New seeding into Knappweed infested field?

[hayray]

Got a new lease on a piece of ground that is a old played out alfalfa field - seeded about 20 years ago - but now is basically a brome field with a lot of knappweed just over taking the field. My plans are to go in there probably about mid- April and do a burn down with glyphosate and then tillage and I would like to clear seed alfalfa, however am worried if the knappweed will come back in strong. The knappweed is a bi-annual, and there should be fall roseattes present this spring to hit but a pretty good seed bank would be anticipated cause as I can find it reproduces by seed for the most part. A extension agent I talked to thought that the tillage and competition from the alfalfa seedlings should be enough to knock back the knappweed. But I would feel alot better hearing from someone who may have actually done this. My other option is to go in with a grass or annual and then use a postemerge to control it seasonally, and with the high price of K/ton then I may not have too much of a prob. doing this seeing that N has come down alot. Thanks for any info.

 

[dun]

I would be seriously tempted to plant a roundup ready alfalfa as my choice of alfalfa.

 

[hayray]

I would be seriously tempted to plant a roundup ready alfalfa as my choice of alfalfa.

That is exactly what I was thinking of a couple of years ago but the round up ready technology is on hold right now for alfalfa. There is a big court battle over it use between seed growers, exporters to Asia on the west coast and the marketers of the round up ready alfalfa. Right now it is illegal to plant.

 

[dun]

I would be seriously tempted to plant a roundup ready alfalfa as my choice of alfalfa.

That is exactly what I was thinking of a couple of years ago but the round up ready technology is on hold right now for alfalfa. There is a big court battle over it use between seed growers, exporters to Asia on the west coast and the marketers of the round up ready alfalfa. Right now it is illegal to plant.

I'ld plant something other then alfalfa then and hope it gets straightened out in the next year or 2. I'm just always really leery of the existing seed bank that will rear it's ugly head in the next few years.

 

[mnmtranching]

I'm going to double check. I'm pretty sure there are herbicides that will work on knapweed and other weeds sprayed on growing alfalfa.
A good stand of fertilized alfalfa will knock back the weeds pretty good in the first cut. The weeds will really show up again during the growth of the second cutting, even more if the weather gets hot and dry.

 

[hayray]

There are some herbicides but they usually are only effective during the seeding stages of weeds. I know there are some herbicides you can spray in the fall like Velpar but that has high crop damage and is expensive. I have used Raptor on new seedings and that worked good and I know you can use Eptam pre-emerge and incorporated. I don't know if those will work on knappweed and Raptor is really expensive to use. The efficacy of any of those herbicides is also pretty minimal most of the time. I have spayed glyphosate and went in and no-tilled alfalfa and had the knappweed come right back. Not sure if it came back from the roots or it was from the seeds. I am worried about the seeds coming back. And that has been the problem with herbicides on alfalfa, a lot of restrictions of effectiveness such as growth stages of alfalfa and weeds otherwise nothing works.

 

[mnmtranching]

Hayray, Yeah, there are a lot of us working on the knapweed problem. Not only in hay but even worse in the pastures. It not only competes with the native grasses but kills it out. Right now it seems the only way to combat knapweed in forage crops is to go with annuals.

 

[hayray]

I got an advertisement in the mail last year from Dow Agri-sciences and they have those new range and pasture sprays like Tordon and Milestone and I know there is a third one also. Anyways, they were advertising those as a control for knappweed. Supposedly these are a big improvement over simple 2-4D because they have some season long residual. I also heard they are not labeled in legume stands, just grass fields. I thought about calling and getting some info. on these if I was gonna go with a all grass stand.