It’s because there are a lot of acres. Whether it’s corn or wheat, that’s the primary production area of the province. If they’re affected significantly, then the province is affected significantly.”

Wheat’s ahead of corn?

Corn and wheat actually share a connection in the mould-and-blight picture in the region since gibberella ear mould (GER) and fusarium head blight (FHB) are caused by the same fungal pathogen, Fusarium graminearum. In corn, GER is named after the sexual stage of the pathogen, Gibberella zeae.

Nomenclature aside, Tenuta notes that in the past five to seven years, the wheat sector has had several fusarium head blight hot spots but they haven’t had the same impact previously observed.

“That tells the story of where the two industries have been moving,” says Tenuta. “It’s the same pathogen but the wheat sector is moving towards creating more tolerant wheat varieties, and more importantly, removing more of those really susceptible varieties from availability to the producers. So we’re planting fewer acres of those susceptible wheat varieties and we’re seeing the development of more and better fungicides that target fusarium head blight.”

A third pillar for wheat is in researching optimal timing for fungicide applications, including the development of the DONcast model, and all of these management tools or strategies have helped reduce the overall risk in some years while decreasing severe losses.

“When we look at the corn side — and 2018 is a great example — we had some high-yielding corn hybrids that were very susceptible to gibberella and DON production, and those hybrids covered a lot of acres in the southwest,” says Tenuta. “Unfortunately, it’s going back to the management decisions by the producers and in many cases, they’re starting to select fewer hybrids for their farm and in doing so, you’re decreasing the diversity on your farm and potentially increasing your risk, as well.”

High turnover on hybrids

That trend presents additional challenges to the grower given the rate of turnover of hybrids together with the focus on yield and on weed and insect resistance by the seed and breeding sector. Yet a silver lining may be that 2018 has reset the focus on diseases.

“Gibberella isn’t a major issue every year and with some of the newer hybrids, we don’t know enough about the level of tolerance amongst the majority of hybrids,” says Leanne Freitag, agronomic services support manager with Syngenta Canada. “There are a few that stand out one way or another, especially in years like 2018, but it can be hard to get a handle on them because of a lot of hybrids don’t last more than a few years, and during that time, DON might not be an issue.”

Some hybrids have been growing for three to five years, during growing seasons when ear rots weren’t an issue, or at the very least, weren’t an issue in those identified hot spots. But in 2018, says Freitag, multiple factors combined and led to a severe outbreak whose effects were devastating to some.

Although planting date wasn’t a direct cause of the epidemic, weather conditions occurred at the right time to infect — i.e. when silks were emerging, causing high levels of infection in several areas. Then the weather conditions during grain-fill were conducive for infection to progress and thrive.

Breeding and selecting for disease resistance is a difficult process, reminds Freitag, adding that the main focus of researchers and breeders in recent history has been on yield and insect resistance. And that tightened focus is shifting as diseases like gibberella or even penicillium and diplodia ear rots become more prevalent.

“Breeders are putting more focus on breeding and selecting for higher tolerance of DON and gibberella but a hybrid still has to be brought all the way up to the commercial level and perform well in the field,” says Freitag.

Increasing aggression?

Freitag has also heard of a disturbing trend that was outlined earlier this year by Dr. Pierce Paul from Ohio State University, who reported that there are two main DON pathogens in corn.

“One is much more aggressive, in that it has a higher ability to produce more disease and more mycotoxins,” says Freitag. According to Paul, 20 years ago, the more aggressive DON represented only three per cent of the pathogen population in corn and the less aggressive represented 93 per cent. A decade later, it had shifted so the more aggressive one represented 44 per cent and the less aggressive was at 56 per cent.

Freitag hasn’t heard what’s happened in the past 10 years but given the progression from the late 1990s to the late 2000s, it stands to reason that the more aggressive pathogen would occupy a greater percentage. And that may be why DON has increased in frequency.

As for dealing with the disease, both Freitag and Tenuta recognize there are strategies that already exist. Freitag points to livestock producers, particularly those in the hog sector, who have worked to understand which hybrids are susceptible and which have better tolerance.

As well, from an agronomic standpoint, working with plant populations, row widths and minimizing plant variability — by conducting proper planter maintenance and monitoring planting speeds to promote more uniform emergence — are all keys to managing risks. Good soil fertility is another fundamental that will help mitigate stress, as well.

Of course, the weather always has the final say.

For Tenuta, management comes with accepting that diseases like gibberella are now a common fact of life for growers. But they also can’t assume that by applying a fungicide, they’re getting ear rot control, which may not be the case.

Fungicide applications pertain to two purposes: for foliar diseases at that tassel or pre-silk timing, and as a method of improving plant health. Neither targets ear rots.

“Just because a grower has applied a fungicide does not necessarily mean they’re getting the benefit of an ear rot or DON reduction,” says Tenuta. “You have to be targeting the silks and the timing, and you need a prothioconazole or metconazole product to help on the gibberella and DON side, as well.”

For growers in the Great Lakes region of Ontario, gibberella ear rot should be one of the highest priorities in corn production, adds Tenuta.

“We have inoculum all around for wheat and corn, ” Tenuta says. “It’s not a limiting factor.”

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