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Extension Entomology

Category: Alfalfa

Alfalfa Update

— by Dr. Jeff Whitworth and Dr. Holly Davis

Several alfalfa fields were sampled in north central Kansas this past week.  The alfalfa canopy remains an excellent habitat for many insects, especially those fields not treated for alfalfa weevils this year.  Many of these insects are beneficial.

Very few pests, or potential pests, were detected although there were a few potato leafhoppers present.  These small, lime green, herky-jerky, moving pests are apparently just beginning to migrate into KS, as we didn’t find any earlier in the week, and now are only finding a couple of adults.  For more information relative to potato leafhopper management, please refer to the KSU 2018 Alfalfa Insect Management Guide:  https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

 

 

 

Soybean Update

— by Dr. Jeff Whitworth and Dr. Holly Davis

The first adult Dectes stem borer was detected on 23 June, from north central Kansas (specifically, DK Co.).  These beetles traditionally spend approximately 7-14 days congregating or aggregating around the borders of stubble fields near where they overwintered.  Then, they disperse throughout soybean and sunflower fields and begin depositing eggs in plants of either crop.  Several more have been collected since the 23rd.

Bean leaf beetle adults have been and will continue chewing characteristic round or oblong holes in soybean leaves.  However, at least around north central Kansas, populations seem reduced from recent years.

 

So far, other than a few small grasshopper nymphs, there seem to be less defoliators than usual in either alfalfa or soybeans.  However, there is still time left for significant populations to develop.  A few garden webworms and yellowstriped armyworms were collected from a couple of fields and many of the soybeans are still very small, in the 3-5 trifoliate stage.

 

Alfalfa Update — pea aphids, spotted alfalfa aphid, Lady beetle, green lacewings

— by Dr. Jeff Whitworth and Dr. Holly Davis

 

Most alfalfa monitored in north central Kanas in the last week has started flowering and swathing seems to be well underway.  Alfalfa weevil infestations, which we sampled throughout NC KS, never did exceed an overall 30% infestation level (using the cut stem bucket shake method).  This year, any time larval numbers started increasing, a sub-freezing cold spell came through and killed many newly hatched larvae.

 

Since alfalfa fields were not treated for alfalfa weevils they are currently a great place for many beneficials. Uncut fields sampled in the last week had healthy populations of pea aphids as well as a few spotted alfalfa aphids.

However, as beneficial populations increase, these aphid populations are rapidly declining.  Presently there are many lady beetles, both larvae and adults, and more adults will be active very soon as there are also many pupae.  There are also significant numbers of parasitic wasps parasitizing these aphids as indicated by many mummies.

Additionally, there are a few green lacewings present.  All this beneficial insect activity results in aphid populations declining significantly in the fields we sampled.  On 11 May, pea aphid populations averaged 50-60/stem, dropping to 6-7/stem on 16 May.  Hopefully, after swathing, the beneficials will still be present in sufficient numbers to continue providing aphid control but fields should still be monitored.  For more information relative to alfalfa insect management, please refer to the 2018 Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

 

Insect Management Guides, 2018

–by Jeff Whitworth and Holly Davis

 

 

 

Ms. Donna Sheffield, Communications Department, recently sent the links to the 2018 Insect Management Guides which can be found as follows:

Alfalfa, MF809: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=42&pubId=1492

Corn, MF810: https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=221&pubId=20262

Cotton, MF2674: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=1081&pubId=20259

Sorghum, MF742: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=281&pubId=20260

Soybean, MF743: https://www.bookstore.ksre.k-state.edu/Item.aspx?catId=281&pubId=20261

Wheat, MF745, https://www.bookstore.ksre.ksu.edu/Item.aspx?catId=299&pubId=1463

 

Alfalfa Update – alfalfa weevil, Lady beetle larva, Pea aphids

— by Jeff Whitworth and Holly Davis

Alfalfa weevils sampled this week were in all stages of larval development, although no pupae or adults were noted in any fields.  Actually, no adult alfalfa weevils have been detected yet this year.  Also, there is relatively little defoliation, at least so far, in north central Kansas.

No infestation levels exceeded 20% this week and most alfalfa is 10 – 16 inches tall and should grow better after recent rains.  Alfalfa weevil infestation levels in north central Kansas have not been this low, overall, for many, many years!

