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Extension Entomology

Category: Soybean

Soybean Stem Borers

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Dectes (soybean) stem borer damage is becoming more and more apparent as soybean harvest is delayed throughout north central Kansas.  The dectes stem borer was first detected infesting soybeans in Kansas in about 1985 in south central parts of the state.  Annually, the adults emerge from soybean stubble, where they overwinter as larvae, around the 4th of July.  They mate and deposit eggs around soybean leaf petioles.  The small larvae bore into the plants and feed, making their way into the main stem.

Dectes stem borer larvae are cannibalistic, so as these larvae come into contact with others only one survives to tunnel down the main stem to the base where they girdle around the interior of the stem, typically just prior to harvest.  This girdling activity often goes unnoticed.  However, the stems are weakened and wind will blow girdled plants over.  Fields with significant infestations will have serious lodging, as we are seeing now in parts of NC KS.  Harvesting these lodged plants is very difficult at best, and if harvest is delayed further, the grain lying on the ground may be lost to rodents, disease, etc.  Infested fields should be harvested as soon as possible, hopefully before any additional lodging occurs!  There is no preventative or rescue treatment available for dectes stem borers in soybeans.

For more information on the biology of the dectes stem borer, please visit Dectes Stem Borer, MF2581: https://www.bookstore.ksre.ksu.edu/pubs/MF2581.pdf

 

Soybean Update — Green Cloverworms

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Green cloverworm larvae have been very numerous throughout north central and south central Kansas for the past 30-45 days.  However, the larval stage and the leaf defoliation that they’re known for, has pretty much ceased as most larvae have entered, or are entering, pupation.

 

 

A few green cloverworm larvae can still be found in late planted beans and alfalfa, but for the most part, their feeding will soon cease.  The most common question is, with all these green cloverworm adults around, will they be in the same fields next year?  They do not overwinter in Kansas and most soybean fields will be rotated, so the answer is no.  If the same fields are infested next year, it will not be because of the green cloverworms that survived the winter in that field.

 

Soybean Update – Green cloverworms and Stink bugs

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Green cloverworm adults are quite numerous and are laying eggs in alfalfa and soybeans.  So, there are, or will soon be, small larvae present.  Feeding by green cloverworms will probably not impact alfalfa or most soybean fields unless there are significant larval populations in really late planted fields.

 

 

Stink bug populations seem to be increasing in north central Kansas but most beans should be far enough along in their development that stink bugs should be of little concern.

 

For management decisions for all soybean pests, please refer to the 2017 Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

Sugarcane aphid in Kansas sorghum, 2017

by –J.P. Michaud, Brian McCornack, Wendy Johnson and Sarah Zukoff

 

As we reach the midpoint of September, it is becoming clear that the impact of sugarcane aphid (SCA) in Kansas will be only a fraction of what it was in 2015 or 2016.  Multi-state monitoring efforts using myfields.info to track SCA have reported SCA in 138 different counties in 8 states in 2017; the first record in Kansas was on August 1 in Sumner Co. You can track county movement by visiting the myFields distribution map, or sign up for an account to receive an email alert when SCA has been detected in your area. Only southwestern Kansas has had some fields with infestations heavy enough to warrant treatment, and many others have remained below threshold (see our Scouting Card for more information).  A large proportion of the earlier planted fields are now mature enough to be safe from yield losses, even though SCA may be able to survive on these plants for some time.  At this point, only the latest planted fields that have not yet filled grain remain at risk, and lower overnight temperatures are slowing aphid activity.  Remember, SCA can survive overnight freezes and continue to feed on plants as long as they have any green tissue remaining, although without any further impact on yield if grain fill is complete.

 

Decreased acreage

 

A substantial decrease in sorghum acreage this year, especially in the regions of central Kansas that were most affected in 2016, has likely impeded northerly movement of the aphid this year.  Reduced sorghum acreage, much of it converted to soybeans and dryland corn, has meant the aphid must traverse longer distances to reach suitable plants on which it can establish populations capable of producing the winged migrants that enable further spread.  But several other factors have likely been even more important.

