Spring time in Baton Rouge brings nice temperatures and excessive rain. The warm and wet weather leads to a large influx of new weeds popping up in your lawn. The weed seeds have waited underground all winter to rise up and show off. Poa annua, aka annual bluegrass, can be an eye sore for many lawns in Louisiana. The weed is an annual, meaning it will die off on its own each year, which is good. Each weed produces hundreds of seeds, which is bad. The seeds can also lay dormant for multiple years, so you will have to have a good treatment plan in place over a long period of time.
How to Control Poa Annua
Poa annua is best treated by preventing the large amount of seeds in the ground from sprouting. Poa annua seeds start to germinate in late fall, so you need to have a pre-emergent down before that and throughout the winter into spring. Since the seeds can stay dormant, this will need to be done for a few consecutive years to get close to eradicating the Poa problem.
Step 1 - Pre-Emergent Herbicide
We recommend using a pre-emergent that has pendimethalin as an active ingredient in September. Follow that up with another round of pre-emergent containing the active ingredient dithiopyr in November and again in either late January or early February. Be sure to check the product label for usage rates, timing between applications, maximum annual rates, and which types of grass your product can be used on.
Step 2 - Post-Emergent Herbicide
Even with perfect pre-emergent timing, some weeds manage to slip through and grow. This calls for post-emergent herbicide treatment. Look for a selective post-emergent herbicide that lists annua poa as a controlled weed and your grass type as a tolerant turfgrass. Alternatively, if you only have a few weeds, you can pull them when you see them.
If you have a really bad weed infestation, be patient. It will take a couple of cycles to get the problem under control. The good news is you will see drastic improvement in the first year. The other great thing for us is poa annua cannot survive in temperatures over 90 F. When May rolls around, your poa problem will go away until fall.