Weed killer will harm Costus/Ginger?

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South Florida zone 10b.
I have planted some Costus (Ginger family) in a 50' long planter area. However the weeds are growing like wild fire and I am unable to keep up with pulling them. I wanted to use some weed killer to control the weeds (clover leaf type, see a pic here
http://www.biology-blog.com/images/blogs/10-2007/clover-leaf-3100.jpg ), but have heard that weed killer will also kill plants that have rhizones which my Costus is.
Is this true? Is there a better way to control the weeds beside hand pulling?
Thanks,
MC
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On 4/4/10 7:47 PM, MiamiCuse wrote:

Take a piece of the weed -- not merely one leaf -- to a "real" nursery (not a lumber yard or hardware store) for identification. This might be oxalis instead of clover.
There is a specific weed control that severely burns oxalis, sufficiently to kill most of it, without harming other plants (except for spotted spurge, another weed). Sold under various brand names, it contains ammonium thiocyanate, which quickly decomposes into a urea form of fertilizer; sodium thiocyanate is about as effective. Any oxalis plants that survive must be hand dug, for which I recommend the use of a paring knife. Be alert! Oxalis readily forms seeds, which are not affected by the chemical; the thiocyanates act only on growing foliage.
If your weed is indeed clover, hand pulling is the best control. Do this before it flowers, and you won't have to repeat. Try to leave some of the roots in the soil; they are an excellent source of nitrates for nurishing other plants.
--
David E. Ross
Climate: California Mediterranean
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Sorry David, but it looks like bullshit to me, thiocyanate is sulfur + cyanide. Pull the god damn weeds. Don't be a lazy ****. You don't want to eat heavy metals. Oxalis isn't that invasive, and kids love to chew it, even if it does bind up calcium.
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merger of state and corporate power." - Benito Mussolini.
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In message

The photo looks like oxalis.

I don't find Ammonium thiocyanate as a narrow-spectrum weedkiller particularly plausible, but there are no heavy metals involved.
Google's not being particularly informative today, but it looks as if ammonium thiocyanate is usually used combined with aminotriazole (amitrole) - and acts by slowing the action of the aminotriazole allowing it to reach the roots and kill the whole plant, rather than just the leaves.
This combination is marketed as an oxalis killer (http://www.agspray.net.au/msds/oxalis.pdf ), but it is also recommended for the control of "grasses, broad-leaved weeds ... & nut-grasses". Given that range I expect that it will kill Costus quite happily.
Aminotriazole, fide Wikipedia, is a carcinogen.
There are products marketed for the control of broad-leaved weeds in pastures and cereal groups. But while Costus is a monocot, sensitivity to weed killers doesn't line up nicely with phylogenetic clades (e.g., fide Wikipedia, bromoxynil is used with flax and mint, as well as with monocot crops), so it cannot be assumed that Costus is not sensitive. Broad-leaved weed killers tend to be nastier chemicals.
--
Stewart Robert Hinsley

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On 4/5/10 1:23 AM, Stewart Robert Hinsley wrote:

The last time I looked at a bottle of Oxalis-X, the only active ingredient was ammonium thiocyanate. No amitrole, no other herbicide.
Ammonium thiocyanate will burn other plants; but in most cases it will not burn sufficiently to kill the plant. However, the label did warn against spraying it on or near junipers. It is effective against growing oxalis and spotted spurge and leaves no residue other than urea (a fertilizer) and sulfur (good in my alkaline soil).
I haven't bought Oxalis-X in a long time. Fortunately, oxalis is now a rare weed in my garden. When I find it, my paring knife digs it out (with help from my right hand).
Unfortunately, spotted spurge is too common in my garden. But it tends to grow my decomposed granite walkways where I can use Roundup.
One precaution in keeping oxalis out of your garden is to inspect carefully all containers of new plants at the nursery. Oxalis is often found growing in the containers that also contain the shrub or perennial you really want to buy. Buy only the desired plant, and reject any that come with oxalis.
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David E. Ross
Climate: California Mediterranean
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On Mon, 05 Apr 2010 17:57:36 -0700, "David E. Ross"

i'm confused. I googled oxalis and clicked on http://en.wikipedia.org/wiki/Oxalis
Is this regular wood sorrel that is trying to be eradicated? (I admit I really like wood sorrel and welcome it.)
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On 4/6/10 3:53 PM, snipped-for-privacy@notme.com wrote:

There are ornamental oxalis that are intentionally planted in gardens. My Sunset's "Western Garden Book" lists O. acetostella (wood sorrel or shamrock), O. adenophylla, O. hirta, O. lasiandra, O. oregana (redwood sorrel or Oregon oxalis), O. pes-caprae or O. cernua (Bermuda buttercup), O. purpurea or O. variabilis, and O. versicolor (candy cane sorrel).
Then there is O. corniculata (yellow oxalis). This is a weed and not at all ornamental.
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David E. Ross
Climate: California Mediterranean
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On Tue, 06 Apr 2010 17:32:19 -0700, "David E. Ross"

Thanks - I've never seen that variety.
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wrote:

I water them, and the ferns until mid-summer, when they disappear with no help from me. I can see purplish-pink ones out my study window right now. For the time being I have the white flowers of wild onions, the oxalis, blue forget-me-nots, and pink dead nettles for color in my yard. It's not that bad.
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What heavy metals?
In any event, I would simply pull the weeds. Do it in spring and you'll be done with them. I'd rather spend a few hours pulling weeds than many more hours researching, shopping for, and applying herbicides.
    Una
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Sorry about that. I probably shouldn't post late at night. Arsnic isn't a heavy metal. It is just very, very, nasty stuff. http://en.wikipedia.org/wiki/Arsnic#Safety
My oxalis disappears mid-summer, even if I water it.
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Billy wrote:

