Tag Archives: Insect Pests

A New Season and Blog: The Virginia Ag Pest and Crop Advisory

soybean crackingLast year, the Virginia Ag Pest Advisory (an email subscription list) became the Virginia Ag Pest and Crop Advisory blog.  As with the old system, you receive weekly emails containing important advisories on your mobile or desktop device, and you can scroll the titles and select only those that are important to you. Normal advisories will be delivered each Friday at 1 am and available for reading first thing on Friday mornings. And as before, there is an ‘Urgent’ option that will be used to provide any advisories that need immediate attention.

I call this to your attention because from now on, I will be publishing up-to-date advisories on the Virginia Ag Pest Advisory and not this blog.  Instead, I’ll use the Virginia Soybean Update blog for more general soybean-related subjects will possibly more detail.

You can find the new blog at http://blogs.ext.vt.edu/ag-pest-advisory .  Please look into and subscribe

Corn Earworm Survey—2013

D. Ames Herbert, Jr.
Extension Entomologist
Virginia Tech Tidewater AREC

Annually, we conduct a survey to estimate Helicoverpa zea (corn earworm) infestation levels in field corn in mid- to late July. Corn is considered a nursery crop for earworm, allowing the pest to complete a lifecycle and then move on to other crops such as soybean, cotton, and peanut in August. Over 30 years of data show that there is a linear correlation between the infestation level in corn and the amount of soybean acreage that gets treated with insecticide for this pest.

To conduct the survey this year, the number of corn earworms found in 50 ears of corn was recorded in 5 corn fields in each of 27 counties, totaling 6,750 ears and 135 fields sampled. When fields were known to contain Bt or non-Bt corn, this was noted. Otherwise, samples were considered to be random and assumed to be representative of the actual Bt/non-Bt composition in each county. Age of earworms, or if they had already exited the ears, was also recorded (data not shown). We greatly appreciate the help of Virginia Cooperative Extension Agriculture and Natural Resource (ANR) Agents, Virginia Tech faculty and staff, and volunteers in this effort. These cooperators are acknowledged below. We also would like to thank the many growers who graciously allowed us to inspect their fields for earworm.

Results of the survey can be found at the Virginia AG Pest Advisory (http://www.sripmc.org/Virginia/View.cfm?lngNewsID=1011). Statewide, approximately 18% of ears were infested with earworms. For comparison, 30% of ears were infested in 2012, 33% of ears were infested in 2011; 40% in 2010; and 36% in 2009. Regional averages for 2013 were 9.2% infested ears in the Northern Neck, 15.1% in Mid-Eastern, 15.7% in South-Central, and 23.4% in the Southeast.

This survey is intended to be a representative sample, not a complete picture. We always recommend scouting individual fields to determine exactly what is happening in terms of corn earworm as well as other pests and crop problems. Also, please check the black light trap data on the Virginia Ag Pest Advisory and other reports posted weekly to keep up-to-date on the insect pest situation.

Kudzu Bug Update

Ames Herbert, Extension Entomologist

The map below lists the progression of kudzu bug in Virginia from 2011 and 2012 (blue and orange counties) though this year (purple counties).  Kudzu bug adultAs of June 27, 2013, we have documented kudzu bug (KB) infestations in soybean fields in 21 of those counties (Accomack, Amelia, Appomattox, Brunswick, Campbell, Charles City, Culpeper, Dinwiddie, Franklin, Greensville, Goochland, Hanover, Isle of Wight, Middlesex, New Kent, Orange, Prince George, Southampton, Suffolk, Sussex, and VA Beach).  The problem is spreading quickly and almost daily I get word of an infestation in another county.  If you find KBs in a soybean field in a county that is NOT listed, please contact me with that information.  If you are growing soybeans (or crop advising) in a county on the list, you should make the effort to check fields.Kudzu bug distribution map 070113 Although adults are still present, nymphs are hatching from eggs masses and dispersing to stems and petioles.  Adult KBs have a strong aggregation pheromone that results in clusters on individual plants with many plants not infested.  This will begin to change as nymphs emerge.Kudzu bug nymphs-first instar

