Help Removing Poa Annua

Question: Hello. I'm in the process of trying to eliminate Poa from my yard. I was in discussion with Brian last fall. No luck last fall killing it off with roundup and reseeding, it came back heavy this spring.  I just finished sod cutting about 4000 sq ft. of my turf. 
I could use your help with a couple thoughts. Can I spray roundup on the bare soil to kill any residual grass and seeds, I know some of the poa seeds have dropped back in the soil during my removal process. My other idea is to use my slitter/seeder to slightly loosen the soil, add a small amount of mulch then spray with Tenacity and reseed the same day. If I use roundup on bare soil, should I wait a minimum of 3 days before mulching and reseeding? I also bought liquid Dimension 2EW for this fall and spring  2024 application.
Any thoughts and recommendations would be appreciated!!!
Thank you,
Chet Wilson Medford OR
email -  <personal data hidden>

responder: The Question Asker Replied May 09, 2023, 7:25 AM EDT
response: Hello again. Upon futher reading of applying roundup to bare soil, it appears to be a bad idea due to residuals. I guess I'll use my slitter to loosen the existing soil, apply new soil, apply Tennacity, seed, roll, mulch and fertilizer. That's my best guess ideas..Thanks again,Chet WilsonSent from my Verizon, Samsung Galaxy smartphone-------- Original message --------From: Ask Extension <<personal data hidden>> Date: 5/8/23 8:35 PM (GMT-08:00) To: Chester Wilson <<personal data hidden>> Subject: Thank you for your Ask Extension question (#0099023)   Dear Chester, Thank you for using Ask Extension. A request for support has been created and a representative will follow-up with you as soon as possible. Questions are usually answered within two business days. You can view this question's progress online. YOUR QUESTION #0099023: Help Removing Poa Annua Hello. I'm in the process of trying to eliminate Poa from my yard. I was in discussion with Brian last fall. No luck last fall killing it off with roundup and reseeding, it came back heavy this spring. I just finished sod cutting about 4000 sq ft. of my turf. I could use your help with a couple thoughts. Can I spray roundup on the bare soil to kill any residual grass and seeds, I know some of the poa seeds have dropped back in the soil during my removal process. My other idea is to use my slitter/seeder to slightly loosen the soil, add a small amount of mulch then spray with Tenacity and reseed the same day. If I use roundup on bare soil, should I wait a minimum of 3 days before mulching and reseeding? I also bought liquid Dimension 2EW for this fall and spring 2024 application. Any thoughts and recommendations would be appreciated!!! Thank you, Chet Wilson Medford OR email - <personal data hidden> Ask Extension offers one-to-one expert answers from Cooperative Extension/University staff and volunteers within participating Land-Grant institutions across the United States. If you wish to provide additional comments or information regarding the issue, please login to your account for a complete archive of your prior questions and answers.  This message for informational purposes only. It is not intended to be a substitute for personalized professional advice. For specific local information, contact your local county Cooperative Extension office or other qualified professionals. eXtension Foundation does not recommend or endorse any specific tests, professional services, products, procedures, opinions, or other information that may be mentioned. Reliance on any information provided by eXtension Foundation, employees, suppliers, member universities, or other third parties through eXtension is solely at the user's own risk. All eXtension content and communication is subject to the Terms of Use which may be revised at any time.

