Soybean losses from diseases

May 28, 2015 in Soybean Disease Management, Soybean diseases

For several years we have been collecting data on soybean yield losses attributable to diseases and nematodes.  These data can be accessed online through the University of Illinois: click here

In 2014 Soybean Cyst Nematode again was the most damaging issue, followed by Sudden death syndrome and seedling diseases.

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Irrigation and Fusarium head blight

May 19, 2015 in Barley, Barley diseases, Wheat, Wheat Diseases

Rain early in the week caused a slight elevation in scab risk for flowering wheat. I expect most of the remaining wheat in Delaware will be flowering next week. Even though it has been a dry season I must caution against irrigation from the start of flowering until 5 days post flowering. This is the most critical time for scab development and any moisture increases your risk at a local level for elevated DON and scab, particularly if you planted a variety that is susceptible to scab. To mitigate localized elevations in scab and vomitoxin, try and fill the soil profile before heads are fully emerged, then continue to irrigate, at least 5 days after flowering has completed. Also, if you do decide to irrigate, try and do as much as possible during the day to allow heads to dry at night. Remember that Caramba, Prosaro, and Proline, at best, give you 45-50% suppression of DON and scab.

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Soybean seed treatment efficacy tables available

May 12, 2015 in Soybean, Soybean Disease Management, Soybean diseases

Seedling diseases in soybeans are not often a huge issue in Delaware. but can be problematic in other parts of the Midatlantic.  One reason we do not often have major issues with seedling diseases of soybeans is the texture of our soils.  Most often seedling diseases take off when soils are wet and waterlogged because either the pathogen does well under these conditions (Pythium, Phytophthora) or the stress caused by the waterlogged soil allows for easy colonization of the roots (Fusarium, Rhizoctonia).  This condition does not occur that often in the coarse textured, sandy soils in many parts of Delaware.  That being said, it is still important for producers, consultants, and industry personnel to understand seed treatments options if for no other reason than to understand what the various active ingredients do and how well they may work.

The members of the Identification and Biology of Seedling Pathogens of Soybean project funded by the North Central Soybean Research Program and plant pathologists across the United States have developed the following ratings for how well fungicide seed treatments control seedling diseases of soybeans in the United States. Efficacy ratings for each fungicide active ingredient listed in the table were determined by field-testing the materials over multiple years and locations by the members of this group, and include ratings summarized from national fungicide trials published in Plant Disease Management Reports (and formerly Fungicide and Nematicide Tests) by the American Phytopathological Society at http://www.apsnet.org. Each rating is based on the fungicide’s level of disease control, and does not necessarily reflect efficacy of fungicide active ingredient combinations and/or yield increases obtained from applying the active ingredient.

The table and ratings can be found by clinking the following link:  2015 Soybean Seed Treatment Fungicide Efficacy Table_final

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Herbicide drift of leaf blotch on small grains?

May 4, 2015 in Barley, Barley diseases, Wheat, Wheat Diseases

gramoxone damage wheat 2015

Herbicide damage on wheat. Note the tan/brown lesion with no yellow margin.

Over the last week we have seen small grains with a small amount of damage to the upper canopy.  Damage includes sparse flecking or brown leasions forming in the upper canopy, with little to no injury lower in the plant.  Lesions are often light brown to white and do not have clorotic halos or black pin heads within the lesion.  Some individuals were worried that this may be Stagonospora, Septoria, or Tan spot lesions in wheat or net blotch and scald in barley.

 

In nearly all the cases I’ve seen this symptom is more likely due to herbicide drift (e.g. gramoxone) blowing in from corn fields being planted in the vicinity.  How can you tell herbicide drift from foliar diseases?

1) Lesions from herbicide drift will not increase over time

2) Lesions from herbicide drift will not contain brown (Stagonospora) or black (Septoria) structures within the lesions

3) Lesions caused by herbicide drift are often scattered and present on the top of leaves.  Leaf blotch diseases move from the residue up the plant.  Therefore, expect to see lesions in the lower, mid, and upper canopy.  Lesion incidence and severity are likely to be greater in the lower and middle canopy as well

4) Leaf blotch lesions can have distinctive shapes or characteristics.  Lesions caused by Stagonospora are elliptical.  Tan spot lesions often have a distinct yellow boarder.  Net blotch lesions are black with a stringy appearance.

gram spot wheat

Lesions caused by herbicide drift are sparse, often located in the upper canopy, and do not grow over time as opposed to leaf blotch diseases.

 

wheat_septoria tritici_far

Septoria leaf blotch on wheat.

DSC_0158

Spot blotch / net blotch on barley

barley scald

Barley scald with distinctive cream colored lesion centers and black/purple margins

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Soybean and Corn Fungicide Efficacy Sheets Available

April 22, 2015 in Corn, Corn Disease Management, Soybean, Soybean Disease Management

Our ratings for soybean and corn fungicides are now available.  To access these sheets click the links below:

Soybean Fungicide efficacy table_2015_final (3)

CDWG Fungicide efficacy table_2015_final (2)

We determine these relative ratings based off of the results of local efficacy trials.  We (plant pathologists) from around the nation then discuss our results and compile them to form these rating sheets.