Their tendency is to disperse to new feeding sites, new plants or areas of plants which will result in a more widespread and more uniform infestation.  As of the last week in June, the nymphs we are seeing are quite small.  You can see them with your naked eye, but it takes either really good vision (those days are over for me) or a hand lens to see that those tiny light colored things on stems are indeed KB nymphs.  This too will change as they gradually grow and molt into larger nymphal instars.Kudzu bug egg to adult Based on all that we know, we should try to keep the management recommendations as simple as possible, trusting those that have done the research—that using their recommendations will result in the best possible outcome: control at the least cost.  As we move forward in the season, the best advice is to treat fields that are flowering or developing pods when an average of one nymph (big enough to see, see image below)Kudzu bug nymphs is captured per sweep net sweep—or, 15 nymphs in a 15-sweep sample.  If this situation is encountered, we are advised to treat that field.  Remember, this insect is a slow feeder—gradually drawing down a plant’s vigor.  This is good in a way, as this gives us plenty of time to sample fields and react with a treatment if needed.  KBs do not eat holes in leaves and do not take bites from pods or seed.  You may find nymphs and second generation adults on pods, but the damage is not direct like a corn earworm that eats the seed or a stink bug that punctures the seed. This is a new pest for us and we will all have to learn how best to deal with it.  For now, we should abide by the recommendations above.  Given the number of infested fields, I fully expect that some will have to be treated, eventually.
What about product choice. We have covered this in an earlier advisory (http://www.sripmc.org/Virginia).  There are many good choices.  Below is an insecticide efficacy chart that was developed by researchers at Clemson University and University of Georgia.  They (and I) do not recommend using any product that falls below 80% control and the higher the better.  I have been asked about a lot of products, some on this chart, some not.  I go with the chart.Kudzu bug insecticides list


Soybean Crop is Still at Risk to Drought & Pests

Our soybean crop is moving right along.  Much of our May-planted crop has hit or it approaching the R6 stage.  Our double-cropped soybeans are in the R4-R5 stage depending on their maturity, planting date, and whether or not they experienced early-season drought.  There’s a tendency for us to believe that the crop is made after the seed have met in the pod.  However, as shown below, only 50% of our yield has been made at the R6 stage. 

Dry weight will continue to accumulate in the seed for the next 3 weeks until the crop reaches the R7 stage (physiological maturity), which is defined as one pod on the plant that has reached its final mature color.  Much of this seed weight is due to translocation from other plant parts, especially the leaves and petioles (remobilization).  Sometimes soybean is called a self-destructing plant.  This is largely true.  As photosynthate is moved from the leaves to the seed, the leaves will turn yellow and drop from the plant.  If the leaves are yellowing and dropping due to this natural process, then we shouldn’t be concerned.  However, if the leaves are dropping due to another reason such as dry weather or disease, we should take notice.  It is important to keep the leaves green as long as possible to maximize yield.

It takes about 2 weeks to move from the R5 to R6 stage and another 3 weeks for to move from R6 to R7.  This is a long time and much can happen during this period.  First, we must protect the developing seed from insects such as corn earworm and stink bugs.  After R6, these two pests are not as much of a concern, but defoliators such as soybean looper can still remove green leaf area, which I’ve already stressed, is vital for maximum yield.  We also need to be concerned about foliar disease, which can also rob us of green leaf area

Early-Season Insect Pests

Potato Leafhopper. This insect overwinters in gulf-coast states and migrates northward each year, typically arriving in Virginia between late April and early June. Adults and nymphs injure the plant by inserting their piercing-sucking mouthparts into plant tissue and removing liquids. High populations can result in visual injury (cupping of leaves) and under drought conditions, can stunt growth, Injury is more severe on varieties with little leaf pubescence. But, the injury will not necessarily result in yield loss. Very dry conditions will increase injury and likelihood of yield loss. The insect can be controlled with pyrethroid insecticides.

