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We've got a small "meadow" area that is in bad shape from new home construction. Despite heavy seeding with native warm-season grasses and proper mowing, the area is overrun with mugwort, curly dock, and burdock. If we don't take this step, the homeowner is going to install sod.

So we'd like to go off our typical organic approach and chemically remove the offenders in a single or single series of applications.

This would be a one-issue chemical treatment in an otherwise toxin-free management - meaning we would consider a series of broadleaf herbicide applications this fall/spring, but would then revert to natural management. We want to leave the native warm-season grasses intact. Everything else is fair game, but the real targets are those listed above.

I would say we would follow up with soil amendments, but soil "improvements" tend to favor weeds over our native grasses. We just need to give them a chance to get established.

  1. What chemical would be most effective?
  2. When and how often should that chemical be applied?
  3. How should the area be prepared for this application(s)?

And finally, is there anything we're failing to consider?

  • Hi there That Idiot! Gotta have some pictures of this area, need to seed proliferation of weeds. What was the seed composition that you planted? Pasture seed with ZERO weed seeds? Not likely but hopefully. How often does this 'pasture' get mowed, eaten? How short is it being mowed? More than 1/3 of the grass plant being mowed? What is your watering schedule? How long have you been maintaining this pasture with mowing/seeding/watering/fertilizing? What animals get to eat here and how long? If chemicals are necessary to control weeds and promote grasses, one application is enuf. – stormy Sep 9 '15 at 21:03
  • No photos, but estimate 70%+ weed coverage. Weeds established during prolonged construction period during which area was used as stockpile and parking. NO soil improvement before we got on site. Reputable seed mix with little bluestem, panicum, purple love, etc. – That Idiot Sep 9 '15 at 21:08
  • The best way to control weeds besides proper grass management is to stop these weeds from being able to seed in the first place. As a pasture, mowing should be held at 6" in height. Few seeds would be able to germinate. Pesticides need not be involved at all. Especially if you've got animals eating this grass. If you do, then no pesticides whatsoever are needed! Just a different kind of management. What do you mean by new construction? Very interesting question!! – stormy Sep 9 '15 at 21:09
  • Is this YOUR home and property? Construction compacts soils horribly. Discing might be necessary, aeration might not be enough. Sigh, if 70% weeds...I'd disc, grade, fine grade, ROLL (if it is going to be a lawn) and then seed again. Do you want a meadow or a lawn? I am a bit confused with details (what else is new). Weed seeds or tough perennial weeds I just would not worry about! Reseed with a pasture mix with ZERO weed seed after fine grading, fertilize (do a soil test for sure before adding any chemicals) and keep soil/seeds moist for 2 weeks. Shoot, NO pictures??? – stormy Sep 9 '15 at 21:17
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Most of these treatments will work best in late spring, when these weeds are growing fastest. Because they work best in quickly growing plants, if you feel it necessary to begin treatment this fall, mow the field high (6-8"), and then treat the regrowth before it matures. Dock has a very deep, resilient taproot, and more than one application may be necessary. Also keep in mind that the ground is probably a decently loaded seed bank for the stuff by now, and you may have to deal with seedlings for years (although after the initial control, it won't be as bad).

So to answer your questions...

  1. What chemical would be most effective?

I'd definitely say I'd have to choose a 2,4-D/Clopyralid mixture (in a ratio of about 8/1 respectively). These are both auxin mimicking chemicals, which together will be extremely powerful against the weeds, without really upping the chemical dose, or really harming the grasses, which don't respond to the broadleaf auxin mimics. As I said, though, with Dock, more than one application may be necessary (Most likely application 2 will finish off anything left).

You (obviously) need a pesticide applicator's licence to apply these chemicals, but they are both legal for residential use in most U.S. localities. Make sure you add a decent amount of surfactant to the mix, as dock tends to shed water droplets easily. Use ~4 quarts per acre.

  1. When and how often should that chemical be applied?

You want to apply it when the plants are actively growing and the faster the better. This is because of the mode of action (auxin mimick). Mowing off most of the leaf surface will cause regrowth, which will be far more susceptible than matured plants. A heavy nitrogen fertilizer will actually make this effect more pronounced, and you get better control.

Within a week of application, the weeds should start curling up. They will steadily decline to a point, at which some die, and some may slowly seem to revive. If you see any new leaf growth after the first major dieback, apply again. That usually finishes off the tough few. You may have enough time for all this before cold weather sets in.

  1. How should the area be prepared for this application(s)?

If the plants have ripened seedheads, it's best to wait for the next season, because coaxing out a good flush of growth will be a challenge. Other than that, if the plants are still quite green, but are simply slowed down, a high mowing will work great. In spring after the weeds go out of dormancy, you can apply any time without treatment.

And finally, is there anything we're failing to consider?

Not certain. My main concern is that Dock often grows most vigorously in damp ground, and I wouldn't recommend using any broadleaf herbicides near groundwater, or in an area that drains directly into a water body. These chemicals tend to be mobile, because they do not bind to soil and can have a persistent half-life. You should be good, though, if this is a normally drained area, away from any creeks, etc.

  • One extra note: 2,4-d is very prone to off-site drifting. If there is any wind above 2-3 mph I wouldn't spray. – GardenerJ Sep 11 '15 at 10:12
  • Thank you for the info about mobility in soils. This area is not near creeks or ponds. It was farmed for hundreds of years up until 20 or 30 years ago, so the groundwater is probably impaired already, but we don't want to make matters worse. But in this case the client is basically saying to make the meadow work "immediately," or we're switching to sod. Its the first time we've been put in this situation. – That Idiot Sep 11 '15 at 14:14
  • @GardenerJ: If your having that issue, switch to a different head that sprays bigger droplets, or calibrate the sprayer for lower output, and move slower. It hasn't been an issue for me. – J. Musser Sep 11 '15 at 14:59

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