Herbicide Timing

bob64(6)March 28, 2008

The advice I read is to use my favorite herbicides when temp's are above 50 degrees fahrenheit and when it is not raining. We are still not getting many moments above 50 degrees and the April showers are starting to begin. I'd like to get the invasives sprayed before the good guys pop up. Do I need a whole day or more above 50 degrees or just for temps to be above 50 degrees at the moment I spray?

Any advice?

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I use glyphosate when it is 60 degrees or higher. It needs to be that warm when spraying and a few hours thereafter for it to be effective.

    Bookmark   March 29, 2008 at 8:08AM
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kwoods(Cold z7 Long Is)

I think the idea is that the target plant has to be actively growing for most herbacides to be effective. It's been above 50 here only a few times and not consistently. I've shot a few perpetrators around here, creeping charlie, garlic mustard, cow bane.... they've now withered (though I know at least charlie will surely return... I've resigned myself to that).

    Bookmark   March 31, 2008 at 12:26PM
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Different herbicides vary in their temperature requirements, but as for Roundup or other glyphosate based herbicides, warm temperatures are not needed. While higher temps will increase the speed at which effects are seen, any temp above freezing will result in normal efficacy. What matters is having a target that is green. Much invasive species spraying/treating is done during cold winter months when many herbaceous natives are dormant.

    Bookmark   April 9, 2008 at 7:13PM
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When all else fails I read the directions, here they are for 41% glyphosate which is what I use. "Use any time weeds are actively growing. For best results apply on a warm sunny day when daytime temperature is above 60 degrees F and no rainfall is forecast for 24 hours."
Having said that, I would have no qualms spraying english ivy, garlic mustard, vinca, japanese honeysuckle during a mild, January thaw. I'm sure that the rules are different in Florida or Gulf Coast.

    Bookmark   April 10, 2008 at 12:58PM
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What initially prompted this question is that there is a short window of time when the nasty, invasive (but, admittedly pretty) lesser celandine is above ground but natives are not.

    Bookmark   April 11, 2008 at 9:55AM
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kwoods(Cold z7 Long Is)

"nasty, invasive (but, admittedly pretty) lesser celandine"

I feel your pain. Stuff w/ waxy leaves you just have to keep on hitting 'til it's done. You never know if it's going dormant or actually checking-out permanently.

Had no problems w/ celandine 'til I had a load of "screened" topsoil delivered a few years back. Absolutely full of the stuff.... and the battle rages on.

    Bookmark   April 11, 2008 at 11:05AM
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Sam MD, please do not spread glyphosate at such a high concentration on leaf foliage! For foliar application, for garlic mustard and others the usual concentration is 2.5% and for the most part that is as "hot" as you'd ever want it to be.

If you are treating stumps of cut brush, then perhaps a 41% solution would be appropriate. Less chemical sparyed means less chemical in the environment, and thinning your mix will save you money too!

    Bookmark   April 11, 2008 at 1:50PM
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growershower(Z7, MD)

Here's some advice: Don't have a "favorite herbicide." It's poison, plain and simple.

    Bookmark   April 27, 2012 at 5:43PM
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