Thrips may be the most abundant insect pest species on soybean.   But, the feeding alone will not usually cause yield reduction.  Under favorable environments, soybean will outgrow thrips damage.  However, if high numbers of thrips coincide with droughty conditions early in the season (seedling plants), then growth can be severely stunted and yield loss might occur.  Thrips feed by rupturing the cell walls of leaf cells and sucking the exudates.  Leaves will take on a silvery appearance from thrips feeding.  The insect can be controlled with insecticides from several chemical classes.  Early-season control can be obtained with insecticide seed treatments.  Ames Herbert is updating thrips counts in cotton and other crops on a regular basis in his Virginia AG Pest Advisory found at http://www.sripmc.org/Virginia/.

Bean leaf beetle is a common pest through all soybean production areas and has become more of a concern in the Midwest in recent years.  These beetles are defoliating insects, whose injury is easily recognized by small round holds between major leaflet veins.  The insect can also feed on the surface of soybean pods, leaving the seed vulnerable to excess moisture and secondary pathogens.  The insect can feed all year, but most concern is during the early vegetative stages.  However, soybean can normally grow out of this injury, without yield loss.  This insect can transmit the virus, bean pod mottle virus.  However, viruses have not traditionally been a problem in soybean.  There is resistance and/or tolerance in many varieties.  However, we suspect that some newer varieties have less tolerance.  The insect can be controlled with insecticides from several chemical classes.

Soybean Aphid.  Soybean aphid is a relatively new pest, first discovered in Virginia just 10 years ago.  It feeds by sucking plant sap, which can cause leaf curling and plant stunting and pod abortion.  At high levels, yield can be seriously reduced.  While an early-season pest in the Great Lake states, it has never occurred in Virginia before July, and rarely before August.  In addition, it only reaches threshold levels on relatively few acres in Virginia each year.  We only mention this pest here because some companies are promoting early-season control of aphid with soil insecticides.  Although soil insecticides may provide some control to seedling soybeans, this is not an issue in Virginia.  Management of this pest depends on regular scouting and applying insecticides when threshold levels are reached (250 aphids/plant before R5).

White Grubs.  With less tillage and more residue buildup on our soils, grubs have become more of a concern.  White grub damages soybean by feeding on soybean roots, killing young plants, and reducing stands.  Insecticide seed treatments have some, but limited effect on grub.

Wireworms.  As the name implies, wireworms are wire-like worms that feed on soybean seed, preventing germination.  This leads to poor and spotty stands when populations are high.  They may also feed on the underground base of the plant.  Later, they may feed on roots.  To determine if wireworms are a problem, bait stations can be employed.  Seed treatments are effective against wireworm.

Lesser cornstalk borer can be a problem on seedling soybean; problems on older soybean are infrequent.  Outbreaks are more likely under hot, dry conditions and in sandy fields with weedy hosts.  Larvae of this insect bore into the main stem at or just below the soil surface.  Numerous seedlings can be injured by a single larva.  Seedlings can be cut off at the soil surface or the tunneling can cause wilting and death.  Surviving plants may lodge and be lower yielding.  Insecticide seed treatments or other applications are not effective.

Insecticide seed treatment to soybean is of limited value in Virginia.  Seed treatments can reduce feeding by some species of insects early on the season, for the first 3 to 4 weeks after plant germination.  However, we do not typically treat for insects early, nor is there data to support the value or need.  Early season insects include thrips (various species) and bean leaf beetle.  Ames Herbert, Extension Entomologist, spent several years doing tests across the state trying to determine the value of treating for thrips and was never able to find a yield advantage.  Bean leaf beetle can feed on seedling plant leaves, but he has never seen a yield reduction from the feeding.  In the north central US, growers use seed treatments to reduce first generation soybean aphid.  In Virginia, we do not see aphids until late July or August long after any seed treatment would be out of the plant system.  Seed treatments may have some utility for wireworms and grubs.

Kudzu Bug.  Although not necessarily an early-season insect, this new pest is showing up early this year just to our south.  Little is known about this insect, but we are learning quickly.  This insect was discovered in Georgia in 2009, moved into South Carolina in 2010 and through North Carolina in 2011.  It was also found in Patrick County, Virginia in 2011.  As of May 2012, it has already been found in at least six N.C. counties and in Greensville County, VA.  It feeds on wide range of legume hosts including kudzu, wisteria, some vetches, and soybean.  It has several generations per year, moving from sheltered areas such as bark or rocks in the winter to kudzu and then on to soybeans.  Like an aphid, it has piercinig and sucking mouthparts, therefore does its damage by sucking juices and nutrients from the plant.  Of the studies conducted in 2010 and 2011, it has reduced soybean yield by an average of 21%.  We need to track this insect, so timely spray recommendations can be implemented.  So if you see this insect, please notify your County Extension office or you can contact Ames Herbert directly at the Tidewater AREC.  You will be hearing more about this insect, so stayed tuned.

