Tag Archives: Fungicides

Soybean Rust Found in Suffolk, VA

Soybean Rust Update: September 18, 2013

On September 17, 2013 soybean (SBR) rust was observed and confirmed on soybean leaves collected from the Tidewater AREC sentinel plots on September 5. Suffolk is the only county in Virginia thus far with confirmed soybean rust, but we will now intensify our scouting efforts throughout the soybean-growing regions of the state. Extension agents and growers should continue scouting for SBR in their respective counties and submit soybean leaves to the Tidewater AREC Plant Disease Clinic for evaluation of SBR and other foliar disease.

So far in 2013, SBR has been confirmed on soybeans in 185 counties/parishes in 10 states in the U.S. (AL, GA, FL, MS, LA, SC, AR, NC, TN, and VA) including two counties in North Carolina and one county in SE Virginia.

Soybean sentinel plots and commercial fields are monitored annually for early detection of SBR and tracking of disease spread. Data are used to make recommendations for timely applications of fungicide sprays for control of SBR. Since August, soybean leaflets from sentinel plots at the Virginia Tech Tidewater AREC in Suffolk, VA have been evaluated on a weekly basis, and as in prior years, the first report of SBR in Virginia was from one of these sentinel plots. Other diseases in soybeans at this time include Cercospora blight, brown spot, frogeye leaf spot, and anthracnose.

Risk of yield loss in soybean is minimal if SBR is detected following the R6 development stage. However, growers with soybeans that have not yet reached the R6 stage should consider spraying fungicides for control of SBR (triazole or pre-mix fungicide). This is particularly relevant for late-maturing/double-cropped soybean.

As part of the scouting effort and to track the spread of SBR throughout Virginia, extension agents are encouraged to submit soybean leaf samples (50 leaflets per sample) for evaluation of soybean rust and other diseases. Moisture is required for infection and development of SBR, so it is best to collect leaves from fields shaded from the sun in the morning since these areas will hold moisture within the canopy longer. A detailed protocol for scouting SBR is attached. Samples should be submitted to the Tidewater AREC with the attached SBR diagnostic form.

Some sources for more detailed information on SBR are listed below:

The USDA soybean rust website (up-to-date reports of SBR incidence) 


Virginia Asian Soybean Rust website (Virginia Cooperative Extension)


Hillary L. Mehl, Ph.D.
Assistant Professor of Plant Pathology
Virginia Tech Tidewater AREC
6321 Holland Road
Suffolk, VA   23437
Telephone: (757) 657-6450
Cell: (530) 906-0807
email: hlmehl@vt.edu

Soybean Rust Moves into North Carolina

Asian soybean rust was confirmed earlier today in Scotland County, NC.  Scotland County is on the NC/SC border (see map below).  There were sporulating pustules on 5 of 50 leaves examined.  No soybean rust was found on leaf samples taken from Lenoir County, which is closer to Virginia.  This puts soybean rust approximately 140 miles from South Hill, 160 miles from Emporia, and 190 miles from Suffolk. sbr_13784910204464

In general, we will only recommend a fungicide spray if soybean rust has been confirmed within 100 miles of our soybean fields.  Therefore, there is no need to apply fungicide for control of soybean rust in Virginia at this time.  Applying fungicide too early will only reduce its effectiveness once the disease arrives.  Furthermore, soybean yield will not be affected if rust infects the crop after the R6 development stage (seed touching each other in the pod); therefore, fungicides are not recommended after the R6 stage, even if soybean rust is found close by.

Although soybean rust is not close enough to Virginia to initiate fungicide sprays at this time, the disease has moved faster than previous years.  Most of our full-season (May-planted soybean) have reached the R6 stage (full-seed); therefore, these soybean are “safe” from any yield loss that may result from soybean rust infestation.  However, much of our double-cropped soybean are still susceptible; they are anywhere from the R3 (early pod) to R5 (late pod) development stages.  We will continue to monitor soybean rust movement across NC, continue to check soybean fields in Virginia, and let everyone know immediately if soybean rust is found in or close to Virginia.

