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Extension Entomology

Category: Corn

Sorghum “Ragworms”

–by Dr. Jeff Whitworth and Dr. Holly Davis

Much of the sorghum around north central Kansas is at, or just coming into, the whorl stage.  As the leaves unfurl and grow out of the whorls, a pretty high number of plants are showing large holes that have been chewed in leaves.  These holes are from smaller larvae (most that we have sampled are corn earworms) that feed on the leaves while they are still furled. When leaves grow out of the whorl they have showy, ragged looking feeding that may cause concern.

Larvae sampled this week still have about one additional week of feeding within these whorls, then they will exit and crawl down the plant to pupate in the soil.  Larvae in the whorl are rarely worth spraying for four reasons: 1) by the time the leaves unfurl making feeding damage visible, most larvae have already accomplished most of their development and thus feeding, 2) insecticides usually can’t penetrate far enough down into the whorl to actually impact the larvae, 3) a general insecticide will kill most beneficial insects, and 4) ragged looking leaves during this stage have little to no effect on yield, and no, you cannot eliminate the next generation by spraying this generation.

 

Corn Update – Corn Rootworms and “Ragworms”

–by Dr. Jeff Whitworth and Dr. Holly Davis

Corn rootworm larvae continue to be very active in fields of continuous corn that have been planted to susceptible varieties.

Corn earworms have been feeding in north central Kansas corn for about a week now and signs of this feeding are now becoming visible as the leave start growing out of the whorl.  The small larvae may consist of corn earworms, fall armyworms, and/or armyworms, but all may cause the same type of ragged looking leaves, earning them the name “ragworms”.

 

 

This type of leaf feeding can be highly visible, and many plants can be impacted, but the data has always indicated there is little to no effect on yield.  In addition, the larvae are well sheltered within the whorl and thus insecticides only impact them when they exit the whorls to pupate in the soil.  And, by that time, all the feeding is completed anyway.

Corn Rootworms

— by Dr. Jeff Whitworth and Dr. Holly Davis

Western corn rootworm larvae have been detected for the 1st time this year in north central Kansas.  All were 1st instar larvae and most were still very small (recently hatched).  Thus, if you have any fields of three-plus year continuous corn planted with corn rootworm susceptible varieties, the rootworm feeding may become more and more evident over about the next three weeks.

For more information on corn rootworm management, please see Corn Rootworm Management in Kansas Field Corn: https://www.bookstore.ksre.ksu.edu/pubs/MF845.pdf

For more information relative to all corn pests, please see the KSU Corn Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF810.pdf

 

Revised Extension Publications

–by Jeff Whitworth and Holly Davis

 

Blister Beetles in Kansas, MF959, originally published by Robert Bauernfeind, Randall Higgins, Sue Blodgett, and Lowell Breeden in 1990 has been revised by Holly Davis and Jeff Whitworth. It is now available at: https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=573&pubId=1549

 

Corn Rootworm Management in Kansas Field Corn, MF845, originally published by Randall Higgins, Gerald E. Wilde, and Timothy Gibb in 1995 has been revised by Holly Davis and Jeff Whitworth.  It is now available at: https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=221&pubId=1502

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

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