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Date: June 2007
[1] _Fusarium_ head blight, wheat & corn - USA (Nebraska)
[2] _Ascochyta_ blight, chickpea - USA (Montana)

[1] _Fusarium_ head blight, wheat & corn - USA (Nebraska)
Date: 18 Jun 2007
Source: North Platte Bulletin [edited]
<http://www.northplattebulletin.com/index.asp?show=news&action=readStory&storyID=12444&pageID=29>

Unusually wet weather is causing scab, or _Fusarium_ head blight, to show up in south central and eastern Nebraska wheat fields, University of Nebraska-Lincoln (UNL) specialists say. However, it is too late in the growing season for wheat growers to combat the problem, said Stephen Wegulo, UNL plant pathologist in the university's Institute of Agriculture and Natural Resources. "This is a really serious problem that is hitting abruptly," Wegulo said. "A lot of growers haven't experienced this and may underestimate the problem." Scab has not been common in Nebraska in recent years due to drier than normal conditions, Wegulo said.

The only way scab can be managed is by planting tolerant cultivars, crop rotation out of cereal grains or grasses, fungicide seed treatments and foliar fungicide applications, which should be timed to prevent infection, which occurs mainly during flowering. Nebraska wheat already has gone through the flowering stage.

Symptoms include premature bleaching of spikelets or the entire immature head. Bleaching can start anywhere on the head and spread until the entire head is bleached, Wegulo said. Bleached spikelets are sterile and contain shriveled and/or discolored seed. During humid conditions, white or pink fungal growth with orange spore masses may be seen on the bleached spikelets. Blue-black fruiting structures also can form, giving the head a scabbed appearance, hence the name scab. The disease can take over an entire field in severe cases.

"During the last few weeks, there have been reports of bleached or white heads in south central and eastern Nebraska wheat fields," Wegulo said. "Surveys in Saline, Saunders, Holt and York counties from 7-11 Jun 2007 revealed these symptoms were caused by scab, or _Fusarium_ head blight."

The toxins

In addition to lowering yields and grain quality, the scab fungus also can produce mycotoxins, said Michael Carlson, UNL diagnostic toxicologist. The total crop may be lost if grain is rejected because of the toxins produced. "Most likely, the fungus will produce vomitoxin (deoxynivalenol) and zearalenone," Carlson said. Vomitoxin was found during the wheat scab epidemic of 1982, and zearalenone was found at a much lower incidence. That was the last year the scab occurred in Nebraska.

Carlson said the presence of zearalenone would be of greater concern than the presence of vomitoxin. Zearalenone acts like estrogen, the female sex hormone, and can affect the reproductive cycle of breeding females, especially pigs. Ruminant animals are not as sensitive as non-ruminants to the effects of zearalenone.

Vomitoxin is not very toxic, Carlson said, but it can affect feeder pig performance. "It is associated with feed refusal in pigs," he said. "Feeder steers and heifers are not adversely affected by vomitoxin in the diet."

"Fumonisins -- common, more toxic mycotoxins -- have not been found in scabby wheat because the species of _Fusarium_ that causes it does not produce them," Carlson said. "In addition, the weather conditions favorable to wheat scab do not favor fumonisin production, and they are usually found in corn."


Implications for corn

Scab may be caused by several species of _Fusarium_ and is favored by wet weather during the growing season. These fungi also cause stalk and ear rots in corn and seedling blights in cereal grains, Wegulo said. "It can survive in soil or corn, wheat and grass stubble. Scab is also more severe in reduced or no-till fields, especially if wheat follows corn," he said.

Spores of the scab fungi are carried by air currents. Most infections occur during flowering because anthers and pollen serve as a food source for the fungi. Infected seed can transmit the fungi to emerging seedlings, Wegulo said. "This can cause severe seedling blight under favorable conditions for disease development," he said.
"During warm temperatures (77-86 F / 25-30 C), blight symptoms appear within 3 days following infections. Therefore, a crop that appeared healthy a few days ago can suddenly show widespread symptoms."

[Byline: by IANR News Service]

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

[Location map of Nebraska at:
<http://www.mapsofworld.com/usa/states/nebraska/maps/nebraska-location-map.gif>
- Mod.JW]

[2] _Ascochyta_ blight, chickpea - USA (Montana)
Date: 18 Jun 2007
Source: Montana State University News [edited] <http://www.montana.edu/cpa/news/nwview.php?article=4928>


_Ascochyta_ blight has been identified on chickpeas in Montana near Bozeman, Billings and Sidney. The rapidly spreading disease is favored by cool, wet conditions such as Montana has been experiencing, said Mary Burrows, Montana State University Extension plant pathologist.

Burrows said that producers with chickpeas should be prepared to spray at least twice with fungicides during the growing season to control the blight. Because the disease can spread very rapidly, producers should spray a fungicide at the 1st sign of disease.
"Producers should scout early and often for symptoms of _Ascochyta_ blight," she said. Those symptoms include circular lesions with black specks that are visible with a magnifying glass. The lesions appear on leaves and stems, and stem girdling and breakage can also be present.

Since fungicide-resistant _Ascochyta_ blight has been identified in North Dakota, it is important to rotate the chemicals used to treat the blight in Montana, Burrows said. No fungicide-resistant _Ascochyta_ has been identified in Montana so far.