For more details on Asian soybean rust and its movement, see the following website:


How Late Can You Spray for Frogeye Leaf Spot?

Frogeye leaf spot is easily recognized by the circular to angular spots on the upper and lower leaf surfaces.  These spots are usually surrounded by dark, reddish-brown margins and can be found throughout the canopy. Frogeye Leaf Spot - Painter 2013 If these spots are numerous enough to cover 30% of the leaf area, leaves will quickly wither and fall off of the plant prematurely.  This is a serious disease and can cause substantial yield loss, so keep a close eye on your fields.

Many, if not most of our soybean varieties have some resistance to the disease.  If the variety is labeled as “resistant”, you’ll usually not experience the disease.  However, I have seen and continue to see significant disease on varieties will “moderate resistance”, especially in non-rotated fields.

The main question that I’m getting now is “How late is too late to spray for frogeye leaf spot?”  First, check the fungicide label that you intend to use.  Applications with some fungicides must cease when the soybean reach the R6 stage.  Others may have a 14 to 21 day pre-harvest interval.  The R6 stage will last nearly 3 weeks and the R7 stage will last another week to 10 days; so the pre-harvest interval is not my major concern.  Regardless, make sure that you follow the label.

Assuming that there are no label concerns with fungicides, my inclination is to spray the field, especially if yield potential is good.  My concern with not treating is that if weather conditions are favorable, the infected areas will produce more spores and cause additional infection.  Keep in mind that at R5, only about 25% of the yield has been made; at the start of R6, only 50% has been made.  So, from this standpoint, there’s still lots of yield to lose if the problem were to get worse.

Seed Formation through MaturitySoybean Yield AchievedIf you decide to spray, I highly recommend a combination product such as Priaxor, Quilt XL, Quadris Pro, or Stratego XL.  There are reports of failures to control frogeye with only strobilurin fungicides (Headline, Quadris, Approach).  We have not documented this, but using a combination product may help prevent.  In addition, a strobilurin + a triazole (or carboxamide in the case of Priaxor) should provide better control.

Frogeye Leaf Spot Increasing in Virginia Soybean

Ed Seymore, TAREC Ag Technician who is scouting fields for brown marmorated stinkbug (BMSB), aphids, kudzu bug, etc., reported to me today that every soybean field that he is checking west of I95 in VirginiaFrogeye Leaf Spot - Painter 2013 (He’s in the Shenandoah Valley today) has frogeye leaf spot.  Some fields are heavily infested (all leaves; up to 20-25 spots per leaflet).

I called this to your attention earlier this year, as I was seeing frogeye leaf spot symptoms in several variety tests.  Many of our varieties have resistance to the disease, but some do not.  In addition, the level of resistance varies with variety.  The disease will also be worse in non-rotated fields (continuous soybean).  In the past, I’ve found that varieties with good resistance truly resist the disease.  Varieties with moderate resistance tend to hold up pretty well if soybean are in rotation.  In rotated fields containing a susceptible variety, the disease can be severe but not devastating.  But, the disease can devastate soybean varieties with no resistance when these soybean are following soybean (see photo below from non-rotated field planted to susceptible variety).Frogeye Brunswick Co - 2004 5

So, be sure to scout your soybean fields for this disease.  Symptoms are round spots with tan/grey centers and reddish halos around the spot.  I have no good threshold for treatment, but if you have a susceptible variety and/or are growing soybean after soybean, a fungicide application is in order.  If you have not already applied a fungicide, I’d also suggest using a fungicide that combines a strobilurin with a “curative” fungicide.  Combination products that have performed well on other disease, but not necessarily on frogeye leaf spot (frogeye has not been a big problem in the recent past) in Dr. Pat Phipps tests include: Priaxor, Quilt XL, Stratego YLD, and Quadris Top.

Foliar Fungicides May Pay in 2013

It seems that it’s been raining constantly in many places this year.  In addition, soybean growth is generally very good, creating a canopy that will maintain high relative humidity through much of the day.  Although the long-term forecast has temperatures getting into the 90’s on some days, it looks as if the 80’s will be the norm for the next 10 days or so.  These high relative humidity, rainfall events, and favorable temperatures will favor foliar disease in soybean.  Therefore, fungicide applications to R3 (beginning pod) to R5 (beginning seed fill) may pay off in 2013.

