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Extension Entomology

Tag: potato leafhopper

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Potato leafhoppers are still common in all alfalfa fields sampled in the last 7-10 days, unless they have been swathed during that period of time.  Fields swathed within the last week did not have enough potato leafhoppers to reach a treatment threshold.  However, fields swathed just 10-14 days earlier are once again loaded with these little lime green, wedge-shaped leafhoppers.

There do seem to be good populations of green lacewings in uncut alfalfa fields.  However, they do not appear to be impacting the potato leafhopper populations.  We did pick up one alfalfa weevil larva and one adult in an uncut alfalfa field but the alfalfa weevils should not be of concern as major defoliators until next spring.

 

 

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Potato leafhoppers have been infesting alfalfa fields throughout north central Kansas for at least the last month.  They continue to be very active, which is causing quite a bit of leaf yellowing, often called ‘hopper burn’, and even stem and whole-plant stress.  Typically, swathing is sufficient to manage leafhopper populations.  However, they have been actively reproducing and there are many nymphs, so it will be especially important to continue to scout these fields after swathing.  If a stubble spray is deemed necessary after swathing, one application is often highly effective and re-infestation is unusual.

 

Alfalfa caterpillars are also quite common in alfalfa fields, where they feed on foliage, although they rarely do enough damage to warrant an insecticide application.  They will eventually pupate and then turn into a yellow or white sulphur butterfly.

Alfalfa

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa pests are still causing concern among alfalfa producers.  In north central Kansas the alfalfa has yet to become dormant, at least as of 29 Nov.  Also, in these slowly growing fields the pea aphids seem to be doing very well and no beneficials, which might help to control them, were detected.  Also, alfalfa weevil larvae are still actively feeding on leaf tissue.  One potato leafhopper was also picked up in sweep net samples.  Hopefully, the colder winter weather will eliminate the pea aphids and alfalfa weevil larvae!

pea-aphid-29-nov

aw-29-nov

aw-single-29-nov

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 Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Swathing seems to have interrupted the potato leafhopper increases that were seen prior to cutting.  All the fields sampled prior to swathing in north central Kansas exceeded the treatment thresholds.  Conversely, all the fields sampled post-swathing had potato leafhopper population well below economic injury levels, i.e. 20 potato leafhoppers per 20 sweeps pre-swathing vs. two per 20 sweeps post-swathing.  Continued monitoring would be prudent as these pests may stray around until October and continue to produce offspring.

 

Spotted alfalfa aphids are still present in alfalfa fields but at relatively insignificant infestation levels.  These aphids seem to do very well in mid-summer’s hot, dry conditions but usually don’t reach densities heavy enough to cause yield-reducing stress.

spotted alfalfa aphid

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

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