Fungicides: Plan for Tar Spot and Cascading Supply Effects in ’22

Growers and retailers will have to contend not only with crop disease management in 2022, but supply challenges that have hit herbicides hard will likely spill over into fungicides as well.

Significant soybean disease pressure affected fields in many soybean-producing states in ’21, and in corn, tar spot has progressed from an isolated disease to one that has been reported in 14 states, agronomists say.

Nick Groth, Agronomy Service Representative with Syngenta, notes that tar spot not only resurged this past season in Wisconsin since its first unwelcome appearance in 2018, but at a surprising clip in August, just when many assumed they could skate by another year.

“A couple of weeks later we got hit hard. It goes to show it can really sneak up on you with the long latent period it has,” he tells CropLife®. From the time the spore lands on the plant to the time a visual symptom appears, there are 14 days of the disease running rampant in the plant and already taking over.

Tar spot — caused by the fungus Phyllachora maydis and aptly named for the small, raised black spots it forms on the leaf, sometimes mistaken for fly excrement — can cause losses of 50 bushel per acre or more. As such, it is not a “wait-and-see” disease to make an application, he warns, but rather one that demands preventative applications and monitoring.

“We know the inoculum is there, so what it really comes down to now is whether the environment is going to be conducive. The number-one cause for tar spot to proliferate is prolonged leaf wetness,” Groth explains. When the dew sets in before nightfall and doesn’t burn off until 10 a.m. the next day is a prime condition for the disease to form.

For prevention, start with hybrid selection. The past year offered lessons on hybrids that are more susceptible to the disease than others, but Groth says any blanket recommendations on such varieties are not yet fully baked. Instead, work with your agronomist to select the hybrid that is best for your field and look to in-season management. Assess environmental conditions around V12 timing when the corn plant is 6 foot tall. With humid days and nights and prolonged leaf wetness, an early application might be warranted. Plan on following up in 14 days if conditions stay conducive.

“When it comes to tar spot, frogeye leaf spot, or any crop disease, it’s best to get ahead and stay ahead,” adds Kelly Liberator, BASF Technical Marketing Manager, Plant Health and Fungicides. “To prepare for the 2022 season, integrating an effective fungicide application into your corn and soybean crop plans will help ensure protection from these and other yield-robbing diseases. Planned, preventative applications are key to success before disease is established in the field.”

Liberator points out that in soybeans, frogeye leaf spot continues to be a major challenge throughout the U.S. and can reduce yields by up to 30%. QoI (Strobilurin) fungicide-resistant populations have become increasingly prevalent and require growers to carefully select effective fungicides to control the disease.

While diseases can attack soybeans at any time, the greatest impact comes early in the growing season, when seedlings are most vulnerable. Some plants show signs of disease early while others, like those impacted by sudden death syndrome (SDS) or Rhizoctonia, may not show signs until later in the growing season.

“The best way to avoid having sections of fields fall victim to soilborne diseases is to try and prevent the diseases in the first place,” says Nathan Wyss, Market Development Specialist for Corteva Agriscience. “Focus on seed treatment with fungicide. It’s not worth it to skimp on seed treatments to save costs. You’ll pay for it down the road with reduced yields.”

Preventing soilborne diseases requires a holistic approach — from seed and seed treatments to drainage and planting date.

Fungicide seed treatments offer broad protection, giving seedlings a strong start. Adding an insecticide to the treatment helps prevent insect feeding, which creates an entry point for disease. Selecting soybean varieties with SDS resistance is important to managing the disease. Improving field drainage and reducing compaction can also help limit disease pressure. Lastly, planting the most problematic fields last allows for warmer soil and decreases the chances of disease.

“What I always tell folks is, let’s develop a plan and let’s try to stick to it as we go throughout the year,” Matthew Wiggins, FMC Technical Service Manager for Tennessee, Kentucky, north Alabama, and southeast Missouri tells CropLife. “I saw a few times this past season personally where growers roam the fence on and whether they were going to spray a foliar fungicide. The timeliness of that application went to the wayside because they waited until the last minute to make those decisions. Be proactive in your thinking and be timely as far as scouting.”

Wiggins points out that tar spot was found for the first time in Kentucky this past year and going forward will need to be closely monitored. In his region in the Ohio River Valley, gray leaf spot and northern corn leaf blight continue to be the largest disease issues. Then, there is the perennial scare of southern corn rust; 2021 proved a light year for the disease.

Supply Chain Issues

Herbicides bore the brunt of the supply crunch of 2021-22, but expect cascading effects on other products, including fungicides.

“Similar to herbicides, growers are going through prepay decisions right now, and some of that is booking fungicides either for soybeans or corn. There is the opportunity there that we could get tight in supply as we move throughout the season, and it depends on a lot, too, on what grain prices do,” Wiggins cautions. “As we go through the process and see what the futures are doing for next year, those purchasing decisions are going to be made and there could be opportunities where we are tight on supply for specific brands.”

Groth has noticed increased chatter about tight supplies for fungicides, although he is hopeful Syngenta will meet the demand. “We’ve had a lot of uptake on bulk orders from our retail partners. That’s going to help a lot to make sure that fungicides can get to the grower when it needs to, and we hope that can continue,” he explains.

BASF is taking a proactive approach, says Robert Upton, Director, Marketing, U.S. Crop Protection. On the production side of the equation, the company is expanding suppliers of raw materials, planning ahead, ordering raw materials earlier, expediting shipments, and making large internal investments to increase its reliability and adaptability in uncertain environments.

On the demand side, he says the company is focusing on transparency and increased planning with customers and partners.

“We are working together to increase awareness on true demand to minimize waste or inefficiency in the systems, we are improving communication and using supply planning process to increase transparency and certainty.

“There will be enough BASF product in the market this year. This is why planning and preparing are the best strategies,” Upton tells CropLife. “This is not the year to wait until the last minute. We recommend planning a comprehensive crop protection program that accounts for the best agronomic choices in case products are hard to find. It would be ideal to partner with a supplier with a broad portfolio such as BASF that you have a number of product choices to select in case there are shortages in one or the other product categories; it’s wise to have a Plan A, Plan B, and Plan C. Many suppliers do not have that depth of a portfolio to plan with in these challenging times.”

Diseases like root rot, stem rot, and sudden death syndrome can result in yield losses of 40% or more. While regular field scouting can help track early emergence of soybean diseases, the best defense is knowing what seed treatments and fungicides to use and when to plant and treat crops.

Preventing and controlling diseases remains critical to seasonal success. The trend of planting soybeans earlier in the spring creates the perfect environment for diseases like Pythium and Fusarium, which thrive in soil temperatures below 60°F. Cool, moist conditions early in the growing season also result in greater SDS pressure. High rainfall paired with low-lying, poorly drained or compacted field areas can foster disease development.