Growers Take Preventive Approach to FHB Control

By Tracy Sayler

Wheat and barley growers can get a leg up on Fusarium head blight (FHB, or scab) merely by taking a more tactical approach.  For instance, Roseau, Minn., grower Richard Magnusson begins controlling scab before symptoms of the fungal disease become visible in his wheat and barley.

“That’s one of the problems with Fusarium; by the time you see the symptoms it’s too late to do much about it.  It’s one of those diseases you need to be proactive in treating,” said Magusson, in one of five “virtual grower roundtables” held via teleconference early this spring.

Sponsored by Bayer, 542 growers from ND, MN and SD representing over 517,000 acres of wheat and barley listened in on the sessions (more information can be found online at www.haltscab.com in which Magnusson and Greg Daws, a Lakota, N.D. grower, described their experiences in managing scab. North Dakota State University extension plant pathologist Marcia McMullen and University of Minnesota small grains specialist Jochum Wiersma also offered tips on managing scab, and understanding the disease better.

Magnusson said that he views fungicides as preventative medicines, which he uses when weather conditions are conducive to the spread of FHB when wheat is ready to flower.  “We really need to be treating the disease before we ever see the symptoms,” he said.

Like many Northern Plains grain growers, the 1993 crop year was Magnusson’s first experience with scab.  “We had an all-out epidemic.  Our crop that year was so infested with Fusarium that it wasn’t even worth harvesting, and we ended up burning the whole crop that year.”

Magnusson’s crop mix has since become more diversified.  He grows wheat, barley, oilseeds, turf grass, even corn and soybeans at his farm, which is about 10 miles from the Canadian border.  He grows spring wheat varieties such as Alsen that are more tolerant of scab.

“We’re using Alsen as a replacement for 2375.  We’re phasing out our acres of 2375. Although we’re still seeding some 2375, I think in another year we’ll be just totally using Alsen rather than a combination of the two. And Alsen has worked well on our farm. In our area at least, it seems to perform as well as anything, plus the grain quality is quite good on it especially compared to some of the other varieties.”

Daws said that he uses a higher seeding rate at planting—about 1.6 to 1.8 million plants per acre—not to increase yield, but to cut down tillering, so that the crop is at a more uniform growing stage for treatments. Daws has also slowed his seeding speed and is now pulling 60-feet of drill (equipped with electronic seeding depth control) rather than 40 feet. “I’m not seeding any more acres per hour than I was before, but we have dramatically slowed the seeder down to get more uniform seeding emergence for product application.”

A more uniform crop, he explained, results in more effective treatments. Like Mag-nusson, Daws also stresses application timing.

Daws said that the use of Folicur has reduced the exposure of his grain to DON (deoxynivalenol or vomitoxin), a contaminating byproduct of scab that can make wheat unsuitable for milling, and barley unfit for malting.

“When we first had scab we struggled with this DON level, especially with barley.  It’s difficult to market (affected) barley. I actually quit raising barley for several years because of the DON level. As we’ve gotten better at putting the fungicide on, we are going back and starting to raise barley again,” said Daws. “We still see some DON in our grain, but we’ve gotten it down to a pretty low level. We’ve had relatively good success selling the crop with a low discount for the DON level.”

McMullen said that Folicur has demonstrated a consistent reduction of DON by about 50% and up to 70% to 80%. “But it depends on the level of DON you start with. If you have a very severe level in a barley field and you start with 10 ppm and you get it down to 5, then that isn’t good enough. But in a more normal year where you have a low degree of infection, you can achieve good reduction.”

Wiersma advised growers to take several factors into consideration when deciding whether to apply a fungicide: Above-normal precipitation and heavy dews, increased crop residue such as no-till, susceptible varieties, short rotations between small grains, and crop stage (wheat and barley are most susceptible to FHB from early flowering up through early grain fill) are all conditions that favor FHB development, in which case the use of a fungicide may be appropriate.  He advised growers who are more at risk—including those who produce durum wheat—to at least budget for the use of a fungicide, and apply it if an FHB infection is likely.

Magnusson said that he follows the NDSU disease forecasting system (On the web: www.ag.ndsu.nodak.edu/cropdisease, or by phone toll-free, 1-888-248-7357) and begins scouting for leaf diseases such as tan spot and powdery mildew when the flag leaf first starts to emerge. 

“If Fusarium looks like it’s going to be a problem, then we tend to delay those fungicide treatments until we get a little closer to pollination,” he said.  “The key is to start monitoring your fields when the flag leaf starts emerging and be on the lookout for tan spot and any of the other diseases, because they can drag down yield just as much as Fusarium.”

McMullen said that symptoms of FHB may not show up until about two weeks after infection occurs.  “So we’re trying to prevent the disease and the infection from occurring to begin with.  And we do that by applying the fungicide around the flowering time for wheat and at early heading to early full head emergence for barley.  That has shown to be the most beneficial timing of application.”

Wiersma pointed out that the seed treatment Raxil and the foliar fungicide Folicur share the same active ingredient, tebuco-nazole. However, while using a seed treatment with tebuconazole will help prevent root rot, it will not prevent the aerial spread of FHB. 

He also cautioned growers that replacing wheat or barley with corn in the crop rotation will not necessarily decrease the risk of FHB. “Believe it or not, corn is almost a better host for this disease than wheat is.  It can produce massive amounts of (FHB inoculum), especially as the corn matures.” McMullen agreed: “the fungus produces probably a million more spores per square foot on corn residue than it does on wheat,” she said.

