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Extension Entomology

Tag: north central Kansas

Japanese Beetles

Posted on by Sharon Schroll

— 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

Posted on by Sharon Schroll

–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

Posted on by Sharon Schroll

–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

Posted on by Sharon Schroll

–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

Posted on by Sharon Schroll

–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

Posted on by Sharon Schroll

–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.

Alfalfa Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Alfalfa weevil populations in north central Kansas seem to be developing as expected.  Fields sampled this week that had not yet been treated had greatly reduced foliage and were showing obvious signs of significant larval feeding, especially compared to fields that had been treated.

 

 

The good news is that the treated fields seem to be doing well and the untreated fields will probably only continue to be seriously impacted for about another week.  Weevil populations are predominately pupae, pre-pupae, or mature larvae which should cease feeding in the next few days.

 

 

This should give the alfalfa a chance to recover.  However, in untreated fields, and even fields that were treated later, after a majority of the larvae pupated, may have some adult feeding, as they may remain in fields until the 1st cutting or until temperatures start getting into the higher 80’s °F.  Adults feed a little on foliage and/or may cause ‘barking’ on stems, but this usually doesn’t stress plants too much unless there are significant numbers of adults.

 

Very few aphids were detected, but there were a few so periodical sampling should continue to ensure that these aphid populations remain at insignificant levels.

 

Alfalfa Update

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are cool weather insects, thriving when temperatures are between 50-75°F and thus mostly affect alfalfa prior to the 1st cutting. That has been the case for about the last two weeks in north central KS. Temperatures have been on the cool side and the alfalfa has not been growing as well as most producers would like.  However, alfalfa weevils have been very active to the point where there are many pupae and even pupal webbing with holes indicating the adult weevils have already emerged and dispersed.  Infestations as of 6 April were composed of very small 1st instar larvae to larger, more mature 3rd instar larvae, as well as pupae, and newly developed adults.  Also, lady beetle larvae were quite common in most alfalfa fields, but no aphids were detected.

Alfalfa weevil feeding damage

 

Alfalfa weevil feeding damage – close

 

Alfalfa Update

Posted on by Sharon Schroll

–by  Dr. Jeff Whitworth, Dr. Holly Schwarting & JR Ewing

Alfalfa weevil larvae continue to hatch throughout north central Kansas.  Plants still do not seem to be growing very much.  The larvae that have hatched are still tucked inside the tightly closed terminals where they do not shake out very readily when utilizing the “shake bucket” sampling technique.  Thus, many producers are underestimating infestation levels.  So, when sampling to determine treatment threshold, be careful to account for the small stems that hold larvae which aren’t shaking loose.  These small plants need to be totally pulled apart to get an accurate count on alfalfa weevil larvae.

22 March, 2017 – Showing little growth in alfalfa

 

As of 22 March, there were various developmental stages of larvae.  Pea aphids were still present in all alfalfa fields that we checked.  However, no infestation level that would be of concern was detected.  Also some producers have/are burning the existing alfalfa as a form of weevil and weed control.

Picture of an apparatus for burning provided by “The Specimen”

 

Alfalfa Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth, Dr. Holly Schwarting & JR Ewing

Alfalfa weevil larvae have been hatching throughout north central and south central Kansas for the last couple of weeks.  However, as of 9 March, there doesn’t seem to be much feeding or development yet (Photo1).  There are also a few of these tiny larvae that are dead (Photo2).  Because these larvae are so small and vulnerable it is difficult to determine the cause of death.  At least some of the mortality could be related to weather fluctuations that have reached mid 70’s for several days but also dropping into the mid to low 20’s some nights.

 

 

 

Most of these larvae are so small that they are well enclosed within the plant terminals to the point that they cannot be dislodged by shaking the stems into a bucket, as the most accurate sampling method specifies.  This can definitely cause you to underestimate larval populations.  Probably the easiest solution is to hold off sampling until the middle of next week, if the weather turns cooler as predicted.  There are a few more mature larvae present, along with adult weevils (Photos 3, 4). Adults will probably continue depositing eggs for a few more weeks, thus extending the period of larval hatching.

 

 

There are also a few pea aphids present.  Populations do not seem to be increasing now, and there are lady beetles and parasitoid wasps actively attacking these aphids.  Also, reports of cowpea aphids in south central Kansas bear watching.  These aphids are usually more numerous in warmer summer months.  They can add stress to plants by feeding, but they also produce copious quantities of honeydew which can become covered with sooty mold.  This may further stress alfalfa by interfering with photosynthesis, especially with small plants coming out of winter dormancy and experiencing dry conditions and fluctuating temperatures.