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Extension Entomology

Category: Alfalfa

Alfalfa Pest Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Potato leafhoppers are still numerous in most alfalfa fields around north central Kansas.  They are causing ‘hopper burn’ which can limit the plant’s ability to translocate nutrients to the roots prior to winter.

potato-leafhopper

hopper-burn

Swathing should help but if you have already cut your fields for the last time this year, monitoring should continue to ensure these little pests don’t cause too much plant stress, especially this time of year.  Hopefully, they will head south to overwinter soon!

 

Alfalfa Pests

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Fields sampled three weeks ago had relatively large numbers of potato leafhoppers, i.e. 20+/20 sweeps.  These fields were swathed approximately two weeks ago and averaged 2 potato leafhoppers/20 sweeps, below the treatment threshold. Thus, timely swathing can be very beneficial in managing potato leafhoppers, without use of an insecticide application.

 

Alfalfa Update

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Potato leafhoppers continue to be very common in many uncut alfalfa fields.  In one field, which was actually flowering, there were more than 40 potato leafhoppers/20 sweeps which exceeds the treatments threshold.  Please see the Alfalfa Insect Management Guide for more information on treatment thresholds: http://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf.

 

This field has serious ‘hopper burn’ already, but timely swathing should alleviate leafhopper pressure.

hopperburn distance

hopperburn close

 

Another field that was swathed about 3 weeks ago, and at that time had about the same level of potato leafhopper infestation as the above pictured field, has only a trace level of potato leafhoppers now (1 potato leafhopper/20 sweeps).

healthy alfalfa distance

healthy alfalfa close

 

Alfalfa Update

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Potato leafhopper populations are very active throughout north central Kansas.  There are small nymphs, many adults, and the adults seem to still be migrating into the fields.

PLH adult2

Leafhopper nymph (2)

PLH burn

Could not find significant populations in fields swathed within the last 7-10 days but as regrowth occurs and immigration continues, these fields need to be monitored.  Fields not yet cut are already showing signs of “hopper burn” and should be swathed ASAP or an insecticide application may be justified.  Potato leafhoppers have few, if any, natural enemies.  Thus, these populations probably will not diminish without management, i.e. either swathing (my preference) or insecticide application.  For more information on potato leafhopper management, please visit the Alfalfa Insect Management Guide: http://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

 

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Potato leafhoppers continue to inhabit every alfalfa field sampled in north central Kansas.  Populations are still mostly composed of adults but a few nymphs are emerging.  These potato leafhoppers have few natural enemies and thus populations will just continue to increase.  There are still relatively plentiful numbers of lady beetles and green lacewings in most alfalfa fields, and while they probably won’t help with potato leafhoppers, they should continue to help control any developing aphid populations.

Alfalfa Update

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Much of the alfalfa in northcentral Kansas that could be swathed has been in the last week.  The cool damp weather has kept the adult alfalfa weevils in the fields.  They are congregated under windrows in the cut fields where they do a little feeding on the stems, resulting in characteristic spots of epidermis removal, called ‘barking’.  As these windrows are picked up there will be the characteristic striping across the fields where the windrows held back the regrowth underneath, plus provided the weevils with a protected site to continue feeding.  Fields not yet swathed also have significant populations of adults but this should not impact the foliage prior to cutting.

AW adult and barking

Windrows

Pea aphids are also present in both cut and uncut fields, but lady beetles and green lacewings are also, so would not expect pea aphid populations to have a negative impact on alfalfa.

Pea aphids adult and nymph

greenlacewing

pinkspotted lady beetle

Sevenspotted lady beetle

Potato leafhopper adults are already present in all alfalfa fields we checked over the past week.  This is earlier than usual for these pests as they typically don’t migrate into the state for another month, between the 2nd and 3rd cutting.  Some of these populations already exceed the treatment threshold with just adults, so hatching nymphs will just increase the populations further.  These potato leafhopper populations need to be monitored throughout the rest of the growing season.

PLH adult and nymph

Alfalfa Update

By — Dr. Jeff Whitworth, Dr. Holly Schwarting

Alfalfa continues to be problematic in NC Kansas.  There seems to be many fields of good alfalfa, apparently treated in an effective manner from both an insecticide and a timing standpoint, and not affected by the freezing temperatures earlier this spring.  Many of these fields have been, or are being, swathed.  However, there are some fields that have had, or are having, a difficult time overcoming the combination of alfalfa weevil larval feeding, early season dry conditions, and the early spring freezing temperatures.  In all fields, the early season warmth sped up alfalfa weevil development and feeding, then the cooler temperatures slowed it back down.  Alfalfa weevil larvae were 1st detected in NC Kansas in early March.  Small, 1st instar larvae are still being detected in some fields.

AW larvae 13

Some larvae pupated and developed into adults as long as three weeks ago, and they are still in the alfalfa fields.  So, NC Kansas still has a significant number of adults.  Treating for adult alfalfa weevils is rarely effective, but swathing within 7-10 days should help manage both larvae and adults without an insecticide application.

AW adult

Adult potato leafhoppers have also been noted in alfalfa fields.  These usually migrate into Kansas between the 2nd and 3rd cuttings, so they are about a month early this year. Leafhopper adult (2)

Alfalfa

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

   Alfalfa weevils continue to be very active throughout NC KS. This past week the weevil populations were still plentiful and in all stages, including very small 1st instar larvae. This is really unusual, as we started finding 1st instar larvae back in the 1st part of March. This is really a testament to the fluctuating temperatures that we have seen over the last 2 months, with a relatively warm winter/early spring then a major cool down with several nights of freezing temperatures which have slowed down weevil development significantly. Please remember, if an insecticide application is still warranted, check the Pre Harvest Interval (PHI) for the product of choice.

Alfalfa Update

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are still active throughout north central Kansas.  Even fields that had insecticide treatments which were well timed and effective have been having more larval feeding.  These fields need to be treated again as soon as possible as these larvae are still capable of considerable defoliation for the next week or so, especially as we continue to see the fluctuating temperatures.  Remember, these are contact insecticides so coverage is very important.  Also, please pay attention to the pre-harvest interval (PHI) for whatever product you use as many fields are getting close to that first cutting.

AW larva 28 Apr

AW damage 28 Apr

Alfalfa – Weevils and Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevil feeding seems to be slowing as pupation has started, but there are quite a few larvae still active.

AW pupa

AW different sizes

The photo below is of our insecticide plots which were treated 8 days after the surrounding alfalfa field, thus the dramatic visual difference insecticide timing can make.

KSU plots 2016

Also, there are some aphids present in the alfalfa.  Dr. Stu Duncan, KSU Agronomist, reported some spotted alfalfa aphids from the AltaVista area and we have a few in our plots in Dickinson Co.  Pea aphids have been present since early March and continue to be found in relatively low numbers.

spotted aphid

spotted aphid