# Grubs eating alfalfa roots



## FarmerCline (Oct 12, 2011)

After baling second cutting in June I noticed some alfalfa crowns didn't regrow and died. I figured it was from drought as the whole field didn't regrow for two weeks after cutting until it rained. Now after third cutting which was baled about 10 days ago I have noticed many of the alfalfa crowns look very drought stressed and the regrowth is minimal. The thing is we have not been overly dry since cutting and many of the plants look healthy with 6-8 inches of regrowth.

I tried to pull up some of the poor looking alfalfa plant and to my surprise they came out of the ground very easy and the taproot was mostly all dead and looked like something had eaten much of it. I also found a couple plants that the taproot had a white grub eating the center out of the root. Anyone know what this pest might be and how to control it? I'm afraid the damage is already done and many parts of the field is going to be thin but I don't want this pest to continue feeding on the healthy crowns.


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## Vol (Jul 5, 2009)

This is a possibility.

Regards, Mike

https://entomology.ca.uky.edu/ef119


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## FarmerCline (Oct 12, 2011)

Vol said:


> This is a possibility.
> 
> Regards, Mike
> 
> https://entomology.ca.uky.edu/ef119


 It looks like that is probably what it is......the grubs/larvae pictured look just like the ones I have and the symptoms of the damage sounds spot on. The only thing is the article says the larvae are present from April through June and only one generation a year but I'm still finding some grubs feeding on the roots.......however I will say I think most of the damage was done earlier in the year by looking at the roots. Also this is an established stand and not a new stand like the article says is typically damaged.

I guess the worst part is there isn't a way to control it with insecticides. Now I'm worried that with all the adults that are now present when the larvae matured what will prevent them from infesting my other fields of alfalfa?


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## Vol (Jul 5, 2009)

FarmerCline said:


> I guess the worst part is there isn't a way to control it with insecticides. Now I'm worried that with all the adults that are now present when the larvae matured what will prevent them from infesting my other fields of alfalfa?


Keep the fields sprayed every 30 days to kill the adult beetles. This will eventually break the cycle. Use Silencer, Warrior, etc. Doesn't take much....usually less than 2 ounces per acre. Be very careful when using insecticides as they require diligence and care when measuring and mixing.

Regards, Mike


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## FarmerCline (Oct 12, 2011)

Thought I would give an update to this thread. There is no doubt what has caused the damage to the alfalfa roots in the clover root curculio. I baled 4th cutting just over a week ago and there must have been some adults in the field and they congregated under the windrows and it was cut. On the underneath side of pretty much every bale that I looked at there were adult weevils that had been picked up with the window and were mashed into the bale.....some bales had up to 10-12 that I could see just on the outside surface.

The alfalfa has been slow to regrow again and I dug up some plants and I am still finding some larvae feeding on the roots. This doesn't match what the article said about the clover root curculio having only one generation a year earlier in the summer but again there is no doubt that is what it is after finding the adults. I should also mention that between 3rd and 4th cutting we had plenty of rain but if we went a day or two without rain the alfalfa looked drought stressed because so much of the stand has feeding damage to the roots.

I'm now trying to figure out the best time to spray to try and kill some of the adults before they reproduce. They were obviously present in the field before I cut even though I didn't notice them. Now I only have a couple inches of regrowth so I'm wondering if they are still some there and I should spray now or wait a little longer for the alfalfa to grow some more in case they moved out of the field since there isn't much cover? I kind of hate to spray without seeing them but they could be there and I just can't find them.

Worried if I don't do something to try to control them they could spread to my other fields of alfalfa as this field obviously has an infestation. I would say most of the field has been affected with some parts much worse than others but around a 25-30% stand reduction across most of the field. Some areas are only slightly thinned but other areas are severely affected and 75% percent or more of the crowns have died leaving very thin patches.


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## somedevildawg (Jun 20, 2011)

Possibly spray before a good rain (hopefully next few days) perhaps orthene may be the better choice....I would spray at least 20 gal to the acre before rain....1qt to acre, I don't really know if it's toxic to Lucerne or not but I think that's the approach I would take in Bermuda.


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## Vol (Jul 5, 2009)

I would spray now....and again in thirty days intervals until we have a killing frost. I would even consider using Sevin.

Maybe add a grass to the stand this fall...this seems to discourage some insects.

Regards, Mike


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## FarmerCline (Oct 12, 2011)

somedevildawg said:


> Possibly spray before a good rain (hopefully next few days) perhaps orthene may be the better choice....I would spray at least 20 gal to the acre before rain....1qt to acre, I don't really know if it's toxic to Lucerne or not but I think that's the approach I would take in Bermuda.


 Looked up the label on orthene and I couldnt find it labeled for use any kind of hay? What kind are you using in bermuda? No rain for at least a week unfortunately.


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## somedevildawg (Jun 20, 2011)

If I remember correctly, it's been a few years, it's a powder marketed under the orthene name, not sure the manufacturer and not sure about generics. Sevin would be a good option and probably more available? Think it's a qt to the acre......