Thus, many of the same management principles used to minimize FHB infections in wheat and barley also apply to corn. That includes shredding or burying corn residue that may harbor the spores that cause FHB, in growing areas at risk to the disease.  “Weather can make a world of difference,” said Wiersma. “Fifty percent of this equation is weather.”

Magnusson says that generally, he tries to plant wheat and barley as early as possible.  However, that doesn’t necessarily mean that the grain will escape scab at flowering. “From what we’ve seen on our farm, the planting dates really don’t make any difference on Fusarium and the outbreak you’re going to have. What’s critical is the weather right at the flowering period, or from heading to flowering to grain fill.  And if you could predict the weather two months ahead, then you maybe could do something with your planting dates,” he said. “So we get the grain in the ground and get it off to as good of a start as we can.  Then in our budget, we plan for a fungicide application every year and generally we’ve always put it on. Not only for Fusarium control, but also for control of the other leaf diseases, tan spot and powdery mildew, in our area.”

Daws said that he grows several different wheat varieties each season, planting the earliest maturing wheat first.  “That’s so I can get my wheat variety flowering. And then I plant the later maturing wheat later so that when my wheat starts to flower, the flowering period is spread out.  This lets my sprayer get from one field to the next when it needs to. It also elongates the flowering period and makes it so I’m not so susceptible to the weather. By going and just planting the entire amount of early maturing wheat and then planting the entire amount of later maturing wheat, it has made it very orderly for our sprayer to go across the field.”

Targeting Treatments
With a flip of the switch from the tractor cab, Daws rotates the spray nozzles forward on his air-assist sprayer when applying a fungicide treatment. “I turn the air up a little bit to tip the wheat over on its side or the heads over so they’re horizontal to the spray pattern,” he said. “We use a little bit higher pressure to get smaller spray droplets so we can get these smaller spray drops to just settle down on the top of the canopy.  Big, heavy droplets tend to drop through the canopy and go to the bottom. So I use higher pressure to make smaller droplets.  And I use the air to push the droplets down onto the upper canopy.”

Daws recommended the use of hollow cone nozzles on a standard sprayer. “I like hollow cone nozzles because they spray out in all directions instead of just forward and back. Also you can put a spinning disk on a hollow cone nozzle to get the spray droplets to rotate down onto the crop canopy.” Twin-head nozzles which spray forward and back are also recommended by many to target fungicide spray at the front and back of heads for scab suppression. “It’s just a matter of learning how to get the spray onto the head,” said Daws.  “I think the air sprayers do a better job than just a traditional sprayer based on what I’ve seen on my farm.”

Durum varieties currently all seem to have about the same susceptibility to scab, said Daws, “so we just go and spray it.  We do not even try to out guess it.  I consider (a fungicide application at heading) to be an insurance policy probably more than just a yield enhancer. It’s protecting the quality of the crop, because even if you’ve got 25 bushels of durum out in the field, if you end up with 25 crappy bushels you don’t get anything. And if you’re protecting those 25 bushels and you end up with 25 good bushels instead of 25 crappy bushels, it pays to put the fungicide on even if you don’t get a yield increase.”

Magnusson said he uses both ground and aerial applications of fungicide on his farm.  “We end up with quite a few acres to spray in a short period and we’re not able to get to them all by ground. We’ve had the best luck with ground applications just because we can get more water on. We’re getting about 20 gallons an acre of water on by ground using the angled nozzle approach.  But we also have to put a fair amount on by air, and we’ve had relatively good results. Not quite as good as by ground, but still very good. The key with aerial application is making sure the pilot puts on enough water—a minimum of five gallons per acre.”

Wiersma said that the use of a fungicide application at flowering when scab threatens will not only improve grain yield, but also test weight. “The fungicide will never hurt the crop.  Some people complain that the crop stays green longer, and that’s because it actually stays alive rather than prematurely dying. The question is always going to be whether an application will be economical.”

There are two cases when using a fungicide would not be economical in scab-prone growing areas, said McMullen: “You have to start with some yield potential and if they don’t have a yield potential to begin with, they wouldn’t want to use fungicides. And the second one would be if it’s just very, very dry, and there’s no stored soil moisture.”

Both Magnusson and Daws agree that, at least on their farms, the application has been worth the investment.

“I think over the last 9 or 10 years of using fungicides for both control of Fusarium and the other leaf diseases, I think our worst year was that we got $1 back in increased yield for every dollar we put into the fungicide. Most years I think we’re averaging at least a 1.5:1 to 2:1 return on our fungicide dollar.  And that’s just yield.  That doesn’t even take into account the quality factors, with better test rates and lowering your damaged kernels. That’s one thing we’ve really seen is that by using a fungicide our grain quality in general has been that much better.  Our wheat is consistently over 60 pounds and it just has a better look to it.”

Daws figures he will get a return on his investment by saving just two more kernels on each head of wheat. “If I have 1.8 million wheat plants out in my wheat field on an acre and I have one tiller head, that gives me 3.6 million heads on an acre.  If I eliminate scab on two kernels and get those two kernels to be healthy, I figure that’s 3.6 million heads times two kernels.  That’s about seven more bushels per acre, just from getting two more kernels out of each head of wheat.”