Southern Rust

Rust in the Ration: How to Combat Southern Rust’s Impact on Corn Silage

Thu, 04 Sep 2025 14:04:48 GMT

With the warm and wet conditions this season, southern rust is on the rise in Midwest corn crops. It may be time to start considering the impact that could have on corn silage and preparing to adjust rations accordingly. While southern rust is not a direct threat to herd health, it has been shown to lower the nutritional value of silage and can compromise feed quality.

Southern rust, a fast-developing fungal disease caused by Puccinia polysora, does not itself produce toxins, but it weakens the plant and provides the opportunity for other diseases to move in. These opportunists include various Furasium species, which produce mycotoxins (fumonisin and deoxynivalenol) that can be harmful in feed.

Southern Rust and Corn Silage Quality

Southern rust is known to impact corn silage quality. A study from the University of Florida showed increasing rust infestation resulted in increased dry matter and fiber fractions, but that dry matter digestibility decreased by 13%. Further, high rust silages had lower neutral detergent fiber digestibilities than medium and no rust silages. Southern rust also affected the concentrations of lactate and volatile fatty acids, causing both to decrease with increasing infestation. These results indicate decreased nutritive value.

The observed increased dry matter also reduced silo packing effectiveness. If moisture levels are too low at harvest, it is difficult to achieve adequate packing, which leads to poor fermentation and an increased risk of mold growth.

Because southern rust coverage reduces the photosynthetic area of the leaf, grain fill is often hindered, leading to a lower energy and protein content in the silage.

Southern Rust Silage Management

There are a handful of strategies producers can apply to counteract the effects of southern rust:

Adjust harvest time based on moisture content. Southern rust can cause corn to dry down faster than normal. Monitor moisture levels closely to ensure the proper fermentation of silage.
Consider a silage inoculant. Inoculants improve fermentation, and the rapid pH drop can inhibit mold and yeast growth.
Ensure good packing and storage. Pack silage well to limit oxygen exposure and prevent mold growth. Cover bunkers immediately and weigh down coverings thoroughly.

Feeding Southern Rust Silage

To counter the nutritional challenges of feeding southern rust-infected corn silage, dietary supplementation may be necessary.

Prior to inclusion, test all potentially infected silage for mycotoxins. This will allow you to determine the safety of the feed and avoid potential health issues. If mycotoxins are high, the incorporation of a mycotoxin binding agent into the ration will help reduce toxin absorption in the animal’s digestive tract. Additionally, supplementation with antioxidants, such as vitamin E and selenium, could help animals by countering oxidative stress caused by mycotoxins and supporting immune function.

If grain fill was affected and starch levels are low, you may need to incorporate an additional energy course to compensate. Further, poor grain fill could reduce the already low protein content of corn silage, and protein supplementation may be required.

When incorporating infected silage, ensure it is thoroughly mixed into the TMR to dilute potential ‘hot spots’. Inclusion levels of contaminated silage in the feed may need to be limited or removed entirely for sensitive animals, including lactating or breeding animals. Livestock should be monitored closely for symptoms of mycotoxin toxicity, such as reduced intake, weight loss, digestive issues or reproductive challenges. Be prepared to respond if issues arise.

When feeding corn silage infected with southern rust, caution is essential to protect livestock health and performance. The thoughtful use of compromised silage can help minimize risk while maintaining efficiency and animal well-being.

Your next read: Southern Rust Set To Take Big Bite Out Of Midwest Corn Crop?

From Challenge to Triumph: Mastering Corn Silage in the Upper Midwest

Tue, 02 Sep 2025 14:42:56 GMT

When it comes to dairying, making informed decisions is an everyday necessity. Recently, the focus has shifted toward feed production and management, which is crucial, especially given the current conditions in the upper Midwest. With tight grain storage and relatively low corn prices, many dairy producers are contemplating the strategic move of chopping additional acreage of corn.

The Value of Corn Silage Reserves
Mike Hutjens, professor emeritus at the University of Illinois Champaign-Urbana, highlights the advantages of increasing corn silage storage. He suggests with corn silage valued around $40 per ton, stockpiling for 2026 could prove advantageous. According to Hutjens, ensuring an ample reserve of 2025 corn silage through December 2026 not only facilitates prolonged fermentation but also enhances starch digestibility. However, he emphasizes the necessity to calculate the required amount based on potential forage level adjustments and possible farm expansions.

“You must have enough harvested and stored to allow feeding 2025 corn silage through December 2026 allowing extended fermentation to improve starch digestibility,” he says, noting it can take three to four months. “Larger inventory depends on the value of the corn silage compared to 2026 (not known) versus not feeding it for a year; you have your funds tied up in feed in storage (banker concerns). Be sure to calculate the amount needed based on ration changes (higher levels reaching 70% to 80% corn silage as the forage level in the ration) and possible expansion.”