This past week, I’ve looked at several variety trials, both on-farm and the Official Variety Tests (OVT).  I’m seeing a significant amount of frogeye leaf spot.  This photo was taken in our OVT in Painter.  Although most of our Frogeye Leaf Spot - Painter 2013varieties have resistance to this disease, some do not.  You should check the seed catalog or with your seedsman to determine whether the varieties that you’re using has resistance to this disease.  If not, a fungicide will be in order if you see leaf spots forming.
Although frogeye leaf spot can be quite devastating, I’m not overly concerned since most varieties are not showing symptoms.  However, I consider this disease an indication that conditions are right for disease formation, sort of a “canary in the coalmine”.  If frogeye is prevalent, then other diseases such as Cercospora leaf blight will likely be raising its head as well.

Dr. Pat Phipps is developing a model to help us predict whether or not a fungicide will be needed.  He has much experience with and has developed effective prediction models in peanut; therefore, we think that such a model may be effective in soybean.  He will present his research at next week’s Virginia Soybean Field Day, so be sure to attend to hear his latest update.  In the meantime, listed below are the conditions that will favor disease development.  We seem to be meeting these criteria.Disease Risk Model

Many of you have likely already applied a fungicide to your full-season soybean.  The most consistent yield response has been when the fungicide has been applied at the R3 development stage.  However, we’ve seen responses as late as R5 (see article in this newsletter for an example of this).  So, with the weather conditions that we’re experiencing, I think that we could see a response even with late applications.

Still, keep in mind that fungicides are preventative; therefore, the weather conditions after the fungicides have been applied are most relevant.  Unfortunately, predicting temperatures and rainfall events is not always accurate.

Finally, it is very important to select the proper fungicide.  Our research has proven that strobilurin fungicides or pre-mixes that contain a strobilurin fungicide are most effective again the most common soybean diseases that we experience in Virginia.  The triazole fungicides are not as effective.  However, strobilurin/triazole tank mixes or pre-mixes have tended to give us the best control.  Products that have proven effective in our tests and that we would recommend using in soybean include:

Headline (pyraclostrobin)

Quadris (azoxystrobin)

Stratego YLD (trifloxystrobin + prothioconazole)

Priaxor (pyraclostrobin + fluxapyroxad)

Quilt Xcel (azoxystrobin + propiconazole)

Quadris Top (azoxystrobin + difenconazole)

Note that all contain a strobilurin, which we think is necessary.

Keep in mind that if soybean rust were to come into Virginia, we will likely need a triazole as these fungicides are most effective against that disease.  Although soybean rust is still far from Virginia (see map below), it is on the move.  I suspect that we’ll see the disease in Virginia this year.  But, I hope that it comes late as it has done in past years.Soybean Rust 081313

Application Equipment for Effective Insect Pests and Foliar Disease Control

Bobby Grisso, Ext. Agricultural Engineer and David Holshouser, Ext. Agronomist

Several years ago, we stressed that proper application equipment, specifically nozzle selection and spray volume, Fungicide Applicationwas critical to obtaining good disease control with foliar fungicides.  At that time, we were trying to prepare for an invasion of soybean rust.  The problem was that soybean rust (and most other diseases) would begin establishing itself in the middle and lower leaves of a full-canopied crop.  Getting enough spray droplets deep into the canopy was required for adequate control.

Although we have yet to see soybean rust early enough in the growing season and at great enough levels to cause a yield loss, we think our efforts to educate the agricultural community on proper application paid off.  Foliar fungicide sprays, now being used to control other soybean diseases, are reaching their target and penetrating to the middle and lower canopy.  Most importantly, it takes spray volumes of 15 to 20 gallons per acre (GPA) and medium-sized droplets to obtain good coverage.

Now we have another pest, the kudzu bug, which will likely require a similar spray strategy in order to get the pesticide down into the canopy where it needs to be.  Although this pest can be found on upper leaves and stems, past observations from states to our south indicate that it likes to bury itself well into the canopy on stems and lower leaves.  Therefore, revisiting nozzle and sprayer strategies for optimum control of this and other pests are warranted.

