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Extension Entomology

Category: Alfalfa

Alfalfa Weevil Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are still very active throughout north central Kansas.  They also range in development from small 1st instar larvae to relatively mature 3rd instars.

Aw life stages

We have also had reports of pupae in south central and north central Kansas.  Many fields are still showing signs of freeze damage.

freeze damaged field

The freeze did seem to affect the weevils by slowing their development but did not kill them.  However, most larvae in freeze-damaged fields are more yellow than the usual greenish color.  Whether that means they are getting the proper nourishment from the yellowed, freeze-damaged alfalfa tissue or not is unknown.

larvae color difference

Weevil larvae in untreated, non-freeze-damaged fields seem mostly about to pupate within 7-10 days if temperatures stay between 45-80°F.  No other pests have been noted in alfalfa fields we visited over the past week.

Alfalfa Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Once again we are in the midst of a typical Kansas spring with warm, bordering on hot, windy conditions interspersed with cold, windy conditions.  However, rainfall (or moisture in any form) has been pretty much lacking throughout south central and north central KS.  Again, as in most KS springs, the weather has variable effects on alfalfa and therefore, the alfalfa weevil.  Some fields are still showing effects of recent freezing temperatures.  Most of the yellowing/silver coloring in these fields is due to the weather.

Alfalfa freeze close

alfalfa freeze field

Fields that were sprayed before last week’s freeze still have live larvae but they are yellowish and moribund compared to larvae from fields not yet treated.

moribund larva

healthy larvae

However, fields not yet treated should be closely monitored as weevil feeding has been significantly slowed by the cold weather and has just started to become noticeable.

silvering alfalfa

This feeding will only intensify for about the next 7-10 days at temperatures ranging between 45-75°F.

Alfalfa Weevil Update

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils continue to be very active throughout north central Kansas, and the Kansas spring weather continues its usual erratic conditions.  However, the alfalfa weevil larvae continue to feed voraciously.  They have been slowed a little by the cooler weather but, remember, they do continue to feed 24/7, any time the temperatures are at least 48°F.  Much like the last few years, 2016 seems to be a good year for alfalfa weevils with most fields having multiple larvae/stem, at various developmental stages.

AW larvae

AW feeding damage

Alfalfa Weevil Update

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are very active in south central and north central Kansas. We sampled many fields from 14 to 17 March and found small to medium sized (1st and 2nd instar) larvae in every field. Infestation levels ranged from 30% to 100+%.

AW early instar

Cooler weather over the next three days should slow down egg hatch and larval feeding activity. However, it does not look like the predicted low temperatures will be cold enough to harm either plants or weevils. Then, with the return of warmer than normal temperatures next week, the weevils will again become very active. Thus, if the winds are calm enough and fields are at or greater than 30% infested, next week seems like the ideal time to treat for alfalfa weevils. Only pinprick holes in leaves and a little feeding on terminals is evident so far. This, however, will quickly change if weevils are allowed to feed in 65+°F temperatures.

AW feeding

 

 

Alfalfa Weevils

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevil larvae were first detected in north central Kansas on 3 March. Mr. Chuck Otte, Ag and Natural Resources Agent, also reported finding small larvae on 5 March in Geary County and Mr. Tom Maxwell, Ag and Natural Resources Agent, also reported finding small larvae and pinprick-sized holes in new alfalfa leaves on 9 March in Saline County. So, ready or not, alfalfa weevil larvae are here and, I would bet, many more will be hatching in the next few days to weeks. Alfalfa weevils will continue to hatch and larvae continue to develop any time temperatures exceed 48°F – and those temperatures have been much more common over the last few weeks than usual. Forecasts for the next 7-10 days also look for warm conditions. Thus, it looks like larvae will be emerging, and damage progressing, relatively quickly. Whether this warm weather will compress the alfalfa weevil larval feeding so that the damage is not as stretched out as usual remains to be seen. There are also many lady beetles present in the alfalfa fields we have checked as well as a few pea aphids. Treatment thresholds we use for alfalfa weevil insecticide applications are 30-50% infestation, i.e. 1 larva/2-3 stems.

For more information on alfalfa weevils, please visit:

http://www.bookstore.ksre.ksu.edu/pubs/mf2999.pdf

eggs in stem

Overwintering alfalfa weevil eggs in stem

alfalfa weevil

Early instar alfalfa weevil larvae

pinprick feeding damage

Pinprick feeding damage

 

Alfalfa Pests

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa continues to cause concern throughout north central and south central Kansas due to defoliation by “worms”.  There seems to be a combination of garden (alfalfa) webworms, fall armyworms, armyworms, yellow striped armyworms, etc. feeding on the foliage.  Generally, if the alfalfa is within 10 days of swathing or if the “worms” are mature, (maybe ½ inch long for webworms which are naturally smaller than the others; or ¾ inch long for the others), it probably is best to just cut the field and not treat.  If treatment is justified, please pay attention to the pre harvest interval (PHI) for whatever product is used.  These worms won’t feed on the foliage after it is cut, but they may feed under the windrows holding back the regrowth and causing striping in these fields.  For more information on these insects and their control options, as well as PHI’s, please visit: http://www.bookstore.ksre.ksu.edu/pubs/MF809.PDF

Alfalfa Aphids

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

Cowpea and spotted aphids continue to maintain their populations in most alfalfa fields throughout north central Kansas.  Lady beetles and other beneficials still appear to be helping control both species, but these fields need to be periodically examined to ensure these aphid populations stay at low levels.

cowpea aphids

 

Spotted alf aphid

 

 

Potato Leafhoppers

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

A few potato leafhoppers are still present in alfalfa fields.  Swathing seems to be doing a good job of controlling their numbers and thus, damage.  They also seem to be relatively numerous in soybeans.  Again, they do not appear to be causing any problems.  Field sampling in northcentral Kansas had very few defoliators yet and most beans were just starting to flower.

Cowpea Aphids

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

We have started finding a few cowpea aphids on alfalfa stems in north central Kansas (see photo).  However, there are also many lady beetles, lacewings, and mummies, which indicate parasitoid activity, present (see photos).  Aphid populations can increase rapidly and swathing will remove many aphids, but not all of them.  So fields should be rechecked weekly.  For more information on cowpea aphids, please visit: http://www.bookstore.ksre.ksu.edu/pubs/MF2865.pdf

cowpea aphids

 

cowpea aphid mummies

 

lady beetle

Blister Beetles

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Blister beetles are aggregating in many different fields throughout north central Kansas. These swarms are causing much concern.  Blister beetles can be controlled, if needed, however they usually do not cause widespread defoliation field-wide.  They normally aggregate in large numbers in localized areas for a week to 10 days.  These swarms can occur in soybean fields (see photo), alfalfa fields, and/or on pigweeds adjacent to these fields (see photo).  These swarms will soon disperse so the females can start ovipositing and thus will not cause as much concern in crop fields.

blister beetle soybeans

 

blister beetle pigweed