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Extension Entomology

Tag: swathing

Alfalfa Update – Alfalfa caterpillars and Potato leafhoppers

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa caterpillars are currently active throughout north central Kansas.  These caterpillars are feeding on foliage, and based upon the size of the larvae in fields, will soon be pupating.  In many fields, swathing is currently, or has just been done and this should help lessen alfalfa caterpillar populations.  However, if the timing is such that these larvae are pupating in the soil and thus swathing does not remove/destroy the pupae, the emerging butterflies may lay eggs on recently cut fields and the developing larvae may feed on regrowth.  This may retard regrowth for a couple of weeks until larvae pupate.

Potato leafhoppers are also very numerous throughout north central Kansas in uncut alfalfa fields.  Thus, their characteristic feeding damage, called ‘hopper burn’, is common.  Swathing should reduce potato leafhopper populations significantly and, hopefully, they will not rebound.  Continued monitoring is prudent as alfalfa caterpillar feeding and potato leafhopper damage may lessen the plant’s ability to store reserves in their roots for overwintering.

 

For management decisions for all alfalfa pests, please refer to the 2017 Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF809.pdf

 

Alfalfa Pest Update

Posted on by Sharon Schroll

–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

Posted on by Sharon Schroll

–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 Update

Posted on by Sharon Schroll

— 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