Innovative Techniques in Forage Harvesting
Echoing this sentiment, Brian Vaassen, Midwest regional business manager for Standard Dairy Consultants, notes the challenges some areas face in harvesting forage. With the opportunity presented by lower corn prices, some producers are expanding their inventory by employing a technique known as high-chop. This method involves harvesting corn plants at an elevated point on the stalk, reportedly resulting in remarkable tonnage per acre. By leaving the lower part of the plant in the field, the silage boasts a higher starch concentration and improved digestibility.

“We are hearing reports of great tonnage per acre,” he says. “I also know of one dairy that goes back and chops the stalks for dry cows and heifer feed.”

Overcoming Crop Health Challenges
Current concerns also revolve around the health of corn crops, adversely impacted by diseases such as southern corn rust and tar spot. These issues can hinder photosynthesis and overall plant health, reducing yield and nutrient quality. Hutjens notes that while these diseases might not directly affect cow performance, they can negatively impact the quality, quantity and fermentation of the feed.

A striking illustration of these crop challenges is captured in a video by Iowa farmer Dan Striegel. The footage shows him harvesting corn blanketed by an orangish-red cloud of southern rust, a testament to the prevailing issues in Keokuk County. Striegel’s experience is a vivid reminder of the importance of vigilant monitoring and adaptive management approaches in farming.

Strategic Planning for the Future
Closer to home, my husband, Scott Bohnert, owner of Bohnert Jerseys in East Moline, Illinois, recently shared his insights when finishing chopping corn silage at the home dairy in late August. With a sudden temperature drop from nearly 100°F to 70°F, moisture levels in his silage decreased from 71% to 66% in just a week. While he reports good grain yields, the crop’s health is a constant concern due to ongoing changes and disease prevalence.

In light of these challenges, Bohnert advises those in the cattle feeding business to consider harvesting additional feed.

“There is surplus of hay on inventory in my area that doesn’t have a lot of value right now, but putting up extra relatively cheap feed is a good idea,” he says.

Navigating these complexities demands strategic planning and proactive management. Engaging with nutritionists and industry experts, alongside staying informed and adaptable, will be crucial in ensuring productivity and sustainability for years to come.

Your Next Read:

Southern Rust Set To Take Big Bite Out Of Midwest Corn Crop?

Thu, 28 Aug 2025 14:17:28 GMT

If one picture is worth a thousand words, then the video Iowa farmer Dan Striegel shot last week must be worth thousands more. In the video, Striegel is shown harvesting a field of emerald-green corn enveloped in a cloud of orangish-red southern rust.

“We were just getting that field opened up, and I looked over and saw that dust boiling up out of the chopper, so I shot the video,” Striegel says.

Southern Rust? Never heard of her.
What Cheer, Iowa. USA. #pftour25 #harvest25 pic.twitter.com/tiIsUc2CHl
— Dan Striegel (@djsinseia) August 21, 2025

To date, Striegel’s video has garnered more than 48,000 views on X, formerly Twitter.

“We’re in southeast Iowa, Keokuk County, and I think the southern rust is as bad here as it is anywhere,” Striegel adds. “Every field you walk in, if you’re wearing a white T-shirt, you’ll come out of there red.”

A Red Path Of Disease Mars The Midwest

Expect to see more red T-shirt-clad farmers walking out of cornfields across the upper Midwest, based on what the Crop Protection Network (CPN) southern rust map is showing.

The CPN continually updates its online, interactive map showing the counties by state where southern rust infections are confirmed. Now, in late August, the counties look like red steppingstones. They form a checkered path from southwest Michigan through northern Illinois and Indiana, into southern Wisconsin, across all of Iowa and nearly two-thirds of the way across Nebraska. Eastern South Dakota is also lit up with a string of red counties, as are parts of southern to central Minnesota.

The amount of southern rust present in the upper Midwest is worrisome to Ken Ferrie, Farm Journal Field Agronomist. In severe cases, the disease can wipe out 45% of the yield potential in a field, according to the CPN.

“At most, one in 10 growers in northern Iowa and Minnesota have seen the kind of southern rust some of them are seeing this year,” says Ferrie, who was working last week with corn growers in both states.

“It was a problem in probably eight out of every 10 fields I was in, and they’d all been sprayed at least once,” he says. “Minnesota has a corn crop that’ll knock your socks off – yield potential of 250, 270. I encouraged every grower to spray their field a second time except for two fields. One had been knocked down by hail, and the other had a hybrid that was clean.”

I spoke with a good friend of mine from Iowa yesterday that is an agronomist and farmer. He said the southern rust in corn across Iowa and much of the Midwest will take 9 to 12 bushel/acre off corn yields on average from what his team and himself are seeing. pic.twitter.com/Ad1VJ9oQBg
— Captain Cornelius1 (@ISU145) August 26, 2025

Hybrids Have Little To No Resistance To Southern Rust

A combination of early-season moisture, heat and wind formed the perfect storm for southern rust this season, allowing the disease-causing fungal spores (Puccinia polysora) to move from southern climes up to the Midwest, according to Kurt Maertens, BASF technical service representative for eastern Iowa and western Illinois.

