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[1] Southern rust, maize - USA (Kansas)
[2] Ear rots, maize - USA (Minnesota)

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[1] Southern rust, maize - USA (Kansas)
Date: Mon 10 Sep 2007
Source: High Plains / Midwest Ag Journal [edited] <http://www.hpj.com/archives/2007/sep07/sep10/Southernrustinfectingcornfi.cfm>

Moderate to high levels of southern rust in south east and east central Kansas corn fields sounded an alarm for a Kansas State University plant pathologist. "Yield impacts should be minimal there, since many fields are within a few weeks of harvest. In the rest of the state, however, some of the corn still has a lot of growing to do. So, scouting for this disease could be important," said Doug Jardine, crop disease specialist with K-State Research and Extension.

Applying a fungicide to infected corn that's already denting doesn't typically pay in terms of increased yields, Jardine said. It might pay for corn in the soft dough stage if the crop's yield potential is 'exceedingly high'. "But in fields where the disease is attacking corn that hasn't reached those stages, a fungicide application would definitely be worth considering," he said.

The spores of the southern rust-causing fungus are wind-blown. New infections can occur every 7 days, Jardine warned. And, when the humidity is high and temperatures are warm, southern rust can cause so many plant lesions that it results in leaf blighting.

Early southern rust lesions on leaves are small and circular to oval in shape, often with a prominent light green to yellow halo. In contrast, common rust lesions are usually larger and longer. "An even more noticeable difference is that southern rust lesions develop almost exclusively on the upper leaf surfaces. Common rust lesions develop on both upper and lower leaf surfaces," Jardine said. "Besides, southern rust lesions can also develop on stalk, husk, and leaf sheath tissues."

As rust lesions mature, the disease-causing fungus erupts through the leaf surface, and spore pustules emerge. With southern rust, the pustules are light orange to cinnamon-red and can be numerous, even clustered. In common rust, they're a darker brick red to red-brown and fewer in number. As the season progresses, both rusts may darken as they produce black teliospores ("resting" spores) in a ring around the lesions.

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communicated by:
J Allan Dodds
former ProMED-mail plant disease moderator <dodds@ucr.edu>

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[2] Ear rots, maize - USA (Minnesota)
Date: Wed 12 Sep 2007
Source: Agriculture Online [edited]
<http://www.agriculture.com/ag/story.jhtml?storyid=/templatedata/ag/story/data/1189620541636.xml&catref=ag1001>

Not only have the hot and dry conditions and hail affected corn yields in Minnesota this year [2007], but these conditions have also favored development of ear rots. Reports of ear rots have been coming in from several different areas, and the quality of grain that comes off these affected fields may be reduced. Aspergillus and fusarium ear rots may be of particular importance due to the hot and dry conditions in much of Minnesota this year [2007].

Aspergillus ear rot is caused by the fungus _Aspergillus flavus_. This disease can become common under high temperatures and low soil moisture.
Patches of green to yellow spores form on or between kernels. The fungus can become dark green to brown as it ages. It is most common at tips of ears and often only affects a few kernels or small areas of the ear.
_Aspergillus_ species can also cause storage rot. This fungus can invade kernels with moisture levels as low as 15 per cent, especially if kernels have been damaged or have come from rotted ears.

Aspergillus can produce aflatoxin, a mycotoxin that is toxic to animals and humans. The presence of the ear rot does not mean the corn definitely has high levels of aflatoxin. The grain must be tested to determine how much aflatoxin is present. Screening tests are available for aflatoxin.

Fusarium ear rot is caused by the fungi _Fusarium verticillioides_ and _F.
proliferatum_. This disease is commonest when the weather is hot and dry at flowering. Infected kernels have whitish-pink to salmon-colored fungal growth that is often seen at the ear tip, but infected groups of kernels or individual kernels may be scattered on the ear. Infected kernels can have a "starburst" symptom, which appears as white lines radiating out from a point on the kernel without the clear presence of fungal growth. Kernels can also be infected at the embryo end and symptoms may not be visible.
Symptoms may vary according to the genotype of the corn hybrid, environment, or disease severity. Infection is favored by damage to the ears.

Fusarium can produce a mycotoxin called fumonisin, which can be harmful to animals and humans. Fumonisin production is reported to be favored by drought conditions. The FDA [US Food and Drug Administration] has recommended different maximum levels for total fumonisins for animal and human consumption. Grain must be tested to determine the levels of fumonisin that may be present.

