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[1] Eyespot, grey leaf spot - Iowa, Nebraska
[2] Crazy top - Iowa
[3] Grey leaf spot - Kansas

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[1] Eyespot, grey leaf spot - Iowa, Nebraska
Date: Sat 18 July 2009
Source: Wallaces Farmer [edited]
<http://wallacesfarmer.com/story.aspx?s=24974&c=9>

Alison Robertson, Iowa State University Extension plant pathologist, has been scouting corn fields. Eyespot is the "disease of this summer" -- so far -- in 2009. "Eyespot loves wet and cool weather so it is probably not surprising that the disease is especially prevalent this year [2009]. If such weather continues, we can expect the disease to spread," says Robertson. Early and severe eyespot can result in yield loss on susceptible corn hybrids. Furthermore, increased [bacterial] stalk rot severity is associated with severe eyespot disease.

Gray leaf spot (GLS) is now starting to show up on the lower leaves of susceptible corn hybrids across the state of Iowa. Tamra Jackson, Extension Plant Pathologist at University of Nebraska-Lincoln, reported GLS is highly prevalent at this time in Nebraska, occurring slightly earlier than normal in that state, and the severity is increasing.

"Here in Iowa, the disease is perhaps a little ahead of schedule,"
says Robertson. "GLS infections in June and early July were associated with the epidemics of GLS in Iowa in the mid 1990s." GLS can result in considerable yield loss particularly when the disease spreads to leaves above the ear soon after tasseling. High GLS severity may also increase the risk of stalk rot.

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[2] Crazy top - Iowa
Date: Tue 14 July 2009
Source: Wallaces Farmer [edited]
<http://wallacesfarmer.com/story.aspx?s=24847&c=9>

The Plant Disease and Insect Diagnostic Clinic at Iowa State University recently received some corn plant samples with symptoms and signs of crazy top, a disease caused by [the fungus] _Sclerophthora macrospora_. Symptoms of this disease vary greatly with time of infection and degree of host colonization by the pathogen. Generally, excessive tillering, rolling and twisting of the upper leaves appear first. Later, infected plants produce a "leafy"
tassel. Flooding is how disease spores can infect corn. Diseased grasses may also be a source of inoculum. Although seed transmission of the pathogen has been demonstrated from freshly harvested seeds, it is generally considered unimportant in the spread of the pathogen.

Crazy top is not a severe disease but it can cause significant losses in low-lying areas of fields that are prone to flooding, since infected plants are often barren. This disease is best managed by improving field drainage or by avoiding low, wet areas in fields.
Rotation may be helpful if care is taken to keep rotational fields free of grassy weeds. Pulling up and discarding infected plants can reduce buildup of inoculum in the field, and thus reduce the risk of disease in subsequent years.

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[3] Grey leaf spot - Kansas
Date: Thu 16 July 2009
Source: Southwest Farm Press [edited]
<http://southwestfarmpress.com/grains/gray-leaf-spot-0717/>

Some parts of Kansas have had recurring problems with gray leaf spot in corn and this year [2009] is no exception, according to a Kansas State University scientist.

"Recent surveying has indicated that it will be a very good year for gray leaf spot in many of the areas where it has traditionally been a problem," said K-State Research and Extension plant pathologist, Doug Jardine. Scouting of fields should be done prior to any fungicide applications. Many of the new hybrids have improved tolerance to gray leaf spot and may not require a fungicide application.

"If you have lesions on the ear leaf at tasseling, you need to spray regardless of the rated resistance," Jardine said. "Reduced rate applications are strongly discouraged because of the possibility of fungicide resistance development," he added.

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[Eyespot of maize is caused by the fungus _Kabatiella zeae_, grey leaf spot by _Cercospora zeae-maydis_, and crazy top by _Sclerophthora macrospora_. An epidemic of grey leaf spot is feared at this time to develop, especially in Nebraska (see links for additional stories below). For more information on the fungal pathogens and bacterial stalk rot see links below.

Maps of USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html>,
<http://www.mapsofworld.com/usa/usa-state-and-capital-map.html>  and
<http://healthmap.org/r/009V>

Pictures
Photo gallery of GLS symptoms:
<http://www.ent.iastate.edu/imagegal/plantpath/corn/grayleafspot/>
Eyespot symptoms:
<http://www.inra.fr/internet/Produits/HYP3/images/6033157.jpg>,
<http://www.inra.fr/internet/Produits/HYP3/images/6033153.jpg>,  and
<http://www.invasive.org/images/768x512/1265065.jpg>
Maize crazy top:
<http://www.btny.purdue.edu/Extension/Pathology/CropDiseases/corn/Img/Small/New-crazy-top.jpg>

Links
Additional news stories, grey leaf spot Nebraska:
<http://cropwatch.unl.edu/archives/2009/crop19/corn_grayleafspot.htm>  and
<http://www.agriculture.com/ag/story.jhtml?storyid=/templatedata/ag/story/data/1247579244980.xml>
Information on maize grey leaf spot:
<http://agriculture.kzntl.gov.za/portal/Publications/TechnicalInformation/GreyLeafSpotofMaize/
tabid/280/Default.aspx> 
and
<http://www.btny.purdue.edu/Extension/Pathology/CropDiseases/Corn/corn1.html#grayleafspot>
Information on maize eyespot:
<http://www.inra.fr/internet/Produits/HYP3/pathogene/6kabzea.htm>  and
<http://www.extension.iastate.edu/Publications/PM963.pdf>
Information on maize crazy top:
<http://www.lgseeds.com/lg_tech2/crazytop.asp>
All fungal taxonomy via:
<http://www.indexfungorum.org/Names/Names.asp>
Information on bacterial stalk rot of maize and sorghum:
<http://pdc.unl.edu/agriculturecrops/corn/bacterialstalkrot>,
<http://cropdisease.cropsci.illinois.edu/corn/Bacterialstalkrot.html>,  and
<http://www.ncbi.nlm.nih.gov/pubmed/857508>.  - Mod.DHA]