Briars such as blackberry and dewberry are seen in pastures this time of year. UGA Forage Team Memeber and Miller County Agent Brock Ward has come up with some pointers on controlling these weeds:
There are many bramble type weeds that are called blackberries by area forage producers. These weeds often require significant growth before we can tell them apart. The good news is that they generally can be controlled using the same chemistry.
For areas where briars are a problem, control is a matter of herbicide timing. For instance, if spring was the first time a bramble weed was identified, you can wait until late September or mid-October to apply a herbicide. Waiting until fall is preferred because most of the herbicides are systemic and need adequate leaf surface to take in the chemical for translocation. During the Fall, the weeds prepare for overwintering.
Water is also needed for many of our herbicides to affect the plants. Timing application both after and ahead of a rain / irrigation will help ensure the plant is actively growing to maximize efficacy. Applying herbicides to drought stressed weeds can lead to a failure in control. Moisture stress can cause the cuticle on the leaf to harden off which reduces herbicide penetration. Delaying applications until brambles have recovered from drought stress will enhance herbicide absorption and improve efficacy for control. It will also take some time for the herbicides to fully control the weeds. Waiting six to eight weeks before mowing the weeds after application of a herbicide is recommended.
If the weeds have been previously mowed or a mature stand is currently overgrown, the area needs to be evaluated and managed to get herbicide on the actively growing material. In the case where a large mass of weeds have grown for more than two seasons, mow the weeds to get a flush of younger, more susceptible leaf tissue. This can be timed by cutting about six months before applying the chemical. A potential method is to cut in the fall through late winter and treat in the fall of the next year. This allows the foliage to have adequate growth for the herbicide to interact with and get better control.
To help your county agent with the herbicide decision, be prepared to discuss your desired grass or forage and what you are looking to control. Oftentimes there are numerous weed species needing treatment. We may prioritize weeds of greatest concern. In most cases, control of multiple broadleaf species with a single application can occur, but timing is critical.