The North Dakota strain is resistant to strobilurins, and North Dakota has recommended against using any strobilurins to control _Ascochyta_ this year [2007]. "Once a fungus is resistant to one strobilurin, it generally is resistant to all strobilurins, and we could lose these as a tool to control _Ascochyta_," Burrows said. To avoid that problem, it is important for growers near North Dakota to use non-strobilurin fungicides this year.

Other options to control _Ascochyta_ blight are use of certified seed and seed treatment with thiabendazole to manage seed-borne _Ascochtya_, even if seed has tested to be disease-free.

Small kabuli and desi chickpeas are generally less susceptible to _Ascochyta_ blight, so fewer fungicide applications may be necessary than for large kabuli chickpeas, Burrows said. _Ascochyta_ also attacks lentils and peas, but the species causing the blight in chickpea is different from the ones causing blight in lentils and peas.

[Byline: Mary Burrows <mburrows@montana.edu>]

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

[Location map of Montana at:
<http://www.mapsofworld.com/usa/states/montana/maps/montana-location-map.gif>
- Mod.JW]

[_Fusarium_ head blight (FHB; scab) is an important disease affecting wheat and barley worldwide, with yield losses often exceeding 45 percent. It was 1st described in England and has been a problem in the USA since the early 1900s.
FHB is caused by _F. graminearum_, but 9 phylogenetic species are currently recognized within this species complex. These are often limited to particular regions of the world. At least 4 of these species contain strains capable of causing FHB on wheat. Only one species is currently known to exist in production wheat and barley fields in the USA.

_Fusarium_ ear rot produces a white to pink mold on corn cobs, with infected kernels often scattered amongst healthy looking ones.
Several _Fusarium_ species may be responsible, but _F. verticillioides_ is of primary concern in the US, since it produces the toxin called fumonisin.

_Ascochyta_ blight of chickpea is caused by _Ascochyta rabiei_ and is considered to be the most important disease of chickpeas worldwide.
The pathogen attacks all aerial portions of the plant and is specific to chickpeas. It can survive in infected plant material for at least 2 years under dry conditions, but viability is lost rapidly in high humidity. The fungus is seed borne at a rate of 50-80 percent. Seed transmission is the primary mode of spread both locally and worldwide.

_A. lentis_ causes blight in lentils and _A. pinodes_ in peas.

Strobilurins are strongly antifungal agents produced by fungi. They were 1st discovered in 1977 in _Strobilurus tenacellus_, a basidiomycete growing on pine cones.

Map of US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>

Pictures
Head blight symptoms, wheat:
<http://www.nwroc.umn.edu/Cropping_Issues/2005/issue6/FHB_examples.jpg>
Ear rot symptoms, maize:
<http://www.ent.iastate.edu/imagegal/plantpath/corn/fusarium/fusarium_insect_inj.html>
_Ascochyta_ blight on chickpeas:
<http://pdc.unl.edu/othercrops/chickpea/ascochyta_blight/leaves.htm>  and <http://pdc.unl.edu/othercrops/chickpea/ascochyta_blight/pods.htm>

Links
_Fusarium_ head blight information:
<http://www.apsnet.org/education/feature/FHB/>  and <http://smallgrains.psu.edu/pdf/FusariumHeadBlight.pdf>
_F. graminearum_ current species complex and FHB information:
<http://www.ars.usda.gov/Main/docs.htm?docid=9821>  and <http://www.cdl.umn.edu/pubs/pdfs/HCK/Pathogen_Profile.pdf>
_F. graminearum_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=200256>
Information on _Fusarium_ ear rot of maize:
<http://www.ipm.ucdavis.edu/PMG/r113101211.html>
_F. verticillioides_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=314223>
Information on the mycotoxins via:
<http://cropwatch.unl.edu/>
Information on chickpea _Ascochyta_ blight:
<http://highplainsipm.org/HpIPMSearch/Docs/AscochytaBlight-Chickpea.htm>  and <http://pdc.unl.edu/othercrops/chickpea/ascochyta_blight/>
_Ascochyta_ blight symptoms:
<http://paridss.usask.ca/specialcrop/pulse_diseases/chickpea/ascochyta.html>
_A. rabiei_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=275994>
Information on strobilurins:
<http://www.ibwf.de/ibwf_his&act_en.htm>,
<http://www.answers.com/topic/strobilurin>
History and development of strobilurins:
<http://www.grounds-mag.com/mag/grounds_maintenance_strobilurin_fungicides_natures/>
- Mod.DHA]

[see also in the archive:
2005
----
Fusarium head blight, wheat - USA (MN, ND) 20050812.2366 Wheat diseases, cereals - USA (ND) 20050731.2227 Wheat diseases - India 20050615.1683
2003
----
Ascochyta blight, chickpea - Chile 20030604.1368
2002
----
Fusarium head blight, oats - Canada (Manitoba) 20021017.5573 Ascochyta blight, chickpea - USA (Nebraska) 20020710.4714
2001
----
Fusarium head blight, wheat - USA (Michigan) 20010725.1452 2000
----
Fusarium head blight: biological control 20000824.1416 Fusarium head blight, cereal - Canada (Manitoba) 20000823.1405 Fusarium head blight fungicide approved - Canada 20000624.1038
1999
----
Scab disease, wheat - Canada, USA 19990508.0756 Scab-resistant wheat, McVey cultivar - USA 19990801.1311]

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