Category Archives: Disease

Wheat Disease Update – May 1, 2019

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There is increased risk of Fusarium head blight (FHB) in some parts of Virginia, especially near the Northern Neck and Eastern Shore of Virginia. Wheat in much of the state is flowering, and if a field is in a high risk area a fungicide application is recommended. Recommended fungicides for control of FHB and DON contamination include Caramba, Prosaro, Proline, and Miravis Ace. Do not apply a strobilurin-containing fungicide after the flag leaf stage since this has the potential to increase DON concentrations in the grain. To maximize their effectiveness, fungicides for FHB and DON control should be applied at early flowering or up to one week later. Fungicides that control FHB and DON will also control foliar diseases including powdery mildew, leaf rust, stripe rust, and leaf blotch.

Wheat varieties vary in susceptibility to FHB and DON, and this should be considered when making decisions of whether or not to apply a fungicide at flowering for FHB control. The FHB Risk Tool (http://www.wheatscab.psu.edu/) allows you to select the susceptibility of your wheat variety to determine risk. You can find information on FHB susceptibility of your wheat variety from your seed dealer or in the Virginia Cooperative Extension Small Grains publication. The FHB Risk algorithm adjusts the relative risk based on the variety susceptibility as illustrated below. For assistance with small grains disease identification or for additional management recommendations contact Dr. Hillary Mehl, Extension Plant Pathologist (hlmehl@vt.edu).

FHB risk for susceptible (S) wheat, May 1, 2019.

FHB risk for moderately resistant (MR) wheat, May 1, 2019.

Wheat Disease Update – April 25, 2019

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Most of the wheat crop in Virginia is currently between flag leaf emergence and heading with some wheat close to the flowering stage. Foliar diseases including powdery mildew and leaf blotch have been observed in some fields, but overall levels of disease have been low so far. As wheat reaches the flowering stage, it is susceptible to infection with Fusarium head blight (FHB), and this is the critical stage for making fungicide applications. Currently, the risk for FHB infection is low throughout Virginia. In addition, the 3-day forecast indicates risk will remain low. FHB risk can be monitored using the Fusarium Risk Assessment Tool (http://www.wheatscab.psu.edu/).
Recommended fungicides for control of FHB and DON contamination include Caramba, Prosaro, Proline, and Miravis Ace. Do not apply a strobilurin-containing fungicide after the flag leaf stage since this has the potential to increase DON concentrations in the grain. To maximize their effectiveness, fungicides for FHB and DON control should be applied at early flowering or up to one week later. Fungicides that control FHB and DON will also control foliar diseases including powdery mildew, leaf rust, stripe rust, and leaf blotch. For specific wheat disease management recommendations or assistance with disease identification, contact Dr. Hillary L. Mehl (hlmehl@vt.edu). The 2019 Fungicide Efficacy Table for Wheat can be downloaded below.

NCERA 184 Wheat fungicide table 2019_Final

Early Harvest Reports – Soybean Seed Quality is Not Good

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David Holshouser, Soybean Agronomist & Hillary Mehl, Plant Pathologist

We appreciated the rainfall this year.  It should lead to some very good yields in many parts of Virginia.  However, the same weather conditions for high yields has led to some of the worst seed quality that we’ve ever experienced.  This is in addition to the pod splitting and seed sprouting that we began observing last month.

We began seeing extremely poor seed quality in our May-planter maturity group (MG) 3 soybean in our Orange variety test last week.  The early MG 4 soybean did not look much better, but they were not yet mature.

The photo on the left is the worst that has been called to my attention.  These are April–planted early MG 3 soybean from Madison County.  To use the farmer’s words, “A real kick in the stomach.”  Soybean in this shape are pretty much a total loss.  It is especially hard when the yield potential was outstanding.

Below are photos from Westmoreland and Dinwiddie counties showing similar results.  We are not seeing the same problems in our May-planted MG 4 soybean in Suffolk, but are seeing quite a bit of purple seed stain in some varieties.