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communicated by:
ProMED-mail
<promed@promedmail.org>

[_Puccinia polysora_ causes southern rust in maize. The fungus occurs in most tropical and subtropical regions. The disease can cause significant losses of over 50 per cent. _P. polysora_ needs living host tissue for survival and spores are wind dispersed. The disease is favoured by warm, humid conditions. Resistant or tolerant ('slow rusting') varieties are being developed. Common rust of maize is caused by the related species _Puccinia sorghi_.

Several species of aspergillus can infect maize in the field. _A. flavus_ is mainly a saprophyte degrading dead tissue of any origin, and it is therefore important in nutrient recycling. However, it can also be pathogenic on some plant species causing, for example, one of the fungal ear rots of maize. Spores can be dispersed in soil, by air or carried by insects. The fungus has also great significance as a post-harvest pathogen of many crops since aflatoxin may cause severe poisoning in animals and humans.

Several _Fusarium_ species may be responsible for another type of fungal ear rot. _Gibberella fujikuroi_ (previously _Fusarium verticillioides_) is of concern because it produces the toxin fumonisin. It is probably the commonest pathogen of maize ears throughout the world. _F. proliferatum_ also produces mycotoxins.

Fusarium ear rots caused by _Gibberella fujikuroi_ (_F. verticillioides_), _F. proliferatum_, or _F. subglutinans_, and _Aspergillus_ ear rot caused by _A. flavus_, are often associated with insect damage to ears or kernels which provides easy entrance points for the fungi. For example, ears infested by earworms are usually infected with _Gibberella fujikuroi_.

Map of US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>
Pictures
Southern rust symptoms, photo gallery:
<http://www.ent.iastate.edu/imagegal/plantpath/corn/southrust/>
Common rust symptoms, photo gallery:
<http://www.ent.iastate.edu/imagegal/plantpath/corn/comrust/>
_A. flavus_ infection on maize kernels:
<http://www.ipm.iastate.edu/ipm/icm/files/images/aspercorn.jpg>
_A. flavus_ fungal structures:
<http://www.cbs.knaw.nl/ICPA/ASPFLA2.JPG>
Fusarium ear rot, maize:
<http://www.ent.iastate.edu/imagegal/plantpath/corn/fusarium/fusarium_insect_inj.html> 

Pictures of assorted maize diseases and pathogens:
<http://lubbock.tamu.edu/cornIPM/DiseaseImages/index.html>
Links
Information on southern and common rusts of maize:
<http://edis.ifas.ufl.edu/BODY_VH051>
_Puccinia polysora_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=179511>
_P. sorghi_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=194826>
Information on fungal ear rots of maize, with pictures:
<http://www.cimmyt.org/english/docs/field_guides/maize/pdf/mzDis_earRots.pdf>
Information on _A. flavus_:
<http://www.aspergillusflavus.org/aflavus/index.html>  and <http://www.doctorfungus.org/thefungi/Aspergillus_flavus.htm>
_A. flavus_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=209842>
_G. fujikuroi_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=265414>
_F. proliferatum_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=362256>
_F. subglutinans_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=115356>
Publication 'Mycotoxin prevention and decontamination -- a case study on
maize':
<http://www.fao.org/docrep/X2100T/X2100T05.HTM>
Extension Plant Pathology, University of Kansas:
<http://www.plantpath.k-state.edu/DesktopDefault.aspx?tabid=49>
US Food and Drug Administration:
<http://www.fda.gov/default.htm>.  - Mod.DHA]

[see also in the archive:
Fungal blights, wheat, corn & chickpea - USA (NB, MT) 20070621.2000 Aspergillus flavus contamination, maize - Kenya: human poisoning 20070502.1422
2006
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Aflatoxin poisoning, fatal - Kenya 20060505.1306
2005
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Aflatoxin poisoning, fatal - Kenya 20050514.1324
2004
---
Aflatoxin poisoning - Kenya (Makueni) (06) 20040903.2460 Aflatoxin poisoning - Kenya (Makuei) (04) 20040607.1532 Aflatoxin poisoning - Kenya (Makueni): susp. 20040514.1306
2003
---
Food poisoning, children - China (Hunan, Hubei) 20031114.2822
2002
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Puccinia polysora, southern rust, corn - Argentina 20020205.3486 2000
---
Mycotoxins: a review 20001130.2089
Aflatoxin-producing fungi, resistant crop plants 20000918.1602 Aflatoxin, maize - Africa (Benin, Ghana, Togo) 20000826.1425]

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