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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

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

 

 

Sorghum Update – (chinch bugs, corn leaf aphids, corn earworms)

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Chinch bugs continue to be very active in both corn and sorghum throughout north central Kansas.  Both nymphs and adults are present.

 

Many adults are still mating, which indicates that there are more eggs, nymphs, and adults yet to come.  One consolation relative to the numerous chinch bugs in sorghum fields is that the four spotted egg eater, Collops quadrimaculatas, seems to be plentiful as well.  They have been collected in samples while sweep sampling alfalfa and are also present in sorghum fields.  These little beetles are predacious on insect eggs, and it has even been reported that they feed on chinch bug eggs.  Not sure they will be able to provide a great deal of control on chinch bug populations but it sure can’t hurt!

 

Corn leaf aphids are also very plentiful throughout north central Kansas.  These aphids usually feed on developing corn tassels and silks, but probably are more commonly associated with, or at least noticed in, whorl stage sorghum.  These aphid colonies sometimes produce enough honeydew, and it is so sticky, that often the sorghum head gets bound up in the whorl and therefore doesn’t extend up properly.  These colonies are not usually dense enough on a field-wide basis to justify and insecticide application.  These plentiful aphids are also serving as a food source for many predators, i.e. lady beetles, green lacewings, etc.

 

 

Corn earworms are still plentiful in corn but as they mature, pupate, and become adults they most likely will migrate to sorghum to feed on developing kernels (between flowering and soft dough), and soybeans where they will feed on developing beans within the pods.

For more information on sorghum and soybean pest management, please consult the KSU Sorghum Insect Management guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

And 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.

 

 

Sugarcane Aphid Update

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

  1. First report of sugarcane aphid on grain sorghum in Kansas this year

The sugarcane aphid (SCA) has now been reported in Sumner County. Sorghum producers in Kansas should begin scouting their fields on a routine basis. More information on scouting and thresholds for treatment can be found in the Agronomy eUpdate article “Start scouting soon for sugarcane aphid” from July 7, 2017, and at the myFields web site at: https://myfields.info/pests/sugarcane-aphid

 

 

Figure 1. Current status of the SCA. The map indicates only the counties in which the SCA has been found, and does not indicate how many or how few aphids were found in that county. Source: https://www.myfields.info/pests/sugarcane-aphid

 

 

Chemical control

Two insecticides are labeled for use on sugarcane aphid on sorghum in Kansas this season:

Sivanto (flupyradifurone)
4.0 – 7.0 fl oz/acre (0.052 – 0.091 lb ai/acre)

Transform (sulfoxaflor)
0.75 – 1.5 oz/acre (0.375 – 0.75 oz ai/acre)

Field trials show good efficacy of the above materials against the sugarcane aphid. Both have the ability to penetrate leaves through translaminar movement and kill aphids feeding on the undersides.

Maximum efficacy will be achieved by application in a large volume of water, preferably 20 gallons per acre or GPA (minimum 10 GPA) by ground or 5 GPA from the air. Laboratory trials indicate that Transform (sulfoxaflor) is relatively safe for important aphid predators such as lady beetles and lacewings and thus can be considered IPM-compatible. This is true to a lesser extent for Sivanto (flupyradifurone), but various trials have indicated a much longer period of residual activity for this material.

Both insecticides have annual application limits and growers are advised to rotate them if follow-up applications are required. Note also that preharvest intervals will be a factor to consider when treating late-season infestations, so applicators should read labels carefully and keep a log of all treatments for each field. Because Transform and Sivanto are absorbed by leaves and eventually metabolized by the plant, reinfestation can occur if large numbers of winged aphids continue to settle in the field.

When inspecting fields for treatment efficacy, note whether any live aphids are winged or wingless, as the former may indicate continued immigration rather than control failure. DO NOT attempt to control sugarcane aphid with contact insecticides that have broad-spectrum activity; these include all pyrethroid and organophosphate materials and combinations thereof. Replicated field trials indicate these materials are not effective, harm beneficial species, and often result in higher aphid numbers than unsprayed control plots.