Pea aphids are still present in all fields sampled but not in population levels that cause concern.  Hopefully, they are currently just providing food for lady beetle populations.  So, at the present time, it does not seem that alfalfa is at risk for damage by alfalfa weevils or pea aphids.  For more information on alfalfa pest management, please see the Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Davis

Alfalfa fields sampled this week in north central Kansas had not really changed a great deal with stems anywhere from 2.5 to 9.5 inches tall.  Sampling the taller stems (8 – 9.5”) resulted in a composite infestation of 10%.  Sampling only the smaller stems (2.5 – 4.5”) resulted in a composite infestation of 27%. The lowest overall infestation level detected from any field was 10% and the highest infestation level was 30%.  Smaller stems had smaller larvae with no, or very little damage or defoliation, while larger stems often had evidence of feeding, but no larvae.  Thus, it seems the earlier hatching larvae may have been killed by the recent cold weather, or at least populations were reduced. However, we did find 3rd instar larvae and even a pupa.  There are also quite a few small 1st instar larvae.  This probably means eggs are still hatching with more larvae to come, so at least 1 more week of monitoring would be prudent.

 

 

Pea aphids are still present in all alfalfa fields sampled but not yet in numbers to be concerned about.  However, there were no beneficials, (lady beetles, lacewings, or parasitic wasps) noted either.

 

 

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

 

Alfalfa Update — pea aphids, green lacewing

— by Dr. Jeff Whitworth and Dr. Holly Davis

 

Alfalfa fields were again sampled 18 April, after the latest bout of sub-freezing temperatures.  Alfalfa weevil larval development does not seem to have progressed much since fields were sampled last week.  All larvae that were collected from plant terminals were still small, 1st instar larvae.  Like the last two week’s samples, there were live 1st instar larvae feeding beside dead larvae.  However, a few larger, 2nd instar larvae were found in the leaf litter under the alfalfa canopy.  Infestation levels varied considerably depending on location.  Open fields with exposure to wind had infestations ranging from 0% (no live larvae found) to a maximum of 10%.  However, one small alfalfa field that was bordered on the north by a windrow had a 35% infestation of live, feeding larvae.

Pea aphids were also detected in every alfalfa field sampled.  Some were already producing nymphs.  Unlike last week, no lady beetles or mummified aphids were noted, but an adult green lacewing was collected from the alfalfa canopy.

For more information on Alfalfa Insect Management, please visit: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

Alfalfa Update – alfalfa weevil larvae, pea aphids, lady beetles

–by Dr Jeff Whitworth and Dr Holly Davis

Sampled alfalfa fields in north central Kansas on 11 April.  Despite the recent cold weather and lack of measurable moisture, the alfalfa did not show obvious signs of stress and had even grown a little since the 4th and 5th of April when we last checked these fields.  The recent cold temperatures apparently took a toll on some of the small alfalfa weevil larvae.  However, it did not kill them all as we found live larvae of different sizes still feeding in terminals and often live ones feeding right beside dead ones.

 

 

In no case did we find more than a 5% infestation.  No adults or larvae were found in the leaf litter below the canopy.  So, apparently, the recent record cold temperatures killed 40-50% of the small alfalfa weevil larvae that had started feeding.  It remains to be seen how many eggs are still to hatch, but so far infestation levels we have noted are not anywhere near treatment thresholds.

 

 

Pea aphids were also noted as were parasitized pea aphids (mummies).  Lady beetles were also active.  For management decisions relative to alfalfa pests, please see the Alfalfa Insect Management Guide, available at: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

 

 

 

Alfalfa Weevil Update

— by Dr. Jeff Whitworth and Dr. Holly Davis

Alfalfa weevils continue to create considerable interest for producers and consultants.  Alfalfa fields sampled on 21 March had small, 1st instar larvae and a few, very few, signs of feeding.  A few pinprick sized holes and small signs of feeding were noted in the terminals.

 

Fields checked 4 and 5 April contained considerably fewer larvae, and still only 1st instars.  Plants were frosty, but no dead or dying larvae were found.  Larvae often crawl down and hide under plant residue on the soil surface during periods of inclement weather and therefore survive.  No fields were sampled that had more than a 10% infestation, yet.  For more information relative to alfalfa weevil management, please see the Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

Fall armyworms, Armyworms, and Army Cutworms in Wheat

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Where wheat has emerged, fields need to be checked for fall armyworms, armyworms, and army cutworms. If you see worms on your wheat this fall, the first thing to do is to determine which worm is present. Proper identification is important because they have different feeding and overwintering patterns.

