Tar spot of corn was found in several Nebraska counties. We are not recommending fungicide applications at this time due to the research from Purdue University and other states. They found it best to wait till disease severity was 5-7% and corn was from tassel to dough stage of development. More info. at: https://jenreesources.com/2025/06/17/tar-spot-of-early-corn-update/.

What to do now:
1-Scout fields and wait till a 5-7% threshold on leaves before applying fungicide
2-Observe fields as to which hybrids have more tolerance to tar spot
3-When irrigating, consider less frequent and deeper irrigations, https://go.unl.edu/vipj
4-Consider plant nutrition?

In managing pests and pathogens, few mention plant nutrition or alternative options. Healthy humans and animals are less prone to disease; why not the same with plants? A book called “Mineral Nutrition and Plant Disease” shares published research on roles of minerals in aiding or managing disease. It was written by Dr. Don Huber, Professor Emeritus of Plant Pathology from Purdue University and there’s an updated version that I have.

There’s a lot of unknowns about tar spot and its control. Dr. Huber shared that the tar spot lesions contain oxidized manganese in addition to the fungal spores. Several journal articles referenced the black “freckles” in Goss’ wilt and the vascular plugging in the systemic version also contain oxidized manganese. When manganese is oxidized, it creates a manganese deficiency in the area which doesn’t allow for photosynthesis. The area runs out of energy and can’t defend itself resulting in disease expansion. Many of us in ag understand that micronutrients are chelated in plants in the process of applying specific herbicides. Companies have developed products to help with chelation and to stimulate plants sooner from the shut-down that occurs from applying herbicides.

I’m wondering about the opportunity to use plant nutrition right now to help stimulate plant defense mechanisms? We may need fungicide at some point, but we don’t right now. I have no research on this, but to me, it makes sense. When we have early symptoms of a cold, we’re told to take zinc to stimulate our defense system. Manganese and Zinc both travel in the xylem and they aid in plant defense signaling. Addition of zinc and copper in particular can reduce manganese oxidation, aiding in plant defense responses. Thus, wondering if zinc, copper, and manganese may help with preventing and fighting tar spot? Boron and sulfur could play a role too. The addition of Calcium increases the oxidation, so it shouldn’t be used alone for this situation. Manganese, Zinc, Copper, Boron, Sulfur all aid in defending plants against pathogens.

If you’re interested in trying something in plant nutrition and would like to work with me via on-farm research, please let me know. I also need to share that many plant pathologists disagree with the thought of using plant nutrition: https://cropprotectionnetwork.org/publications/mythbusting-tar-spot-separating-fact-from-fiction.

For those in industry, many of you have products in trials that reduce the chelation processes and/or that help stimulate plants after being shut down (ex. from 10 days to 2-3 days) after a pesticide application. I’m curious if aiding crops out of chelation/shut down sooner helps with reducing pest/pathogen pressure? How can we better share what we observe with each other?