In the world of agriculture, staying ahead of new diseases is crucial for maintaining crop yield and health. This blog post dives into Craig Allaman's recent presentation at Post Harvest meetings on tar spot. Tar Spot is a relatively new but increasingly significant disease affecting corn in the Midwest.

Identifying Tar Spot:

Tar spot shows as black, tar-like spots on corn leaves that cannot be scraped off. Some of the black tar like spots could be surrounded by a circular halo. This halo makes it worse, because we have less green surface on the leaf when that happens. But that Halo is not a secondary disease in the U.S.

The Disease Triangle: Using the disease triangle to explain how tar spot thrives:

• Host: Corn is the host, inherently susceptible.
• Pathogen: While corn faces multiple fungal diseases like gray leaf spot and northern corn leaf blight, tar spot is uniquely problematic due to its consistent presence once established.
• Environment: Tar spot favors moderate temperatures and long periods of leaf wetness. This makes late summer conditions (like those in August) ideal for its proliferation.

Impact on Corn Yield: Tar spot alone might not decimate yields, but when combined with other diseases like southern rust or gray leaf spot, it can lead to significant yield losses. This combination often results in early leaf senescence, reducing the plant's photosynthetic capability which is vital for kernel fill and overall plant health.

Management Strategies:

• Genetic Resistance: While newer hybrids have some tolerance, genetic resistance isn't sufficient against heavy tar spot outbreaks.
• Chemical Control: Apply fungicides with long residuals at the R1 stage (silking). This strategy not only targets tar spot but also controls other fungal diseases until late in the season when tar spot becomes more prevalent.
• Scouting: With tar spot, scouting practices have evolved. An additional check in early August is advised to catch any premature outbreaks, allowing for timely interventions.

Tar spot represents a new challenge for corn growers, emphasizing the need for ongoing research, adaptive management strategies, and vigilant scouting. Understanding its lifecycle, environmental preferences, and interaction with other diseases is key to mitigating its impact. As we move into future growing seasons, staying informed and ready to adjust practices will be vital for managing this persistent fungal threat.

Consider integrating disease management early in your planning stages. When it comes to the growing season be sure to contact one of our team members to come out to help you identify any diseases. You can also keep in touch with local research and extension services' recommendations. Most importantly, share data and experiences with your agricultural community to better combat this and future diseases.

Looking for a hybrid with good tar spot resistance? We recommend our C6847TRE-RIB variety as it has average plant health and is known for good tar spot resistance.

Craig Allaman

Lead Agronomist

Cornelius Seed