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Taking on those weeds

M.G. Gallagher

EAGLE COUNTY – I’m working on a somewhat difficult lawn situation at a residence. More on the factors later, but the symptoms are a classic example of the dandelion invasion.A question that has come in more than once asks why various weeds come back after they have been sprayed. Different weeds are tough for different reasons. Canada thistle has a big root system that takes a while to kill. Some plants shed herbicide because of their leaf characteristics. So not all lawn weeds are going to croak with one application.I did some testing. I mixed some standard strength Weed-B-Dead type broadleaf weed killer for lawns at two rates. The regular rate calls for 2 ounces per gallon. In the lawn, it didn’t handle all weeds. However, it is important to know that temperature is a factor in herbicide effectiveness and uptake by the plant. The lawn is in the cooler end of the county, and air temperatures have been in the 60s during the spray period.At 4 ounces per gallon, the dandelions are dying. The thistle is wilting visibly. In hotter temperatures, herbicides generally have more punch. It’s also easier to not increase the spray solution as much, but depending on what you’re trying to get rid of, you might want to use a little stronger solution for some weeds.Pre-emergent herbicides do work. File this for the fall, but one reason I don’t talk about them much is that I personally don’t like putting down herbicides that persist unless absolutely necessary. Another effective product that is also muy toxico is granular system insecticide, sometimes used for aphids and scale. Use carefully. I recommend digging or raking it in when possible, so the granules aren’t on the surface. Don’t breathe it.Pesticides vary a lot in toxicity. Pesticidal soaps are tame. Glyphosate herbicides (like Roundup and Kleenup) are broad-spectrum herbicides that have virtually no overall impact on anything other than what they are sprayed on.Don’t confuse “broad-spectrum” with “broadleaf.” Roundup is the one you do not use in your lawn. It kills all grasses and broadleaf weeds. Weed-B-Gone type weedkillers are for your lawn. Dandelions, thistle, clover and such are broadleaf weeds. Grasses are not broadleaf weeds.There are products for crabgrass, nutgrass, and other sorts of crapgrass that work well. Crabgrass killers don’t kill lawn grass.In non-turf situations, I urge using Roundup-type herbicides instead of the quite toxic alternatives. With more resistant weed species, mix it stronger instead of going to a poisonous spray. In general, weed killers are a necessary evil, but this is the real world. Also, some weeds are bad for the environment, so the trade-off is valid. The way to best manage it is to minimize impact, and be conscientious. Really conscientious. Back to the factors. The original lawn was laid on so-so soil. In short, it badly needs a layer of compost and topsoil mix, and an aeration. The soil mix will also level the lawn out. There has been plenty of tree root activity over the years, and it makes a lawn lumpy.It also is more porous, and uses excessive fertilizer. But if it were at peak health, it would be much more weed resistant. And that’s the point. M.G. Gallagher writes a column about plants and landscaping in the mountain zones.Vail, Colorado


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