Corn looks beautiful from the road, but crop consultants are looking for Goss's wilt signals

  We're fortunate that Goss's wilt doesn't challenge the corn crop every season like it did in 2011, and again in 2015.  But it's advisable to scout this season's fast-growing corn for early signals of this bacterial disease. Symptoms vary, and a good refresher is to browse this article written by Alison Robertson, Department of Plant Pathology and Microbiology at Iowa State. 

June 15, 2018 — The symptoms vary considerably, and diagnosis can zero in more reliably if you use an Immunostrip test from Agdia of Indiana

Choose the "ImmunoStrip® for Clavibacter michiganensis subsp. michiganensis" -- a five-strip packet is $55 plus shipping.  The Agdia website will select FedEx shipping for you, but if you ask for delivery via the U.S. Postal Service, it's about half the cost of Fed Ex. 

Ground-level corn leaves show symptoms
which Bob Streit attributes to Goss's wilt

 

On May 13, Iowa crop consultant Bob Streit went on Goss's wilt patrol in central Iowa. The nearby photo came from that scouting trip. He reported on an e-mail to clients including us:

"It was about the right time and right growth stage so I was looking for brownish colored lesions at ground level on the corn plants in a field I was in last night. They were present as shown faintly in the pictures. So the timing will be right this and next week for the first application of Bio Empruv."

He found symptoms in most fields, and told us "I'd bet my eye teeth they'll test positive for Goss's wilt."

The Bio Empruv product Bob mentions is a biologically active agent he has found effective against bacterial disease. It was formulated by biochemist Dr. Salam Awada. We tested the early versions of it a few years ago, foliar-applying it with a Hagie sprayer post-tassel — which is far too late for the most beneficial timing. Yet it showed economic results. Bob and his partner Marv Mortensen at Central Iowa Agronomics can provide the product to growers. For a thorough overview of Bio Empruv, here's a link with several videos and other detail on their website

In 2015, we published a report by Bob Streit on the difficulties with Goss's wilt that season. It's still very relevant, and you can read it here. Our field studies showed that foliar applications of Bio Empruv had enhanced effectiveness when tank-mixed with WakeUP Summer to improve leaf coverage, penetration and systemic transfer into the corn.

Light symptoms were showing up today
on this corn in Black Hawk County,
northeast Iowa.

We're based in northeast Iowa, almost on the border between Black Hawk County and Grundy County. Some of the nation's best soils for corn production are under our feet. A scouting trip this morning showed garden-of-Eden corn ranging from V5 to V9. Few fields here showed disease symptoms of any kind. However, some did present lesions on those basal leaves which looked similar to those Bob found in central Iowa.

This is how the sample of June 15, 2016 tested.
Two definite red lines but not sharp and bright.

Although these leaves tested positive for Goss's with the Immunostrip "stick," the two red lines were not clear-cut. Our reagent is outdated and we want to check again when a new supply comes from Agdia. When we asked Bob Streit about this indistinct reaction, he said, "My guess is that the infections are new and still quite small in size and quantity of sugar by-products that cause the immune reaction of the kit. We saw that early in the season when symptoms were still faint. Sometimes it took overnight for the two faint lines to appear. Then later in the season when the symptoms left no doubt due to their strong appearance, it often took less than 30 seconds for the two lines to appear."

Update June 21: A packet of new agdia strips arrived today and we sampled the same field. the readings looked the same as in those above: Definite lower red line, faint upper red line. Probably the infections are very slight.  So far, so good.

 

Two distinct red lines on the Immunostrip
signal a positive reaction to Clavibacter.
This photo is from a previous test in 2015.
Our test this season showed two red lines,
but they weren't as distinct as in this photo.

 

In previous years, counties in central and southeast Iowa have typically encountered worse Goss's wilt problems than us tundra dwellers in northern counties of Iowa and on into Minnesota. 

While you're doing your refresher homework on Goss's wilt, an excellent scientific paper was published a few months ago and is available to the public at this link.   We've also locked a permanent link to a PDF of the report on our site at this link; download it here.

This paper's exhaustive data analysis by five authors (including Alison Robertson and colleague Tamra Jackson, Department of Plant Pathology, University of Nebraska) reveals what looks like a "first" to us. By examining the correlations of many "management factors" with the occurrence and severity of Goss's wilt, the researchers were able to create a chart showing the degree of association between each of several agronomic management factors and the incidence of the disease. For example, planting a hybrid rated as vulnerable to Goss's wilt emerged as having the closest correlation to getting the disease. High population was close behind, as you might expect, because increased populations intensify stress. Lower in the array of practices were planting date and residue cover. Surface residue has been long suspect for harboring the clavibacter bacteria. 

Interestingly, the management practice "glyphosate application" is among the top third of agronomic factors related to incidence of the disease. This study is the first we've seen suggesting that glyphosate treatment is related with Goss's.

The study did not include the "agronomic practices" of GMO-traited corn and non-GMO corn. That probably would have been difficult, as over 80% of Midwest fields are traited hybrids.