A scouting trip through the Corn Commentary field in central Indiana at the end of July revealed the value of crop scouting, even after corn pollinates and begins the grain fill stage. Virtually disease free two weeks ago, the crop now exhibits considerable gray leaf spot lesions on lower leaves.

Lesions were spotted on the leaf below the ear leaf in many cases, but not on the ear leaf itself. However, farmer reports indicate that in bottom land fields planted earlier, gray leaf spot has advanced to the ear leaf and even to leaves above it.

The Corn Commentary field was sprayed by drone about a week ago, at the end of the silking phase. Dan Quinn, Purdue Extension corn specialist, notes that R1 is still the recommended time for fungicide application if you believe you need fungicides. Based on university research, that is the application window that provides the biggest return on investment.

“We encourage growers to continue scouting even after a fungicide was applied earlier,” Quinn says. “Applications are only effective for two to three weeks, depending upon the product and upon the target disease.”

Other disease issues

Gray leaf spot isn’t the only disease threat this summer for corn. In eastern Nebraska, southern rust has been confirmed in many counties. Southern rust is also confirmed in Iowa, Missouri, Kansas, Kentucky, southern Illinois and southern Indiana. Some suspect it traveled northward with the remnants of Hurricane Beryl and is now making its appearance. To see where it is confirmed county by county, visit the Corn IPM Pipe website.

Related:Corn plant miscues: What went wrong?

“We really need to see a sample to confirm whether it is common rust or southern rust,” explains Darcy Telenko, Purdue Extension plant pathologist in Indiana. “We confirm it by examining the spores under a microscope.”

So far, southern rust is confirmed in two southwestern Indiana counties, Knox and Dubois. “Some fungicides are better on controlling southern rust than others,” Telenko says. “Growers can check university ratings for effectiveness of various fungicides on specific diseases.”

Find ratings for fungicides on various diseases at the Crop Protection Network.

Tar spot is the disease causing Telenko the most concern in Indiana. It has been confirmed in roughly 40 of Indiana’s counties, with no corner of the state immune from it.

“If you’ve had it before, you probably need to be checking for it this year,” Telenko says. “Even growers who have already sprayed for it are questioning if they will need to spray a second time.

Related:Scout tar spot until black layer

“The dip in corn prices factors into that decision too. You need to factor in cost of the product and application versus expected yield benefit, and figure it at lower corn prices. It is too early to tell if second applications might be warranted in some situations. However, it is important to continue monitoring fields for symptoms.”

Tar spot is also confirmed in a significant number of counties in Iowa, Missouri, Nebraska, eastern Kansas, southern Wisconsin and Michigan; and in scattered counties in southern Illinois, northern Kentucky, Ohio and even as far east as Pennsylvania. Follow progress on the Corn IPM Pipe website.

Across the rows:
Disease kicks up across the Midwest

Most reports indicate that despite a shaky start during planting season and localized severe flooding and wind events, corn looks good so far in many areas. However, diseases and other issues, including dry weather — yes, dry weather — are raising their heads in some locations. Here is a closer look:

In Nebraska. “Southern rust has been confirmed in more than a dozen counties in eastern Nebraska. Southern rust is patchy at local levels in affected counties, meaning it’s easy to find across some fields, but seemingly not present in other nearby fields within a handful of miles. This distribution pattern is common for southern rust early after it moves into the state.

“If weather conditions remain favorable, southern rust will likely continue to worsen within fields and continue to spread within and between fields and to more counties. Southern rust development and presence in several eastern Nebraska counties during the week of July 15 was earlier and more widespread than documented in recent history. This year, there is a wide range of planting dates, with many Nebraska corn acres planted later or replanted due to the wet conditions this spring. Later planting and cooler growing conditions have slowed crop growth and development in some parts of the state, where some corn is still in vegetative growth stages. Development of southern rust in these fields, especially those that are pretassel or in early grain fill stages, creates increased risk for impact on yield later if disease severity continues to increase.

“Southern rust may be confused with common rust, also present in many Nebraska cornfields. Common rust is of lesser concern and rarely requires treatment in dent corn. But differentiating common rust from southern rust can be difficult due to similarities in their appearance. The color of some common rust pustules appeared more orange than the typical brick red/brown, making them appear more similar to southern rust this year and more difficult to differentiate.” — Tamra Jackson-Ziems, Extension plant pathologist, and Kyle Broderick, Extension educator and coordinator of the University of Nebraksa-Lincoln Plant and Pest Diagnostic Clinic, reporting in Nebraska Crop Watch, July 25 edition

In Minnesota. “Growers have been asking if applying extra nitrogen is worth it in these conditions. If additional nitrogen is to be applied, it should be done no later than V14.

“Pollination status is also a common question this time of year. Weather conditions have been favorable for pollination, unlike previous years, but ear tip dieback after pollination is the main concern right now as plants may abort kernels. Temperatures should moderate and reduce stress on crops in mid-July.

“However, stunted corn may not produce even an ear this year due to delayed development, or may not reach maturity if an ear is produced. That means the fall outlook for harvest will be a mix of mature versus wet immature corn throughout a field, depending on how staggered development was.” — Jeff Colter, University of Minnesota corn agronomist, responding to questions about corn in the July edition of Minnesota Crop News

In Illinois. “Corn and soybeans across the area continue to look healthy, and growing progress remains steady. Many cornfields have been successfully pollinated. Spray planes have also been active the last couple of weeks, with producers putting on fungicides. Soybeans have nearly all flowered, with most also starting to grow pods. Some rain would be welcome, but there does not appear to be a lack of moisture in the soil.” — Reagan Tibbs, commercial agriculture educator, Logan County, reporting for Illinois Extension in The Bulletin on Farmdoc

In the Dakotas. “Cool, wet conditions at the beginning of the growing season have made way to warmer weather, which is progressing the crop along in the Dakotas. Heat is benefiting wheat and small grains, peas, and sunflower crops.

“Soil moisture is not in short supply for the central part of the state and is more plentiful moving east. This moisture is helping the corn crop become well established as roots move down with the moisture. The corn is expected to be pollinating soon, at least in the next couple weeks.

“The wheat crop, mostly spring wheat, has benefited greatly from recent high temps. With a good growing season and okay temperatures during flowering, good yields are expected, but only time will tell if the protein will come along with the yield too.” — Sarah McNaughton, editor of Dakota Farmer