Assessing the risk of white mold (Sclerotinia stem rot) of soybean in 2013

White mold of soybean (a.k.a. Sclerotinia stem rot), caused by the fungus Sclerotinia sclerotiorum, is a disease that can occur in the northern half of the state in cool, wet years.  The most recent white mold epidemic in Illinois occurred during the 2009 season, where several fields in the northern half of the state were affected.

The white mold fungus overwinters in the soil as, small, black, and dense structures known as sclerotia.  These sclerotia germinate and form mushroom-like structures known as apothecia when soil remains moist for several consecutive days and soil temperatures are at 60 degrees F or below.  These apothecia generally will not form until the soil is shaded from sunlight due to soybean canopy closure.  Spores of the white mold fungus are shot out of the apothecia and land on senescing flower petals, where infections first occur on the soybean plants.  The white mold fungus becomes inactive when temperatures within the soybean canopy are above approximately 82 degrees, so infection and disease development may cease or slow down during periods of hot and dry weather.  The 2013 season started out similar to the 2009 season, with frequent rainfall and cool temperatures, but warmer and drier conditions have been observed more recently.

 

Fig. 1. Apothecia of the white mold fungus germinating from a sclerotium. Image courtesy J. Venette, North Dakota State University.

 

Fig. 2. Soybean plant with symptoms and signs of white mold (a.k.a. Sclerotinia stem rot). Image by C. Bradley.

 

So, what does the risk of white mold look like for 2013?  This is not an easy question to answer since we have had fairly favorable weather for white mold initially with some stretches of non-favorable weather in-between.  In fields that were not planted late and have been in full-canopy for the last couple of weeks, it is likely that apothecia have developed and that some infections may have occurred already.  However, the progression of infection and disease development likely came to a stop with the hot and dry conditions observed last week.  For fields planted later that just recently closed their canopy (or have not yet closed their canopy), apothecia likely have not emerged because of the hot dry weather experienced last week.  The weather from this point forward will likely dictate how bad white mold will be in 2013, although, I believe that it is safe to say that it will be less severe and less widespread than it was in 2009.

In University of Illinois research trials, some fungicide products have shown efficacy against white mold.  Foliar fungicides will not provide complete control of the disease, but may reduce disease.  The results of University of Illinois trials conducted in 2009 and 2010 are shown in Tables 1 and 2.  Note that some of the more popular, frequently marketed fungicides are not listed in the tables since many do not have white mold on their label because of no to poor efficacy.  In these trials, the primary targeted growth stage to apply foliar fungicides was at R1 (beginning flower).  Because of the late-planted soybean fields this year, R1 may occur before canopy closure.  If this is the case, then an application at canopy closure (rather than R1) might be more effective in protecting against white mold.  Also note that some treatments in these research trials were applied twice during the season (R1 and again 7-9 days later).

 

Table 1. Results of soybean foliar fungicide research trials focused on white mold conducted in 2009 at the University of Illinois Northern Agronomy Research Center (DeKalb County).

Treatment Rate/A Incidence (%) 

8-11-09

Incidence (%) 

9-14-09

Yield (bu/A)
Untreated check 75 95 24
Topsin 4.5 L 20 fl oz 43 96 24
Proline 3 fl oz 38 95 24
Domark 5 fl oz 68 98 23
Cobra herbicide 12.5 fl oz 15 51 42
Endura (2x)* 8 oz 38 86 39
Aproach (2x)* 8 fl oz 35 80 40
LSD 0.05** 33 15 8

*All treatments were applied at the R1 growth stage (July 20, 2009).  Treatments followed by “(2x)” were applied again 9 days later.

**Least significant difference (alpha level = 0.05).  Treatment values that differ by this number can be considered significantly different from one another.

 

Table 2. Results of soybean foliar fungicide research trials focused on white mold conducted in 2010 at the University of Illinois Northern Agronomy Research Center (DeKalb County).  Funded in part by the Illinois Soybean Association.

