Article Source: Dr. Gary Bates, Director of the UT Beef and Forage Center

Pasture and hay production in Tennessee follows a relatively predictable pattern. Forages begin to grow in March, do well until mid-June, slump some until September, grow in fall until November, then slump until the next March. This cycle is one that many of you have seen completed dozens of times. Another component of this cycle occurs during the summer season. It is the emergence of warm-season weeds.
After the spring growth of tall fescue is either cut or grazed, weed seeds will germinate and an entire crop of summer weeds begin to develop. Horsenettle, ragweed, spiny pigweed, and tall ironweed are just a few examples. If left unchecked these weeds can quickly begin to dominate a pasture. In my opinion, there are few things that make a pasture look worse than a heavy population of summer weeds. Part of the problem is that these weeds can take over because the tall fescue is slumping, offering very little competition to keep these weeds from dwarfing everything else in the field.

One of the control methods many producers have used is clipping. Trying to stay ahead of the weeds by timely mowing has been used for a long time. This method can reduce the amount of weed in the field, as well as reduce the seed production from these weeds. The problem is that being just a little late on the mowing can dramatically reduce the benefit. At minimum the weeds can dominate the field, but you could also be late enough that the plants have been allowed to produce seed for next year’s weed crop.

Fortunately, there are herbicides that are available to control many of these weeds. Whether it be GrazonNext for horsenettle or 2,4-D for spiny pigweed or ragweed, we have several tools to help control these troublesome pests. A key component to effective herbicide use will still be proper timing. Let the weeds get too big and the level of control will drop. You need to apply the herbicide when the weeds are generally 4-6 inches tall. If you let the weeds get larger, they are much harder to control, plus they have already caused competition problems for your forage crop.

Another problem with many of these weeds is that you can get seed germination basically the entire summer. Let’s say you have an area in which you fed hay last winter. The stand of grass is poor and spiny pigweed begins to germinate all over that area in June. You spray and get good control. Then a few weeks later it rains and another crop of spiny pigweed germinates. If that crop is not controlled, it is almost as if you haven’t accomplished anything.

Because of this, some of the weeds, particularly the areas that are dominated by annual weeds like spiny pigweed and ragweed, may need to be sprayed twice to get season long control. You have to stay diligent and evaluate these areas constantly to determine if another herbicide application is needed. If you need more information on specific weeds and the appropriate herbicides to use, contact your local Extension agent or check UTBeef.com. Look under the Forage/Weed Management section for specific recommendations.