3 Questions to Ask Your Corn Seed Dealer about Goss’s Wilt Ratings

Goss’s Wilt was reported in several areas of Manitoba during the 2016 growing season. Goss’s Wilt is a bacterial disease and CANNOT be controlled by a fungicide. Managing Goss’s Wilt include weed control, tillage and most importantly rotation and hybrid selection (genetics!). And with the seed ordering season quickly upon Manitoba corn growers, here are 3 questions you should ask your seed dealer about Goss’s Wilt ratings.  The more information you have, the more informed decision you can make.

But before that, some key points:

  • there is no third party data available for Manitoba hybrids;
  • ratings will likely change over time as more years of testing are completed, in different locations and conditions;
  • resistance does not equal immunity! Plants don’t have immune systems and therefore can’t be immune to any disease. Depending on the level of disease pressure, hybrids that are rated as resistant/tolerant can still be infected to some degree. If disease pressure is high (i.e. high inoculum levels, conducive environmental conditions for a long period of time), yield loss due to Goss’s Wilt can still occur in the best rated hybrids.

But First! Before you start asking your seed dealer questions, if you experienced Goss’s Wilt this year perhaps there’s a few questions you can ask yourself (or your neighbor if they had Goss’s Wilt). Was Goss’s Wilt present in every corn field, just one or a few? What were the levels of Goss’s Wilt in individual fields? Do you (or your neighbor) know the resistance rating of those hybrids, both exhibiting symptoms or not exhibiting symptoms? Are you keeping good field notes? While there is no third party data available, you could start making subjective on-farm comparisons (but at the same time recognizing the limitations of those comparisons).

Question 1: What is the rating scale used?  Since there is no universal system for determining Goss’s Wilt ratings in Manitoba, there can be differences between companies and their hybrid ratings. For some companies, a rating scale of 1 to 9 is used, where 1=Poor and 9=Excellent.  However, other companies use the same 1 to 9 scale, but 1 = Resistant and 9 = Susceptible. Then there are others that only use a 1 to 5 scale.  So read the fine print….what does a 3 really mean? And remember, since there is no universal system in Manitoba, you can only really compare between hybrids within a single company.

Question 2: How is the testing done to establish the ratings? Ask if the testing is done under natural infection or through disease nurseries with inoculation.  Relying on natural infection to determine ratings is not as dependable as disease nurseries with inoculation (and wounding). Goss’s Wilt typically shows up in patches and can be very weather –dependent. Also, Goss’s Wilt needs an entry point, often caused by hail, wind damage, etc. No symptoms under natural infection may not indicate resistance, but instead conditions weren’t conducive for infection, i.e. escape.  Artificially inoculated nurseries may be resource intensive, but provide a better chance for determining resistance levels of hybrids being evaluated.

Question 3: Where is the testing done to establish the ratings? For some companies, testing is done in the United States, while other companies have established trials in Manitoba.  Why would this be important? There is variability in the pathogen population, where strains are separated into groups based on DNA analysis. Further research is on-going at the University of Manitoba with funding provided by the Manitoba Corn Growers Association and Growing Forward 2 to determine the strains of Goss’s Wilt present in Manitoba. We are only beginning to understand the pathogen population here in Manitoba so there is more research that needs to be done to fully understand the role of host resistance. In the meantime, testing conducted with disease nurseries and inoculation, either here or elsewhere, is a good step to provide information on hybrid resistance ratings.

Remember, resistance ratings to Goss’s Wilt is only one of many hybrid characteristics producers should consider when choosing their hybrid!

Written by: Pam de Rocquigny, Provincial Cereal Crops Specialist & Holly Derksen, Field Crop Pathologist, Manitoba Agriculture

For more information on Goss’s Wilt, visit Manitoba Agriculture’s website at https://www.gov.mb.ca/agriculture/crops/plant-diseases/goss-wilt.html

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Manitoba Insect & Disease Update – Issue 10: July 20, 2016

The Manitoba Insect and Disease Update is now posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-report-2016-07-20.html

Some highlights from the update:

Insects:

  • Pea aphid levels are still a concern in some pea fields, although many fields will be getting to the stage where management would no longer be economical.
  • Aphid levels have dropped in many cereal fields where previously levels had been increasing. High levels of natural enemies have been noted in some of these fields, and some intense rains may have also contributed.
  • In some areas of Central and Southwest Manitoba, greater than 90% of the wheat midge are expected to have emerged. In many areas of Manitoba about 50 to 90% of wheat midge are expected to have emerged. A reminder that wheat that has already produced anthers is no longer susceptible to feeding by wheat midge. Even if adults are still active in these more advanced fields, the larvae will not feed on the grain.
  • Egg masses of European corn corer are starting to be noted in some fields of corn. So far there are no reports of high levels, but now is the time to be checking fields for the egg masses.
european-corn-borer-egg-masses

Figure 1. Egg masses of European corn borer.