Treatment Rate/A Incidence (%) 

8-11-09

Incidence (%) 

9-14-09

Yield (bu/A)
Untreated check 18 95 62
Topsin 4.5 L 20 fl oz 9 83 61
Proline 3 fl oz 11 93 64
Domark 5 fl oz 7 76 63
Cobra herbicide 6 fl oz 6 86 56
Endura 8 oz 4 79 69
Aproach (2x)* 8 fl oz 11 79 66
LSD 0.05** 11 NS 8

*All treatments were applied at the R1 growth stage (July 10, 2010).  Treatments followed by “(2x)” were applied again 7 days later.

**Least significant difference (alpha level = 0.05).  Treatment values that differ by this number can be considered significantly different from one another.  “NS” indicates that no treatments were significantly different from each other.

 

Overall, the highest level of white mold control will be achieved when several management practices are integrated (i.e. choosing the most-resistant varieties, utilizing recommended seeding rates, applying a foliar fungicide, and applying a biocontrol product).  For more information about white mold and management of this disease, go to http://www.planthealth.info/whitemold_basics.htm, where a recently-developed 7-page publication on white mold can be downloaded and several podcasts on white mold can be accessed (all funded by the North Central Soybean Research Program).


Brownstown Agronomy Research Center Field Day – July 25

The 2013 Brownstown Agronomy Research Center Field Day, presented by the University Of Illinois Department Of Crop Sciences, will be held on Thursday, July 25. Extension researchers and specialists will address issues pertinent to the current growing season. Tours will start at 8 a.m., with the second and third groups leaving the headquarters around 8:20 a.m. and 8:40 a.m. The tours will last about two and a half hours and will be followed by lunch provided by U of I Extension.

Shaded tour wagons will take participants to each stop. These topics will be addressed:

  • Nitrogen Sensors & Variable-rate N Applications – Dennis Bowman
  • Wheat Disease I.D. & Management – Dr. Carl Bradley
  • Emerging Developments in Weed Management – Doug Maxwell
  • Crop Rotation:  Another Risk Management Tool – Dr. Emerson Nafziger
  • Agronomic and Environmental Assessment of Cover Crops – Dr. Angie Peltier

 The 208-acre Brownstown Agronomy Research Center has been conducting crop research on the claypan soils of southern Illinois since 1937. More than 30 research and demonstration projects are conducted at the Center every year. Visitors are always welcome.

The research center is located south of Brownstown on IL Route 185, approximately 4 miles east of the IL Route 40 / 185 junction.

For more information, contact Robert Bellm (618-427-3349); rcbellm@illinois.edu
Visit us on the web at http://web.extension.illinois.edu/barc/


Stormy weather and Goss’s wilt go hand in hand

Goss’s wilt of corn often is most severe after fields are exposed to high winds and/or hail damage, because the causal bacterium, Clavibacter michiganensis subsp. nebraskensis, readily infects corn leaves through wounds.  With the recent storm activity across the state, growers should be on the lookout for the appearance of Goss’s wilt symptoms.  Goss’s wilt lesions on the leaves generally have wavy margins with a water-soaked appearance on the edges of the lesions.  Dark spots, known as “freckles”, almost always can be found within the lesions.  The affected areas of the leaves will have a shiny appearance when observed in the sunlight, and bacterial exudates may be on the leaves that resemble drops of maple syrup.

 

Goss's wilt symptoms on a corn leaf. Note the wavy margins of the lesion, the dark spots ("freckles") inside the lesion, and the water-soaked appearance of the lesion margin.

 

Bacterial exudates (circled in red) of the Goss's wilt pathogen, which appear as drops of maple syrup.