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## FarmerCline (Oct 12, 2011)

Was looking online to see if I could find any kind of insecticide that could be applied to the soil to kill the larvae and I came across an article from New Mexico on a white fringed beetle. After reading that article I'm almost positive that is what I have rather than the clover root curculio. I went to try to find some dead weevils in a bale of hay and upon closer inspection they appear to be the white fringed beetle. NC had some info I found on the white fringed beetle being a pest in tobacco and cotton. It apparently likes most any broadleaf crop with a tap root. Unfortunately it sounds like this pest is just as hard or even worse to control than the clover root curculio. I think I'm going to go ahead and spray a pyrethroid today in case there are an adults still in the field and spray something else with more residual in a week or two. I'm starting to wonder if I should have the ground fumigated or something before they spread to my other fields.


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## FarmerCline (Oct 12, 2011)

http://aces.nmsu.edu/pubs/_circulars/CR659.pdf
https://tobacco.ces.ncsu.edu/tobacco-pest-management-soil-pests-white-fringed-beetles/
http://ipm.ncsu.edu/AG271/tobacco/whitefringed_beetle.html


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## Vol (Jul 5, 2009)

I found this Hayden. It is from the US Entomology Division.

Regards, Mike

CONTROL

You can control the white-
fringed beetle by applying an insec-
ticide. Good farm practices are
necessary to produce satisfactory
crop yields.

The best method of controlling
these insects is to kill the larvae
with an insecticide. A single appli-
cation to the soil remains effective
for several years.

Aldrin, chlordane, DDT, cliel-
clrin, and heptachlor will provide
effective control when used as indi-
cated. These insecticides are avail-
able in one of the following forms :
Emulsifiable concentrate or wetta-
ble powder, from which sprays can
be prepared ; granule ; or dust.

Sprays, dusts, or granules may be
applied by power or hand equip-
ment, or by airplane. Consult
your nearest white- fringed beetle
inspector or your county agricul-
tural agent for information on the
best method of application.


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## Apm1026 (Feb 11, 2012)

Well too bad all the chemicals in that list are no longer on the market. Too persistent in the environment and too toxic, that's why they used to work so good.


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## Vol (Jul 5, 2009)

I thought it was odd that the list included DDT which has been banned since the early sixties....but I was unaware that all have since been banned......figures.

Regards, Mike


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## FarmerCline (Oct 12, 2011)

I guess I'm out of luck then on a insecticide that will kill the larvae in the soil. At this point I'm not against something that is off label in alfalfa.....even if I would have to discard the next hay cutting to get rid of this pest. I can't help but wondering if there might be something used in vegetable crops that would kill the larvae but maybe there is not?

I think I have decided to kill this field off after last cutting this fall and plant corn next spring. I sprayed the field with karate today and it looks much worse than I first thought.....a lot of bare patches and by the looks of the stunted alfalfa regrowth I think it is going to get worse.

I had planned on planting the field right across the highway from this one into alfalfa next spring but now I'm thinking that may not be a good idea as it could easily become infested with the weevils coming from the existing field. Oh well for my hopes of really boosting my alfalfa production next year.


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## Apm1026 (Feb 11, 2012)

The chemicals that will penetrate the soil and remain active against the pest have all been taken off market. if they will go into the soil , then they can make their way into water, streams and ground water, that's why there are not available anymore. Those chemicals except for ddt were used for and highly effective in killing termites and leaving a long soil residual barrier. Now we have to bait termites to a trap .


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## FarmerCline (Oct 12, 2011)

Had a thought today.......I remembered about 10 years ago back before I started farming I was growing a couple acres of vegetables just for fun. I had some cabbage transplants that right after planting were withering and dying and after pulling them up I found maggots eating the roots off. I remember taking them to the extension office and they told me they were some kind of root maggot which was the larvae of a fly and there were not many control options. I do remember them saying that Lorsban would be the best option and should kill them but I did not have restricted chemical liscense at them time so I had no way to spray and I ended up losing the whole half acre of cabbage.

That got me to thinking today that if Lorsban would kill the maggots in the soil why wouldn't it kill the beetle larvae that are eating my alfalfa roots? I'm not familiar with Lorsban and I'm surprised the name even stuck in my head for this long. Any thoughts if this would be a product that may work for my situation?


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## Vol (Jul 5, 2009)

I think from what i have read that Lorsban is no longer available either.

Regards, Mike


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## FarmerCline (Oct 12, 2011)

Vol said:


> I think from what i have read that Lorsban is no longer available either.
> 
> Regards, Mike


 Talked to my chemical dealer today and Lorsban is still available but he had no idea if it would work for my situation. I tried looking up the label online and there are apparently a few different Lorsban formulations......unsure which would be the best to use. I did see on the label I looked at that alfalfa is a labeled crop but it only listed foliage feeding insects. Other labeled crops such as corn and peanuts it had some root feeding insects that it is supposed to control....however the application rate was higher than what is listed for alfalfa. Im thinking I may give it a try.


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## r82230 (Mar 1, 2016)

Vol said:


> I think from what i have read that Lorsban is no longer available either.
> 
> Regards, Mike


They (EPA) is trying to get rid of Lorsban, onion farmers are in a up roar. Seems without it 90%+ of onions will get bugs of some sort.

