More and more reports of tar spot on corn

Aug 13, 2019

By Alison Robertson,Edward R. Zaworski

This past week there have been numerous new reports of tar spot within the Midwest, including Iowa (Figure 1). For updates maps, please visit https://corn.ipmpipe.org/tarspot/

Figure 1. Map of the Midwest showing where tar spot has been confirmed (red) or is pending confirmation (yellow) as of 9 August 2019

Although tar spot is reasonably easy to identify - small, raised black spots on the lower leaves of corn that do not rub off - we are requesting that suspected samples of a few leaves get sent to the ISU Plant Disease and Insect Clinic. Please include the date, county (or nearest township) and information on how much disease is present in the field. This may include:

Percent of plants in the field with tar spot?
Which leaves on the plant have tar spot?
Approximately how many tar spot occur on each leaf?
Does the field have a history of tar spot? If yes, in what previous years was tar spot observed?

These data will be shared with colleagues in the Midwest who are researching tar spot with a goal of understanding how the disease is spreading.

Source : iastate.edu

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.