Kansas State University

search

Extension Entomology

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.

Wheat Aphids

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

We checked several wheat fields in north central Kansas this past week.  Once again, very few pests of any kind were detected.  As last week, there are a few aphids present, but not in any significant numbers.  With continued strong south winds, aphids will continue to migrate into the state.

greenbug

BCOA small

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

Wheat Insects

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

We checked several wheat fields without finding much insect activity. There are a few greenbugs and bird cherry-oat aphids but not really enough to worry about yet. There are also many green lacewings and lady beetles present and feeding on these aphids which will help reduce populations.

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