February 7, 2001 | By: Laura Skillman

While pastures may not be a key issue on the minds of many Kentucky farmers, it is never too early or too late in the season to begin considering weed control methods.

In grazed pastures and other forage crop systems, weeds or unwanted plants can reduce the quantity and the stand-life of desirable forages. Weeds often are more aggressive than seeded forage species and can compete for light, water and nutrients.

In some cases, weeds also can diminish the quality of forage available for livestock grazing and certain weed species are potentially poisonous to grazing animals.

However, not all plants considered to be weeds are detrimental to grazing systems, so prudent management decisions often are needed to ascertain when and if weed controls should be initiated.

How a pasture is utilized and management decisions can have a major impact on the presence of weedy plants, said Jimmy Henning, a University of Kentucky College of Agriculture Extension forage specialist. Over-grazing and poor fertility levels favor emergence and propagation of weeds.

Henning was one of several UK forage specialists who conducted a forage profitability symposium at the Kentucky Cattlemen's Association annual meeting in January.

When the weeds are most obvious in fields, may not be the time to try to control them.

For example, if a field has buttercups, a farmer needs to do something in November or February to control it, not wait until the summer months when it is obvious. Using a calender can be the best place to begin gaining a control on weeds.

Sometimes all the field needs is a little help. For example, farmers may have to contend with some weeds while establishing an alfalfa crop that once the crop is established will not be a problem again, Henning said. Some crops are aggressive enough not to let weeds become established and become a problem.

When determining weed control measures, the type of forage needs to be known, such as cool season or warm season or whether it is a grass or legume. It also is important to determine how the forage is going to be used and if control would be economically beneficial.

"We've got some weapons that don't say herbicide on them," Henning said.

Integrate strategies, mechanical, cultural and chemical, in combating weeds in pastures. These weapons include cultural, fertility and grazing practices.

Good grazing practices that do not leave the stand short are going to be helpful in keeping weeds from gaining a good foothold.

Nitrogen and other fertilizer applications at the appropriate times can affect weed control.

"You don't feel like you have hurt weeds when you put the fertilizer on but I can assure you that you have and it is a big player," he said.

Fall is a great time that is missed for control of broadleaf weeds. Fall applications of nitrogen can help thicken up the pasture and eliminate opportunities for weeds to gain control.

Periodic mowing or clipping pastures can be beneficial in keeping seed heads from developing and spreading undesirable weeds throughout the fields.

Deciding when herbicides are needed can be a difficult question to answer, Henning said. The best answer is when the benefits will outweigh the costs of control such as in the case of a poisonous weed or a noxious weed.

Henning said there is no herbicide that can be broadcast over the top of grasses that will not hurt clover, a common combination in Kentucky pastures.

"If you're going to use weed control on pastures, you've got to find the time that either you can stand the damage to the clover or the clover is winding out and I'm going to say it is a grass pasture, now what can I do," he said.

Strengthen base pastures and use the cultural methods and management decisions first in combating weeds, he said. Then, look at what herbicides would work best in your individual situation.


Jimmy Henning, (859) 257-3144