Microbial allies may help corn

Mar 07, 2024

The U.S. Department of Agriculture's Agricultural Research Service scientists are leaving no stone -- or rather, leaf -- unturned in their search for new ways to counter the fungus that causes tar spot, a yield-robbing disease of field corn in the midwestern United States.

First reported in Illinois and Indiana in 2015, tar spot has now expanded to include other nearby states, as well as Florida and Canada. The disease manifests as raised black spots that mottle the leaves, husks and stalks of susceptible corn varieties, diminishing their photosynthetic ability and, in severe cases, killing the plants and inflicting grain yield losses of 20 to 60 bushels an acre.

Now, however, those same spots may reveal a hidden foe of the fungus that causes tar spot, Phyllachora maydis. The spots, called stromata, are a tough structural form of the fungus that enables it to survive the winter and release a bevy of spores the following spring that infect the next corn crop. But a team of sharp-eyed scientists with USDA Agricultural Research Service’s National Center for Agricultural Utilization Research in Peoria, Illinois, observed that some stromata specimens they collected failed to germinate -- the “handiwork” of other fungi and bacteria that parasitize the tar spot fungus, potentially opening the door to a biologically based approach to controlling it.

The scientists’ observation came while inspecting a research plot of corn near the Agricultural Research Service center in April 2022. Mild outbreaks of tar spot can generally be reduced with synthetic fungicide applications and corn varieties that can tolerate some damage from the fungus. But under the right weather conditions, severe outbreaks can overwhelm those defenses, exacting a costly toll on farmer profits and underscoring the need for additional countermeasures that can be deployed.

Fortunately, nature, with its system of checks and balances, offered several different species of fungi and bacteria that grow and reproduce on or inside the fungus’s stromata -- some of which appeared as a whitish fuzz on the stromata when researchers examined them under a microscope in the laboratory.

The researchers’ use of DNA-based identification methods revealed that some of the fungi and bacteria were known biological control agents of diseases affecting other crops. In trials, exposure to spores of Gliocladium catenulatum, which is a commercially available biocontrol fungus, prevented 88 percent of the tar spot fungus’ stromata from germinating.

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Video: Spring 2026 weather outlook for Wisconsin; What an early-arriving El Niño could mean

Northeast Wisconsin is a small corner of the world, but our weather is still affected by what happens across the globe.

That includes in the equatorial Pacific, where changes between El Niño and La Niña play a role in the weather here -- and boy, have there been some abrupt changes as of late.

El Niño and La Niña are the two phases of what is collectively known as the El Niño Southern Oscillation, or ENSO for short. These are the swings back and forth from unusually warm to unusually cold sea surface temperatures in the Pacific Ocean along the equator.

Since this past September, we have been in a weak La Niña, which means water temperatures near the Eastern Pacific equator have been cooler than usual. That's where we're at right now.

Even last fall, the long-term outlook suggested a return to neutral conditions by spring and potentially El Niño conditions by summer.

But there are some signs this may be happening faster than usual, which could accelerate the onset of El Niño.

Over the last few weeks, unusually strong bursts of westerly winds farther west in the Pacific -- where sea surface temperatures are warmer than average -- have been observed. There is a chance that this could accelerate the warming of those eastern Pacific waters and potentially push us into El Niño sooner than usual.

If we do enter El Nino by spring -- which we'll define as the period of March, April and May -- there are some long-term correlations with our weather here in Northeast Wisconsin.

Looking at a map of anomalously warm weather, most of the upper Great Lakes doesn't show a strong correlation, but in general, the northern tiers of the United States do tend to lean to that direction.

The stronger correlation is with precipitation. El Niño conditions in spring have historically come with a higher risk of very dry weather over that time frame, so this will definitely be a transition we'll have to watch closely as we move out of winter.