lawn weed explosion - Ask Extension
Weeds have flourished in my lawn this year and nothing I have tried so far has seemed to help. Attached are pictured of several of those weed varietie...
Knowledgebase
lawn weed explosion #638539
Asked May 20, 2020, 4:20 PM EDT
Weeds have flourished in my lawn this year and nothing I have tried so far has seemed to help. Attached are pictured of several of those weed varieties and I am hoping that you will be able to identify them and recommend a course of treatment.
Here, briefly, are my efforts so far.
• I used a pre-emergent at the beginning of the season
• I have been mowing every four days with the mower set at its next-to-the-highest setting.
• Earlier in the year I applied Scotts Weed and Feed
• Later on, I applied two applications of Ornamec Over the Top, spaced two weeks apart
• Most recently, I applied one application of Tenacity
As you can see from the photos, the weeds have simply laughed at me and continued to prosper.
HELP!
Thanks a million for any help that you can give me.
Washington County Maryland
Expert Response
Glad you are asking. Correctly identifying the weed and knowing it's life cycle is crucial to getting control, and saving you time and effort, as well as less pesticide use in the environment.
Here is our page that will help you identify and fight our most common weeds:
https://extension.umd.edu/hgic/topics/lawn-weed-id-and-management
This page would also be helpful to you: https://extension.umd.edu/hgic/topics/lawn-herbicides
Your first photo shows Poa annua, or annual bluegrass, which can be difficult to control. You were on the right track with pre-emergent, but your timing was wrong.
Mid-August to early September is the best time to apply to prevent germination.
Here is our page on Poa annua: https://extension.umd.edu/hgic/topics/annual-bluegrass
Your second photo looks like a perennial grassy weed, which are the most difficult to control, and likely spot treating with a non-selective herbicide to kill it in the summer so that you can overseed in late summer into early fall is the way to go for this. (Note that you can't overseed and at the same time use your pre-emergent for the poa annua.)
The second and third photo (showing Veronica: (https://extension.umd.edu/hgic/topics/speedwell-veronica)), both the whitening and browning make it look like there is definite injury and that control (Tenacity) is working. For many herbicides to work well it needs to be in the 60's or 70's, with 50 degrees being a minimum which will slow down action, so it takes time and patience.
Ornamec has very specific application timing, the use of a sticker/spreader and says on the label it can sometimes take a season or more to gain control. It's not your best option.
Finally, we do not recommend Weed-n-Feed type products, as fall fertilization is best in our area. Weed preventer alone (without the 'feed') is available and a better choice overall. More about that here: https://extension.umd.edu/hgic/topics/lawn-care
Christine
Here is our page that will help you identify and fight our most common weeds:
https://extension.umd.edu/hgic/topics/lawn-weed-id-and-management
This page would also be helpful to you: https://extension.umd.edu/hgic/topics/lawn-herbicides
Your first photo shows Poa annua, or annual bluegrass, which can be difficult to control. You were on the right track with pre-emergent, but your timing was wrong.
Mid-August to early September is the best time to apply to prevent germination.
Here is our page on Poa annua: https://extension.umd.edu/hgic/topics/annual-bluegrass
Your second photo looks like a perennial grassy weed, which are the most difficult to control, and likely spot treating with a non-selective herbicide to kill it in the summer so that you can overseed in late summer into early fall is the way to go for this. (Note that you can't overseed and at the same time use your pre-emergent for the poa annua.)
The second and third photo (showing Veronica: (https://extension.umd.edu/hgic/topics/speedwell-veronica)), both the whitening and browning make it look like there is definite injury and that control (Tenacity) is working. For many herbicides to work well it needs to be in the 60's or 70's, with 50 degrees being a minimum which will slow down action, so it takes time and patience.
Ornamec has very specific application timing, the use of a sticker/spreader and says on the label it can sometimes take a season or more to gain control. It's not your best option.
Finally, we do not recommend Weed-n-Feed type products, as fall fertilization is best in our area. Weed preventer alone (without the 'feed') is available and a better choice overall. More about that here: https://extension.umd.edu/hgic/topics/lawn-care
Christine
