Wet stretch fuels crop disease, damage concerns

A cornfield near Mount Sterling (Brown County) reveals significant leaf and tissue damage caused by a recent hailstorm. (Photo courtesy of Matt Montgomery, Pioneer field agronomist)

Multiple rounds of severe weather impacted locations around the state the first half of July, dropping some much-needed moisture but also creating crop and structure damage.

The wet pattern, which featured a stretch of 18 out of 26 days with measurable rainfall in central Illinois, also fueled concerns about crop disease outbreaks.

Matt Montgomery, Pioneer field agronomist, discussed the situation while scouting hail-damaged fields in western Illinois. Recent storms produced significant flash flooding near Augusta (Hancock County), reports of brief tornado touchdowns and damage near Virginia (Cass County) and Fisher (Champaign County) and incidents of wind and hail damage among other issues around the state.

“When you look at the crops, it’s a spectrum,” Montgomery told the RFD Radio Network while scouting damaged fields near Mount Sterling (Brown County). “There’s a pretty brutal swath with a lot of tops out of corn and some beans have been stripped down (by hail that stretched into Schuyler and Morgan counties). Some fields I walked will be zeroed out.”

The first full week of July featured rainfall totals between 1.5 to 3 inches in much of western and southern Illinois, 1 to 1.5 inches in the central part of the state and lesser amounts to the north, prior to more rounds of storms the second week of the month.

How spotty are the rainfall patterns?

Portions of McLean County received nearly 14 inches of precipitation in just a few weeks while a section of northeast Illinois remains in severe to extreme drought, with moderate drought to abnormal dryness extending all the way across the state’s northern border down to around the Interstate 88 corridor, according to the U.S. Drought Monitor.

The portion of crops rated good to excellent in the state slipped 5 points the second week of July, to 60% for corn, and down 7 points to 56% for soybeans, with rainfall patterns playing a key role.

“We’ve been getting rains. The corn’s taking off and the beans look pretty good,” FarmWeek CropWatcher Larry Hummel told RFD. “The only issue showing up now is some soybeans are yellowing (from excessive moisture).”

Another key concern, particularly in areas that received significant moisture, includes crop disease outbreaks.

“We’re already seeing gray leaf spot and northern corn leaf blight,” Montgomery said. “There’s plenty of humidity.”

There also have been reports of tar spot in northern Illinois cornfields.

Evergreen FS reports not every situation requires a foliar fungicide. However, productive fields at elevated risk for yield-limiting diseases may benefit from the added protection.

Trials suggest fungicides applied at VT/R1 growth stage for corn and R3 in soybeans have better than a 60% chance of paying off in high-risk situations. Many farmers currently face these situations and fungicide applications were made, with diseases such as frogeye leaf spot, leaf blight and brown spot a concern for soybeans.

“The amount of humidity we’ve run into this year matches patterns that result in returns on fungicide applications,” Montgomery said.

Factors that can increase the risk of foliar diseases, along with the recent wet, damp conditions, include the following, Evergreen FS reported.

  • History of disease in the field.
  • Non-rotated crop production systems. Major residue-borne fungal diseases feed on and infect either corn or soybeans.
  • Minimal or no-till production systems. Residue provides sustenance for residue-borne foliar plant pathogens.
  • Hybrid or cultivar susceptibility to commonly encountered foliar fungal diseases.

The risk of foliar diseases, and potential return on fungicide, also increases if a disease is present before critical stages of plant growth and if the weather forecast contains a likelihood of significant rainfall events.

Weather forecasts as of mid-July predicted temperatures could warm, but mostly just back to highs in the 80s, with possibly drier conditions the rest of the month compared to the first half.