Increase the effectiveness of glyphosate herbicide by adding nitrogen

Shawn weighs out ammonium sulfate in the Mesa County CSU Lab.

Glyphosate, the herbicide ingredient most commonly known as Monsanto’s Roundup went off patent several years ago. As a result many companies now produce and sell this herbicide sometimes at a lower cost than previously.

While this herbicide is much more effective on grassy weeds than broadleaf weeds (dandelions, purslane, bindweed, etc.) you can increase the overall effectiveness of this chemical by adding nitrogen to the spray. A spray mix containing 0.5 to 1% nitrogen is recommended.

So how do you figure out the amount of a nitrogen fertilizer to add to the glyphosate/water spray?

Let’s say you are mixing up five gallons of spray for a backpack sprayer. One gallon of mixed glyphosate and water weighs about 8.35 pounds, thus 5 gallons of this spray will weigh 41.75 pounds. The steps are as follows:

1. We first need to convert 0.5% to a decimal by moving the decimal point over two places to the left. This gives us 0.005.

2. We next multiply 41.75, the weight of the five gallons of spray by 0.005. (0.005 X 41.75 pounds = 0.209) That is the weight in pounds of nitrogen we need to add to the five gallons of spray.

3. We then can convert 0.209 to ounces. There are 16 ounces in a pound and 0.209 X 16 ounces = 3.34 ounces. Now we know the amount (3.34 ounces) of Nitrogen in ounces we need to add to the each five gallon tank of spray, but not the amount of fertilizer.

4. Fertilizers contain varying amounts of Nitrogen depending on their formulation. Ammonium sulfate contains 21% N; Ammonium nitrate 33%; and Urea 48%. For this exercise I’m going to use Ammonium sulfate.

5. We next have to convert 21% (the percentage of nitrogen in ammonium sulfate) to a decimal. WE do that by moving the decimal point two places to the left. (21% = .21 – there is a decimal between the 21 and the %, you just can’t see it.) We then divide 3.34 ounces (the amount of nitrogen we need) by .21. This gives us the amount of ammonium sulfate needs to be added to every 5 gallons of glyphosate spray. (3.34 divided by 0.21 = 15.9 ounces or one pound).

If you have an eight ounce cup handy, you would need to add two of these, full to the top, to the 5 gallons of spray. This will give you the 0.5% nitrogen mix you need.

To figure out the amount of ammonium nitrate or urea to use, divide the amount of nitrogen needed by the percentage (changed to a decimal) of nitrogen in the fertilizer.

Fountain grass invades lawns

I took this photo today, November 18, 2010.  The color is bleached out at this time of year.

Many of you have seen Fountain grass also called Crimson Fountain grass (Pennisetum setaceum rubrum) in your neighbors’ gardens. Some of you may have this weedy grass in your own gardens and more than likely growing as a weed in your lawn.

Fountain grass foliage does not cut smoothly but shreds and the cut ends turn white. The shredded tips are highly visible on the right side of this photo.

Once in lawns Fountain grass can be difficult and costly to control.

Voight and Reicher found one or two spot treatments of glyphosate were very effective in killing Fountain grass in lawns but since this chemical also kills all other grasses this may not be a great choice especially for lawns with a heavy infestation of this weedy grass. In most cases reseeding would be required.

Products containing quinclorac would be a better choice as this chemical won’t kill bluegrass, tall fescue, ryegrass or zoysiagrass. (See the Drive 75DF label at http://www.cdms.net/LDat/ld4BF000.pdf for more detail). The problem with this chemical is it will most likely damage trees, shrubs and other ornamentals that have roots in the treated area.
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Late Breaking News from Dr. Tony Koski, CSU Turfgrass Specialist - "Drive, when used to spot treat these clumps, will not pose a problem for trees. I've never seen ornamental injury caused by Drive, even when broadcast. Drive and quinclorac-containing products are the only effective selective options. Two applications of Drive XLR8 at full rate, about 10-14 days apart, provides good control. The homeowner RTU products (WeedbGon Maxx plus Crabgrass Killer, for example) will require more (maybe 3-4) sequential applications due to lower quinclorac concentrations. And definitely remove seedheads to prevent further problems."
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If you decide to apply quinclorac it needs to be applied when the grass is in active growth as it is absorbed through the leaves and the roots.  A 1.5 ounce bottle covers a 4000 square area. Online prices range from ~$17 to $40 for this size container so shop carefully. If you would prefer to have someone else do the treatment check with your local lawn care company or pesticide applicator for a quote!