 

Goss’s wilt incidence was at an all-time high in the 2011 season, with over 30 Illinois counties having positive detections via samples sent to the University of Illinois Plant Clinic.  This high incidence observed in 2011 means that the causal bacteria is present in the state and can cause infections again in the 2013 season if the conditions are favorable.  Fields that are at the most risk to Goss’s wilt are those that have been grown to continuous corn, have been planted to a susceptible hybrid, and have received wind or hail damage.  Because other diseases and disorders can resemble Goss’s wilt, it is important that suspicious samples be sent to the University of Illinois Plant Clinic for the most accurate diagnosis.  Be cautious of results received from test kits designed for the related bacterial canker of tomato pathogen, Clavibacter michiganensis subsp. michiganensis, because these kits have been shown to give false positives.

Unfortunately, no consistently-performing in-season control options are available for Goss’s wilt management.  Because Goss’s wilt is caused by a bacterium, foliar fungicides are not effective.  Other products may be marketed as providing control of Goss’s wilt, but field testing of these products by universities have shown these to be inconsistent and/or ineffective in providing reliable control of Goss’s wilt.  The best way to manage Goss’s wilt is to rotate to a non-host crop, such as soybean, and plant the most resistant hybrid available the next time corn is in the field.  Because the Goss’s wilt bacterium survives in corn residue, fields with severe Goss’s wilt can be tilled after harvest to help decompose the residue, which may help reduce the inoculum level in the field.


Wheat scab rearing its ugly “head”

Head scab of wheat (a.k.a. Fusarium head blight) is showing up in Illinois wheat fields.  Incidence is ranging from low (less than 10% of the heads affected) to moderately high (over 25% of the heads affected).  Affected wheat heads will appear “bleached” in color.  Heads often are partially affected, with both healthy green and affected bleached areas being present in the same head.  Although I have not been in all wheat production areas in the state, my general observations are that fields in southern Illinois (south of Interstate 70) range from low to moderate incidence of scab, while fields in central Illinois seem to have moderate to high incidence of scab (it may be a little too early to see scab in northern Illinois fields currently).  These differences in scab incidence from field to field likely are due to differences in susceptibility of the varieties planted, application or no application of fungicides, and local weather.

Wheat field affected by head scab (Fusarium head blight). Note the "bleached" heads. (Photo by Carl Bradley)

Wheat head affected by scab (Fusarium head blight). (Photo by Carl Bradley)

Wheat growers may want to evaluate the level of scab in their fields.  It is easiest to observe this disease before heads completely mature.  Growers with moderate to high levels of scab should consider making adjustments to their combine that would allow low test-weight, scabby kernels to be blown out the back of the combine.  Recent research conducted at the Ohio State University indicated that adjusting the combine’s fan speed between 1,375 and 1,475 rpm and shutter opening to 90 mm resulted in the lowest discounts that would have been received at the elevator due to low test weight, % damaged kernels, and level of the mycotoxin deoxynivalenol (DON; vomitoxin) present in the harvested grain (Salgado et al., 2011).

Reference:

Salgado, J. D., Wallhead, M., Madden, L. V., and Paul, P. A. 2011. Grain harvesting strategies to minimize grain quality losses due to Fusarium head blight in wheat. Plant Disease 95:1448-1457.


Mark Your Calendars for the 2013 AGMasters Conference

The 2013 AGMasters Conference will be held at the i Hotel and Conference Center in Champaign, IL on December 2 and 3. The conference will begin with a morning general program followed with 1 1/2 days of specialized sessions. Participants will be able to pick and choose the sessions of most interest to them. These sessions are designed to encourage interaction between instructors and students and cover a broad range of topics including crop production challenges, soil fertility, water resource management, entomology, plant pathology, weed science, and introductory statistics. Each session is taught twice and is limited to 40 students (per session). Registration for the most popular topics is very competitive. The overall conference is limited to the first 160 registrants. The conference will be pieced together over the summer and registration information will become available by early fall. For now, please add these dates to your calendar and look for more conference information to follow in this Bulletin. Conference co-chairs include Dennis Bowman, Carl Bradley, Aaron Hager, Sandy Osterbur and me, all members of the Crop Sciences Department. As the growing season unfolds, please contact any of us with your suggestions for the 2013 program. We welcome your input.