Larry


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## CoraJase (Jul 9, 2013)

Hi FarmerCline, just came across this thread - I had exact same issue as you last year, Lucerne Weevil or white fringe weevil infestation. I'm in Australia though. It was a dry year and I had patches of my field start dying off in ever increasing circles - I pulled a few of the dying plants up by the root and would find the roots severed and occasionally a grub still embedded in a hollow in the root it had eaten away.

After I got a positive ID on the pest by finding some of the adult weevils, I approached my local agronomist with the problem looking for a solution. They were initially a bit taken back, it appeared they had never come across it before - at least not in our area? After some investigation they suggested I spray with chlorpyrifos - or basically what you call Lorsban in autumn when the adult weevils are present. Then a repeat application a few weeks later to get any late emerging adults.

It is now a year on and so far this season I haven't noticed any further damage to the stand but I have spotted a couple of adult weevils around so plan on spraying again this autumn to keep on top of them.


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## FarmerCline (Oct 12, 2011)

CoraJase said:


> Hi FarmerCline, just came across this thread - I had exact same issue as you last year, Lucerne Weevil or white fringe weevil infestation. I'm in Australia though. It was a dry year and I had patches of my field start dying off in ever increasing circles - I pulled a few of the dying plants up by the root and would find the roots severed and occasionally a grub still embedded in a hollow in the root it had eaten away.
> 
> After I got a positive ID on the pest by finding some of the adult weevils, I approached my local agronomist with the problem looking for a solution. They were initially a bit taken back, it appeared they had never come across it before - at least not in our area? After some investigation they suggested I spray with chlorpyrifos - or basically what you call Lorsban in autumn when the adult weevils are present. Then a repeat application a few weeks later to get any late emerging adults.
> 
> It is now a year on and so far this season I haven't noticed any further damage to the stand but I have spotted a couple of adult weevils around so plan on spraying again this autumn to keep on top of them.


 Glad you replied to this thread I was actually getting ready to give an update and ask some opinions on what I should do next. I ended up spraying lambda-cy in late September which is late summer/early fall here in the U.S. That killed a lot of the adult weevils.....if you looked close there was at least one dead weevil around every single alfalfa crown. A few weeks later I dug up some more alfalfa crowns and unfortunately there were still a lot of the grubs(larvae) feeding on the roots so as expected the insecticide was not effective in killing the larvae. Now that it is winter I dug up some more alfalfa crowns and found the larvae hibernating in the soil near the roots but not feeding.....they were also much larger than they were back in August when I started this thread. This gives me the impression that they over winter as a larvae which will emerge as an adult weevil in the spring.

By late fall I also started seeing a small amount of damage in a different alfalfa field that was a new seeding last spring(May). Sure enough it was white fringed beetle larvae feeding on the roots. I'm hoping I can do something to control them before they completely ruin this field like happened to the other field.

I'm now wondering if I could fumigate the ground to kill the larvae before they emerge in the spring as adults and that would end the infestation I have? I'm not really sure how fumigation even works or if it would be effective in killing the larvae. Or maybe I should just keep spraying an insecticide every couple weeks to kill any adults that may be present? Kind of hate to have to do that much spraying though. If I'm going to keep growing alfalfa I'm going to have to find a way to control or eliminate this pest. Local agronomists and extension agents haven't been of much help finding any answers.


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## CoraJase (Jul 9, 2013)

Your infestation sounds a little more advanced than mine was. My stand was only 2 yrs old last year when I discovered the weevils. One thing I read about them is that they don't fly, so only spread very locally(.ie over fence lines from one field to another) or transported by equipment. The contractor that sowed my field was another lucerne grower in the area who was at the same time re-establishing some fields he'd had for a few years. I believe he must have bought them in on the equipment he used to do my place.

You may need to be careful taking your equipment from your infected fields to others so as not to spread them further?


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## FarmerCline (Oct 12, 2011)

CoraJase said:


> Your infestation sounds a little more advanced than mine was. My stand was only 2 yrs old last year when I discovered the weevils. One thing I read about them is that they don't fly, so only spread very locally(.ie over fence lines from one field to another) or transported by equipment. The contractor that sowed my field was another lucerne grower in the area who was at the same time re-establishing some fields he'd had for a few years. I believe he must have bought them in on the equipment he used to do my place.
> 
> You may need to be careful taking your equipment from your infected fields to others so as not to spread them further?


 My field was a two year old stand as well. I didn't noticed any damage the first year but then last year in mid summer I started seeing a lot of damage all at once. My guess is that they were there the first year but not in enough numbers to cause highly visible damage and they reproduced and then the population exploded last summer when I started seeding all the damage. Since they don't fly I was hoping this one field was an isolated case and if I could eliminate them from there I would no longer have a problem. Now that I have seen them in another field over 5 miles away though I'm worried they may be more widespread. I guess it is possible though that some could have hitched a ride on the mower or baler before I realized I had an infestation in the one field. I'm the only alfalfa producer in my area and have only been growing it three years.


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