Production Blog

Watch for Spots, Rots and Crazy Top

Pamela Smith
By  Pamela Smith , Crops Technology Editor
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Should you patch in wet holes with cover crops? It's one strategy, but keep an eye on herbicide carryover and other management considerations. (DTN photo by Pamela Smith)

Tar spot, Physoderma node rot, gall midge, corn borers and more ... Name a crop pest or pestilence and a notification warning seems to be showing up in the inbox this season.

The crop is all over the board in growth stage and condition. And this year, many pests seem to be on an accelerated timetable, showing up one to two weeks early. Here are a few agronomic situations DTN is monitoring and resources that might help.

THE QUESTION OF FLOODING

Top of mind this week is what happens in those severely flooded areas and what problems could appear in those crops as waters recede? Iowa State University plant pathologist Alison Robertson wrote that several diseases of corn including crazy top, Physoderma brown spot and node rot, Goss's wilt and bacterial stalk rot are a worry. Correct diagnosis is important because it should influence management going forward and what hybrid resistance to choose, she noted. Read specifics on each of those problems here: https://crops.extension.iastate.edu/…

Patches of fields left bare from flooding or prevented planting can lead to weed nurseries and possible fallow syndrome. Here's a rundown of management options from Iowa State Extension educators for flooded soils: https://crops.extension.iastate.edu/…

Cover crops are often a good plan B to fill in fields and Sara Bauder, South Dakota State University extension forage field specialist, covers herbicide carryover and many other management considerations here: https://extension.sdstate.edu/….

A University of Minnesota paper takes a look at how cover crops can help reduce the risk of fallow syndrome: https://extension.umn.edu/…

A past DTN article drills down on managing for fallow syndrome: https://www.dtnpf.com/…

This DTN article looks at how long crops can survive flooded conditions:

https://www.dtnpf.com/…

GET THE SPOT OUT!

Tar spot is showing up early this year. The first cases have been reported in Indiana, Iowa, Kansas, Michigan, Missouri and Nebraska. Extension specialists are urging farmers to stay calm, but scout carefully to make sure fungicide applications are targeted properly.

A good place to keep track of tar spot is the ipmPIPE, a pest mapping and forecasting system that was developed by the National Institute for Food and Agriculture (NIFA) and its land-grant partners, along with Animal Plant Health Inspection Service and Risk Management Agency. It was initially developed as part of the effort to manage soybean rust as it spread across the southern United States. The system provides a network of crop pest monitors (primarily Extension specialists) working together to find, report, and track key diseases and pests, providing information to growers for responsible and timely treatments.

Find the ipmPipe link to the tar spot map here: https://corn.ipmpipe.org/…

Purdue University plant pathologist Darcy Telenko has a video on fungicide timing for tar spot. Find it here: https://indianafieldcroppathology.com/…

Telenko talked to DTN about early tar spot detections: https://www.dtnpf.com/…

Scientists working on tar spot collaborated on an interesting look at how weather influences tar spot. Find it here: https://cropprotectionnetwork.org/…

MORE GALLING DISCOVERIES

Soybean gall midge hasn't been on our watch list long (2018). But researchers have unlocked a few of its secrets and developed an excellent resource in The Soybean Gall Midge Alert Network (www.soybeangallmidge.org). The website is a place to monitor emergence, damage and find new research information. A phone/text notification service is available to alert growers when to scout.

As of last week, orange and white soybean gall midge larvae had been reported at all sites in east-central Nebraska. On June 21, wilting and dead plants were observed in low frequency in three east-central Nebraska counties. Larval presence or wilting/dead plants had not yet been reported in Iowa, South Dakota, or Minnesota this year, but the season is young.

University of Nebraska entomologist Justin McMechan said in a recent video that pressure could be higher this year in Nebraska because of recent wet conditions. See that video here: https://www.youtube.com/…

For McMechan's blog post on gall midge activity go to: https://cropwatch.unl.edu/….

EUROPEAN CORN BORER RETURNS

Just when you thought it was safe to scratch European corn borer (ECB) from your pest bingo card, it is once again causing concern. Expect to hear a lot more about it at field days this summer.

ECB wreaked havoc for decades in cornfields across North America before the adoption of transgenic traits (Bt) in the late 1990s. The success story of Bt corn on ECB has been impressive, said Jocelyn Smith, a University of Guelph entomologist.

Traits for ECB benefited those who grew them and helped reduce overall numbers of ECB, which benefited non-traited and organic corn, as well as vegetables, Smith said. The pest feeds on about 200 other crops, she observed during a Michigan State University webinar on June 27. You can view her presentation here: https://www.canr.msu.edu/…

About 85% of growers in Canada and the U.S. use Bt corn to control ECB.

However, in 2018, field-evolved resistance to the Bt protein Cry1F in populations of ECB were discovered in Nova Scotia. Resistance has since been documented in New Brunswick, Manitoba, and Quebec. In 2022, the same field with Cry1F resistance in Nova Scotia was found to also have resistance to the Cry1Ab protein. In 2023, researchers documented unexpected injury to corn hybrids expressing the Cry1A.105 + Cry2Ab2 proteins in Nova Scotia and Connecticut.

While Smith said resistance isn't necessarily widespread, monitoring is kicking into gear. Entomologists are encouraging farmers to scout for first- and second-generation ECB and if it is spotted, to ask for assistance in determining possible Bt resistance levels.

For more information on this pest from the University of Minnesota go to: https://blog-crop-news.extension.umn.edu/…

For information on the original detection in Canada go to: https://fieldcropnews.com/…

Confused by the corn trait alphabet soup? Go to the Handy Bt Trait Table to sort through all the traits and trade names. Find it here: https://www.texasinsects.org/…

BOOTS-IN-THE-FIELD SEASON

White mold, waterhemp, bindweed, sudden death syndrome, black cutworm, Western bean cutworm, Japanese beetle -- you can't outrun the abundant warnings. It's boots-in-the-field season. Here are a few more timely articles to help if "stuff" crops up.

Read DTN's report on rapid corn growth and how that influences greensnap and brittle snap: https://www.dtnpf.com/…

It's the time of year to start digging for answers on soybean cyst nematode (SCN) and see if they are working on soybean roots. Read more here: https://www.dtnpf.com/…

For a refresher course on how to dig for corn rootworm larvae: https://www.dtnpf.com/…

Worried about waterhemp escapes? Here's a recent article from DTN on herbicide resistance:

https://www.dtnpf.com/…

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on social platform X @PamSmithDTN

Pamela Smith

Pamela Smith
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