Tar Spot Isn’t Going Anywhere — Is Your Fungicide Plan Ready?
In recent years, tar spot has expanded its footprint, becoming a persistent challenge for farmers across the U.S., writes Tim Abbe at Winfield United. The disease has long been a problem in South and Central America but has progressively moved northward in the past decade. Early on, there were questions as to whether it would be able to overwinter in the cooler climate of North America, but it seems those speculations have been put to rest, and the answer is not what U.S. producers were hoping for. However, each year brings new insights, and with that, we’re gaining better knowledge of the disease’s biological characteristics and evolution, which can help us dial in on the most effective management strategies.
Why Does Tar Spot Management Matter?
Tar spot is a fungal disease that affects corn, causing black, tar-like spots on leaves, which can reduce the plant’s photosynthetic capacity and steal resources the plant would otherwise use to fuel growth and reproduction. In severe cases, it can lead to significant yield losses of up to 30%. On a 200-bushel-per-acre corn field, this can translate to a staggering 60-bushel loss, or nearly a third of a farmer’s income potential on that acre. Beyond direct yield losses, tar spot also seems to decrease the plant’s natural defense mechanisms, which it relies on to fight off infections from various stalk and crown rot pathogens. This can result in compromised standability and a more challenging harvest.
Unlike some diseases, such as southern rust, which depend on windborne spores traveling through the jet stream, recent findings suggest that tar spot can overwinter in most U.S. soils. This makes the disease a significant annual threat, especially for northern producers. Studies indicate that up to 25% of spores may remain viable in springtime, making it a recurring problem from one year to the next.2 The disease’s ability to thrive under diverse climatic conditions – ranging from high humidity to moderate rainfall – also complicates prediction models and management programs.
Historically, farmers have used several cultural and/or chemical strategies to anticipate and manage fungal diseases. Based on our latest information, here’s a breakdown of what is and is not effective when it comes to controlling tar spot.
Fungicides
Given tar spot’s persistence and destructive potential, fungicides have emerged as the primary line of defense to protect yield. Until recent years, the return on investment (ROI) for foliar fungicides has lacked consistency, particularly in the northern geographies; however, tar spot has changed this dynamic, making fungicide applications a more reliable and necessary investment across most regions in the U.S.
Read more at Winfield United.
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