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  4. 1997
  5. March

Indicator Plants

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Indicator Plants: Lanceleaf ragweed, Western ragweed, and Annual broomweed are the most frequent forbs that we have to deal with in pasture management. We should look on the presence of high populations of these plants in our pastures as indicators that something is not right in the management of our forage resource.

These plants are highly susceptible to 2,4-D and each year thousand of dollars are spent to rid them from our pastures. What is it about our management that allows these plants to dominate? I think it is the pure and simple fact that we weaken the desired plants by overgrazing. This allows weedy plants to emerge when there is lack of ground cover and competition. What is overgrazing? This word has not been defined in the scientific journals because we look on overgrazing as a result of overstocking.

When we look at a pasture and see the above mentioned forbs, we say it has been overstocked. This is not how we should define overgrazing. Overgrazing is the continuous act of an animal biting the same plant over and over again, causing the plant root system and crown reserves to be depleted.

The plant loses its ability to be dominant or competitive with less desirable forbs that are seldom grazed. To stop overgrazing, plants have to rest after being grazed. Even when plants are only 50% grazed, do these plants need rest? Yes, remember, a plant tries to regrow shortly after being bitten and it's that regrowth that animals relish. By eating fresh regrowth, further stress is put on the plant; therefore, regrowth is diminished.

In 1987 when we first began managing the Coffey Ranch, it contained 26% Western ragweed according to our transect surveys. In traditional management, one would conclude that this ranch should be sprayed with 2,4-D and the stocking rate should be reduced. This ranch had been under continuous grazing for many years. Spraying with 2,4-D would be a quick fix in getting rid of Western ragweed, but would it come back?

The answer is yes, but we still would not have addressed what was causing the problem. Instead of spraying with 2,4-D, we opted to address the problem of overgrazing. The long term solution was a grazing method that allowed time management so plants could have recovery periods after a short graze period. To do this, a multi-paddock grazing cell was created so livestock could move through a series of paddocks giving rest to plants after being grazed.

The accompanying figure shows what happened to the Western ragweed. In time, the plant was reduced to a non-competitive level. In its place desirable grasses became dominant and this allowed a doubling of the stocking rate within 5 years (see figure) instead of a reduction in stocking rate. When your pastures have the above mentioned indicator plants, is it going to be a quick fix or a permanent solution?