ASK THE AGRONOMIST BLOG

On June 23, Iowa State University Extension and Outreach announced that tar spot has been observed in six counties in central Iowa. Stine agronomists and sales reps have also received reports of suspected tar spot in corn throughout the Midwest and the Eastern Corn Belt. The disease, which was first discovered in the U.S. in 2015 in Indiana, traveled from Central America and Mexico. Since then, it’s moved from east to west and is quickly becoming a concern. The earlier it moves in during the season, the more time it has to spread and lead to yield loss.

Meaghan Anderson, field agronomist for central Iowa at Iowa State University Extension and Outreach, recently sat down with Stine Seedcast host David Thompson to discuss tar spot. In their conversation, which will air on Tuesday, July 18, Anderson notes that the severity of the disease this year will depend on the weather. “We’re certainly setting up to potentially have an issue if the weather does what we are worried it could do.”  

The disease thrives in moist environments with moderate temperatures. ISU Extension and Outreach notes, “the daily minimum or the daily mean temperature over the past 30 days was the most strongly correlated with tar spot development and increased severity. Moderately warm (below 70F) mean temperatures increased development and severity.”

How to identify tar spot in corn

Tar spot symptoms are typically observed later in the season during grain fill or around R3 to R6. The fungal disease appears as black lesions on the leaf called stromata. Anderson notes, “Stromata can break open and then they’ll release spores. Then those spores will get in the air or splash in raindrops and then move to new leaves and to new plants and elsewhere like new fields. They can consistently spread as weather conditions are good for it.”

Earlier in the season, you can find tar spot in the lower canopy. As the season progresses, it starts to infect the upper canopy. “This time of year, I recommend looking at the lower canopy, about knee high to try and find tar spot,” said Anderson.

Anderson also notes that tar spot is easily misdiagnosed. Growers might think the lesions are soil splashed onto the plant, dead bugs or other diseases that create similar shiny or semi-shiny black spots on the leaves. The main indicators that it’s tar spot, however, are 1. you can’t scrape tar spot off the leaf and 2. when you flip the leaf, you will be able to see lesions on the bottom. They impact both the top and bottom sides of the leaves. 

How do you control tar spot disease?

Tar spot treatment can depend on the severity of the disease. The best thing you can do is get out and scout. When scouting, use any local extension tools available that can help you diagnose the disease as tar spot and determine the severity of infection. The Crop Protection Network has a Disease Severity and Insect Defoliation Training tool to assist growers in diagnosing disease and defoliation ratings on field crops, including corn.

Anderson notes that scouting should begin just prior to tassel to make fungicide application decisions. Late in the season, fields should be re-scouted at around R5, the dent stage in corn. At this point, you can determine what’s happening at the ear leaf and upper canopy, which can tell you a lot about what happened earlier in the season. She adds that at R5, if you have more than 5% tar spot coverage on the ear leaf, it will likely impact yield. If you have less than 5% coverage, then it’s fairly unlikely that a fungicide would have been economically viable to treat it. She notes experts from Purdue Extension have experience in detecting and treating tar spot as it was first state where the disease was detected in the U.S., so growers can utilize their resources as well.  

If you need additional help with treating or identifying tar spot, contact your local Stine agronomist or sales rep for more information. Stine offers high-performing seed corn with the industry’s most desirable trait packages to combat disease. And stay tuned for Anderson’s full interview on tar spot on the July 18 episode of the Stine Seedcast.

The June 27, 2023, U.S. Drought Monitor Map reports that large areas of Nebraska, Kansas and Missouri, and some areas of Iowa, South Dakota, Oklahoma and Texas, are experiencing extreme to exceptional drought conditions. Many areas of the Midwest, South and East Coast are experiencing abnormally dry, moderate or severe drought conditions. The National Drought Summary states, “The Midwest and east-central Great Plains saw mostly worsening conditions and widespread crop stress and low streamflows after another week of mostly dry weather.”

Stine^® agronomists and sales reps have been fielding questions recently about managing Stine corn and soybeans during a drought.

“There are a number of concerns growers need to be aware of when it comes to drought and crop production,” says Tom Larson, Stine’s director of agronomy. “Drought stress in plants obviously impacts plant performance, but growers also need to be aware of issues related to herbicide carryover.”

What are the effects of drought on plants?

The U.S. Drought Monitor notes that 70% of corn and 63% are soybean production areas are currently impacted by drought conditions. 

The negative effects of drought on crops can result in significant yield loss if dry conditions persist throughout the growing season, especially right before or during the critical pollination stages.  

Drought symptoms on corn

The initial symptom of drought stress in corn is leaf rolling. This typically occurs during the day. Long periods of drought during the vegetative stages can result in shorter, stunted plants and less leaf area. Growers may also note leaf discoloration. If drought persists through the pollen shed stage, yield loss can truly gain ground.

Dr. R.L. (Bob) Nielsen of Purdue University notes, “Stress during pollen shed and silking can cause more yield loss than almost any other period in the crop's development … During the silking and pollen shed period, severe stress may reduce yield up to 8 percent per day. During the 2 weeks following silking, severe stress may reduce yield up to 6 percent per day.”

Later in the season, if pollination was impacted by heat stress, it can lead to poor grain fill, aborted kernels and leaf tissue death.