 

Improved management

 

There has been a much higher level of awareness among sorghum growers, and much better preventive and remedial management of the aphid in the southern regions that are the source of aphids for Kansas infestations.  The widespread adoption of seed treatments in south Texas effectively prevents the infestation of young plants for up to a month or longer.  An increase in the acreage planted to the many hybrid varieties expressing resistance to the aphid has greatly impeded its ability to produce large populations so quickly.  Timely scouting and identification by concerned growers has resulted in the early discovery and effective treatment of fields that did exceed economic thresholds, which in turn reduced the number and size of alate swarms that dispersed northward in 2017. Look for more help on scouting and determining treatable infestation levels here: KSU Scout Card

 

Evolving natural enemies

 

Just as pest species can evolve new behaviors (for example, attacking a new host plant), so beneficial species can quickly evolve new pest/host plant associations.  An example of this is provided by the Asian multicolored lady beetle, Harmonia axyridis, which last summer produced very large populations in Kansas sorghum for the first time, feeding primarily on SCA.  This lady beetle was not found in sorghum previously, but was drawn into fields by abundant SCA, and is now responding to sorghum as a habitat containing many types of suitable prey.  This year we have found it regularly feeding on corn leaf aphids and greenbugs, in the absence of SCA, something we had not previously observed.  Similarly, H. axyridis did not frequent soybeans until the arrival of soybean aphid in 2002, whereupon it quickly became a key source of mortality for this aphid, and has remained a regular resident of soybean fields ever since.  While the example of H. axyridis is quite obvious and visible, many changes in the responses of other aphid natural enemies in the sorghum agroecosystem are more subtle, but also important.  For example, the greenbug parasitoid, Lysiphlebus testaceipes, appears to be gradually overcoming SCA immunity to parasitism, and we are starting to find some successfully mummified SCA.  Aphid natural enemies are now colonizing sorghum faster, and in greater numbers, in response to SCA.  Surveys for SCA in central Kansas revealed many small colonies of greenbug, corn leaf aphids, yellow sugarcane aphids, and English grain aphids, all approaching extinction due to heavy predation and parasitism.  Lacewings and hoverflies were especially abundant, with adults flying everywhere and several lacewing eggs on almost every lower leaf, independent of the presence of any aphids.

 

In summary, we are clearly advancing from the epidemic phase of the SCA invasion to the attenuation phase, and considerably faster than we might have expected.  Vigilance will be required for the next few years, and appropriate monitoring and management will need to be maintained, but it is quite possible that 2016 will mark the high point for SCA problems in Kansas and we will not see another year that bad again.

 

Photo caption:

 

A colony of sugarcane aphid showing evidence of substantial predation.  Note ‘bloodstains’ (aphid hemolymph) along leaf midrib and the fact that aphids are widely scattered rather than forming a compact colony.

Soybean Update – Defoliators, Pod and Bean Feeders

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Soybeans continue to be the focus of attention of many defoliators, as well as bean and pod feeders, throughout north central Kansas. Thistle caterpillar populations seem to be largely late instar larvae and/or pupating inside of their very characteristic chrysalis.  Green cloverworms also seem to be increasing in both size and densities.  These are the main two species feeding on the leaves, but throw in a few yellowstriped armyworms and blister beetles and they all add up to a formidable group of very active defoliators.  Fortunately, soybeans are very resilient at coping with the loss of leaf tissue.  However, periodic monitoring should be continued, and if considering insecticide applications, please consult the 2017 KSU Soybean Insect Management Guide for treatment thresholds and insecticides labeled for these pests.

 

 

Pod and bean feeders seem to be just getting started. Bean leaf beetle adults may feed on the pods and will continue to do so until pods dry.  Soybean podworms (aka corn earworms) may feed upon the bean within the pod and thus both may reduce yields relatively quickly.  Fortunately, podworms will only feed on the beans for about two weeks.  However, bean leaf beetle adults may feed on the pods as long as they remain green.  Stink bug populations are also increasing and these may also feed directly on the developing beans within the pods.  Again, for management decisions, please refer to the 2017 KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

 

 

 

 

Soybean Update – Green Cloverworms, Thistle Caterpillars, Stink Bugs, Soybean Aphids, and Beneficials.

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Insect activity is still increasing around north central Kansas.  One positive, bean leaf beetles seem to be at really low densities in most fields, at least so far.  Green cloverworm larvae are at various developmental stages but there are still many early instars.  This means there probably is considerable defoliation to come because, as the larvae get larger, they simply eat more leaf tissue.  However, as green cloverworm populations increase, they are often infected with an entomophagous fungus which decimates their populations.

 

There also are many areas with significant infestations of thistle caterpillars and garden webworms.  Both species web leaf tissue around and over themselves, creating a relatively secure area from which they feed on leaves.  Many thistle caterpillars are really small right now and may not be noticed yet.  So, continued monitoring is important, especially with soybeans just entering the reproductive stages of development.

 

Green stink bugs are relatively common in both conventionally planted and double-cropped soybeans.  There are eggs, nymphs, adults, and mating adults all present at this time so sampling needs to be conducted periodically as these bugs can feed on the beans while they are developing inside the pods.

Soybean aphids were detected in double-cropped soybeans in Dickinson Co. on 24 August. Many soybean fields have significant populations of green lacewings and lady beetles, both of which may help control soybean aphids if and when they migrate into these fields.  So, as always, please take these into consideration if insecticide applications are contemplated.

