The Low-Down on New Brush-Control Weapons
by Larry Thomas

Dow AgroSciences - April 14, 2001

This field of thistles in Stony Plain provided a real test

It's been a long time since we've had any new herbicides for brush and broadleaf weed control on grass pastures and range, but Dow AgroSciences Canada Inc. changed all that when they registered Remedy* (triclopyr) last spring and Grazon* (2,4-D+picloram) in November. Picking which one to use will depend on the target species and, of course, your brush-control budget.

Calling Grazon new is a little misleading. Dow has had an identical product, Tordon*101, on the market for decades. The only difference between them is in the label restrictions. Tordon 101 is used for industrial vegetation control (brush and broadleaves) on rights-of-way, rail lines and the like. Grazon is registered for broadleaf and brush control on permanent pasture and range. Both have the same active ingredients and the same price tag.

Dow pasture and range market specialist Tyler Groeneveld says they are targeting Grazon mainly for broadleaf weed control on pasture and range, even though it is registered for both weeds and brush. "If guys want to talk about brush control, we're talking Remedy because we feel it's more affordable," he says. At brush-control rates, however, Grazon does cover a wide spectrum of woody species, plus a very wide range of broadleaf weeds. It also has residual qualities and may provide more than one year's control on broadleaves and, possibly, some brush species.

Making the choice between these 2 products depends on the target species, the site and, of course, your weed-control budget.

Most broadleaf plants are sensitive to the picloram in Grazon. In Alberta ranch trials, Grazon at 1.5 L/ac. gave good control of pasture weeds such as Canada thistle, oxeye daisy, tall butter-cup, common burdock, pasture sage, and diffuse and spotted knapweed among others. Grass production 15 months after spraying increased 67%. At the labeled 2.8 L/ac. rate, it covers a somewhat wider range of weeds that includes dandelion, wild carrot, burdock, common ragweed, prickly lettuce, fleabane and vetch. At suggested prices, these 2 rates would cost $20.60 and $38.50 per acre, respectively.

Dave Ralph, a weed technician with the B.C. ag ministry in Kamloops, also likes the way Grazon controls some noxious weeds. "Although it's not on the label, it will have great efficacy on the knapweeds. My research last year showed excellent control of sulfur cinquefoil and good control on orange hawkweed and rush skeletonweed," he says. "With the picloram for residual and the 2,4-D for a quick knock-down effect, I'll bet it will be effective on other species we haven't tested it on yet."

Grazon for brush
Like Tordon 101, Grazon kills a wide range of brush species at rates between 7.3 L and 10.1 L/ac., with a cost spread from $100.37 to $138.70 per acre. At these rates, alder, birch, maple, pine, spruce and most other brush species are controlled effectively. It has to be applied while green growth is underway for best results.

The area to the right had been treated with Grazon 15 months before

While the company is not emphasizing Grazon's brush control, some producers and weed control experts see advantages in the residual nature of this product. If weeds not controlled by Remedy (e.g. Canada thistle) are alongside the brush, Grazon will also get them.

That's not to say follow-up maintenance applications won't be necessary with Grazon, but the residual nature of this product could be appealing. There's also a chance Grazon's persistence could reduce the need for follow-up brush treatments, though this idea needs more field testing. "If you look at woody plants, for instance, maple, aspen, poplar and alder, they will tend to sucker, so it would be effective to have some residual activity to control that," says Ralph. "Right now, though, because the product is relatively new, we haven't been able to measure the amount of residual activity we'd get from Grazon. That will have to come as we get more field sites set up."

Dow AgroSciences would rather emphasize the fact that picloram has a half-life of 3 months under most western conditions. Should it get into water, it will break down in 7 to 22 days. However, common sense suggests that if Grazon is identical to Tordon 101, and Tordon 101 has proven residual activity at higher rates on certain soil types, then some persistent activity can be expected from Grazon.

Another perk: Grazon is approved for aerial application.

Picloram has a low toxicity to animals but lactating dairy cattle should be kept out of a sprayed field for 7 days. Clippings from treated areas and manure from cattle grazing these areas may carry enough chemical to damage susceptible plants.

At rates between 1.6 and 3.2 L/ac. costing $45 to $90 per acre, Remedy is a logical new option for ranchers looking to control brush species such as alder, ash, aspen, poplar, wild rose and maple encroaching on grazing lands, or for opening up new grazing land. As with Grazon, plants need to be treated while actively growing. Remedy is not yet cleared for aerial applications but Groeneveld expects it will get the nod by this summer.

Some Alberta field trials have shown good results using Remedy to control brush. For about $60 per acre, the Connor Creek Grazing Reserve in north-central Alberta sprayed about 40 acres by helicopter last July at a rate of 2 liters of Remedy per 5 gallons of water. They focused on spraying willow, poplar, rose, aspen and other brush encroaching onto grasslands around the 30,000-acre reserve. Some of the trees were 15' or more in height but the ideal coverage is best on brush 12" to 5' high. Still, it was estimated Remedy offered between 90% to 95% control. This spring, when the new growth kicks into gear, reserve staff will have a better idea of how effective the treatment was and if there was any suckering that will require follow-up treatments.

Brush control with Remedy

In a similar trial, Remedy was sprayed on birch, willow, aspen and cinquefoil stands on the OH Ranch west of Longview, Alta., with good results.

If the intent is to spray out older, taller stands of brush, and ranchers don't want to bother managing deadfall later on, Groeneveld has a suggestion. "The best-case scenario is to mow the brush or blade it, let it sucker and regrow to 2' to 6', then come in with Remedy and treat that suckering brush. Remedy will kill anything under 6', and it will fall down in a year or 2 and not be a deadfall problem," he says. "But if you have stands over 8' tall and you go in and spray it out, there will be a need for deadfall management as that treated brush comes down later on."

Remedy has a narrower target range of broadleaf weeds than Grazon. At rates between 0.4 and 1.6 L/ac. it will control 11 weeds including burdock, chicory, lamb's-quarters and dandelion. Remedy does not have any residual properties, so some brush species such as pine, raspberry and chokecherry may require a higher rate at least to 3.2 L/ac., and may need to be retreated the following year.

Specific grazing, greenfeed and dried forage feeding restrictions exist with Remedy. On the grazing and greenfeed end, at rates over 2 L/ac., keep the beef cattle off the pasture for 14 days and dairy cattle off for 60 days post-spraying. If you're putting up dried hay for beef cattle, wait 7 days to cut it if applying less than 2 L/ac., and 14 days if spraying 2 to 3.2 L/ac. For lactating dairy cattle, don't feed hay harvested within 60 days of treatment with Remedy.

Other notes
Grazon and Remedy are safe for grass but deadly for many broadleaf species such as alfalfa and other legumes. If you want legumes in your pasture, these are not the products to use.

Avoid spray drifting, especially when non-target broadleaf plants are nearby. Drift-control additives are recommended for ground and aerial applications.

Both products are also toxic to certain kinds of fish, aquatic plants and aquatic invertebrates. Abide by provincial restrictions regarding the use of these products and observe required buffer zones around open water and wildlife habitat. As with all pesticides, read the label before applying these products.