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Extension Entomology

Tag: north central Kansas

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

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

 

 

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

 

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.

 

Chinch Bugs

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Chinch bugs are numerous and very active throughout north central Kansas, and have been for at least the last month.  The overwintering adults deposited eggs in wheat and oats, as far as our agricultural crops are concerned, and apparently the overwintering survival was relatively high because there have been huge numbers of chinch bugs migrating from these two crops.  Fortunately, most of the corn and sorghum have developed enough to be able to withstand relatively large numbers of chinch bugs as they suck plant nutrients.  Chinch bug populations sampled this past week consisted of 90% nymphs (both the very small reddish orange and larger gray nymphs, both of which have a transverse white stripe).

 

 

These nymphs, for the most part, are around the base of the plants feeding behind the leaf sheaths.  These bugs will feed and develop for approximately another couple of weeks, then mature into adults.  Mating and oviposition then will start another generation of chinch bugs that will continue to feed in corn and/or sorghum fields.  With good growing conditions, most of this feeding will go unnoticed and have little effect on yield.  However, if growing conditions deteriorate but bugs continue feeding, they can cause stalk lodging, which makes harvesting much more difficult.  Spraying for chinch bugs at this stage of crop development is usually not effective as most bugs are relatively inaccessible to insecticides at ground level behind leaf sheaths.

 

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Potato leafhoppers have been infesting alfalfa fields throughout north central Kansas for at least the last month.  They continue to be very active, which is causing quite a bit of leaf yellowing, often called ‘hopper burn’, and even stem and whole-plant stress.  Typically, swathing is sufficient to manage leafhopper populations.  However, they have been actively reproducing and there are many nymphs, so it will be especially important to continue to scout these fields after swathing.  If a stubble spray is deemed necessary after swathing, one application is often highly effective and re-infestation is unusual.

 

Alfalfa caterpillars are also quite common in alfalfa fields, where they feed on foliage, although they rarely do enough damage to warrant an insecticide application.  They will eventually pupate and then turn into a yellow or white sulphur butterfly.

Bean Leaf Beetles in Soybeans

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Soybeans seem to be growing really well around north central Kansas.  As these plants start germinating and growing, however, they provide very attractive hosts for bean leaf beetles.

 

These soybean pests have been inhabiting alfalfa fields and grassy areas since last fall, waiting for these first soybeans.  They are very efficient at finding young, succulent soybeans when the plants start emerging.  They are also relatively unique as foliage feeders because they usually chew round and/or oblong holes in the leaves.

These beetles can eat an alarming number of holes in these small plants.  However, the young plants are very resilient at overcoming this leaf feeding and so there is normally very little impact on yield.  For more information on bean leaf beetle biology, treatment thresholds, and management options please see the following:

Bean Leaf Beetles: https://www.bookstore.ksre.ksu.edu/pubs/MF2824.pdf

Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

Wheat Update – Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Wheat aphids have really started showing up in wheat fields throughout north central Kansas.  English grain and bird cherry-oat aphids are the two most commonly observed so far.

These aphids usually do not build up in sufficient populations to stress wheat or impact yield, especially when growing conditions are good, which they have been for the last couple of weeks.  These aphids can vector barley yellow dwarf virus, however at this time of year this should not impact yield.  These aphids are providing a plentiful food source for lady beetles, and all wheat fields sampled in the last seven days contained significant numbers of lady beetles.

Therefore, it is prudent not to spray for these wheat aphids unless there are 20+/tiller on a field-wide basis.  Especially do not include an insecticide in a mixture with a fungicide “just in case”.

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevil feeding activity has slowed significantly in north central Kansas, at least south of I-70.  North of I-70, larvae are still developing and thus feeding, but even in the northern counties this feeding and resultant damage should be significantly reduced by the end of the next week.  There are still some small larvae but the majority of populations are pupating or have pupated.  Adult weevils are still hanging out in alfalfa fields and probably will until that 1st cutting, or temperatures get into the mid-80’s or warmer.

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