The single most important factor affecting prevention of disease and/or control of insect pests is good coverage of the plant with pesticide.  Fortunately, the technology is available.  You may however incur additional expenses with adaptation to current application equipment.

Remember the five major principles that result in satisfactory and economic control of the problem: 1) Positive identification of the insect pest or disease; 2) Correct pesticide; 3) Selection of the right equipment, particularly the right type and size of nozzle; 4) Timely application; and 5) making sure of the accuracy of equipment to confirm correct application amounts based on label recommendations.

First and probably most important, apply 15 to 20 gallons per acre of spray solution when using ground applicators.  Only with enough volume can we penetrate a large soybean canopy and cover the leaves with pesticide.  With aerial applications, this can be reduced to 5 gallons per acre (see the pesticide label for specific requirements).

Just as important, select the nozzles and pressures that will result in medium sized droplets (226 to 325 microns).  Pressure is not as important.  Depending on the nozzle selected, too high of pressure will just create fine and very fine droplets that are prone to drift.  Too low of pressure may create large droplets that may penetrate the canopy but not coat the leaves.Spray Droplet SizeFlat-fan pattern nozzles are still the best choice as long as most of the droplets from these nozzles are categorized as medium.  A flat-fan nozzle will normally be operated between 30 and 60 pounds per square inch (psi), with an ideal range of 30-40 psi.  Extended-range flat-fan nozzles are a modification of the flat fan that allows the applicator to spray at lower pressures and still maintain uniform distribution.  Regardless of the type of flat-fan nozzle selected, insure that the selected nozzle size will produce a medium-sized droplet at the operating pressure range and speed that the sprayer will be traveling.  Most nozzle catalogs will contain this information.  An example is shown below.Droplet Size Classification Chart - XRThe twin orifice flat-fan nozzle produces two spray patterns: one angled 30 degrees forward and the other directed 30 degrees backward.  Such a nozzle may provide better penetration and coverage of plants with fully developed canopies. This is mainly due to being able to double the gallons per acre while still maintaining the desired droplet size.  Still, hitting the target from two different angles, with one forward and one backward spray pattern may also provide a more effective coverage than spraying with just one spray pattern shooting down.  Twin orifice nozzles can be designed with a twin spray pattern from one tip or special fittings/caps that allow the producers to place two nozzles in the same cap, one pointed forward, and the other one pointed backward. Nozzles producing cone pattern are not recommended for foliar soybean diseases; droplets are usually too fine and will not penetrate the canopy.Nozzle PatternsHere are recommendations to help achieve the best coverage and control when spraying for soybean rust.

  • Keep spray volume above 15 gallons per acre for best results (20 gallons per acre is better).
  • Choose the appropriate size and type of nozzles and operate them at a pressure that will allow them to produce medium-size droplets (200-300 microns).
  • Nozzles producing a flat-fan pattern provide better coverage than the nozzles producing cone pattern when there is full canopy.
  • Use directed spraying, if applicable, to improve coverage.
  • Use twin nozzle/pattern technology. Two spray patterns, one angled forward and one angled backward, generally perform better than single nozzles spraying in one direction.  This is primarily due to being able to increase the spray volume, while maintaining medium-sized droplets.

For more information on sprayer technology, see the following VCE publications:

Nozzles: Selection and Sizing. Virginia Cooperative Extension publication 442-032, May 2013; http://pubs.ext.vt.edu/442/442-032/442-032.html (accessed: June 2013)

Droplet Chart/Selection Guide. Virginia Coopera­tive Extension, publication 442-031, May 2009; http://pubs.ext.vt.edu/442/442-031/442-031.html (accessed: June 2013)

Asian Soybean Rust – Frequently Asked Questions VI: Sprayer and Nozzle Technology.  Virginia Cooperative Extension publication 450-306, May 2009; http://pubs.ext.vt.edu/450/450-306/450-306.html (accessed June 2013)

Foliar Fungicides for Soybeans

Ten years ago, few farmers considered applying foliar fungicides for soybeans.  These crop protection products had their home with higher-value crops such as vegetables and peanuts, where a return on investment was more likely.  But with soybean futures topping $16, more growers are using fungicides to protect their soybeans from common diseases and hopefully to increase yields.

