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Extension Entomology

Tag: depositing eggs

Alfalfa Update

–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.

 

 

 

 

Soybean Pest Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

What a difference a few days makes in the world of insects!  Two weeks ago, and prior, there were very few insect pests in soybeans throughout north central and south central Kansas.  Now, most soybean fields are loaded, with more coming all the time.  Some of the insects common to soybean fields throughout north central, south central, and south east Kansas right now are as follows:

Dectes stem borer adults. These have been actively depositing eggs in petioles for a few weeks although populations seem somewhat reduced compared to the past few years.  Larval tunneling within the petiole and resultant petiole death has not yet become very apparent.

Dectes

Bean leaf beetle adults. These feed on the leaves, usually causing mostly round or oblong holes, which are of little consequence.  However, these same adults can also feed on the pods which may damage the bean inside and thus cause significant yield reductions.

bean leaf beetle feeding

Bean leaf beetle

bean leaf beetle pod feeding

“Worms”. There are also significant numbers of a variety of “worms” or caterpillars in most soybean fields.  These include various stages of yellowstriped armyworms, which may feed on the leaves but not enough to impact plant health or yield.

yellowstriped armyworm

There are also numerous green cloverworms, which are also leaf feeders.  These are the “inchworms” that wiggle like crazy when disturbed.

green cloverworm_feeding

They are usually highly susceptible to a fungus that turn infected larvae white and decimates the population rapidly over large areas.  Green cloverworms may cause a great deal of concern because of the defoliation they cause, but rarely are they any real detriment to the plant.  However, make sure to properly identify the worms as there are also corn earworms, aka soybean podworms, which may be mistaken for green cloverworms.

Soybean podworm

Soybean podworms will feed on leaves but more worrisome is when they start feeding on the developing seeds within the pods.  Two or three pods fed on per plant may justify control if there are still larvae in the field.  Otherwise, they may have pupated and treatment should be delayed until sampling indicates the next generation of larvae is actively feeding on seeds within pods.

Alfalfa caterpillars are also feeding on leaves and adding to the worm variety but will not cause any detrimental impact on yield.

alfalfa caterpillar and green cloverworm

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