So, what caused this?  From these photos, we are seeing signs of several diseases, including Phomosis/Diaporthe, Cercospora, and anthracnose just to name a few.  However, we have not yet confirmed the diseases – samples are on the way to the Tidewater AREC’s disease lab.

But that is just the possible diseases.  What caused the disease to be so bad?

I think that we can blame it largely on excessive rainfall (and many rainfall events) and a very warm September.  Most of the seed diseases come on strong during maturation; hence, our early MG soybean, especially those planted in April and early-May experienced those conditions.

Below is a weather summary from the month of September in Orange County, showing 2018 and long term average temperatures and accumulated precipitation.  Notice the high rainfall, especially during the latter part of the Month, when our MG 3 and early-4 soybean were maturing.  Secondly, notice the temperatures during that same time period.  This set up nearly perfect conditions for many seed diseases to form.

  

What can we do about it?  Unfortunately, we cannot control the weather.  And what we have done this year cannot be undone.  But, here are a few pointers for that may help this and in future years.

  • Harvest as soon as possible after soybean are mature. The diseases will only continue to grow and develop.  If you have drying capability, harvest at a little higher moisture and dry it down to 13%.
  • Plant varieties best adapted to your farm(s). While you have discovered (and heard me – David – say) that early-planted early-maturing varieties have very good yield potential if we have a cool and wet July and early-August (not the normal), there is always the risk of poor seed quality.  Only if September is cooler than average and rainfall is not excessive will this system give us good quality seed.  Year in and year out, May-planted late-MG 4 and MG 5 soybean are our best overall choice.  Also, it is rare that double-crop soybean have poor seed quality.
  • Select disease resistant varieties. Most companies do not list resistance to many of our seed diseases, but we have seen differences in varieties.  Look over our final soybean variety test results for more information on seed quality scores and purple seed stain ratings.
  • Select disease-free varieties. Next year, notice your seed quality.  While most companies will not bag disease-ridden seed, some could sneak through.  Seed treatments may be in order.
  • Minimize insect damage to pods. Though not necessary for infection, insect damaged pods are more likely to be colonized by fungal pathogens.
  • What about foliar fungicides? We have not found that foliar fungicides can overcome warm and wet conditions during seed maturation, especially when applied to the R3 stage.  Will a later application help?  That is hard to say. In some cases, applying a fungicide at R5 will improve seed quality, but this is not a sure thing and a yield is unlikely to be improved with later applications.

Is it too late to apply foliar fungicides in soybean?

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Hillary L. Mehl, Extension Plant Pathologist & David Holshouser, Extension Agronomist

The wet weather conditions, along with relatively cool temperatures over the last few weeks have been nearly perfect for disease development in soybean.  As always, keep in mind the disease triangle – all 3 conditions must be met before a disease can form.

In most cases, one or more soybean pathogens are out there.  Refer to previous blogs for more information on common soybean diseases: Now is a Good Time to Evaluate Your Varieties for Foliar Diseases and Foliar Fungicides for Soybeans.  You can also access the Mid-Atlantic Soybean Disease Scouting Guide here. For a positive identification of the disease, send leaf samples to our diagnostic lab.

We also need a susceptible soybean variety (host).  Some varieties are resistant to specific pathogens; others have some tolerance; many have neither.

Of the 3 conditions, the environment is the most difficult to assess.  In general, we need high relative humidity (RH) for an extended period of time, usually over several days, and cool to moderate (e.g. not hot) temperatures.

Our research indicates that about 1/3 of the time, a foliar fungicide will result in yield increase.  The probability and amount of response will of course depend on the disease.  Frogeye leaf spot can be a quite devastating disease in susceptible soybean that have not been rotated.  Cercospora leaf blight (sometimes called late blight) is less devastating, but is common in almost all of our soybean when conditions are right.

We have attempted to create a foliar fungicide decision aid that would help decide on whether or not to spray.  The decision aid is based on the total number of favorable days for disease development, based on the data shown below.