The question that is still plaguing nearly everyone is will the fungicides pay for themselves this year?  The answer is really quite simple – We Don’t Know!  Why don’t we know?  First, the fungicides that effectively control our most common soybean diseases, the strobilurin fungicides (e.g., Headline, Quadris, etc.) are preventative.  In other words, they must be applied before the disease develops.  So, we’re applying a chemical to prevent a disease that may or may not progress to yield-reducing levels.  Unfortunately, our ability to predict soybean disease development is not very good.  Therefore, we rely on results from applied research, experience, and the probability of getting a response.

How likely are we to get a response to fungicides in Virginia?  We regularly test fungicides on soybean and have built up a fairly large database.  While disease incidence is reduced with fungicide application, a significant yield response occurs only about 1/3 of the time.  The average yield response is 3 to 4 bushels per acre, regardless of whether we average over only experiments with significant responses or over all experiments.  We’ve seen yield increases up to 12-14 bushels, but that type of response is rare.  So, if you can average 3 to 4 bushels per acre over all acres, then a fungicide will likely pay for itself – unless we experience one of those years where disease is nearly absent (remember how dry it was last year?).  If there’s no disease, we’ve wasted our money.

Although we do not yet have an effective weather model (such as is being used in peanut) that will guarantee success, we can make an informed, although not perfect, decision.  We must remember that three conditions must be present in order for a disease to develop: 1) a susceptible host; 2) the pathogen; and 3) a conducive environment.  This concept is commonly referred to as the plant disease triangle.  If any of these three is missing, then the disease will not develop.  We have the host – soybean.  And we usually have some yield-robbing pathogens present – especially the Cercospora species.  But the variety used must be susceptible to the pathogen.  This includes two things: genetics and stage of soybean development.  From the genetic standpoint, we have many varieties with resistance to frogeye leaf spot (Cercospora sojina), probably the most damaging disease that is annually present in Virginia.  So, if you’re using a frogeye leaf spot resistant variety, response to fungicides is less likely.  Certain varieties are more susceptible to cercospora blight (Cercospora kikuchii); some are less susceptible.  But few have true resistance.  Cercospora blight is likely most responsible for yield loss to to foliar disease and the reason that fungicides prevent soybean yield losses in Virginia.  Regarding stage of development, soybean disease usually appears after full flower (R2) and the soybean are just beginning to pod (R3).  This can be attributed to a larger canopy at this stage (which is related to the environment side of the triangle – see below discussion), but may also be related to physiological changes taking place in soybeans as plants transition from vegetative to reproductive growth.  So if the pathogen is present on a susceptible host, there is a greater likelihood that a disease will develop.  Still, the environment has to be right.

What is the right environment?  Temperatures ranging from 60 to 85 F in periods with moisture provided by rainfall, dew, or high relative humidity is usually required.  The greater number of days that these conditions are met, the more disease there will be. The weather service is pretty good at predicting temperatures, but not so great with rainfall.  Additionally, even if rainfall is predictable, the environment within the soybean canopy (micro-environment) is usually what matters most.  A tall soybean crop that has completely closed its canopy and is growing in good soil moisture will result in a micro-environment more conducive to disease development than a short crop that has not closed the canopy and is growing in a relatively dry soil.

In summary, all three conditions shown on the disease triangle must be present for a disease to develop to yield-robbing levels.  We do not yet have a good model to predict common soybean diseases – but we are working on it.  Until such a model is developed, Dr. Pat Phipps and I suggest the following guidelines on whether or not to spray a foliar fungicide on soybeans:

  • Soybeans are growing well, have a full canopy, and are in the R3 (beginning pod) to R5 (beginning seed) stage.  Research indicates that applying fungicides at R3 is better than later stages.  Note that most fungicides cannot be legally applied after they have reached the R6 (full-seed) stage.
  • Daily air temperatures averaging between 60 and 77 F and accumulations of rainfall were ≥ 0.5 inches in the previous 5 days or ≥ 1.0 inches in the previous 10 days, or periods of relative humidity were ≥ 95% for ≥ 12 hours per day.  The greater number of days that these conditions are met, the greater likelihood for a response to fungicide application.