To avoid the problem of Fountain grass invading your lawn avoid purchasing this grass.
A better option would be to select a Muhly grass such as Muhlenbergia capillaris as seen in the following photo. This is a native and hardy from zones 5 to 10. Some local nurseries should have Regal Mist or other cultivars of this colorful grass available in the spring.

Photo courtesy of Park Seed Co.

Cheatgrass control should be accomplished this fall. Don't wait!

Downy Brome, Bromus tectorum, known as cheatgrass, is a weedy grass that germinates in the fall, goes dormant in the winter, begins growth again in the spring and will complete growth next summer.
The long sharp awns on the seed penetrate the skin and ears of cats, dogs and other animals. When the plant dries the chances for fire is very likely.

This grass is soft and hairy on the upper and lower side of the leaves. When you pull a leaf down and look at the point where the leaf touches the stem, you will see a membrane (the ligule)  that is very thin and hairy or toothed as seen in the photo below.  The  photo is courtesy of http://www.ppws.vt.edu/scott/weed_id/brote.htm

This weedy grass should be sprayed now if at all possible. Glysphosate is a great herbicide with systemic properties killing roots along with leaves and stems.  However, this herbicide is likely to kill plants you don't want killed if the spray gets on those plants. If you use glyphosate, use it carefully.  Safer chemicals to use include fluazifop-P-butyl and sethoxydim. Fluazifop-P-butyl and sethoxydim are also systemic and will kill roots and rhizomes.

Fluazifop-P-butyl sis old as Ornamec 170 and Ornamec Over-The-Top.  These products can be used in and around ground-covers, shrubs and trees  in landscape beds, container yards and grower nursery fields without damaging broadleaf plants.  Over 500 plants are listed on the label over which this product can be sprayed. Other Fluazifop-P-butyl products registered for use in Colorado in 2010 include Green Light Bermudagrass Killer and Ortho's Grass B Gone Garden Grass Killer.

Sethoxydim is effective on annual and perennial grasses to include turfgrasses.  This material is not effective on sedges. Sethoxydim is sold as Bonide Grass Beater Over-the-Top Grass Killer Concentrate (13% sethoxydim), Ferti-lome Over-the-Top II (18%), Hi-Yield Grass Killer Post-emergence Grass Herbicide (18%), and Poast Herbicide (18%). . Not all of these products are labeled for landscaped areas so read the label.   Treatment of reed canarygrass, a major weed along irrigation ditches significantly reduced seeding and biomass production of this grass, especially when the dead grass was mowed down prior to the next year's application of Sethoxydim.

Products used for burn-down only.  These are not systemic and will not kill the roots.

Scythe is a pelargonic acid and similar fatty acid combination that burns back the top of the plant.  Since cheatgrass is an annual, it has no below ground buds from which to recover.  When used on perennial weeds, you can expect the plant to recover from its below ground buds.  There is no systemic activity with Scythe. This product is not approved for organic production.

BurnOut II is a blend of lemon juice, clove oil and citric acid and provides non-selective control of herbaceous broadleaf and grass weeds. This product is a contact kill and has no root activity. BurnOut II is approved for organic production by OMRI.

Weed-Aside, an ammoniated soap of fatty acids, has no root activity and thus does not kill the roots of perennial weeds. It is quite effective on annual weeds such as cheatgrass.  While this is said to be organic, I can not find any agency that has certified Weed-Aside as approved for organic production.

The smaller the grass is when it is sprayed the more effective the treatment.  Don't wait until next summer to try and control cheatgrass.  Treat and kill it now!

Glyphosate damage on ash tree.

This photo of an ash tree shows symptoms of glyphosate uptake. Glyphosate, initially sold as Roundup by Monsanto, is now available in generic form at many farm cooperatives, and retail businesses.  When this product is misapplied it can cause damage.  In this case the owner sprayed glyphosate to control weeds at the base of the tree last year.   These symptoms appeared this year.


Glyphosate may drift onto the buds or be taken in through green tissue at the base of tree . 

Symptoms of glyphosate toxicity the year after glyphosate uptake results in clusters of leaves where shoots should develop.  I've seen these same symptoms on trees in local retail nurseries where the wholesale nursery applied glyphosate to control weeds around the trees the previous year. These symptoms are also occasionally seen on grape vines when glyphosate is used to control weeds at the base of the vines.

Herbicides should be used with care.  Don't assume they are safe.