Category Archives: Fungicides

Where are the kudzu bugs–soybean update (Ames Herbert, Extension Entomologist)

Where are the kudzu bugs–soybean update
The big question today iswhere are the kudzu bugs we expected to see in our soybean crop? As of this week, we have not seen any adults or nymphs in the early planted full season crop. In fact, the same situation is being reported for much of the eastern US. Dominic Reisig at NCSU says that even in NC, the only reported infestations are from southernmost counties. Last summer by this time we were seeing many full season early planted files with infestations of adults that have moved from adjacent overwintering sites. The only bugs we have found so far have been in kudzu patches. So, whats the difference in years and why the delayed movement of adults? All we can say is that it must be related to the colder than normal temperatures we experienced during the winter. We know that in the Suffolk area there were at least two nights when temperatures dropped below zero (æF), and of course it was even colder north and west of us. Could those cold temperatures have killed some of the overwintering adults reducing the overall population levels? We do know from our adult overwintering emergence traps that were placed throughout much of the state that adults survived and emerged this April and May in about 12 counties in the southern part of the state. Why they did not move into early planted soybean fields is another unanswered question. From what I can gather from reading and talking with other entomologists in the southeast, 2014 is shaping up to be similar to 2011 when the first generation of kudzu bugs developed in kudzu (mostly) and other alternate hosts and only the second generation moved into soybean fields. This certainly seems to be what is happening this year. In some ways this scenario, if it plays out, will simplify the field scouting and threshold determination. The original kudzu bug threshold developed in the southeast was based on this second generation that moved into reproductive stage (floweringearly pod) soybean fieldsand it is based on number of nymphs (see below). We have initiated our 2014 soybean insect pest survey so will be reporting updates as they come in so stay tuned. Treatment Thresholds for 2nd Generation Kudzu Bugs, Nymphs Present Sweep Net ” An average of 1 nymph/sweep, 15/15 sweeps ” Take at least ten 15-sweep samples to represent the entire field ” Sampling should not be biased by sampling close to field edges where populations may by congregated Canopy Observation ” At least 10 observation spots representing the entire field ” Nymphs easily found on main stems, leaf petioles or leaves

Don’t loose 1/2 Bushels of Soybean Per Day With Late Planting

A few weeks ago, I thought double-crop soybean planting would be delayed due to a late wheat crop.  However, the wheat seems to have caught up in most areas.  So, we’re right on track to producing another good soybean crop.

Virginia data estimates that every delay in planting past mid-June will cost you about 1/2 bushel per acre.  Using future prices (approximately $12/bushel), this translates into about $6 loss per day.  The exact date when yield drops rapidly from delayed planting cannot be predicted; some years this may be June 10 and others this could be July 10.  Yet, on average, the date is in the second or third week of June.  Therefore, be sure that the planter is following close behind the combine.

Also, our data indicates that we need, on average of 180,000 plants per acre to economically maximize yield.  Yes, this is double what is needed for full-season production, but it will usually pay.  Note that I stated, “on average”, however.  Like most things, averages rarely reflect the season.  If we have plenty of rainfall early in the year that stimulates vegetative growth, then we won’t need as many plants.  Likewise, if you’re growing soybean on a field that consistently averages 50-60 bushels (rarely experiences severe water stress during the vegetative stages), then less seed is required.  But, if you have poor vegetative growth followed by relative good conditions during pod and seed development, more plants will maximize yield.  I can’t predict the season; therefore I use the average response.  If you need more information, contact me.

What if soil moisture is lacking?  My philosophy is to plant into moisture.  By June and July, the soil is warm, therefore you can plant deeper to reach moisture and get adequate emergence.  But, don’t plant deeper than 2 inches; I prefer 1 to 1.5 inches.  Although many disagree with me, I don’t recommend planting into dry soils and waiting for a rain.  Why?  I don’t often see a entire field that is completely dry unless it is a tilled field.  I’m not saying this is not possible; wheat and barley can extract nearly all of the moisture from the soil.  But, dry fields usually contain some wetter areas.  And these wetter areas will sometimes contain enough moisture to germinate the seed but not enough for it to emerge.  This results in re-planting, which can be expensive.  Still, the soybean seed will usually wait for a rain; so planting into dry soils is an option, especially if you have large acreages.


Flat Pods Showing Up in Virginia’s Soybean Crop

The following is a question directed to me by one of our County Agents.  It’s an excellent question that is worth repeating and relates to the flat pods that are evident in this year soybean crop.

“I have seen a lot of flat pods this year and received a few calls about them.  I have attached some pictures.  Flat Pods 2013 aIs there a physiological reason other than wet then drought?  Flat pods can be found in both full season and double crop so the weather conditions have been variable.  Stink bug damage is not evident on the outside of the pod.  Disease is evident on some and not others.  Some pods have 0, 1, or 2 beans.  I am not convinced all of them are disease related.  (Photos) #1 and #2 are on tFlat Pods 2013 bhe same raceme from double crop.  (Photos) #3 is a selection from full season with full pods on top and various flats on bottom.  I would say we have many more totally flat pods this year.”


I looked at our soybean variety test here in Suffolk yesterday. I too am seeing lots of flat pods (seed have aborted within the pod). Basically, something is causing the seed not to fill out in the pods. There are several things that can cause the flat pods. You mentioned two of them – stinkbugs and disease. However, if you are not seeing punctures or black/brown seed within the pod, it’s not likely stinkbug. Certain disease can also cause seeds not to fill out. Basically anything that restricts movement of water or photosynthates through the plant and eventually into the seed can result in flat pods. This could be a stem or root disease that is restricting movement of nutrients to the seed. It could also reflect a nematode infestation coupled with dry weather; hence restricting root uptake and resulting in drought effects. Or it could be a foliar disease that has lessened leaf area; therefore, reduced the amount of photosynthate into the seed. The first photo is showing symptoms of Cercospora blight and leaf spot on the stem in the background. Flat Pods 2013 cThe photo to the right also seems to be showing symptoms of this disease on the pods, although those symptoms could also reflect phomopsis or another late-season disease.  Cercospora blight and leaf spot, along with several other foliar diseases, was rampant this year. Foliar disease can result in less effective leaf area, but also early defoliation; the result in less photosynthate to fill the seed.