When soybeans were $5 to 6 per acre, very little foliar fungicide was being applied to soybean.  However with today’s prices, yield is king; therefore, a small yield increases resulting from an external input such as foliar fungicides can be cost effective.

Fungal Seedling Disease in Soybean

David Holshouser, Extension Agronomist

Pat Phipps, Extension Plant Pathologist

Rhizoctonia Damping Off and Root Rot.  Rhizoctonia root rot is probably the most common soilborne disease in Virginia soybeans.  Even if other diseases pre-dominate in a diseased plant, rhizoctonia could easily be a component of the problem.

Preemergence symptoms are typical of common seed rots, but are not usually recognized just because these plants never emerge.  More recognizable is the damping off that occurs in the seedling stage.  This will usually occur before the first trifoliate leaf develops.  Infected plants will have a reddish brown lesion on the emerged shoot at the soil line.  This lesion is most visible after the seedling is removed from the soil.

 Resistance to rhizoctonia is not available; variations in variety tolerance have been reported though.  Stresses such as herbicide injury, poor soils, insect damage, and feeding by soybean cyst nematode will increase damage.  Several fungicide seed treatments are effective for this disease.

Fusarium Root Rot.  Fusarium is another common disease in Virginia.  It is one of the diseases that has been implicated in “Essex Syndrome” that we continue to battle in some parts of Virginia.  There are several species of fusarium and each can cause a different plant reaction and/or disease.

 Two of the species, F. oxysporum and F. solani can cause root rot.  The root rot caused by F. oxysporum usually develops on seedlings and young plants during cool weather (<60O soil temperatures).  Older plants are generally less susceptible than younger ones.  Seedlings will emerge very slow and the resulting seedlings are stunted and generally unhealthy.  Symptoms are usually found confined to the roots and lower stems.

F. solani causes preemergence damping-off and root rot.  Damping off after the seedlings emerge is less of a problem, but can occur.  Lesions are generally on the roots and are dark brown to reddish brown to black.  Lesions can also occur on the young stem.

This disease is common in nematode-infested fields.  Soybean cyst, root knot, and sting nematodes will predispose seedlings.  Soybeans growing in soybean cyst nematode-infested fields will frequently develop fusarium symptoms.  This is less likely in root knot infested fields because the injury to the plant from root knot nematode is limited to the root tip.  In contrast, larvae of soybean cyst nematode migrate within the cells and cause more wounding.  In addition, F. oxysporum often interacts with rhizoctonia.

There is some variety resistance to the disease, but this information is not always published in the company literature.  Warm soils that are well-drained are helpful in managing the disease.  Good soil fertility should be maintained and soil compaction avoided.  Fungicide seed treatments provide some, but limited control.

Pythium Damping-Off and Root Rot.  There are many different species of pythium and the dominant species that is present will vary from geographical region to region, usually depending on temperature.  Pythium will cause pre- and postemergence damping-off during the young seedling stages.  It can also cause a root rot in later vegetative stages.  Seedlings may fail to emerge and will have a short, discolored root.  After emergence, symptoms can resemble those of other seedling diseases, especially fusarium and phytophthora.  The disease begins as water-soaked lesions on the young stem or on the cotyledons (seed leaves), and then followed by brown soft rot.

Variety resistance to pythium is not available, but fungicide seed treatments containing metalaxyl or mefenoxam will control the disease.  The best way to avoid the disease is to avoid planting into cool soils (<60oF).

Phytophthora Root Rot.  Of all the seedling disease that you may have heard about, phytophthora is probably the one that you hear and read about most.  It is a serious problem in the Midwest and affects young seedlings and older plants.  Many of our varieties that we grow in Virginia have varying levels of resistance to multiple races of phytophthora.  Yet, most of you have probably never had the disease.  Why is that?

