Dr. Richard Ludwig on Organic Weed Control
Planet Perfect Weed Control
Going green while keeping an eye on the bottom line.
By: Richard Ludwig, EdD
Landscape managers rank weed control as one of their most time-consuming and challenging activities. Historically, there's been quite an array of synthetic products available. Some will take down anything green and others can cherry-pick one species from a planting. Recently, however, residential and commercial clients have increasingly demanded organic alternatives.
True to our traditional roots, many green industry professionals are still sitting on the fence. One reason might be a Duke University study that says 78% of all consumers will only try an organic solution if it is less expensive or more convenient. Other concerns are effectiveness and cost compared to traditional synthetic products.
A European study found organic herbicides using D-limonene, such as Nature's Avenger, seemed to give longer-lasting effects. Consider products with D-limonene (also known as orange terpene) as a main ingredient for extended control.
Strategies for Going Green
Here are a few strategies to go green while you're paying attention to the bottom line:
- First, always make organics an option, but if your current weed control program is working, don't eliminate it regardless of your earth ethics.
- With weed control, a great offense is always a good defense. Robust, actively growing turf or groundcover won't kill weeds, but they'll compete nicely. Create the optimum environment for your plants and turf so they will thrive.
- Seeing moss in turf probably means an overly acidic, poorly drained area. Fix that before purchasing a moss killer.
- Core-aerated your turf lately? Clay soil is almost always poorly drained and anaerobic. Lots of low-oxygen weeds, like annual bluegrass, love clay soil.
- Remember that many weed seeds require the sun's UV rays to germinate. If plants are massed together, shading the ground, few weeds will emerge. Conversely, a sparsely planted bed in full sun is summer camp for weeds.
- Under-fertilization as well as over-fertilization can encourage weeds. One massive application in the spring causes intense, rank growth. Once the fertilizer is used up, the plants starve the rest of the year. This actually weakens the plant rather than strengthening it, giving weeds a foot in the door. Instead, consider a gradual release of balanced nutrients over the entire year. Here's a planet-perfect place for an organic fertilizer that slowly breaks down.
- Pre-emergents rock! Remember Barney Fife on The Andy Griffith Show? Barney's famous saying was, "Andy, we need to nip it in the bud." That's the perfect strategy for earth-friendly weed control: keep weed plants from maturing and setting seed. Cornell University reports that one pigweed plant can produce 100,000 seeds if allowed to mature. Ouch! Get them when they're young if you can figure out when those weed seedlings emerge. The challenge for those of us who garden in Zone 8 is that we live in what's known as the transition zone, where cool and warm season weeds germinate year-round. The best organic pre-emergent is corn gluten meal (CGM). It's reasonably effective but seems to work best as it builds up with multiple applications over several years (needless to say, don't use it when you are reseeding). One major problem with CGM is cost. Prices range from $3 to $40 for a 50-pound sack, depending on where you live. Apply 10-40 pounds per 1,000 square feet.
- Hand pulling weeds is very organic and great for the soul. However, it is immensely expensive and not very permanent. If the weeds are out of control, however, it may be your only option. Spraying a large weed, letting it die to leave a dead carcass is just crazy. At least knock 'em down with a string trimmer before you spray. You'll have little visible plant material that can easily be tamed with an organic herbicide.
Organic herbicides such as Ground Force and Burn Out contain various combinations of citric acid, vinegar, garlic, yucca and clove oil. They're all contact herbicides and seem very effective in quickly destroying the above-ground portions of herbaceous material. They're not translocated to the root, though, so offer little long-term control, especially with perennial weeds. They're best on young annual weeds, since destroying the top will pretty much end their existence. This means you might have to spray on a more regular basis.
A European study found organic herbicides using D-limonene (also known as orange terpene, a cousin to citric acid that is extracted from orange peels), such as Nature's Avenger, seemed to give longer lasting effects. This study found that terpene-treated weeds took longer (over 19 days) to re-emerge. Consider products with D-limonene as a main ingredient for a extended control.
Landscape management will always include weed wars. Offering organic alternatives is a smart way to control weeds in you garden and if you're in the business, add new clients and upgrade existing ones. Just make sure you consider all the options and develop a bill of fare that puts groceries on the table as well as saves the earth.
Richard
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