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Extension Entomology

Category: Sorghum

Sorghum Update

–by Jeff Whitworth, Holly Davis and J.R.Ewing

 

Chinch bugs continue to feed and develop all around north central Kansas.  However, growing conditions have improved significantly and thus the plants are much better able to tolerate this feeding.

 

As sorghum reaches the whorl stage corn leaf aphids are becoming more common.  These aphids may cause some concern as their honeydew production will occasionally be so thick and sticky as to retard the heads extending up from the whorl.  This is not typically a field-wide problem, just a few places or plants in a field and these aphids are a good source of nutrition for beneficials.

Photo by JR Ewing

In addition, as sorghum leaves grow out of the whorl stage, they are showing signs of feeding.  Fall armyworms have been feeding as small larvae within the whorl and as plants grow out and the leaves unfurl, these leaves have a very ragged appearance.  Many of these ‘ragworms’ have finished feeding and are now pupating in the soil.  Thus, spraying is not necessary as the damage is done.  Even if the worms are still in the whorl, they will not be contacted by the spray.  This whorl-stage leaf feeding doesn’t negatively impact the plant, or yield.  There will probably be a least one more generation of fall armyworms and these may be more problematic if they start feeding in the head between flowering and soft dough stages.  Feeding on these developing kernels is generally considered to cost 5% loss/worm/head.

 

 

 

 

For more information regarding sorghum insect pest management please refer to the KSU 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

Chinch Bugs and Ragworms in Sorghum

–by Dr. Jeff Whitworth and Dr. Holly Davis

Chinch bugs continue to develop and increase in numbers throughout north central Kansas.  However, recent rains have significantly improved growing conditions.  Thus, sorghum seems to be tolerating these chinch bug populations well.  However, some fields and field borders have been treated for chinch bugs.

Fall armyworm larvae have been feeding in sorghum whorls and this leaf feeding is starting to unfurl from the whorl and thus become highly visible.  That is where the name “ragworms” comes from as they do cause ragged looking leaves, although this foliar feeding does not impact yield.

 

For more information, please see the 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

Chinch Bugs in Sorghum

–by Dr. Jeff Whitworth and Dr. Holly Davis

Chinch bug adults continue to mate and deposit eggs, especially around the base of young sorghum plants.  As these eggs hatch, nymphs are increasing in both numbers and size and thus are removing more and more of the moisture from the plant.

 

 

This trend will probably continue from now until September and thus cause serious stress to plants, especially if environmental moisture is limited.   If treatment is warranted, it is important to use directed sprays and adequate carrier to reach the base of plants where chinch bugs are actively feeding.  This will also avoid non-target organisms as much as possible. 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 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.

 

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

 

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

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.

Sorghum Update – Chinch Bugs, Sugarcane Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Chinch bug populations throughout north central and south central KS are not going away. These small sucking insects may still cause plant lodging, especially in these areas where moisture has been lacking

 

 

A small colony of sugarcane aphids was detected in Dickinson County on 30 Aug.  The colony was on the underside of one leaf on whorl-stage sorghum.  Tom Maxwell, Saline Co. Agricultural Extension Agent reported finding sugarcane aphids in Saline, Seward, and Ottawa Counties, also on 30 Aug. To see the current 2017 Sugarcane aphid distribution map, please visit MyFields: https://www.myfields.info/pests/sugarcane-aphid

For monitoring and management considerations for sugarcane aphids, please refer to the Sugarcane Scout Card: https://www.myfields.info/sites/default/files/page/ScoutCard%20KSU%20v05312017.pdf

Or see the 2017 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF742.pdf

 

 

 

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