Tar Spot Showing Early this Year: a Note on Diagnosis

Jul 13, 2021

By Pierce Paul

I have so far only received one confirmed report of Tar Spot in the state, but the fact that the disease has been reported in a few neighboring states has some stakeholders asking questions about diagnosis and management. Tar Spot is a relatively easy disease to diagnose. As the name suggests, it usually shows up as raised, black spots, primarily on the leaf blast. The size of the spots may vary, but they all have a very similar appearance – raised, circular-to-irregularly shaped, black spots. However, is you do have trouble with diagnosis, please feel free to send me images and samples (1680 Madison Ave, Wooster, OH 44691).

This is the earliest we have seen Tar Spot in the state since it was first reported in 2018. Results from studies out west suggest that yield losses due to Tar Spot tends to be highest when it develops and spreads before tasseling (VT) on susceptible hybrids. Warm, wet, and humid conditions seem to favor the development and spread of Tar Spot, so keep your eyes on the weather, and watch the progress of the disease. If it continues to spread, a fungicide application may be warranted, but efficacy of fungicides against Tar Spot is still being investigated.

Source : osu.edu

Video: Wisconsin Corn and Soybean Weed Management Updates and Considerations for 2026 and Beyond

Dr. Rodrigo Werle, associate professor and extension weed scientist, UW–Madison, shares the latest updates and future considerations for corn and soybean weed management in Wisconsin. This presentation covers herbicide resistance trends in waterhemp, including newly confirmed cases of HPPD and S-metolachlor resistance, and emphasizes the importance of residual herbicides and strategic tank mixes for consistent control. Rodrigo also introduces upcoming technologies like Vyconic soybeans and new herbicide products, discusses integrated weed management strategies such as planting green with cover crops, and highlights practical recommendations for 2026 and beyond.

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