Kansas State University

search

Extension Entomology

Category: Corn

Corn and Sorghum Update

— by Dr. Jeff Whitworth and Dr. Holly Davis

Chinch bug populations continue to increase at a very disconcerting rate.  Most corn throughout north central Kansas is far enough along in its development to tolerate large numbers of chinch bugs.  Smaller sorghum can still be seriously stressed by growing populations of chinch bugs, especially as the hot and dry conditions return.  For more information of chinch bug management in sorghum, please see the KSU 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

One relatively mature fall armyworm larva was also detected.  Thus, in approximately 2-3 weeks there will be a new generation of fall armyworm larva ready to start feeding, most likely, on sorghum.

 

Green June Beetles vs. Japanese Beetles

— by Dr. Jeff Whitworth and Dr. Holly Davis

Adults of both green June beetles and Japanese beetles seem to be ramping up their activity throughout eastern Kansas.  These two relatively large, conspicuous beetles are being confused.  Green June beetles, at 1 inch long, are considerably larger than Japanese beetles.  Also, green June beetles are green to copperish green in color and more pointed toward the anterior (head) end.  Japanese beetles are probably only 1/3 to ½ as big as the green June beetle.  They also have small, but highly visible, little white tufts of hair on both sides of the abdomen sticking out from under the elytra.

 

 

Japanese beetles may be found feeding on silks in corn fields and/or pollen or leaves in soybeans while green June beetles are more confined to feeding on nectar from flowering bushes or trees close to where the larval stage, i.e. grubs, were developing in the soil.  Green June beetles are not an agricultural concern while Japanese beetles occasionally can be.

 

Chinch Bugs

— by Dr. Jeff Whitworth and Dr. Holly Davis

 

All life stages of chinch bugs seem to be extremely active at the present time in both corn and sorghum.  Nymphs and adults started migrating out of wheat fields at least two weeks ago, moving into any adjacent corn or sorghum fields.  Those smaller reddish nymphs have grown considerably since then, and are now either late instar nymphs or adults.

 

Many of these recently matured adults are now mating and have even started egg deposition.  These eggs are, and will continue to be, hatching which means more bugs and thus more feeding on these plants.  Fortunately, most corn is large enough to withstand considerable feeding by chinch bugs. Plus, the recent rains greatly enhanced growing conditions, which increases the plant’s tolerance for chinch bug feeding.  However, most sorghum is much less developed and won’t be able to tolerate as many chinch bugs as the larger corn plants.  Treating plants much after the V-6/V-7 growth stages is not as effective as treating smaller plants.  Like corn, good growing conditions significantly help plants withstand chinch bug feeding.  However, if dry, droughty conditions return, chinch bug feeding can significantly weaken stalks and cause lodging later in the season.  For more information on chinch bugs, management decisions, and/ or insecticide recommendations, please see:

Chinch Bugs MF3107:  https://www.bookstore.ksre.ksu.edu/pubs/mf3107.pdf

2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

Corn Rootworms

— by Dr. Jeff Whitworth and Dr. Holly Davis

The first western corn rootworm (WCR) adults were observed on 12 June from north central Kansas.  There are still larvae feeding on roots but most are/have pupated and adults are emerging from soil.

 

None of the corn sampled in north central Kanas has tasseled or started silking yet.  Thus, these adult WCRs are feeding on leaf tissue in the early morning or early evening and resting in shady places during the hottest part of the day.

A great example of WCR larval root pruning is seen in this picture compared to a non-infested root system.

Chinch Bugs in Corn and Sorghum

–by Dr. Jeff Whitworth and Dr. Holly Davis

As the wheat senesces, it continues to be less and less succulent.  Thus, chinch bugs have been, and will continue to, migrate to find a suitable food source.  They will utilize any actively growing grasses in the vicinity.  The small nymphs cannot fly and thus must crawl to the nearest food source.  They are pretty fragile and therefore can’t go very far without finding a food source before they perish.

 

Most corn planted adjacent to wheat is already large enough to withstand chinch bug feeding.  However, seedling sorghum, especially if it is already stressed by the heat and dry conditions, may be overwhelmed and thus killed by this additional stressor.  Sampling wheat for chinch bugs now, as it is still senescing, should give an idea about potential chinch bug numbers migrating from wheat.  If several samples of different 1 ft2 areas detect an average of 1 chinch bug, some chinch bug management technique should be utilized.  For more information on chinch bug biology and management recommendations please see MF3107, Chinch Bugs: https://www.bookstore.ksre.ksu.edu/pubs/mf3107.pdf and/or the 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

Corn Rootworms

–by Dr. Jeff Whitworth and Dr. Holly Davis

Corn rootworm feeding should be mostly completed by mid-June throughout north central Kansas.  Thus, if there is any lodging or goose necking caused by corn rootworms, it should be showing up in the next week or two.  In-furrow planting time insecticide applications still seem to work really well, as do Bt corn rootworm varieties.  Crop rotation and adult management also work exceedingly well. For more information regarding corn insect management please see the 2018 Corn Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf810.pdf

 

 

 

 

 

 

Insect Management Guides, 2018

–by Jeff Whitworth and Holly Davis

 

 

 

Ms. Donna Sheffield, Communications Department, recently sent the links to the 2018 Insect Management Guides which can be found as follows:

Alfalfa, MF809: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=42&pubId=1492

Corn, MF810: https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=221&pubId=20262

Cotton, MF2674: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=1081&pubId=20259

Sorghum, MF742: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=281&pubId=20260

Soybean, MF743: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=281&pubId=20261

Wheat, MF745, https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=299&pubId=1463

 

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.

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.

 

Japanese Beetles

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Adult Japanese beetles have been detected around north central Kansas in the last 7-10 days.  These adults may feed on corn, sorghum, and soybean leaves, as far as field crops are concerned, and may cause some “window paneing” much like the leaf feeding of adult corn rootworms.  However, this leaf feeding usually is of little consequence.  In corn, these beetles will be attracted to the silks and, as they can be very veracious feeders, may clip these silks at a pretty good rate.  Fortunately, they are usually localized to small “hot spots” in some fields and thus do not really justify any insecticide application.  These adult Japanese beetles may be active for another couple of weeks, after which only eggs and larvae will be present, and these life stages are not a threat to these crops.

 

Subscribe By Email

Get every new post delivered right to your inbox.

Please prove that you are not a robot.