We think that during the period of 1 week before and 1 week after mid-R3, yield-robbing disease levels may develop if we have 3 favorable days with 10 or more hours of relative humidity at or above 95%  and temperatures in the optimum range (77 to 86 F).  When these conditions are met, we would suggest a fungicide application.

However, after 3 years of on-farm testing we only improved the predictability of a yield increase slightly (approximately 50% versus the 33% we see on average).  Why?  We have not been able to predict the weather after the fungicide application.  If things turn dry, the disease will decline and a yield response is not likely.  If conditions remain favorable for disease, then a yield response to a fungicide application is more likely.

So, back to our original question, is it too late to apply a fungicide?

Most of our full-season soybean are past the R3 stage (though many acres were planted in June due to wet weather); so a yield response is not likely if fungicides are applied now.  Generally, it takes about 65 to 80 days after planting to reach the R3 stage, depending on planting date and relative maturity.

Double-crop soybean will usually take 40 (MG 4 planted in July) to 60 days (mid- to late-5 planted in June) to reach R3.  Since most double-crop soybeans recently entered or will enter the R3 stage, a yield response to a fungicide application is more likely.

What about seed quality?  We’ve seen little relationship between an R3 fungicide application and improved seed quality.  To insure good seed quality, we would suggest 2 applications (R3 and R5).  The R5 application might help with our biggest seed quality issue, Phomopsis seed decay, which tends to develop later in the season.  For seed growers, a late application is a good insurance treatment, but keep in mind that if long periods of wet weather delay harvest, seed quality will deteriorate even if a late fungicide was applied.  Be aware that most fungicide labels restrict applications once soybean enter the R6 stage.  Always follow label instructions.

In summary, there are several things that you need to keep in mind that will affect whether or not you will see a yield response to fungicides:

  • Non-rotated soybean will generally have more disease.
  • Variety Resistance. Many varieties have very good FLS resistance; some have only moderate resistance – this may work pretty well if soybean are rotated, but don’t depend on it if soybean were grown last year (or many of the previous years).  Generally, soybean are not resistant to Cercospora blight, but we have seen differences in varieties.  We measure % purple seed stain in our variety tests; however, this is not always a good indicator for resistance to the leaf spot and blight.
  • Timing & Soybean Stage. R3 applications are usually best; not always, but most of the time.  Still, we occasionally see a response with R5 applications.  I (David) have only seen a yield benefit from 2 applications (R3 and R5) once – this was in 80-bushel double-crop soybean in a very wet and cool year.
  • Historically, strobilurin fungicides were our most effective on most soybean disease.  However, FLS is now largely resistant to that class of fungicides, and control of our other diseases have declined.  However, the strobilurins still have utility.  We suggest a fungicide containing a strobilurin along with a good triazole. The 2018 soybean fungicide efficacy table can be downloaded here.
  • Spray Volume & Droplet Size. Good coverage of fungicide throughout the canopy is necessary.  Use at least 15 gallons per acre spray volume and make sure that your nozzles will deliver medium-sized droplets.  Small droplets will not penetrate the canopy to the lower leaves, where the fungicide is most needed.  Large droplets will not provide uniform coverage.  For more detail on this, see Application Equipment for Effective Insect Pests and Foliar Disease Control.
  • Seed Quality. Although, we don’t always see a seed quality benefit from an R3 application, two applications should improve seed quality.  Furthermore, a late-season (R5) application should help with certain seed diseases such as Phomopsis seed decay. However, keep in mind that if cool, wet conditions delay harvest seed quality will deteriorate even with a late fungicide application. Controlling late season insects such as stink bugs is also critical for preventing fungal infection and maintaining seed quality.