“We’ve seen it all – southern rust, tar spot, northern corn leaf blight, gray leaf spot. Our corn has been inundated with all these fungal diseases, and we started seeing them early,” says Maertens.

If there’s a silver lining to southern rust, it’s that it does not overwinter in corn residue like tar spot does. But like tar spot, southern rust takes advantage of hybrids that have no built-in resistance. For many growers, that was an Achilles heel this season.

“When you’re dealing with a 117-day hybrid like they grow in southern Illinois, Tennessee, and Kentucky, you don’t grow corn that doesn’t have good southern rust resistance, because they deal with it every year,” Ferrie notes. “When you move to Minnesota, and you’re planting 102- to 95-day corn, you’re probably not going to find hybrids with southern rust resistance.”

Striegel says that was true for his neighbor’s cornfield, which he custom chopped for silage. “That field had two hybrids in it, one was worse than the other, and the field had been sprayed with a fungicide,” he says.

He adds that he also sprayed his own cornfields with fungicide, but they are still inundated with southern rust.

“We’ve had southern rust before, and it’s not usually something we have to worry about, but this is really bad,” Striegel says. “I’m standing on my deck looking at the cornfield next to my house, and you know, all of the leaves from the ears down in that field are covered with it.”

Southern rust is real in eastern Nebraska. Fungicide 3 weeks ago, 2nd app today with some potassium acetate pic.twitter.com/WZubU6IBwz
— Trent Mastny (@TrentMastny) August 21, 2025

How Late Is A Fungicide Application Still Worthwhile?

Ferrie says the fields he scouted last week were at late R3 to early R4 and had already been sprayed with fungicide at least once, but the disease was rebuilding.

“Any field where farmers had sprayed two weeks previously, the southern rust and northern corn leaf blight, to a lesser degree, were coming back, especially the southern rust. It was resporating,” he says.

The intense disease pressure from southern rust, tar spot and others have kept fungicide use at high levels this season, despite poor commodity prices.

“Because of that [amount of disease pressure], we have seen increased demand for our fungicides this year,” says Maertens, who encouraged customers to get applications made at the beginning of tassel.

Maertens says he has fielded a lot of questions this summer from farmers, asking how late they could go with a fungicide application and still benefit.

“Our recommendation is to get in front of disease,” he says. “Generally, we stop applications before we get to dent (R5). That’s not to say a later application can’t have some benefit, but our best results have been before infection was able to take place.”

Southern rust is a yield enemy farmers routinely face in the Southeast, reports corn yield champion Randy Dowdy, Valdosta, Ga. He participated in the Pro Farmer Crop Tour last week and said on U.S. Farm Report he believes many Midwest farmers still have time to address disease.

“We need to implore the fungicides, the technologies out there and get after it and protect this crop, especially that crop that still has not reached dent,” he says.

Farm Journal Field Agronomist Missy Bauer likes to see farmers complete their fungicide applications on the front side of dough (early R4). “Once we get to early dent, I think it’s a little more challenging to get the payback consistently, though we’ve applied at early dent (R5), and seen a nice response,” says Bauer, who is based in south-central Michigan.

Under the tough disease pressure farmers are facing this year, Bauer is telling growers to scout fields and evaluate what growth stage their crop is in before they walk away or pull the fungicide trigger one last time.

She adds that farmers need to check the label to make sure the product used is able to address southern rust effectively. She describes these as “Cadillac” products containing the newest chemistry.

“When it comes to some of these diseases, especially southern rust and tar spot, I do believe a little bit of a Hail Mary pass can be effective,” she says. “Will it be as effective as an application you could have made on a more timely basis? Well, no, you could have made more money doing it timely, but you’re still protecting bushels and gaining ROI at the end.”

Ferrie adds that farmers might want to do the late-season fungicide application to keep their corn crop standing until they can put their harvest plan in place.

“Be doing the push test to check stalk quality,” he advises.

Southern Rust/Silage Alert!!

Southern Rust has been aggressively advancing in many fields, especially those without a fungicide treatment. In some situations the plants are shutting down prematurely and plant material is senescing rapidly.

While we typically want to get down… pic.twitter.com/aK3hGgZE19
— Pioneer Troy (@deutmeyer_troy) August 26, 2025

Striegel says some of the farmers around him are heading to fields to harvest their silage corn sooner than later, because of standability concerns. “Some of this corn got planted early, and we had a lot of heat. The crop matured quickly, and the diseases are kind of shutting it down. It’s just dying out, and guys are going to go get it,” he explains.

That’s the strategy Ferrie encourages farmers to use in regular production corn, too.

“Harvest the fields most at risk first. But if a field of corn goes down, go combine the fields where the corn is still standing and come back to that one later,” he recommends.

The reasoning is you don’t want to risk more corn going down while you’re harvesting the field of corn that already has.

“While I was driving through Iowa last week, I kept thinking that if I built corn reels to pick up down corn I’d bulk up my inventory, because I know where they’re going to get used,” Ferrie says, only half joking. “Yes, harvesting corn at 25% moisture is expensive, but down corn will kick your butt.”

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