Plant Pathogens:

  • Some infections of blackleg in canola and fusarium head blight in cereals have been reported.
  • A few cases of loose smut in barley were also reported.
  • Two positive identifications of Goss’s Wilt in corn were made. The positive identifications were made based on immunostrips and/or polymerase chain reaction (PCR) assays.

Submitted by: John Gavloski, Entomologist & Pratisara Bajracharya, Field Crop Pathologist, Manitoba Agriculture

Manitoba Agriculture website: www.manitoba.ca/agriculture
Manitoba Agriculture on Twitter: @MBGovAg
Manitoba Agriculture on YouTube: www.youtube.com/ManitobaAgriculture

 

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Goss’s Wilt in Corn: 2014 Manitoba Disease Survey

Goss’s Wilt of corn is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis, and has been present in Manitoba since it was originally identified near Roland in 2009.

In 2014, 74 corn fields were surveyed across the major grain corn growing areas of the province. The disease was detected in 14% of the fields randomly surveyed.  Goss’s Wilt was detected in the rural municipalities (RM) of Roland, Thompson, Dufferin, Montcalm, Morris and Portage la Prairie.  In addition, the disease was observed in the RM’s of Stanley and Rhineland, although not in the fields that were part of the survey. In past years, Goss’s Wilt has also been detected in the RM of Hanover.

Figure 1: Goss’s Wilt provincial survey results where red crosses indicate fields where disease was found and green dots indicate fields where disease was not detected.

Goss's Wilt survey map

Results indicate that Goss’s Wilt has spread to most of the grain corn growing areas of Manitoba, and therefore, is something  that must be scouted for and managed by all growers.

For more information on disease symptoms of Goss’s Wilt, life cycle of the disease, management options and complete methodology and results of the 2014 survey, please view the attached poster which was presented at the 2014 Manitoba Agronomists Conference:

Goss’s Wilt in Corn: 2014 Manitoba Disease Survey (Holly Derksen, MAFRD & Morgan Cott, MCGA)

Submitted by: Holly Derksen, Field Crops Pathologist, MAFRD

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Manitoba Disease & Insect Update – August 8th

A Manitoba Insect and Disease Update for the week of August 4-8, 2014 has been posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-update-2014-08-08.html.

Highlights Include:

  • Scouting for canola diseases has begun. Blackleg, root rots, white mold, aster yellows and alternaria pod blight will be surveyed.
  • Lygus Bugs in canola – The growth stage where canola has the most potential to have yield reduced by Lygus bugs is the early-podding stage.
  • In corn, scouting for Goss’s wilt and leaf blight disease will help growers understand the status in their crop. A few plants are showing common smut, which is not a serious disease.
  • Some have been asking about red mites seen on the wings of grasshoppers.
G

Red mites on grasshoppers.

Submitted by: John Gavloski, Entomologist & Vikram Bisht, Pathologist, MAFRD

 

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Manitoba Insect & Disease Update – July 28 to August 1, 2014

A Manitoba Insect and Disease Update for the week of July 28-August 1, 2014 has been posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-update-2014-08-01.html

Highlights include:

Pathology:

  • Fusarium head blight risk for wheat is moderate to low in different areas of Manitoba. Most of the wheat crops have finished flowering and thus at low risk. By end of the month, Fusarium head blight risk maps may not be needed.
Entomology:
  • Grasshoppers continue to be a concern in some fields.
  • Canola growers should be checking canola for Lygus bugs. Lygus can potentially be of concern when they feed on the pods of canola if levels are high, although feeding to flowering crops is not likely to be economical as canola has a very good ability to compensate for damage to flowers, especially when soil moisture is good. So far Lygus levels appear to be below economic levels in canola, with a few exceptions in the Eastern part of Manitoba.

