This is a topic that is being discussed and practiced frequently in this region of the country. I have always been very uneasy about recommending dormant applications of non-selective herbicides, but this is a good post-emergent weed control opportunity in our region of the country. I have seen applications similar to this go wrong at spring green-up, which is why this practice should be performed with care. I do not know that I would be comfortable with this application in the Southeastern US, but here in Lubbock; I have little doubt that the bermudagrass is fully dormant and would not be injured.
If you have been following my posts, Lubbock received “normal” rainfall this past year totaling just over 20 inches. On top of that, we have received about 1.5 inches of rainfall in January when we typically only receive 0.5 inches. The increased soil moisture is a blessing in many ways, but it has greatly increased the weed infestations on golf courses in out of play areas that typically receive less herbicide applications.
Additionally, many home lawns around town are full of broadleaf and grassy winter annual weeds.
In areas where bermudagrass goes fully dormant in winter months, the application of non-selective herbicides for weed control is a viable option for a few reasons: 1.) cost, 2.) loss of selective herbicides, 3.) herbicide resistant weeds. Applying these non-selective herbicides are generally much more cost effective compared to some of our selective herbicide options available for turf. The loss of MSMA has left a hole in the chemical weed control arsenal in many areas where bermudagrass is grown, especially in those situations with lower operating budgets. Being able to remove actively growing weeds prior to spring green-up can be a successful option in those sites. Herbicide resistant weeds have been confirmed in many locations that will limit efficacy of those herbicides to resistant populations. This method can assist with those resistant populations during dormancy; however, there may be concerns with glyphosate-resistant weeds in high agriculture production areas. Hopefully the majority of weeds will be controlled with the application and alternative options can be included to manage small portions of weeds remaining with selective herbicide applications after spring green-up.
When applying non-selective herbicides to dormant bermudagrass, care should be taken to apply the herbicide at a lower output rate. There is more potential for error and injury if the application is made at a high rate. Generally speaking, this is a more significant problem for homeowners applying with a backpack sprayer. At full pressure, it is not uncommon for applications to be made at 80-100 GPA, and this can deliver the herbicide deeper into the turf canopy. At lower output rates, the herbicide will stay in the dormant foliar material reducing the potential for injury. If the application is being made on fully grown turf areas, tank-mixing a pre-emerge herbicide with the non-selective herbicide can provide residual control of weed emergence further into the spring. Irrigation would need to be withheld for 1-2 days to ensure weeds have ample time to take in the non-selective herbicide.