 

For more information of thresholds and management options for these pests, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

Soybean Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Thistle caterpillars have not all pupated or emerged as adults yet in north central Kansas.  However, probably the majority of the larvae have finished leaf feeding and the adults have initiated oviposition.  There are still large numbers of adult butterflies navigating throughout soybean and sunflower fields.  Thus, scouting for the larvae should be an ongoing endeavor for probably another three weeks.

 

At the same time there are starting to be pretty good populations of green cloverworms in these same soybean fields.  Fields in the early to mid-reproductive stages are less tolerant to defoliation.  Populations last year caused considerable skeletonizing and resulted in many acres being treated.  However, there were also numerous fields that had green cloverworms controlled by an entomophagous fungus.

 

 

 

 

This highly visible white fungus will probably attack the green cloverworms again this year and may even do so, so effectively that insecticide applications are not necessary.  However, please keep in mind there is a lag time between a green cloverworm infestation of soybeans and larval infection by the fungus leading to their destruction.  But, they usually slow down or stop feeding soon after becoming infected, even if not actually killed for a few days.

Soybean stem borers seem to be relatively numerous around north central Kansas as well.  Oviposition by the females in the stem, at the site of the petiole attachment, is continuing.  Many eggs have already hatched and larvae are tunneling downward in stems where they will internally girdle around the interior of the stem and end up in the base of the taproot where they overwinter.

 

 

 

 

Spider mites are still present in north central Kansas, but so far seem to be very spotty.  These populations need to continue to be monitored during the plant’s reproductive stages.

 

 

Corn earworm larvae (soybean podworms) seem to just be getting started in south east Kansas and can cause considerable damage quickly by feeding on seeds within the pods.

 

 

Soybean aphids were first reported on 11 Aug, 2017, from the KSU Research Farm at Ashland Bottoms, just south of Manhattan, KS, by Rene Hessel and Bill Schaupaugh. These aphids have been found in the state every year since their first detection in 2002.  Beneficial’s are usually very active around these aphid colonies and help keep them from flourishing.  However, these small aphids need to be monitored periodically, especially in soybean fields treated for other pests, as these treatments may reduce the beneficial’s, and thus, any control which they may have provided.

For management of all these soybean pests, and others, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

Soybean Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

(thistle caterpillars, painted lady/thistle caterpillar chrysalis, garden webworm, bean leaf beetle, false chinch bug)

Soybeans seem to be the crop getting the most attention throughout north central Kansas.  Thistle caterpillars have been pupating in their unique little chrysalis that can be lime green to brownish in color and is often found hanging on the underside of leaves within the soybean canopy.

 

Some fields, especially in areas north of I-70 Highway, have many thousands of these painted lady butterflies flying around, often focused around the borders of soybean fields.  These fields are where the thistle caterpillars have been feeding and pupating.  The orange, black, and white spotted butterflies will be depositing eggs in soybeans, sunflowers, and many different weed species and the small spiny larvae will then begin feeding.  So, sampling in soybeans and sunflowers should continue for about the next three weeks.

 

 

 

Webworm larvae are feeding on soybean leaves and bean leaf beetle adults are starting to emerge and both are adding to overall defoliation in soybeans.  For management decisions regarding soybean defoliators, please refer to the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

 

 

False Chinch bugs have also been reported from soybeans.  These bugs are often mistaken for chinch bugs, hence the name, but unlike chinch bugs, they will sometimes feed on soybeans after their natural weed hosts are killed.  However, this feeding is usually of little consequence.  Although these bugs often congregate by the hundreds and thousands, they usually disperse within a few days with no tell-tell signs that these huge numbers were ever there.

 

 

Soybean Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Spider mites are infesting soybeans relatively early this year in several areas in north central Kansas.  These mites damage plants by feeding on individual plant cells, usually starting on the undersides of lower leaves.  Under less than ideal growing conditions, these mites can turn leaves brown and cause them to die in a few days.  Mite populations can build up quickly and if treatment does become justified please use enough carrier to penetrate into the canopy and reach the undersides of leaves.  Also, realize that if using an insecticide to control other pests, the predators will likely be significantly reduced which may allow mite populations to increase.   For more information on spider mite management, please see the Corn Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF810.pdf

 

 

Soybean Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Adult bean leaf beetles are present, but scarce, in soybean fields in north central Kansas as of 20 July.  This indicates that the majority of the population is in the larval stage, feeding on soybean roots, and/or is pupating in the soil.  There are also some garden webworms and a few painted lady, or thistle caterpillars, in some fields, but not enough to be of concern.

 

 

For more information on treatment thresholds and management options, please see the Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

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