Note: For those monitoring traps for bertha armyworm, the traps can be removed after you do your counts this week. We have enough weeks of data to know what the regional risks are. Overall trap counts in Manitoba were quite low this year. A map of the cumulative counts, as of July 28th, is posted in the update, and risk maps are also posted at the following MAFRD website (the July 28th map will be posted tomorrow): http://www.gov.mb.ca/agriculture/crops/insects/bertha-armyworm-forecast.html

Submitted by: John Gavloski, Entomologist & Vikram Bisht, Pathologist, MAFRD

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Manitoba Insect & Disease Update – Week of July 21st to 25th

A Manitoba Insect and Disease Update for the week of July 21-25, 2014 has been posted at: http://www.gov.mb.ca/agriculture/crops/seasonal-reports/insect-report-archive/insect-update-2014-07-25.html

Highlights include:

Pathology:
  • Goss’s wilt and leaf blight disease are showing up in corn.

Corn leaf with well developed leaf blight of Goss’s Wilt disease. Photo: Vikram Bisht, MAFRD

  • Ergot disease infection is now showing up in fall rye and grasses.
  • Blackleg infection on lower stems/roots on canola is showing up.
  • Downy mildew on sunflowers is reported.
Entomology:
  • Grasshoppers are starting to mature to the adult stage. How much they move into crops from surrounding vegetation may partially depend on how lush the roadside vegetation remains relative to the crop.
  • Still no soybean aphids found in Manitoba in 2014.

Submitted by: John Gavloski, Entomologist & Vikram Bisht, Pathologist, MAFRD

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Sandblasting Injury in Cereals & Corn

On May 29th, there were extremely windy conditions in some areas of Manitoba.  The strong winds may result in sandblasting injury in young and emerging cereal and corn crops.  Sandblasting injury is caused by winds impacting soil particles against the plant leaves.  Light, sandy soil areas are the most common areas of sandblasting in a field.

Symptoms include:

  • Small abrasions on leaves caused by blowing sand, which are often copper-tone in color
  • Shredding of leaf tissue, making them prone to desiccation
  • Plants may be cut off at the soil surface in severe cases.

In cereal crops the growing point remains below ground until approximately the 5-leaf stage, so if only leaves are affected the plant should recover.  In corn, the same principle applies.  The shredding of exposed leaves is not likely to cause substantial yield loss because the growing point in corn remains below ground until the V5 growth stage.  For cereals and corn, favorable weather will promote development of new leaf growth, so the recent rainfall will help.  However, if the growing point in either crop type has been impacted, reduced stands will likely result.  So the key is to keep scouting for the next few weeks to assess the full impact.

Goss’s Wilt in Corn

In corn, another point to keep in mind is plants that are damaged by hail, wind, or sand-blasting are susceptible to Goss’s Wilt infection as the bacteria can infect corn throughout the growing season and can enter through the wounds caused by sand-blasting.

As you are scouting for Goss’s Wilt throughout the season, focus your attention on fields that are:

  • planted to a Goss’s susceptible hybrid,
  • have a history of Goss’s Wilt,
  • have surface corn residue, and
  • may have been injured by severe weather.

Initial symptoms of Goss’s Wilt include water-soaked lesions on the leaves later accompanied by “freckling”. Bacterial ooze may also occur on the lesion, giving it a wet or greasy appearance. When the ooze dries, it leaves a shiny residue on the surface of the lesion.  More information and photos can be found at: http://www.gov.mb.ca/agriculture/crops/miu/2012/2012-08-24/report.pdf

Submitted by: Pam de Rocquigny, Provincial Cereal Crops Specialist

 

 

 

 

 

 

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Goss’s Wilt in Corn

Symptoms of the bacterial disease, Goss’s Wilt, have been reported in corn fields yet again this season.  Reported hot spots in 2012 include west of Altona to south of Winkler.   This disease causes a leaf and vascular blight which can result in severely wilted plants and yield loss.

Initial symptoms include water-soaked lesions on the leaves later accompanied by “freckling”. Symptomatic leaves often appear shiny due to the bacterial exudate present on the leaf surface. Plants that are damaged by hail, wind, or sand-blasting are susceptible to infection by the bacteria. Wet weather and high humidity favour development of the disease, although disease spread under hot, dry conditions has also been documented.

Management of Goss’s Wilt includes tillage, crop rotation, removal of grassy weed hosts (green foxtail, barnyard grass, etc.), and genetic resistance. Fungicides are not effective against this disease as it is caused by a bacterial pathogen. Genetic resistance is the primary management strategy, and therefore affected growers should contact their seed providers about resistant corn hybrids.

Above information taken from the August 24th edition of the Manitoba Insect & Disease Update.

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