Still, the most likely culprit is the dry weather we experienced in September. We had very good yield potential going into September. There were lots of pods and most of these pods were set (they were not going to abort). Therefore, the effect of the drought at this time would not be less pods (the most important component of soybean yield), but less viable seed per pod or smaller seed size. When the crop can no longer support the pods and seed load on the plant, something has to give. In my opinion, the aborted seed in the pod (resulting in flat pods) that we are experiencing is primarily the result of a dry September. Drought stress is largely responsible for the flat pods.

In addition to the flat pods, I think we’ll also see smaller seed that we have in the past. Seed size is usually the second most important component of yield, behind pod number. But with the large number of flat pods (less seed per pod), we may not see as big of an effect on seed size, especially with the recent rainfall. Regardless of whether the problem is aborted seed within the pod or seed size, our yields will likely be lower than we think they will based on a visual inspection because of less seed per pod or smaller seed.

Finally, keep in mind that a combination of things (drought stress, disease, etc.) may be causing the flat pods. In my experience, I rarely can attribute such an event to just one factor. If you take the “glass half full” attitude, this could be an opportunity to discover an unknown problem (nematodes, compaction, improper variety selection, etc.) and begin future efforts to solve the problem. If this is occurring in just one field and not another that is close by; then it’s an opportunity to find out what’s wrong with that field.

The take-home message is that soybean will compensate for stresses by either dropping pods, producing less seed per pod, aborting seed (resulting in flat pods), or reducing seed size, depending on when the stress occurs. The timing of the dry weather following a very wet year that resulted in a heavy pod load likely resulted in the flat pods that we’re experiencing.

If you have further comments or questions, please contact me and/or respond to this post.

Soybean Rust Update: August 28, 2013 – Hillary L. Mehl, Extension Plant Pathologist

So far in 2013, Asian soybean rust (SBR) has been confirmed on soybeans in 99 counties/parishes in seven states in the U.S. (AL, GA, FL, MS, LA, SC, and AR) including seven counties in South Carolina.  Fields in both North Carolina and Virginia are being scouted, but SBR has not been detected.Soybean Rust 082813

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.  Currently soybean leaflets from sentinel plots are being evaluated on a weekly basis and no SBR has been detected thus far.  Diseases in soybeans at this time include Cercospora blight, brown spot, and frogeye leaf spot.  Anthracnose and target spot are likely to appear on soybean in the near future.

In 2012, SBR was first detected on samples collected from sentinel plots on October 12.  Since soybean was past the full seed (R6) growth stage prior to the appearance of SBR in Virginia, fungicide sprays were not recommended.  The risk of yield loss decreases if soybean rust is detected after the R6 development stage.  When deciding if and when to spray, it is important to consider disease pressure, weather conditions, and crop maturity.  If current weather patterns continue, SBR may appear in Virginia by mid-September.  Earlier maturing soybean are less likely to be exposed to high inoculum levels of SBR than later maturity groups.  Soybeans at earlier developmental stages (before R6) when SBR arrives in Virginia are more likely to require one or more fungicide applications.

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)

For additional information, contact:

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

Will Slugs Be A Problem in 2013?

Slugs are not a new problem, but they continue to be an unpredictable one.  It seems that they show up when and where we least expect them and never show up when and where we do.  But considering the cool and wet weather we’re experiencing, we should be on the watch.

The photo below was taken last May, 5 days after planting in a no-till field with a rye cover crop.  Stand was about half of what was expected and feeding scars could be seen on the hypocotyl and cotyledons.  When digging in the seed furrow, slugs were more often present than not.

Slug Damage Soybean

Cold, wet weather slows seedling growth; therefore reducing the plant’s ability to outgrow slug damage.  Slugs will feed on all crops, taking large chunks out of the stem and sometimes cutting the plants like a cutworm.  They feed mostly at night although I’ve seen them feeding during cloudy days (see photo below).  In general, they are more of a problem in wet, poorly drained fields or in low-lying portions of fields.  Still, we’ve seen them on hilltops.  Slug on SoybeanThey are usually a problem in no-till fields with high residue crops such as corn or grain sorghum and/or in fields the slug underneath last year’s corn stalk.  If the seed furrow doesn’t fully close, slugs will follow this “highway” and eat seedling after seedling before it emerges from the soil.

Slug Under corn residueWhat can be done about this problem?  First, scout the field before you plant, paying close attention to poorly drained or low-lying portions of the field.  If you find slugs, you have a couple of options.  One is to not plant and wait for warmer and dryer weather.  Slug damage usually disappears under warm and dry conditions.

Another alternative is to apply the slug bait/molluscicide, Deadline®, which contains the active ingredient metaldehyde.  It is sold at Deadline® M-Ps™ Mini-Pellets (colored with a blue dye) and Deadline® Bullets (dye-free).  This is the only reliable treatment that we have available.  It must be spread evenly at 10 to 40 lbs per acre over the infested area.  The product is fairly expensive, so the 10 lb rate is the most common and has worked well in my experience.  The product is not commonly stocked by local retailers, so it can be hard to find.

Will slugs be a problem?  Maybe.  Maybe not.  But, with the current weather conditions, I’d suggest scouting those slug-prone fields.

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.