Category Archives: Disease

Soybean Fungicide Advisory – August 15, 2019

For soybean that is at or near the beginning pod (R3) stage, it is time to consider whether or not a fungicide application is needed to control foliar diseases and protect yield. Most of the soybean in Virginia is past the beginning pod (R3) stage, and fungicide applications are more likely to be profitable when applied at or near R3/R4. The Virginia soybean fungicide advisory indicates that disease risk is variable across the state. Fields with moderate risk should be scouted since foliar diseases will not be an issue in every field every year.  Keep in mind that other risk factors also contribute to disease severity and yield loss to fungal diseases. High risk fields include those where susceptible soybean varieties are planted, there is a recent history of soybean foliar diseases, and/or rotations out of soybean are short or soybean is planted continuously over several years. Foliar fungicides are ineffective for control of most stem and root diseases. If based on the soybean fungicide advisory or other factors you decide to apply a fungicide, applications are generally the most effective when applied between R3 and R4 stages (no later than R5). The most recent Soybean Fungicide Efficacy Table can be downloaded from the Crop Protection Network website. Instructions on how to use the Virginia soybean fungicide advisory can be found in the July 19 blog post. A summary of disease risk and spray recommendations for different locations in Virginia can be found below. If you have any questions, contact Dr. Hillary Mehl (hlmehl@vt.edu).

Region of VirginiaLocation of weather stationSoybean disease riskRecommendation
Eastern ShorePainterHighSpray
SoutheasternSuffolkModerateScout
SoutheasternVirginia BeachHighSpray
Northern NeckWarsawHighSpray
CentralBlackstone ModerateScout
NorthernMiddleburgModerateScout
NorthernShenandoahModerateScout
NorthernWinchesterLowDon’t spray
WesternCritzHighSpray
WesternBlacksburgHighSpray
WesternGlade SpringHighSpray

For detailed daily advisories, select the location closest to your field and download the corresponding file here:

Soybean Fungicide Advisory – August 8, 2019

For soybean that is at or near the beginning pod (R3) stage, it is time to consider whether or not a fungicide application is needed to control foliar diseases and protect yield. The Virginia soybean fungicide advisory indicates that disease risk is variable across the state. Fields with moderate risk should be scouted since foliar diseases will not be an issue in every field every year.  Keep in mind that other risk factors also contribute to disease severity and yield loss to fungal diseases. High risk fields include those where susceptible soybean varieties are planted, there is a recent history of soybean foliar diseases, and/or rotations out of soybean are short or soybean is planted continuously over several years. If based on the soybean fungicide advisory or other factors you decide to apply a fungicide, applications are generally the most effective when applied between R3 and R4 stages (no later than R5). The most recent Soybean Fungicide Efficacy Table can be downloaded from the Crop Protection Network website. Instructions on how to use the Virginia soybean fungicide advisory can be found in the July 19 blog post. A summary of disease risk and spray recommendations for different locations in Virginia can be found below.

Region of VirginiaLocation of weather stationSoybean disease riskRecommendation
Eastern ShorePainterHighSpray
SoutheasternSuffolkModerateScout
SoutheasternVirginia BeachModerate to highScout
Northern NeckWarsawModerate to highScout
CentralBlackstone ModerateScout
NorthernMiddleburgModerate to highScout
NorthernShenandoahHighSpray
NorthernWinchesterLowDon’t spray
WesternCritzHighSpray
WesternBlacksburgLowDon’t spray
WesternGlade SpringHighSpray

For detailed daily advisories, select the location closest to your field and download the corresponding file here:

Soybean Fungicide Advisory – August 3, 2019

For soybean that is at or near the beginning pod (R3) stage, it is time to consider whether or not a fungicide application is needed to control foliar diseases and protect yield. The Virginia soybean fungicide advisory indicates that disease risk is variable across the state. Fields with moderate risk should be scouted since foliar diseases will not be an issue in every field every year.  Keep in mind that other risk factors also contribute to disease severity and yield loss to fungal diseases. High risk fields include those where susceptible soybean varieties are planted, there is a recent history of soybean foliar diseases, and/or rotations out of soybean are short or soybean is planted continuously over several years. If based on the soybean fungicide advisory or other factors you decide to apply a fungicide, applications are generally the most effective when applied between R3 and R4 stages (no later than R5). The most recent Soybean Fungicide Efficacy Table can be downloaded from the Crop Protection Network website. Instructions on how to use the Virginia soybean fungicide advisory can be found in the July 19 blog post. A summary of disease risk and spray recommendations for different locations in Virginia can be found below.

Region of VirginiaLocation of weather stationSoybean disease riskRecommendation
Eastern ShorePainterHighSpray
SoutheasternSuffolkLow to moderateDon’t spray
SoutheasternVirginia BeachModerateScout
Northern NeckWarsawModerate to highScout
CentralBlackstone LowDon’t spray
NorthernMiddleburgModerate to highScout
NorthernShenandoahModerate to highScout
NorthernWinchesterLow to moderateDon’t spray
WesternCritzHighSpray
WesternBlacksburgModerateScout
WesternGlade SpringHighSpray

For detailed daily advisories, select the location closest to your field and download the corresponding file here:

If you have any questions, feel free to contact Dr. Hillary Mehl (hlmehl@vt.edu).