 

 

 

Walk Your Fields

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For greater soybean yields, one of the best things that you can do is walk your fields.  Many problems reveal themselves during the summer.  Actions taken or not taken can be very noticeable.  By walking fields, we can see what’s working and what’s not working.  Certain problems can be solved, some cannot.  For those that cannot be solved this year, we can do better next season by understanding why we have the problem.  Therefore, a review of how to diagnose your crop will likely beneficial.

A few years ago, I published “Troubleshooting The Soybean Crop“.  Although a little dated, most of the information is still good.  This publication will guide you through how to go about diagnosing problems, includes a vegetative- and reproductive-stage outline with lots of photos, and also includes a sample crop scouting and diagnostic form.  You can download a view a PDF copy, or contact me – I still have a few hard copies left.  By following some general guidelines, one can become quite good at diagnosing problems.  Below is a summary.

First, document everything!  Memories tend to fade.  We often forget or overlook details. You can document by taken notes (many phone apps or iPad/tablets work well for this).  Make a recording.  Take pictures – this is especially useful when you need help – and send those photos to others.

PRELIMINARY FACT FINDING.  You can obtain plenty of information before you even get to the field.  Although I call this preliminary (as if you’ve not seen the problem), you may need to go back to the office to refresh your memory of what you did.  Information that can be acquired beforehand or back in the office includes:     

  • Cropping History
  • Equipment
  • Soil Information
  • Weather
  • Pest Management Information
  • Tillage and Other Cultural Practices

THE FIELD VISIT

  • Take all materials and equipment needed (e.g., phones, paper, shovel, plastic bags, soil probes, etc.)
  • Windshield/Whole Field Investigation
  • Above-Ground Inspection
  • Take Appropriate Plant or Soil Samples
  • Equipment Check
  • Interaction with Others
  • Document Everything!

ANALYSIS OF DATA AND FINDINGS

  • Patterns
  • Look-Alike Symptoms
  • Interacting Factors/More Than One Problem

DRAWING A CONCLUSION. Review the facts and data.  Eliminate unlikely causes.  Validate likely causes.  You may be able to drawn a conclusion in the field, but lab analysis may be needed.

FOLLOW UP. Revisit the field.  If you took corrective action, did it work?  Why or why not?

This is a very rough outline of the guide.  Again, if you want a hard copy of Troubleshooting The Soybean Crop, contact me.

Peanut iPiPE and Disease Advisories

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Especially with all the wet weather we have been having in much of the region, it is time to start thinking about peanut diseases. We do not typically see a lot of disease until the canopy closes, but once the vines are touching the environment within the canopy becomes favorable for disease development. Leaf spot programs should be applied beginning at early beginning pod then according to a calendar-based (usually 14 day intervals) or advisory based program. The leaf spot advisory for Virginia can be found at https://webipm.ento.vt.edu/cgi-bin/infonet1.cgi. Some keys to a successful leaf spot fungicide program include:

  1. Make the first application at the appropriate time (not too late).
  2. Apply fungicides regularly before leaf spot outbreaks are observed (once disease is present it is difficult to slow down the epidemic).
  3. Stick to a regular calendar-based program or utilize leaf spot advisories.
  4. Be mindful of fungicide resistance management (rotate chemistries and/or tank mix with chlorothalonil).
  5. Scout for soil-borne diseases and utilize fungicides with activity against both leaf spot and other target diseases (e.g. for both late leaf spot and southern stem rot control use a product such as Provost, Elatus, Priaxor, etc.).

Data are currently being collected to improve both leaf spot and Sclerotinia advisories and to develop a southern stem rot fungicide advisory for peanut. This is being conducted through the Peanut iPiPE program. The Integrated Pest Information Platform for Extension and Education (iPiPE) is a program that allows farmers and extension agents to share information with each other through the internet.  iPiPE works by allowing users to enter pest data such as presence and severity of diseases or insects. This data will be shared with everyone in an effort to create a more precise system of pest monitoring and management. The Plant Pathology program at the Virginia Tech Tidewater AREC is leading the Peanut iPiPE and using it to improve disease advisories based on observations of disease onset in peanut fields throughout the region. Two undergraduate interns are currently scouting for peanut diseases in the region, and they will enter disease observations into the iPiPE database.

