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A New Weed Weapon

With the launch of Reclaim last July, Dow Agro- Sciences now has four herbicides specifically designed to control a wide spectrum of broadleaf weeds, shrubs and trees on native rangeland and permanent tame pasture.

“Reclaim has become the go-to product for controlling weeds and brush, says Candice Manshreck, the company’s range and pasture territory manager for the southern Prairies and Manitoba. It has the widest spectrum of control of any of their herbicides, including buckbrush, wild rose and wolf willow.

It is also the choice when targeting weeds alone, although Tordon 22K may still be your best option for attacking deep-rooted, hard-to-control weeds such as toadfl ax and leafy spurge.

Though Grazon does control broadleaf weeds, it has become the product of choice as an alternative to mechanical or fire control of encroaching trees such as willow, aspen, birch and cedar species.

“Herbicides alone are not the silver bullet for a grass management plan,” Manshreck stresses.

Many techniques can be applied in an integrated pasture management plan to increase grass productivity. Manshreck strongly recommends starting with a rotational grazing plan tailored to your management style and circumstances. As long as it provides enough rest for recovery between grazings it will strengthen the root systems of desirable grasses so they outcompete weeds to fill in any bare ground.

Soil testing and fertilization, particularly in areas with poor grass production, is an important part of an overall plan. As are snow-trapping techniques and improved litter cover to retain moisture.

Top seeding with new grass species can also improve productivity. When you consider the cost in terms of fuel, equipment, erosion and lost time breaking up permanent pasture to re-establish a grass stand is a last resort.

As you would do for any pasture-improvement project, Manshreck advises pencilling out a cost-benefit analysis first to determine whether a herbicide application is warranted. The cost is usually straight forward, but remember to calculate them over time. For example, the expense of cross-fencing can be spread over many years. Likewise, the extended control achieved by treating a stand with a herbicide will provide benefits for three to seven years. The income side of the equation is more difficult to pin down because it is difficult to accurately estimate the increase in grass yield.

You also have to account for the cost of not controlling weeds. It snowballs when you factor in the time and expense of purchasing, transporting and feeding hay to fill the void.

“Grazed grass is always your cheapest feeding option,” says Manshreck. “The cost-effectiveness of a herbicide application will totally depend on how you manage the pasture after treatment.”

What to expect

Following an application of Reclaim or Restore, growth of the susceptible species will stop within a day or two and you can expect to see them under control within four to eight weeks. It takes 45 to 60 days before the impact of Grazon and Tordon 22K becomes fully apparent.

Manshreck says the two most common reasons for an apparent herbicide failure are environmental factors and timing of the application.

Rainfall within four hours of an application could dilute the active ingredient. On the other side you won’t get as much bang for your buck if it’s dry after spraying because the grass won’t grow as well as it would with some rain.

Timing of an application is all important since these products work by systemic action, meaning they’re taken up by the leaves and transported throughout the plant. So a spray is only effective after the target weed has emerged and set enough leaf to capture the herbicide.

The extended control provided by the four Dow Agro- Sciences products comes from soil-active ingredients that control susceptible germinating seedlings. The herbicides are most effective when the plants are actively growing and efficiently transporting nutrients. Control can also be delayed or less than optimum when plants are stressed by excessive heat, cold, moisture or drought.

Target your spray to hit the most troublesome weed when it is most susceptible. Buckbrush, for example, should be sprayed from mid-June to mid-July. For Canada thistle wait until most of the thistles have emerged, which could be anytime in July. So the best time to go after buckbrush and Canada thistle would be mid-July, although that may vary with growing conditions.

Plants that emerge after the spray won’t be controlled, and sometimes you can get a flush of secondary weeds or shrubs after the dominant one is eliminated. Susceptible seedlings germinating in the layer where the soil-active ingredients are at work will be controlled, however, plants that draw nutrients from a lower soil layer won’t be and may warrant a second application.

Reclaim A is a granulated product to be mixed in water containing active ingredients from herbicide Groups 2 and 4. Reclaim B, a liquid concentrate, Restore, Grazon and Tordon 22K contain one or more active ingredients from Group 4.

The Products

The active ingredients work like the natural growth-regulating hormones found only in plants, however, instead of promoting normal plant growth, they disrupt the normal pattern of plant development.

Group 4 herbicides disrupt plant cell growth in newly forming stems and leaves. They affect protein synthesis and normal cell division throughout the plant. This leads to visual signs, such as twisted stems and curled leaves, indicating the herbicide is working.

Group 2 herbicides work by blocking the normal function of an acid that is essential for plants to synthesize proteins — in essence creating a lack of protein and starving the plant.

Mammals are incapable of metabolizing these plant-specific herbicides. If ingested, they are rapidly excreted from the body in the urine and do not accumulate even with repeated exposures. There are no grazing restrictions, other than a seven-day restriction for lactating dairy cattle.

Risk assessments show Restore and Reclaim have low environmental impact relative to other registered products. Reclaim has very low toxicity for fish, aquatic invertebrates, honeybees and earthworms and does not accumulate in the environment.

None of the four herbicides are registered for use on cropland, hay, or turf grass. Reclaim, Restore and Grazon are registered for spot, ground and aerial applications, whereas Tordon 22K is approved only for ground and spot applications.

These are broadleaf herbicides, so most warm-and cool-season grasses will tolerate them, but they will severely injure or kill legumes.

Overseeding with new grass species can take place 10 months after an application. You’ll need to wait five years or longer if the soil pH is greater than 7.9 when you want to establish legumes in the pasture.

For more information contact the company at www.dowagro.com/ca or 1-800-677-3852.

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