Mike Gray


Stripe rust of wheat observed in Illinois

Stripe rust of wheat was observed in Champaign County, IL on May 10, 2013 (Fig. 1). The incidence of the disease was very low. The observation of this disease in Champaign County indicates that stripe rust likely is present in southern Illinois counties too.

Fig. 1. Beginning symptoms/signs of stripe rust of wheat that were observed in Champaign Co., IL on May 10, 2013 (Photo by Carl Bradley).

 

Wheat producers will need to continue to scout their crop for stripe rust, and apply an effective fungicide if necessary (see this previous post for additional information about stripe rust and fungicides: http://bulletin.ipm.illinois.edu/?p=456). Some varieties may have good levels of resistance to stripe rust, in which a fungicide may not be needed. In a University of Illinois research trial conducted in 2012, stripe rust affected yield of some varieties, but not others (Table 1).

Table 1. Effect of Prosaro fungicide (applied at Feekes 10.5.1 at 6.5 fl oz/A) on stripe rust and yield of six different wheat varieties. Trial was conducted at the University of Illinois Crop Sciences Research & Education Center near Urbana, IL in 2012 and was funded by the U.S. Wheat & Barley Scab Initiative.

Variety

Fungicide

Stripe rust severity (%)

Yield (bu/A)

Pioneer 25R54

No

20

74

Yes

2*

84*

Pioneer 25R47

No

8

82

Yes

1

84

W1104

No

14

77

Yes

2*

90*

Kaskaskia

No

57

69

Yes

7*

79*

BW5530

No

65

67

Yes

7*

72

BW5228

No

28

55

Yes

5*

64*

*Indicates that the fungicide treatment was significantly (alpha = 0.05) different than the untreated check for that variety.

If conditions and risk are favorable for Fusarium head blight, then growers may want to wait to spray an effective triazole fungicide at Feekes 10.5.1 (early flowering), which will help manage both Fusarium head blight and stripe rust (see this previous post about Fusarium head blight: http://bulletin.ipm.illinois.edu/?p=548).


Conditions favorable for Fusarium head blight (scab) in southern Illinois

Wheat plants are now beginning to head out and flower in parts of southern Illinois. During this critical time of wheat development, wheat becomes susceptible to infection by Fusarium graminearum, the causal agent of Fusarium head blight (FHB; also known as scab) (Fig. 1).  This disease can cause reduced grain yield, test weight, and quality.  In addition, the fungus can produce toxins that will contaminate grain such as deoxynivalenol (DON; also known as vomitoxin).  Harvested grain with high levels of DON may be discounted or outright rejected at the elevator.  To achieve the best management of FHB, different management practices must be implemented, such as planting wheat into fields that were previously cropped to soybean (rather than corn), planting wheat varieties with moderate to high levels of resistance to FHB, and applying foliar fungicides at the proper timing.  Of these different management practices, the application of foliar fungicides is the only one that can be done during the growing season and is the main focus of this article.

Fig. 1. Symptoms of Fusarium head blight of wheat (scab) (note the "bleached" heads) (Picture by Carl Bradley).

Multiple fungicides are registered for use on wheat, but only a few have efficacy in managing FHB.  Fungicides available for FHB management all belong to the triazole class of fungicides and are Caramba (BASF Corporation), Prosaro (Bayer CropScience), Proline (Bayer CropScience), and products that contain tebuconazole as their solo active ingredient.  Of these products, the best efficacy has been obtained with Prosaro and Caramba in multi-state university field research trials.  Proper fungicide application timing is critical in achieving the best efficacy.  The best application timing is considered to be when plants are beginning to flower (early anthesis – Feekes growth stage 10.5.1), but some efficacy may still be achieved slightly before or after Feekes 10.5.1 (Table 1).  In regards to fungicide application timing, it is important to always follow the label recommendations and consider the preharvest interval (PHI) requirements (PHI for Caramba, Prosaro, Proline, and tebuconazole products is 30 days).  Fungicide products that contain strobilurin active ingredients are not labeled for control of FHB, and in multiple university research trials, strobilurin fungicides have been shown to increase DON levels in grain compared to non-treated checks.  Therefore, it is extremely important that only effective triazole fungicides be applied for management of FHB.