Soybean Fungicide Advisory – July 25, 2019

For soybean that is at or near the beginning pod (R3) stage, it is time to consider whether or not a fungicide application is needed to control foliar diseases and protect yield. The Virginia soybean fungicide advisory indicates that disease risk is moderate to high in most locations. Fields with moderate risk should be scouted since foliar diseases will not be an issue in every field every year.  Keep in mind that other risk factors also contribute to disease severity and yield loss to fungal diseases. High risk fields include those where susceptible soybean varieties are planted, there is a recent history of soybean foliar diseases, and/or rotations out of soybean are short or soybean is planted continuously over several years. If based on the soybean fungicide advisory or other factors you decide to apply a fungicide, applications are generally the most effective when applied between R3 and R4 stages (no later than R5). The most recent Soybean Fungicide Efficacy Table and instructions on how to use the Virginia soybean fungicide advisory can be found in last week’s blog post. A summary of disease risk and spray recommendations for different locations in Virginia can be found below.

Region of Virginia Location of weather station Soybean disease risk Recommendation
Eastern Shore Painter High Spray
Southeastern Suffolk Moderate Scout
Southeastern Virginia Beach Moderate Scout
Northern Neck Warsaw Moderate to high Scout
Central Blackstone Low to moderate Don’t spray
Northern Middleburg Moderate to high Scout
Northern Shenandoah High Spray
Northern Winchester Moderate Scout
Western Critz High Spray
Western Blacksburg High Spray
Western Glade Spring High Spray

For detailed daily advisories, select the location closest to your field and download the corresponding file here:

Glade_Spring_soyadv_25Jul2019

Middleburg_soyadv_25Jul2019

Painter_soyadv_25Jul2019

Shenandoah_soyadv_25Jul2019

Suffolk_soyadv_25Jul2019

VA_Beach_soyadv_25Jul2019

Warsaw_soyadv_25Jul2019

Winchester_soyadv_25Jul2019

Blacksburg_soyadv_25Jul2019

Blackstone_soyadv_25Jul2019

Critz_soyadv_25Jul2019

If you have any questions, feel free to contact Dr. Hillary Mehl (hlmehl@vt.edu).

Peanut Disease Update – July 25, 2019

As August approaches, now is the time to be scouting peanuts for leaf spot and soilborne diseases and making timely fungicide applications. Calendar-based or advisory-based spray programs can be followed, but be sure to make your fungicide applications before rainy weather makes it difficult to get into fields. Many of our leaf spot outbreaks over the past couple of years were due to extended periods of rainfall and delayed fungicide applications. Cooler, wet weather over the past several days has increased the risk for Sclerotinia blight. In our research plots at the Tidewater AREC, we found small amounts of late leaf spot, Sclerotinia blight, and southern stem rot this week. The leaf spot and Sclerotinia blight advisories, which  can be found on the Peanut Cotton Infonet website, indicate disease risk is currently high. For fungicide recommendations, contact your county extension agent or Dr. Hillary Mehl (hlmehl@vt.edu).

Soybean Fungicide Advisory – July 19, 2019

Based on research conducted since 2014, we have developed a disease favorable day threshold for predicting when a fungicide application in soybean will be economical. The favorable day threshold is based on daily average temperature and hours of high relative humidity, and these parameters are being monitored from weather stations located at Virginia Tech Agricultural Research and Extension Centers (AREC) throughout the state. We have determined that weather conditions approximately three weeks prior to the beginning pod (R3) stage of the soybean crop are the most critical for determining if disease will impact yield and if a foliar fungicide application will be economical. Fungicide recommendations for different locations throughout Virginia can be downloaded below. To use the advisory, follow these steps:

1) Identify the weather station (AREC) closest to your field. A map of the AREC locations can be found here.

2) Download the PDF for your location below.

Blacksburg_soyadv_18Jul2019

Blackstone_soyadv_18Jul2019

Critz_soyadv_18Jul2019

Glade_Spring_soyadv_18Jul2019

Middleburg_soyadv_18Jul2019

Painter_soyadv_18Jul2019

Shenandoah_soyadv_18Jul2019

Suffolk_soyadv_18Jul2019

Warsaw_soyadv_18Jul2019

Winchester_soyadv_18Jul2019

VA_Beach_soyadv_18Jul2019

3) Under the “date” column, find the date that corresponds to approximately when your soybean crop has reached or will reach the R3 (beginning pod) stage).

4) In the row that corresponds to your R3 date, determine if disease risk is low, moderate, or high based on the favorable day threshold.

5) The last column indicates if a spray is recommended based on your R3 date.

Keep in mind that other risk factors also contribute to disease severity and yield loss to fungal diseases. High risk fields include those where susceptible soybean varieties are planted, there is a recent history of soybean foliar diseases, and/or rotations out of soybean are short or soybean is planted continuously over several years. If based on the soybean fungicide advisory or other factors you decide to apply a fungicide, applications are generally the most effective when applied between R3 and R4 stages (no later than R5). The most recent Soybean Fungicide Efficacy Table can be downloaded below.

Soybean Fungicide efficacy table_2019_final

If you have any questions, feel free to contact Dr. Hillary Mehl (hlmehl@vt.edu).

 

 

Wheat Disease Update – May 9, 2019

Fusarium head blight (FHB) risk is continuing to increase in parts of Virginia. Upcoming rain events will increase risk over the next three days (see figure below). Much of the wheat in the southern part of the state is past the vulnerable flowering stage, but wheat that is at or about to enter flowering may be at risk. Consider applying a fungicide if risk is moderate to high, especially on susceptible or moderately susceptible varieties. 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, Proline, and Miravis Ace. Increased incidence and severity of leaf blotch and powdery mildew have been observed in some fields, and these fungicides will also provide control of foliar diseases.

Wheat Disease Update – May 1, 2019

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

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

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.