Disease and pest observations can be easily uploaded to the database through a mobile phone app or the online platform. We are encouraging anyone who scouts peanuts to help us collect disease observations. To become a participant, you can request an iPiPE account by visiting the iPiPE platform (http://www.ipipe.org/). Detailed information on the iPiPE platform and a user guide for the mobile app can be downloaded below. Alternatively, you can email disease observations to Dr. Hillary Mehl (hlmehl@vt.edu). In addition, if you are located in southeastern Virginia or northeastern North Carolina and are interested in having your peanut crop scouted for diseases by our iPiPE interns, please contact us.

Peanut iPiPE Stakeholder Card 2018

Peanut iPiPE Users Guide 2018

For more information or questions regarding the Peanut iPiPE contact Dr. Hillary Mehl (hlmehl@vt.edu).

 

 

 

New Crop Disease Management Resources

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Though it has been around for several years, the Crop Protection Network (CPN) has recently added several publications on disease management in corn, soybean, and small grains that are relevant to growers, crop consultants, and extension personnel in Virginia and the surrounding region. These can be accessed at the CPN website cropprotectionnetwork.org. As stated on the website:

“The Crop Protection Network (CPN) is a multi-state and international partnership of university and provincial Extension specialists, and public and private professionals that provides unbiased, research-based information. Our goal is to communicate relevant information to farmers and agricultural personnel to help with decisions related to protecting field crops.”

Extension specialists throughout the country (including myself) contribute to the publications and other resources posted on the website. An example of a recent publication on optimizing fungicide use for control of Fusarium head blight can be downloaded below. The CPN library includes over 30 publications on crop management, and additional publications are in development.

CPN-3001-Optimizing Fungicide Use for FHB

Wheat Disease Update – May 24, 2018

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Fusarium head blight (FHB) risk for Virginia continues to be to high throughout the state due to recent wet, warm weather (http://www.wheatscab.psu.edu/). Most of the wheat is past the flowering stage and no longer at risk, but later flowering wheat may still need a fungicide application. Triazole fungicides including Prosaro, Caramba, and Proline are recommended. Do not apply fungicides containing a strobilurin since this can increase DON. For wheat that is past flowering, a fungicide application will not reduce FHB or DON contamination of the grain. Grain harvested from fields with signs and symptoms of FHB should be kept separate from non-infested grain.

For assistance with disease identification or management recommendations, contact Dr. Hillary L. Mehl, Extension Plant Pathologist (hlmehl@vt.edu).

Wheat Disease Update – May 15, 2018

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Three-day forecast for Fusarium head blight (FHB) risk on susceptible wheat varieties.

FHB risk is increasing in Virginia and will continue to increase over the next several days. Risk is highest on the Eastern Shore, but susceptible varieties such as Shirley that are flowering over the next week will be at moderate to high risk in many portions of the state. Growers should monitor the FHB risk tool (www.wheatscab.psu.edu) as their wheat crop begins to flower. Consider applying a fungicide if risk is moderate to high, especially on susceptible or moderately susceptible varieties. Wheat that has completed flowering is no longer at risk. Fungicides should be applied at early flowering or up to one week later. Do not apply a strobilurin-containing fungicide since this can increase DON contamination. Recommended fungicides include Prosaro, Caramba, and Proline.

Steve Rideout, Extension Plant Pathologist at the Eastern Shore AREC, confirmed stripe rust on research plots of Shirley on Monday. FHB risk continues to be high on the Eastern Shore, so growers in this part of the state with varieties that are susceptible to stripe rust should consider an application of Prosaro, Caramba, or Proline since these will control both FHB and rust.

Stripe rust on wheat.

For assistance with disease identification or management recommendations, contact Dr. Hillary L. Mehl, Extension Plant Pathologist (hlmehl@vt.edu).