 

Table 1. Effect of fungicide application timing on Fusarium head blight (FHB) control in wheat.  Results represent data collected from Dixon Springs, IL in 2009, and Brownstown, IL, Carbondale, IL, Dixon Springs, IL, and Urbana, IL in 2010 (University of Illinois and Southern Illinois University trials funded by the U.S. Wheat & Barley Scab Initiative).

Fungicide Application timing FHB (% control)*
Prosaro @ 6.5 fl oz Feekes 10.5 35 b
Feekes 10.5.1 59 a
5 days after Feekes 10.5.1 37 b
Caramba @ 13.5 fl oz Feekes 10.5 38 b
Feekes 10.5.1 61 a
5 days after Feekes 10.5.1 36 b

*Values followed by the same letter are not significantly different with 95% confidence.

 

When making a decision on if a fungicide application is needed, FHB risk should be assessed.  A FHB Prediction Tool is available on-line at www.wheatscab.psu.edu.  This risk is based on weather conducive for FHB, and should be assessed for each field as they begin to develop heads in anticipation of flowering.  On May 9, 2013, a medium to high risk of FHB was present in parts of southern Illinois where wheat may be flowering already or will be in the next few days (Fig. 2).  For fields that have not yet begun to flower, continued monitoring of the FHB Risk Prediction Tool is recommended.

Fig. 2. Screen capture of the Fusarium head blight prediction tool from May 9, 2013 (available at www.wheatscab.psu.edu).


Wheat – foliar disease update and outlook

Symptoms of some foliar diseases of wheat are apparent in Illinois wheat fields, and the threat of other diseases is on the horizon. Current wheat diseases that have been observed in the state are Septoria and Stagonospora leaf blotch, Barley yellow dwarf, and other virus diseases.

Septoria leaf blotch on wheat (note dark pycnidia within lesion) (Photo by Carl Bradley).

Symptoms of Barley yellow dwarf on wheat (Photo by Carl Bradley).

Mosaic symptoms on wheat caused by Wheat soilborne mosaic virus (note that other virus diseases can have similar symptoms) (Photo by Carl Bradley).

Of these diseases, only the fungal leaf blotches (Septoria/Stagonospora) can be managed with foliar fungicides.  Although a flag leaf emergence timing for a foliar fungicide application may be recommended sometimes, University of Illinois research results have shown that a single application at early flowering (Feekes 10.5.1), timed to manage Fusarium head blight (scab), may provide adequate protection of the flag leaf for management of foliar fungal diseases.  If the decision is made to apply a fungicide at Feekes 10.5.1, only a few fungicides are recommended (and labeled) for this timing (Prosaro, Caramba, and tebuconazole products).  For more information about available fungicide products and efficacy, please see the NCERA 184 Small Grains Disease Multi-State Committee’s Fungicide Efficacy Chart (NCERA 184 Wheat fungicide table 2013).

Stripe rust has not yet been detected or reported in Illinois, but is headed this way.  Recently, plant pathologists from Kentucky, Tennessee, and Arkansas have reported stripe rust in their states.  Stripe rust will continue to move northward, so Illinois wheat growers should be prepared to manage this disease with a fungicide, if necessary.  Scouting for stripe rust will help with fungicide application decisions.  Symptoms of stripe rust first appear as narrow, chlorotic streaks on the leaves.  As the disease progresses, orange-yellow pustules will form on these streaks, giving a “striped” appearance.  Some varieties may have a higher level of resistance to stripe rust than others, so it also is important to know how susceptible a particular variety is when making the decision to spray a fungicide for stripe rust management.