Una wrote:

Billy wrote:

What arsenic?
    Una
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Excellent point. I assure you that arsenic is, occasionally, the right answer to some questions. I'm afraid that I had been thinking about pesticides at the turn off the 20th century, here in the US of A, and lead arsenate was a prominent culprit. Late at night (for me), and I jumped the track. It's 6:30 PM where I am. Disregard all further posts until tomorrow. Now where did I put my happy hour?
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I am confused. You all suggested to pull the weeds. I have spent 3-4 hours on my knees pulling the weeds. Two weeks and one rain storm later they are all back, in full force. The weeding has to be done every two to three weeks, continuously from March to November. That's what I have been doing last year.
So this year, I dug up ALL the costus, all their roots along the entire planter area. I then turned the soil over several time, pull out all the weeds and their roots. I then laid down weed barriers, except for a sliver down the middle. Planted the costus back in, then put 3" of granite over the entire area.
So far so good.
Then we had some heavy rain. Then they are ALL BACK, again, through the weed barriers, through the granite.
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Please, give us a picture. You have been asked many times. Your plant doesn't sound like oxalis.
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merger of state and corporate power." - Benito Mussolini.
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I think we need to see a photo of the actual weeds in your Costus bed.
Also, do you literally "pull" the weeds?
    Una
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Yes I try to pull the weeds, sometimes I was able to get the roots out, sometimes the stems broke.
Here are some pictures. The first picture are the Costus with the weeds underneath, and the second one is of the weeds.
http://i173.photobucket.com/albums/w67/143house/pub/P1000002.jpg
http://i173.photobucket.com/albums/w67/143house/pub/P1000003.jpg
Thanks,
MC
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Now we're getting somewhere. That looks like Oxalis. Try chewing one. If sour, probably it is an Oxalis. Trifolium (clover) has a flavor that reminds me of grass. In mid-day full sun do the leaves droop (not wilt!), as in this photo?:
http://en.wikipedia.org/wiki/File:Oxalis_acetosella_flowers.jpg
Can you find any in flower (look in lawn adjacent to your Costus bed)? The flowers of Oxalis and Trifolium are easy to tell apart.
Here's a pamphlet about Oxalis in Florida: http://edis.ifas.ufl.edu/pdffiles/FW/FW02900.pdf
These are distributed like seedlings, so from seeds falling there after you laid the gravel. Source is likely your lawn or your neighbor's lawn. Explore a bit in the crushed stone to see if the roots are little bitty seedling roots or what. Some Oxalis produce bulbils on their roots and when you pull out the root you are likely to leave the bulbils behind. The bulbils sprout new plants.
Here's what I do with seedling crops. I first wait for most of them to die. That is the fate of most seedlings. Or I would lightly rake the rocks with a gardening claw, taking care not to damage the Costus. Any seedlings that survive I would dig out using a gardening tool to ensure I get enough of the root that it does not come back.
To prevent future seedling crops, find and eradicate the source. If this is Oxalis, you can treat with the specific herbicide others have mentioned. But if you don't eradicate the source, it will return.
Are the Costus growing on top of the fabric, or did you puncture it for each plant?
You have a "stone mulch" there. If you decide you don't like it after all, now is the time to take it all out and replace it with an organic mulch. I like organic mulches in part because it is easy to add more right on top of a seedling crop like this and kill the seedlings. However, if cats messing in the flowerbed are a concern, the stone mulch should discourage them.
Hope this helps,
    Una
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On 4/7/10 4:41 PM, MiamiCuse wrote:

If it is oxalis, new plants will arise from pieces of stem. When you pull them, they will regrow unless you also remove the root. And the plant is perennial; if it appears to have died, it is only dormant.
If you let it bloom, the tiny seed pods (about 1/2 inch long) will release their seeds explosively, scattering their seeds widely. Walking across an infested lawn while wearing shorts, the seeds feel like gnats keep flying onto my legs. The seeds are slightly sticky and are thus easily spread by humans and other animals walking over a patch of oxalis.
As I indicated earlier, I use a paring knife to ensure that I get some of the roots. I attack oxalis before it can bloom. If I see it, I stop whatever else I'm doing and remove it. Fortunately, prior use of ammonium thiocyanate (YES!) eliminated the worst of the infestation.
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David E. Ross
Climate: California Mediterranean
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Someone said:

You obviously got lousy advice... who's the imbecil who told you to place stone chips over cloth weed barrier?!?!? DUH Stone chips go over heavy polyethelene sheeting that won't decay fro many, many years... used where you never want anything to grow, in lieu of concrete... the stone chips (hopefully decorative) are for hiding the ugly poly and to keep it from blowing away. Your weed barrier cloth didn't work for one reason and one reason only, you used the crappy el cheapo kind. Buy premium weed barrier cloth, even use it double in problem areas, like slopes... then cover with shredded bark, wood chips, or any other organics that will slowly decompose, adding fresh as needed. Stone chips do absolutely nothing to improve soil, and even if laid down a foot thick weeds will grow, because some weeds can push through from below and some seeds will fall on the chips and will root through... plus bits of organic matter and clumps of soil will constantly sift through creating a very nice substrate for all manner of native plants to propogate... I suggest you get rid of all those stone chips before you find them strewn all over your property... save them for when you plan to mix up a batch of concrete, or add to a crushed stone driveway.
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