Two Corn Diseases To Keep An Eye On This Summer

Two Corn Diseases To Keep An Eye On This Summer

In some areas of Iowa in 2014 Northern Corn Leaf Blight is prevalent; so far only a few fields have Goss's wilt.

In their weekly telephone conference call, Iowa State University Extension field agronomists are reporting fields with Northern Corn Leaf Blight in most areas of the state in mid-July 2014. But it's at low levels of infestation in those fields—so far. If you are thinking about applying a foliar fungicide and are considering the choices of products available—scouting your fields and knowing for sure which diseases are present can help you make the best decision, they say.

Large elliptical lesions of Northern corn leaf blight.

KEEP SCOUTING: Northern Corn Leaf Blight (pictured) is being reported in a number of Iowa fields in mid-July 2014. You really have to look hard, however, to find any Goss's wilt, say ISU agronomists. But it is early and favorable disease conditions may be back next week.

"If there is Northern Corn Leaf Blight or Gray Leaf Spot or other fungal diseases present, these diseases can be managed with fungicides," says Clarke McGrath, ISU Extension agronomist at Harlan in western Iowa. "You'll want to consider using the preventative/curative products rather than just the straight preventatives. This NCLB link to the website will show you the product choices, and they are numerous." That link you can click on is: Northern Corn Leaf Blight (NCLB).

Spraying fungicide won't do anything on Goss's wilt
What does McGrath have to say about Goss's wilt? "What I'm finding at this time is pretty sporadic," says McGrath. "I've only seen Goss's wilt in a few fields so far this summer, and it was at pretty low levels. You have to really hunt for it. That doesn't mean it isn't out there in force somewhere, but so far it seems most of our area here in western Iowa is at pretty low levels. Goss's can ramp up pretty quickly on susceptible corn hybrids though, begging the question—what can we do about it?"

Goss's wilt is bacterial—it's caused by a bacterial pathogen, not a fungal pathogen. So, fungicides do absolutely nothing to control it. There are a few bactericides out there being marketed for control of Goss's. "But we have little solid information to go on for sure, when making recommendations whether or not to spray for Goss's wilt," he notes.

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McGrath says what he advised farmers to do a couple years ago when there was Goss's wilt showing up in some cornfields still probably holds true for in-season management of Goss's wilt today. Here's what McGrath wrote previously in his Wallaces Farmer column two years ago:

University preliminary tests on bactericide/fungicide combo
Procidic is a product advertised as a broad-spectrum fungicide and bactericide combination with citric acid as an active ingredient. Research we are familiar with reports on the effect of citric acid on fungal pathogens of horticultural crops, but no reports of results against bacterial diseases, and no reports on corn. Procidic is labeled for use in Iowa to control Goss's wilt, and ISU plant pathologist Alison Robertson is in the process of evaluating it in depth for Goss's management.

Another product that has been suggested for use to manage Goss's wilt is Kocide. At last check, while Kocide was labeled for field corn, it wasn't listing Goss's as a target pest; this is a gray area where you will want to check with your local ag chemical dealer. Since it may be labeled in the future, several Midwest universities are looking at this product. Preliminary work from University of Nebraska was inconclusive.

A third product ISU agronomists are often asked about is a copper-based product called Intercept. There is very little information available on this product. Apparently it has been used successfully to control citrus canker, which is caused by a bacterium. But there is no published information on the efficacy of Intercept against Goss's wilt or citrus canker. Research will likely be done on this product as well in the future.

Why don't we have updated information on these products?
As we look at how similar products are used in citrus and vegetable crops, it becomes evident that it will be challenging to find the right fit for products like these against Goss's wilt. These products don't "cure" bacterial diseases; rather, they are more effective as preventatives with some suppressive capabilities. Multiple applications are mentioned in the label language of some of the products, so scouting after treatment is a must and if Goss's continues to be an issue, you'll have to consider making another spraying pass.

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This of course raises the question—why don't we have the updated information on these bactericides on Goss's? Many Midwest Land Grants tried to do Goss's research (including pretty extensive efforts in both of these years by ISU)… Mother Nature didn't play ball, though. Trials conducted in 2012 and 2013 had little to no disease present in the field due to the dry weather not completing the disease triangle. That is, the pathogen must be present at problematic levels, you must have susceptible crop genetics, and you must have the proper weather for sustained infection of the disease. That's the triangle.

Research Goss's wilt control is being conducted this year
"More research is being conducted this year; so far it looks like we may have the triangle completed so we can get some relevant data on the few products submitted for testing," observes McGrath.

McGrath sums up the situation with this advice: "The good news is that many, probably the majority, of our corn hybrids planted in west central and southwest Iowa today are pretty tolerant/resistant to Goss's wilt. So, we advise farmers to check with their seed supplier and find out which, if any, of the hybrids they've planted need to be watched more closely for Goss's. If it is showing up in the field at levels you are uncomfortable with and the weather looks like it will be favorable for continued infection… your only choices are to leave it and see what happens, or to take a shot at managing it with products we have little experience with. I would like to provide a better answer, but that is our reality in dealing with Goss's wilt at this point in time."

Other sources of information he advises you read:
* Fungicide Applications may be more profitable this year according to ISA info.

* And a few thoughts from Dr. Mueller, Dr. Robertson and McGrath.

* And to make things more interesting, we are seeing some Northern Corn Leaf Blight start to show in our area, here is an article about that.

TAGS: Extension
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