Early symptoms of stripe rust on wheat (note the chlorotic streaks) (Photo by Carl Bradley).

Stripe rust on wheat (note the "stripes" of orange-yellow pustules) (Photo by Carl Bradley).

 

 


Plant Diagnostic Clinic Ready for the 2013 Season

2013 Season at the University of Illinois Plant Clinic

After the extra early season last year, now we are in the midst of an extra late one. Samples have been slowly appearing this spring here at the Clinic in our 38th year of operation.  The unusually cool wet weather has kept many out of the field and landscapes.  The University of Illinois Plant Clinic began year-round operation in the fall of 2011, when we moved from our facility on St. Mary’s Road to our new location in Jonathan Baldwin Turner Hall on the south end of the Urbana campus.    With the new phone system at the U of I we actually have voice mail too.  During the winter our hours are reduced, but, we resumed regular business hours, 8am-12pm and 1pm-4:30pm on Monday April 29th, 2013.

 

One of the Diagnostic labs at the University of Illinois Plant Clinic

Plant Clinic services include plant and insect identification, diagnosis of disease, insect, weed and chemical injury (chemical injury on field crops only), nematode assays, and help with nutrient related problems, as well as recommendations involving these diagnoses. Microscopic examinations, laboratory culturing, virus assays, and nematode assays are some of the techniques used in the clinic. Many samples can be diagnosed within a day or two. Should culturing be necessary, isolates may not be ready to make a final reading for as much as two weeks. Nematode processing also requires about 1-2 weeks depending on the procedure. We send your final diagnoses and invoices to you through both the US mail and email.  If you provide your email address on the sample form you will get your information earlier.

Please refer to our website http://web.extension.illinois.edu/plantclinic/ for additional details on sampling, sample forms, fees and services offered. If you have questions about what, where, or how to sample call us at 217-333-0519 during operational hours.  Whenever submitting a sample, provide as much information as possible on the pattern of injury in the planting, the pattern on individual affected plants, and details describing how symptoms have changed over time to cause you concern.

Our fees vary depending on the procedure necessary.  General diagnosis including culturing is $15, ELISA and immunostrip testing is $25, Nematode analysis for SCN or PWN is $20, Specialty Nematode testing (such as corn) is $40.  Please include payment with the sample for diagnosis to be initiated. Checks should be made payable to the University of Illinois or to the Plant Clinic. Companies can setup an account, call and we will accommodate you. Call if uncertain of which test is needed or how to send a sample.

Preparing media for diagnostic culturing

 

 

Sending a sample thru US mail or Overnight delivery service address packages to:

University of Illinois Plant Clinic
1102 S. Goodwin, S-417 Turner Hall
Urbana, IL 61801

 

 

 

Map to the University of Illinois Plant Clinic S-417 Turner Hall, 1102 S. Goodwin, Urbana IL 61801

Drop off a sample:

You can also drop off a sample at S-417 Turner Hall. Park in the metered lot F 28 on the east side of Turner or at the ACES library metered lot on the west side of Turner. Come in the South door. Take the elevator located in the SE corner of the building.  Turn left when exiting the elevator; we are located along the SE corridor of the 4th floor.  Please use the green drop box located just outside S-417 if we are temporarily out of the office.

Social Media:

We have a lot of ways to keep you up to date on what is happening at the Plant Clinic and about other plant and pest issues.  Follow the U of I Plant Clinic on Facebook, http://www.facebook.com/UofIPlantClinic or, follow U of I Plant Clinic’s Stephanie Porter on Twitter: http://twitter.com/skporter or,  check out our Illini Plant and Pest podcasts http://web.extension.illinois.edu/podcasts/plantandpest/ or,  follow the U of I Plant Clinic on Blogger http://universityofillinoisplantclinic.blogspot.com

Regards, Suzanne Bissonnette