Sorghum headworm infestations are often present when SCA is observed in a field, since this pest migrates using the same weather events. When choosing an insecticide to control headworms, use products that are less harmful to natural enemies such as Prevathon or Blackhawk, as these have proven compatible with Transform and Sivanto and less selective materials risk flaring the aphids.

The myFields web site: Keeping updated on SCA in Kansas and reporting findings

For ongoing current information on SCA in Kansas, check out the myFields web site often in the coming weeks and months: https://www.myfields.info/pests/sugarcane-aphid

It would be helpful if producers would report findings of SCA in their fields on the myFields web site as soon as the insects are found. Reports of findings are used in developing the map seen in Figures 1.

The reports used to develop each map are, in part, those submitted through the myFields web site from account holders that also have special permissions as “Verified Samplers.” Only reports submitted by these verified samplers get mapped so that we can account for data quality. However, we do encourage any account holder to report their observations on the SCA. Web site administrators can see these reports and can contact the submitter for a confirmation, a great way to get an early detection in new areas. Web site visitors will need to: 1) sign up for an account, 2) log in, 3) to get access to the ‘Scout a Field‘ feature to make reports. The Scout a Field tool is easy, you just map the observation location and select yes or no for SCA presence.

Here is the sign up page: https://www.myfields.info/user/register

Also, if sorghum producers are interested in receiving alerts, which are triggered by new reports submitted by verified samplers, they just need to sign up for a myFields account. Signing up for an account automatically signs them up for SCA alerts, but they can also opt out of them in their user preferences. The alerts include a statewide email notice when SCA is first detected in the state, and then are localized by county as SCA moves into the state. The notices will also contain latest recommendations and contact info for local Extension experts.

 

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

 

 

Sorghum Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Chinch bugs are very active in double cropped sorghum in north central Kansas.  They are also numerous in corn but the field corn is mature enough that chinch bug feeding should be of little consequence.  However, young sorghum plants, especially under less than ideal growing conditions may be seriously stressed.

For more information on chinch bug biology, management decisions, and insecticides registered to control chinch bugs please see the Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

and Chinch Bugs: https://www.bookstore.ksre.ksu.edu/pubs/MF3107.pdf

 

 

Corn Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Have received several inquiries relative to corn earworms in field corn and there does seem to be a good infestation of them throughout north central Kansas.  100% of the ears we have randomly checked currently are, or have recently been, infested with corn earworm larvae.

Many of these larvae are still relatively small and thus will be feeding for another week or two.  The two most common questions received this week relative to these pests are; 1) Will a rescue treatment work?  The answer – no.  Once the larvae have hatched from eggs deposited on the silks and moved into the husk, they will be protected from contact insecticides.

 

 

2) Will they re-infest these corn ears?  The answer – no.  Field corn will be too tough by the time these larvae finish feeding, pupate in the soil, emerge as adults, mate, oviposit, hatch, and larvae initiate feeding.  But, the adults of this generation will move to soybeans (soybean podworms) and/or sorghum (sorghum headworms) to oviposit and larvae can do considerable damage by feeding on soybeans within the pods and/or directly on the kernels of the heads of sorghum plants.  So, the larvae currently in corn are the “spring board” for the next generations moving into soybeans and sorghum.

 

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

 

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Potato leafhoppers are still common in all alfalfa fields sampled in the last 7-10 days, unless they have been swathed during that period of time.  Fields swathed within the last week did not have enough potato leafhoppers to reach a treatment threshold.  However, fields swathed just 10-14 days earlier are once again loaded with these little lime green, wedge-shaped leafhoppers.

There do seem to be good populations of green lacewings in uncut alfalfa fields.  However, they do not appear to be impacting the potato leafhopper populations.  We did pick up one alfalfa weevil larva and one adult in an uncut alfalfa field but the alfalfa weevils should not be of concern as major defoliators until next spring.

 

 

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