Phytophthora rot is most severe in poorly drained clay soils that are readily flooded.  Most of our soils are sandy in nature, or if a clay, are well-drained.  This doesn’t mean you can’t have the problem just that it is less likely.  Plant loss can occur in lighter soils or on well-drained soils if they are saturated for an extended period of time when the plants are young.

Symptoms are the typical root rot and pre- and postemergence damping off.  The disease is often not diagnosed because it is confused with flooding damage.  Root and stem rots occurring later in the season will occur under similar, saturated conditions.  Tolerant cultivars may escape damage.  Damage does increase with reduced tillage, especially no-till, mainly because those fields absorb more rainfall and can be more easily saturated if the field is poorly drained.  Like most diseases, continuous soybean will increase likelihood of infection and damage.

Seed Treatments Have Their Place

Planting soybean into cool and wet soils is a recipe for more seedling disease problems.  Sometimes, you may never notice that there is a problem and, other times, certain areas of the field may be almost wiped out.  More commonly, the field in general is just not growing the way it should.

Some of our most noteworthy seeding diseases include: fusarium root rot, phytophthora rot, pythium damping-off and root rot, and rhizoctonia damping off and root rot.  Of these, fusarium and rhizoctonia are the most common in Virginia.  Some of these diseases can be managed with fungicide seed treatments, but some cannot.

Certain insect pests can also cause problems to seedling soybeans.  Thrips or leafhoppers can stunt growth when in high numbers on drought-stressed plants.  Bean leaf beetle seem to feed on young plants every year.  Both insects can transmit certain viruses.  Some companies are promoting insecticide seed treatments to help manage soybean aphid, but this is not relevant in Virginia.  Other soil insect problems include seed-corn maggot, wireworm, grub, and slugs.

Seed treatments are becoming more and more popular in all crops.  Benefits over soil treatments include lower use rates, less direct contact with toxic chemicals, and ease of use.  Fungicide seed treatments are sold under various brand names, but usually include one or more of the following active ingredients (with their most common trade names):  captan (Captan), thiram (Thiram), fludioxonil (Maxim), thiabendazole(TBZ), carboxin (Vitavax), PCNB (Rival), metalaxyl (Allegiance, Acceleron DX-309), mefenoxam (Apron XL), ipconazole (Racona), azoxystrobin (Dynasty), pyraclostrobin (Acceleron DX-109), or trifloxystrobin (Trilex).    Insecticide seed include the active ingredients:  thiamethoxam (Cruiser) and imidacloprid (Gaucho, Acceleron IX-409), and clothianidin (Poncho).

Finally, there is a new seed treatment (VOTiVO) that employs a biological mode of action with bacteria.  The product is being marketed in combination with clothianidin as Poncho/VOTiVO.  The bacteria lives and grows with young roots and supposedly creates a barrier against nematodes.  The verdict is still out with this product.  We have seen it increase yields in some nematode infested fields but not in others.  We will continue to evaluate this product.

In the near future, I’ll be exploring some of the disease and insect pests that could be causing early-season problems in soybeans.  We’ll start with an overview of individual pests and describe their potential damage.  Then later, we’ll talk about the potential benefits, if there are any, to applying one of the seed treatments currently available.

Is it Too Late to Spray Fungicides?

Over the past week, it seems that we’ve been living in a rainforest.  Today is the first day  in several that it has only rained once.  Pluse, we’ve had several very hard rains each day.  In many areas, we’ve had more rainfall after Hurricane Irene that we received during the that storm.

These wet and humid conditions have set up our double-crop soybean for some late-season foliar disease.  If you haven’t sprayed your soybean and they have not yet reached the R6 (full-seed stage), you may want to consider another fungicide application.  We have seen yield responses, when conditions were right, as late as the R5 stage. The soybean pod below is still in the R5 stage (the seed are not yet meeting), but will be at R6 in just a few days.  R5 is as late as you can legally spray soybeans with fungicides.

If you decide to spray, stick with the strobilurin fungicides such as Headline, Quadris, or Stratego.  Using a triazole fungicide (Folicur, Domark, Tilt, etc.) are not effective on most of our common foliar soybean disease.