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Review and history of Cucurbit Downy Mildew

April 18, 2015 in Vegetables

Downy mildew of cucurbits is a serious disease for vegetable growers in the Midatlantic.  The epidemic in 2004 changed the way we manage this disease.  The downy mildew picture continues to change, and we continue to learn more about this pathogen and its management.  A recent article published in the journal Plant Disease gives an excellent overview of the history of this disease and the current knowledge status.  The article can be found by clicking this link:  CDMReviewpdis-09-14-0990-fe

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2015 wheat fungicide table now available

April 13, 2015 in Barley diseases, Wheat, Wheat Diseases

Each year our national wheat pathology working group gathers and publishs an updated list of fungicides for small grains.  We utilize our local data to determine the relative performance of products on specific diseases.  This year’s list is changed somewhat from last years.  Please note the footnote on fungicide resistance in leaf blotches at the bottom of the table.

The table can be accessed by clicking the following link: NCERA 184 Wheat fungicide table 2015_V3

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New work on tillage and fungicides for Phomopsis and Purple Seed Stain in soybean

April 3, 2015 in Soybean, Soybean Disease Management, Soybean diseases

Phomopsis seed decay (PSD) and purple seed stain (PSS) are two seed-borne diseases that can impact soybean quality.   PSD-infested seeds are often lightweight and show reduced germination, whereas PSS infected stain often develops a purple discoloration.  PSS also can result in leaf blighting and seedling death in some instances.   Therefore, both PSD and PSS can reduce value of soybean grown for seed or sent overseas.  Management of these diseases often is achieved by planting clean, certified seed, crop rotation, deep tillage to bury infested residue,  and in very limited situations, fungicide applications between R3 and R5.  Many growers are switching to no-till or conservation-tillage systems, which may influence the severity and incidence of soybean diseases such as PSS and PSD and also impact disease management.  Unfortunately, there simply isn’t much out there in terms of replicated, applied research in this area.

Researchers at The University of Tennessee conducted trials over a 4 year span that looked at the impact of tillage and fungicides on PSD or PSS.  However, the use of a fungicide reduced PSD in tilled but not no-tilled settings.  In addition,the application of Headline at either R3 or R5 resulted in greater levels of PSS across tillage treatments.  Their results were recently published in the journal Crop Protection.

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2015 small grains disease outlook

March 28, 2015 in Barley, Barley diseases, Wheat, Wheat Diseases

For the second year in a row, we are dealing with the aftermath of a cold, prolonged winter.  In addition, a wet end to the summer resulted in much of the small grains being planted later than normal.  How might this impact the 2015 diseases and what should you be looking for?

Barley yellow dwarf virus (BYDV) is unlikely to show up in any significant amount.  This virus is spread by several species of aphid, and severity and intensity is related to the amount of aphid activity early in the season.  Late plantings coupled with a cold, prolonged winter make it highly unlikely to see much of this disease in 2015.  BYDV symptoms will be most evident around heading, and manifest as discolored flag leaves, stunted plants, and deformed heads.

Other cool season viral diseases that prefer wet soils, such as Wheat Spindle Streak Virus may be more pronounced in fields where this virus has appeared in the past.  Look for stunted, plants before Feekes 8.  Stunted plants often occur in low lying areas of the field , but may also be found throughout the field in some instances.  Viruses can only be confirmed through special tests such as PCR or ELISA.

A cool , delayed spring means that our crop is a behind.  The cool temperatures in the south have resulted in flare ups of Stripe rust.  Stripe rust needs to blow up to our region from southern areas, and the combination of a high inoculum load in the south, cool temperatures, and a delayed crop increase the chance that we might see a bit of this disease in 2015.  Keep an eye out for this disease as under the right conditions flare ups can cause some significant reductions in yield.  Click here for a detailed factsheet from KSU on stripe rust.

 

 

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Glyphosate application does not increase Soybean Sudden Death Syndrome

March 9, 2015 in Soybean, Soybean Disease Management, Soybean diseases

Sudden death syndrome (SDS) is a soilborne disease of soybeans caused by the fungus Fusarium virguliforme.  This disease infects soybeans during the seedling stage during prolonged periods of cool, moist weather, resulting in root rot.  Rains at the reproductive stage of growth cause the fungus to deeply colonize the roots and produce a toxin, resulting in the characteristic interveinal necrosis.

A leaf with interveinal chlorosis characteristic of SDS

A leaf with interveinal chlorosis characteristic of SDS Photo by N. Kleczewski

If you are lucky, you will see blue growth around the soil line, which is indicative of SDS.

Blue growth (within circle) on the roots or soil line indicates the presence of SDS.  Photo by N. Kleczewski

Blue growth (within circle) on the roots or soil line indicates the presence of SDS. Photo by N. Kleczewski

 

SDS has become a yield-limiting disease in high input fields in the Midwest, and is present at low levels in the mid-Atlantic.  Glyphosate-resistant soybeans are commonly planted because they facilitate weed management.   Over 90% of soybeans planted in the United States contain glyphosate resistance.  There have been reports of glyphosate related issues with diseases in soybeans, including SDS, with some studies showing an increase in disease, and others indicating a reduction of disease when glyphosate is used.

A paper recently published in Plant Disease  examined the effects of glyphosate on SDS severity, grain yield, and plant nutrition in studies conducted across five states in the US  and one site in Ontario, Canada from 2011-2013.  What did they find?  There were no effects of herbicide on disease, and treatments with glyphosate tended to yield more than treatments with non-glyphosate containing herbicides.  In addition, there were no effects of glyphosate on plant nutrition.   For additional information follow THIS LINK

Reference: Kandel, Y. R., Bradley, C. A., Wise, K. A., Chilvers, M. I., Tenuta, A. U., Davis, V. M., Esker, P. D., Smith, D. L., Licht, M.A., and Mueller, D. S. 2015. Effect of glyphosate application on sudden death syndrome of glyphosate-resistantsoybean under field conditions. Plant Dis. 99:347-354.
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