“Now that we’re getting closer to the pollination stage in corn, that’s when heat stress can really take hold and damage yield,” said Larson. “Drought conditions can lead to delayed silking or stunted silks, which greatly impact the pollination process and grain fill. Fortunately, Stine has many corn hybrids that feature some drought resistance and are bred to perform under drought stress. While we’re hoping for rain, it will be interesting to see how these hybrids yield come harvest if the current conditions persist.”

Stine has several corn hybrids that have a longer flowering period, which can help insulate the crop from drought stress to a degree by having pollen shed over a longer period. Connect with your local Stine sales rep to explore these options for the 2024 season.

Drought symptoms on soybeans

“While soybeans are also subject to yield loss related to drought stress, they’re not affected as severely as corn,” said Larson.

Soybean drought stress can initially appear as leaf curling (or flipping) in the vegetative stages. Continued drought stress can further impact the plant by stunting leaves and early flowering, which affects pollination.

Experts from Iowa State University Extension and Outreach note that the “Soybean is most susceptible to water deficits

during germination and the reproductive growth stages. Soybean yield loss from water deficits is caused by a reduction in flower number, pod number, and seed fill during the reproductive stages of growth.”

Drought stress can also lead to fewer seeds per pod, smaller seed size and seed abortion in soybeans.

Drought and herbicide carryover

“Herbicide carryover should be a consideration for growers during a drought year,” says Larson. “Plants under stress don’t metabolize chemistries properly, so it takes longer for it to flush through their systems. Herbicides carried over from the previous year may be present in the soil as this year’s crop grows. If this year’s crop doesn’t have tolerance to that chemistry, you could have a big issue on your hands.”

Herbicides applied in the spring or early summer have more time to break down in the soil. However, herbicides that are sprayed in season post-emergence have a shorter half-life and may cause issues for the next growing season. 

“For any corn herbicides that were sprayed late last season, we’re seeing some of that chemistry impact this year’s crop as the chemical has not broken down by now,” said Larson. “To ensure this year’s herbicides don’t carry over into next year, you need to time your herbicide applications and select your chemistries wisely. Look for something that you know won’t impact next year’s crop or choose a corn or soybean product that has tolerance to that chemistry. Your Stine agronomist or sales rep can help you with these decisions.”

To learn more about drought’s impact on corn and soybean crops and the potential for herbicide carryover, contact your local Stine sales rep or regional sales agronomist today.

Stine^® has yield and that goes well beyond the farm. Now, Stine has the opportunity to cultivate wishes for critically ill children in the communities we serve.

Through a partnership with Make-A-Wish® Iowa — a nonprofit organization with the mission to grant life-changing wishes for critically ill children — Stine has signed on as a premier, exclusive and inaugural sponsor for the Harvesting Wishes Program.

About Harvesting Wishes

Harvesting Wishes is a unique program to engage farmers and agricultural workers across the country to participate in granting life-changing wishes for kids in their communities. Individuals can participate in the program by providing in-kind, monetary or supply requests, which can be done through the program’s website, HarvestingWishes.org. Alternatively, farmers can donate Gifts of Grain. Proceeds from donations go directly to funding the wishes of a critically ill child in the donor’s community or state. Donations can also be used towards tax deductions.

STINE'S COMMITMENT

Stine has agreed to be the premier and exclusive sponsor of Harvesting Wishes. As the premier sponsor, Stine will advocate for the program, communicating its benefits to Stine employees, sales team members and grower customers across the country to expand the reach of this important effort. As our reach across the country is vast, our involvement can help grow Harvesting Wishes to have a national impact.  

seed purchase program

Stine has created a customer incentive program to donate funds to the Harvesting Wishes Program. Stine growers interested in participating will receive a seed purchase incentive from Stine upon donating to the Harvesting Wishes Program. All proceeds from the program go directly to funding the wishes of a critically ill child in the donor’s community or state should they designate the gift to stay local. As Make-A-Wish Iowa is a 501(c)(3) tax-exempt organization, financial contributions may be deductible for federal income tax purposes. Growers should consult with their financial advisor to determine the extent of tax deductibility.

If you are interested in learning more about our seed purchase program through Harvesting Wishes, we encourage you to connect with your local Stine sales rep for more details. Please note: This is not just an Iowa program. Growers across the country can participate by connecting with their local rep.

power of a wish

In Iowa alone, nearly 400 critically ill children are waiting for their wishes to be granted. But the need for granting lifesaving wishes and cultivating hope for these children is not just happening in Iowa; it’s impacting communities across the country. Programs like Harvesting Wishes help bring awareness to this important cause and the impact a wish can have on a struggling child and their family.  

The families and children who have received a wish know the power of a wish is truly remarkable. Through Harvesting Wishes, Stine and Make-A-Wish Iowa will work together to see even more wishes come true and greatly improve the quality of life for critically ill children. In the recent “Impact of a Wish” study, research showed:

• A wish can give kids the strength to fight against and even overcome a critical illness. 
• 99% of doctors say wishes help relieve a family from traumatic stress.
• 87% of wish alumni say their wish was a turning point in their treatment. 

To learn more about or to participate in the Harvesting Wishes Program, visit HarvestingWishes.org. Or to participate in Stine’s seed purchase program through Harvesting Wishes, connect with Stine today.