Late Season Onslaught of Corn Earworm (Dr. Ames Herbert)

It may be happening for the first time that I can recall a late season infestation of corn earworms in soybeans. The last couple of nights we have trapped more corn earworm moths (about 1800 and 1500, respectively) in our pheromone traps than we have ever captured. These are alarmingly high numbers and I am getting reports that folks are seeing a lot of moth activity in and around fields of cotton, soybean and peanut. I got the first report today that some growers in southern Southampton County are having to retreat some soybean fields. I have been telling folks that as best I can remember, I have never seen a new infestation of earworms develop in September. Well, as one of my earlier mentors said to me one day. Dont make predictions about insects. Theyll make a liar out of you every time. Seems he was right. So, what crops are at risk? The cotton and peanut crops are safe as we are close to defoliation time with cotton and digging time with peanuts. Only late planted soybean fields that still have susceptible pods (earlier than R7 growth stage) are at risk. The good news is that our corn earworm pyrethroid vial test results have been showing a gradual decrease in the percent of moths surviving (see the attached graph) to levels below 10%, which means that pyrethroid insecticides should provide good control, relatively inexpensively. If I was someones mentor, I would want to go down in history as saying, Never let your guard down. Never stop checking fields for insect pests until the crop is mature

Brown marmorated stink bug in soybean, summary to date (Dr. Ames Herbert)

The brown marmorated stink bug (BMSB) which was first identified in 2001 in Allentown, PA, is now infesting soybean fields in parts of Virginia. This stink bug, although similar in appearance to our native brown-colored species, can be easily distinguished by the white bands on their antennae, and the white bands on the legs of nymphs. BMSB is a known pest of many crops, wreaking havoc on fruit crops, wine grapes and many vegetable crops, especially sweet corn. Although the epicenter for this pest is still the mid-Atlantic region (PA, DE, MD, VA and WV), a few have been found in states as distant as California. BMSB, like our native stink bug species, feeds directly on developing soybean pods and seed. If the damage occurs very early in seed development, pods will be flat and brown, but still be attached to the plant and easy to see. If damage occurs later in seed development, pods will appear yellow and speckled, and opening the pod will reveal damaged, crinkled, stained seed. Last summer (2010) we began a monitoring program for BMSB in soybean and found them in soybean fields in 15 Virginia counties, but always in low numbers. In Maryland where they had seen these same kinds of low numbers the previous year (2009), last summer (2010) they found large infestations on field edges. The same pattern has occurred for us. This summer (2011) we have found several fields with very high numbers. So far, the heavily infested fields are confined to one geographical areathe north-central piedmont counties of Orange, Culpeper, Madison, Fauquier and Clarke. Very low numbers have been reported in other counties. A pattern seems to be emerging that is playing well for us in terms of managing BMSB in soybean. To date, yield threatening infestations seem to be confined to field edges, not going beyond 30 to 50 feet into the field. Heavy infestations also seem to be associated with fields with wooded borders, especially if there are concentrations of the invasive weed, Tree-of-Heaven (Ailanthus altissima). Both BMSB and Tree-of Heaven are native to China and other parts of Asia. BMSB seems to be strongly attracted to that host, especially when the trees are putting out their seed clusters. Not coincidently, the north-central piedmont area where we are finding the highest densities of BMSB in soybean is the area with the highest concentration of Tree-of-Heaven. I encourage you to Google Tree-of-Heaven and become familiar with what it looks like. This strong field edge effect has made it possible for our local soybean growers to make edge treatments applying insecticides in one spray-boom width around a field, without having to treat the entire field. We are revisiting as many of these edge treated fields as often as we can, and so far, the edge treatments are holding. Another bit of good news is that many of the insecticides commonly used in soybean are effective against BMSB. This summer, we were able to put out three insecticide trials in growers fields in Orange County and most of the products we applied worked very well (including Baythroid XL, Belay, Brigade, Cobalt Advanced, Endigo ZC, Lannate LV, Orthene 97, and Vydate L). The problem for fruit growers is not that they cannot kill these critters, it is that they continue to reinvade their orchard which necessitates repeated sprays. Will this also occur in soybean fields? We are not certain. How should growers react to this new pest? We are recommending that growers stay vigilant until the latest planted fields reach the R7 growth stage when beans would no longer be susceptible to stink bug feeding. Scout field edges, especially fields with wooded edges with clusters of Tree-of-Heaven. Use a sweep net to sample the plants by making successive 15-sweep samples. We have no exact threshold, but suggest that greater than an average of 4 adults or nymphs per 15-sweeps would constitute a risk to the pods and seed. We have encountered fields with 8 to 10 per 15 sweeps, and in some extreme cases, more than 20 to 30 per 15 sweeps. So, the bad news is we have another established insect pest of soybean in Virginia. The good news is we have already made some progress in terms of how best to manage it. As a final note, we are also in the process of doing field cage studies to determine 1) how damage by BMSB may differ from damage by our native stink bug species, and 2) what a damage threshold might be more on this later.

