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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

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

 

Metopolophium festucae cerealium (Stroyan), a new aphid in Kansas wheat

— by Dr. J.P. Michaud — Hays, KS

In 1982, Stroyan distinguished a subspecies of Metopolophium festucae, sensu stricto, as M. f. cerealium based on morphological characters.  Whereas the former subspecies infests various wild grasses and is only incidental on grain crops, the latter is a potentially significant pest of cereals, especially wheat.  Although this aphid complex has been present in North America since the 1970s, it was not until 2011 that significant M. f. cerealium infestations of wheat (as well as barley and oats) were discovered in the Pacific Northwest.  The winged adults are pale yellowish with dark markings on the dorsal surface (Fig. 1), whereas apterae are pale yellow, similar in color to sugarcane aphids, but with a more elongate body shape (Fig. 2).

Fig. 1

Fig 2

On the morning of May 17, 2018, we collected a number of winged M. f. cerealium using a sweep net in wheat plots on the Agricultural Research Center-Hays.  Other aphids present included Sitobion avenae and Rhopalosiphum padi, but all three species were present in low numbers, and were attended by the usual complex of aphid predators.  It should also be noted that apterous M. f. cerealium were not found, so the winged forms are most likely very recent migrants.  It is quite possible that existing biological controls will maintain this new aphid below economic levels along with all the other species present in wheat, but farmers should be vigilant for possible outbreaks in particular fields, especially later-maturing varieties that will give the aphids more time to feed and increase their numbers.  It is also possible for these aphids to move to spring oats and barley after winter wheat matures.

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

Sugarcane Aphid Monitoring Network

——-by  Brian McCornack, Wendy Johnson, Jeff Whitworth, J.P. Michaud, Sarah Zukoff

 

Kansas State University is leading a Sugarcane Aphid Monitoring Network comprised of researchers across the Southern half of the US. This group effort results in a national reporting and mapping of aphid distribution in real-time during the growing season using the online Extension program, myFields.info.

 

In general, migrating populations of sugarcane aphid disperse north from Southern Texas and northern Mexico into Oklahoma and then Kansas depending on weather patterns, temperature, and potential factors limiting aphid population growth, including natural enemies and use of resistant sorghum hybrids. No overwintering in Oklahoma and Kansas has been reported due to a lack of host plants (i.e. grain sorghum and green Johnsongrass) during winter months. Real-time tracking of migrating populations of sugarcane aphid into Kansas results in early detection of this pest for local farmers, which is necessary for timely applications of insecticide, a primary practice for protecting sorghum crops. See our Scouting Card (see picture below) for more management information.

The first observation of sugarcane aphid occurring in production sorghum this season was in southern Texas on March 28, which is not unusual. Colleagues in Texas have indicated that overall aphid presence and population levels at this time are sparse in comparison to previous years. By April 19, SCA was detected only several counties (see picture below) north of the initial report, suggesting that northern movement could progress much slower than past seasons, even in regions where these aphids are known to overwinter on Johnsongrass. As we wait to see how northern migration of SCA plays out, you can plan your management strategy by reviewing current recommendations using the following link to myFields.info: https://www.myfields.info/pests/sugarcane-aphid. In addition, create a free account on myFields.info and be automatically signed up for state- and county-level email alerts when SCA is detected in your area. Furthermore, localized alerts will include contact information for Extension support in your area.

Future monitoring group efforts will include the release of a threshold-based sampling plan for help in making management decisions for SCA, improved mapping features for displaying the change in aphid distribution over time, and mapping the predicted movement of SCA before it happens to help inform farmers.

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

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