We have been hearing about and seeing a mixture of both armyworms and fall armyworms on wheat and other host plants this fall. These small worms start by causing small “windowpanes” in wheat or alfalfa. No army cutworm infestations have been verified yet on wheat.

Flocks of birds in wheat or alfalfa fields in fall or early spring are often indicative of a “worm” infestation as the birds are feeding on the larvae. Fields with 25-30% of the plants showing “windowpane” feeding need to be monitored frequently as these larvae consume more as they get larger. Treatment should be applied before stands become threatened.

Fall armyworms

When scouting fields for fall armyworm damage, look for “windowpane” injury caused by tiny larvae chewing on seedling leaves. Each individual field should be scouted in several locations, including the field margins and the interior. The larvae themselves are usually too small to be easily observed after they first hatch, and hide in or around the base of seedlings. Within a few days of hatching, the larvae become large enough to destroy entire leaves.

The suggested treatment threshold is 2-3 actively feeding larvae per linear foot of row in wheat. Fields with 25 to 30 percent of plants with windowpane injury should be re-examined daily and treated immediately if stand establishment appears threatened. Larvae increase in size at an exponential rate, and so do their food requirements. Later instars do the most damage, sometimes destroying entire stands, and are the least susceptible to insecticides. Without treatment, problems can continue until larvae reach maturity or until a killing frost. Thin strands of wheat are especially at risk.

 

Fall armyworms will feed until the temperatures cool into the mid-20’s or they pupate, whichever comes first. If a killing frost does not occur soon after the treatment threshold is reached, fields may require chemical treatment.

 

Armyworms

Armyworm larvae are green to black with stripes of various colors. The head capsule is medium brown with dark markings. Most damage to wheat in Kansas occurs in southern and eastern areas of the state during warm, moist periods from late April to early June rather than in the fall. Like fall armyworms, armyworms will feed until the temperatures cool in the mid-20’s or they pupate, whichever comes first.

Most armyworm damage occurs during the last three to five days of larval feeding. When leaf feeding is observed, look for larvae curled up on the ground under litter, especially in patches of lodged plants. Treatment is usually not necessary below levels of four or five larvae per foot, but is probably justified at infestations of five to eight per foot depending upon larval maturity in relation to crop maturity.

 

Army cutworm

The army cutworm is a late fall /early spring pest in Kansas. Leaf damage by early stage army cutworm larvae  looks very similar to that of fall armyworms. However, army cutworm larvae are typically very small in the early fall – smaller than fall armyworms or armyworms. If the worms causing defoliation in wheat in the fall are relatively large, ½ inch or more, they are probably armyworms and/or fall armyworms.

Adult moths lay eggs in soil in the fall. The brown, faintly striped larvae hatch during the fall and early winter. They will feed throughout the winter (unlike armyworm and fall armyworm larvae), burrowing in the soil to escape frost and emerging again to feed during sp

Unlike other cutworms, only above ground plant parts are consumed, giving plants the ap­pearance of being grazed by cattle.

Infestations in well­-established stands will probably not require insecticide appli­cations while wheat is dormant, but some fields never green up in the spring because of cutworm feeding. Along with fall scouting, frequent inspections during warm periods in February, March, and early April are strongly encouraged, particularly when preceded by a dry fall.

Moisture availability, crop condition, and regrowth potential are all factors influencing potential losses to this pest. Late­-planted fields under dry conditions with poor tiller­ing may suffer economic damage with as few as one or two larvae per square foot.

In most fields, treatment will not be necessary until populations average four to five worms per square foot. Vigorous, well-­tillered fields under optimal growing conditions can tolerate even higher popu­lations, as many as nine or 10 larvae per square foot, without measurable yield loss. Infestations in later stages of crop develop­ment are less damaging than early ones because established plants can compensate for considerable defoliation and larvae normally finish feeding before wheat enters reproductive stages.

Mixed populations

Mostly the same insecticides are registered for control of these species of worms, but higher rates are recommended for fall armyworm. Any fields with mixed populations should be treated with the fall armyworm rate.

For treatment options, please refer to the latest K-State Wheat Insect Management Guide 2017 at: http://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

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