Brown marmorated stink bugs found in high numbers in soybean fields (Dr. Ames Herbert)

Thanks to the conscientious effort of our field scout, Ed Seymore, we have located several soybean fields in Orange County, Virginia (about 20 miles NE of Charlottesville) with large numbers of brown marmorated stink bugs. These high density areas are very much restricted to field edges next to woods, especially where there are groups of tree or heaven. On these field edges we could easily capture 10 to 20 adults and nymphs, or more, in a 15-sweep sample. The ratio of adults to nymphs was heavy on the nymph side, with evidence of old egg masses on the leaves. As best we could determine these infestations went only about 30 feet into the fields, then numbers dropped to 1 to 2, or less per 15 sweeps. There was evidence of feeding with flattened pods and discolored pods with damaged seed. There is no question that these infested areas will suffer from stay green syndrome at the end of the season. We are not sure how widespread this problem is, but are doing what we can to locate other problem areas/fields. So far, we have no other reports. In one field, we were able to put in a couple of fairly primitive insecticide efficacy trials. I use the word primitive because we had to fit plot plans into these narrow field edges with their curves and ups-and-downs (not much flat ground in that part of the state). We hope to take post treatment ratings soon and will post results, if we are successful.

Virginia AG Pest Advisory – Dr. Ames Herbert

Update on corn earworm and brown marmorated stink bug in the Virginia soybean crop.

The corn earworm pyrethroid vial test data are showing some decline in the percent surviving…which is good. But levels are still high enough to indicate possible control problems. As I said in last weeks advisory, I think high rates of pyrethroids will work well enough in soybean fields with threshold or just above numbers of worms. If we get into a situation like last year with high numbers (e.g., 15, 20, 30 or more per 15 sweeps) then misses are much more likely and non-pyrethroids would be needed to achieve good control. In general, the non-pyrethroids will not do a good job of controlling stink bugs so if they are also present, pyrethroids, which do a good job on stink bugs, would need to be tank-mixed. The CEW moth flight from corn seems to be a little slow in developing. Our traps are catching an average of about 60-70 per night, but elsewhere in the state counts are still pretty low. As far as we can determine, no worms have been found yet in any soybean fields in Virginia. We expect to find some in the southeastern part of the state by next week. It is a bit too early to speculate, but we may have a much easier year this year with fewer infested fields compared with previous years. Our survey for brown marmorated stink bugs started this week and we found them in several soybean fields (Orange and Fauquier Cos.). But they were very scattered in fields and in low numbers (well below 1 per 15 sweeps). We found both adults and nymphs and in one field, egg masses. Delaware reports seeing low numbers in most soybean fields, and I suspect, as we progress with our survey, we will find the same thing. So far, these very low numbers do not represent any threat to the crop. How will this evolve? My best guess is that as populations increase and begin to move from other plant hosts, we may see larger numbers build up toward the end of the season, especially in our double-crop fields.