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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

Armyworm in Brome and Rye

— by Dr. Jeff Whitworth and Dr. Holly Davis

We have received several calls and emails relative to armyworms feeding in brome and/or rye fields.  Larvae sampled this week are relatively mature and should finish feeding and pupate within the week.  This larval feeding (defoliation) should not impact a healthy brome stand as they just graze on the foliage.  However, rye that is not growing well may have some stand reduction.  Whether feeding on brome or rye, the larvae we sampled should cease feeding within the next 3-4 days, or less.

 

 

 

 

Alfalfa Update — lady beetles, green lacewings, potato leafhoppers, Fall armyworms, green cloverworms

— by Dr. Jeff Whitworth and Dr. Holly Davis

Alfalfa is really living up to its reputation as a ‘sink’ right now for many different insect species, including many beneficials such as lady beetles and green lacewings.  The one and only potentially serious pest that we are still seeing is potato leafhoppers, and they are in densities that exceed treatment threshold in all fields sampled.  These very small, lime green, wedge-shaped insects that move in a herky-jerky manner remove fluid from the alfalfa leaves.  This feeding may also introduce a toxin which initially causes the tips of leaves to turn yellow (hopper burn), but may impact the entire stem, and eventually the whole plant. This can be especially problematic this time of year when the plants need to utilize the foliage to transfer nutrients to the roots before winter.  The potato leafhopper populations will hopefully be diminishing as they don’t overwinter in Kansas and thus should be heading to the southern U.S. soon. Swathing should also help diminish populations.

 

This time of year fall armyworms may move into alfalfa where they can add to the defoliation caused by other chewing insects already present.  Fall armyworms are more commonly thought of as a pest of corn and sorghum.  This time of year those crops are too mature to support the larvae and therefore the adult moths may oviposit in alfalfa.

We also noticed several green cloverworms along with one larva infected with an entomopathogenic fungus.

 

 

For more information relative to insect pest management in alfalfa, please see the KSU 2018 Insect Pest Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

Soybean Update – Green Cloverworms and Stink Bugs

–by  Dr. Jeff Whitworth and Dr. Holly Davis

Probably the most common defoliator of soybeans throughout Kansas, for the past 6-7 years, has been the green cloverworm.  This year has been no exception to that although there have not been the significant densities throughout most of the state as in 2015-2017.  Most green cloverworm larvae are relatively mature or have pupated and the adult moths are, and will continue to be, emerging.  In south central and north central KS, these moths are gaining attention as they congregate around lights at night and can be found hiding under boards, logs, rocks, etc. around soybean and/or alfalfa fields during the day.

 

One point of concern is relative to the next generation of larvae.  The adults that are present now are from the 2nd generation.  In KS, we can have 3 generations/year.  So, current adults may oviposit in alfalfa and soybean fields and the larvae may feed for the next few weeks.  However, both alfalfa and soybeans are far enough along that this late season feeding should not impact yields of either crop.  Another concern is about these moths congregating in and around fields and what that means for next year.  Green cloverworms do not overwinter in KS.  So, wherever they migrate, or are blown, in next summer is where they will initiate infestations.  Therefore, infestations next year have nothing to do with infestations this year.

 

Stink bugs are also causing some concern for soybean producers.  The two most common stink bugs found in KS soybean fields are the brown and green stink bugs.  Both lay eggs in groups or clusters and green stink bug nymphs are red, black, yellow, and green while brown stink bug nymphs are generally just yellow to brown.

 

 

 

 

 

 

After emerging from the eggs, nymphs stay in the same vicinity for the 1st couple of molts and then disperse.  So, sampling in areas with clusters of nymphs will often overestimate the density.  They all have sucking mouthparts but must have tender, succulent tissue to suck the juice from.  Treatment should only be considered while beans are still filling in the pods.  Stink bugs have a wide host range of plants including other crops, vegetables, and weeds.  So, make sure they are feeding upon the developing seeds before making treatment decisions.

For more information on management of soybean pests, please refer to the 2018 Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf743.pdf

 

Volunteer Wheat

–By Dr. Jeff Whitworth and Dr. Holly Schwarting

Again, please remember every moisture event prompts the growth of volunteer wheat.  This volunteer wheat needs to be controlled at least 2 weeks prior to planting to help mitigate all wheat pests;  pathogens, mites, and insects.

 

Sorghum Update – ‘Headworms’, Beneficials, and Aphids

–By Dr. Jeff Whitworth and Dr. Holly Schwarting

Sorghum continues to get the attention of many pests and beneficials.  Chinch bug populations are not diminishing even though they are not as noticeable because most are feeding around the base of the plants and behind leaf sheaths on the stalks.  Much late planted, or at least slower developing, sorghum is still vulnerable to these chinch bugs.  Bugs may also move up to the heads as they emerge from the whorl to feed on the forming kernels that provide a succulent source of nutrients.

‘Sorghum headworms’, mostly corn earworms but also a few fall armyworms, are infesting all sorghum fields (not yet in the soft dough stage) that we monitored throughout north central Kansas.  Most fields have close to, or are exceeding, 100% infestation levels (1 or more larvae/head).  These larvae are present in all different sizes, or developmental stages, from 1st to 4th instars.  Thus, they will be feeding on these kernels for at least another 7 – 10 days.

Remember, between flowering and soft dough, these larvae will cause 5% yield loss/ worm/ head.  Very few beneficials are available to help control headworm populations.  However, there are huge populations of beneficials currently present to help control any aphid pests that are, or might be present in the near future.

 

 

Corn leaf aphid populations were common on earlier planted sorghum, and still are on later planted sorghum that is just reaching the whorl stage.  These corn leaf aphids have really helped fuel the beneficial populations.  Fields that have headed out are swarming with lady beetle adults and larvae, syrphid or hover flies, green lacewings, and parasitic wasps.

 

 

 

Sugarcane aphid (SCA) populations are becoming scattered around north central KS, slowly so far, and are really attracting the attention of all these beneficials, which will hopefully help control colony growth.

For management considerations and recommendations for these, and other sorghum pests, please refer to the 2018 Sorghum Insect Management Guide:   https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

 

Soybean Update – Defoliators and Podworms

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Soybeans seem to be attracting the attention of many different types of pests, including many defoliators.  Currently, they are mainly green cloverworms, yellowstriped armyworms, and thistle caterpillars.  Fortunately, populations of these species, or any others for that matter, have not reached densities that have warranted insecticide applications, for the most part.

Unfortunately, soybean podworm (a.k.a. corn earworm/sorghum headworm/cotton bollworm) populations are on the increase in south central and north central Kansas.  These worms eat right through the pod to get at, and consume, the seeds within.  So, as the seeds are filling, they are susceptible to being fed upon by these podworm larvae.  They will feed on smaller, more succulent beans for 10-14 days, then cease feeding to pupate.  Since they are feeding directly on the marketable product, it doesn’t take much of this feeding to reduce yield.

 

 

One important point to remember relative to treating for soybean podworms: these are contact insecticides and thus they must physically contact the targeted pest.  Therefore, you need to utilize enough carrier (water) to penetrate throughout the soybean canopy to get to where these larvae are feeding.  But, you need to do this while the larvae are still small and before they have negatively impacted the yield.  There will probably be at least one more generation this year, so monitoring needs to continue as long as plants are adding pods and there is succulent green reproductive tissue to feed on.  For treatment thresholds and insecticide information, please refer to the 2018 Soybean Insect Management Guide available at: https://www.bookstore.ksre.ksu.edu/pubs/mf743.pdf

 

Volunteer Wheat

–by Dr. Jeff Whitworth and Dr. Holly Davis

 

It is once again time to control volunteer wheat!  This needs to be done at least 2 weeks prior to wheat planting and will help mitigate problems with Hessian flies, wheat curl mites, wheat aphids (Russian, bird cherry-oat, greenbug, etc.) and diseases.

Sorghum Update – ‘Ragworms’, ‘Headworms’, and Aphids

–by Dr. Jeff Whitworth and Dr. Holly Davis

Late planted sorghum is still causing considerable concern throughout north central Kansas as the leaves grow out of the whorl and are significantly ‘chewed up’ looking.  These ‘ragworms’, primarily corn earworms and fall armyworms but also a few cattail caterpillars, are still active in younger plants.

 

As these plants reach reproductive stages, i.e. flowering, there will be a high probability of having ‘headworms’ (corn earworms and fall armyworms) infesting the kernels.  Sorghum heads are the most vulnerable between flowering and soft dough.  There are currently significant infestations of these headworms throughout north central Kansas with worms in various stages of development.  Headworms cause approximately 5% loss per worm, per head.

 

There are large numbers of corn leaf aphids, greenbugs, and even a few yellow sugarcane aphids around north central Kansas.  The first report of a sugarcane aphid colony from Saline Co. was made on 16 August. These aphids are attracting, and providing food for, large numbers of beneficials which seem to be keeping aphids relatively well controlled.  Insecticide applications have not been needed for aphids. More information on sugarcane aphids in Kansas can be found at My Fields: https://www.myfields.info/pests/sugarcane-aphid

 

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

Sorghum Update – Chinch bugs, Headworms, and Corn Leaf Aphids

–by Dr. Jeff Whitworth and Dr. Holly Davis

 

Chinch bug populations continue to increase dramatically throughout north central Kansas.  Adults are still active, mating and ovipositing in both the developing heads and around the base of plants.  There are also large numbers of nymphs, mainly feeding in and around the base of plants, but some are on the developing kernels.  The significant populations of chinch bugs, along with continued hot and dry conditions, are causing some plants to lodge as the stalks dry down prematurely.

 

‘Headworms’, both fall armyworms and corn earworms, are also very common in all the fields we sampled that were in the flowering stages.  On 6 August, there were all different sizes of larvae detected in heads.  Many fields throughout north central Kansas are just starting to reach the reproductive stages, so these ‘headworms’ will continue to be problematic in any field that is in the flowering to soft dough stage.  Past research has indicted that ‘headworms’ may cause approximately 5% loss/worm/head.  It is important to sample in a timely manner to detect these pests while they are still small, before most of the feeding damage has been done.

 

Corn leaf aphids (CLA) continue to cause considerable concern throughout north central Kansas as these populations are still very widespread and become more apparent as the heads start to extend out of the whorl.  However, there are many beneficials present as well.  CLA should have little to no negative impact on plant development or yield other than potentially a few individual plants.

 

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

 

 

 

 

Soybean – Bean Leaf Beetles and Defoliators

–by Dr. Jeff Whitworth and Dr. Holly Davis

Soybean fields around north central Kansas still seem to be relatively unbothered by defoliators.  Bean leaf beetle adults are increasing in numbers and may begin feeding on the succulent pods as they form.

The next generation of corn earworms (coming from sorghum fields) may start feeding on the beans within the pods, although we did not find any pod feeding yet.  The only defoliators sampled this past week were a few green cloverworms, thistle caterpillars, and yellowstriped armyworms.  None were in sufficient numbers to cause concern, individually or collectively.

For more information relative to soybean insect management, please see the 2018 Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf743.pdf

 

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