responder: Brian McDonald Replied May 10, 2023, 2:32 PM EDT
response: Hello Chet,  The best approach is to try and obtain a sterile seed bed before seeding. Since you already sod cut your lawn, smooth, and prep the soil before seeding. Get the surface as smooth and as possible. Note, there can be some slope to it, but the surface should be smooth. Once you are ready to seed, DO NOT APPLY THE SEED.  Instead, irrigate the area lightly to keep the soil moist for a couple weeks. Usually, once in the morning and a couple times in the afternoon is enough. But if the weather gets hot, you may want to irrigate 4 times in the afternoon. You only need to water 6 - 10 minutes at a time unless you have pop up spray nozzles (not rotators) that put out a lot of water, in which case, 3 minutes is probably plenty. You do not want the water to pool on the surface.   The goal is to get all the poa seeds and other weeds to germinate. Once things germinate, spray them with roundup. You may want to go through this cycle a couple of times. Then, seed your grass without disturbing the soil.  The best time to seed is late June into July as poa does not like to germinate during this normally hot period. There is a downside to seeding during this period which is there is a risk of getting "damping off" fungal disease which might kill your new seedlings.  The fungal disease occurs because of frequent watering in warm weather which creates high humidity around the new seedlings. You have to balance giving your new seedlings enough water in the afternoon without creating a humid environment. The key is to cut the number of times you water in the afternoon, if possible, to only once after the seeds germinate. Once the seeds germinate, water more thoroughly in the morning as the seedlings have a root system.  Damping off is only a problem after the seeds germinate, not before. Watch the seeds carefully starting 5 days after planting. There are a few critical days where the seedlings are most at risk (from germination to about 7 days afterwards). If you can time your seeding for a weather forecast that is not going to be really hot, that would help a lot. For example, a high temperature of 75 degrees probably will not require an afternoon watering. But look to see if the seedlings are wilting.   Since our humidity declines as our temperatures go up, damping off is not a huge problem in western Oregon.  It is only a problem when we create it by watering frequently in the afternoon during hot weather.  Also, to prevent the risk of "damping off", you can apply a fungicide (Subdue GR) which can be applied with a drop spreader at the time of seeding. In Oregon, you will only have to make one application. The downside is that it is expensive.  A cheaper option is just to take your chances and re-seed any areas that die. In most cases, all the seeds won't die, just a few small patches.  You also want to be sure and fertilize at the time of seeding your lawn. This will ensure the seedlings grow as fast as possible to develop a healthy root system which will allow you to eliminate the light afternoon watering more quickly.  If you are planting perennial ryegrass and you really want to ensure a clean stand, hire a licensed pesticide applicator to spray Prograss SC or EC on your new stand of grass at the 1 - 3 leaf stage of your new ryegrass seedlings and then 4 weeks later. This will kill any emerging poa annua that did not germinate when you did the sterile seed bed.  Then, as you mention, apply a pre-emergent herbicide in late summer (early September) and next spring to keep the poa from germinating. You will have to do this every year.  Also, keep your lawn well fertilized in late summer going into fall. Make two or three fertilizer applications (for a perennial ryegrass or tall fescue lawn) one month apart. This will maintain the density of your lawn and reduce encroachment of poa and other contaminants.  Keep in mind that what you are doing is simply delaying the inevitable. But if you do all these things, you can get a clean stand to start with and it will be reasonably clean for 4 or 5 years. You may want to hand pick any poa that invades as soon as you see it.  Good luck.

responder: The Question Asker Replied May 10, 2023, 11:13 PM EDT
response: Hi Brian. Thank you for your recommendations for planting new turf seed. Your suggestions make sense and I will use them.  I have some left over Poa Constrictor that I will use at the 3 leaf stage. The topsoil company suggested I use their mulch to top dress the seed for moisture retention and bird control. I've used peat moss in the past but prices have gone from $15 a bag to $22 a bag this year. Do you have suggestions what to put on the seed after I lightly sow and roll it, is mulch OK? Again, thank you for helping me through my journey or maybe nightmare. lol Chet Wilson ----------------------------------------- From: "Ask Extension" To: "Chester Wilson" Cc: Sent: Wednesday May 10 2023 11:32:50AM Subject: Re: Help Removing Poa Annua (#0099023)

responder: Brian McDonald Replied May 11, 2023, 3:40 PM EDT
response: Chet,  We primarily use horse compost and roll it on with a peat moss spreader that you can rent cheaply from a rental store.   I purchase it for around $20 per yard from a place that sells horse gear and has stalls to keep horses.  You can also use sawdust, but you need to fertilize more if you do because it has a high carbon to nitrogen ratio and the microbes will break down all the carbon and use all the available nitrogen. The horse compost has some nitrogen in it which is good, but it needs to be high quality meaning it has completely broken down and not in chunks.  Horse compost is simply composted horse manure (the nitrogen) and straw that they use for bedding.    The primary benefit of mulch is that is results in a more uniform establishment for two reasons: first it holds moisture in so the soil surface doesn't dry out as fast so you don't need to water as much, and second, it prevents earthworms from moving the seed into clumps.    Earthworms come up at night, crawl around, the seed gets stuck to their bodies, and then they burrow back into the soil leaving a clump of soil with a bunch of seed and a bunch of bare spots where they pulled the seed from.    Not every soil has high populations of earthworms, but we have had seedings dramatically impacted by earthworms.  I don't think birds eat enough seeds to be a problem.  Perennial ryegrass has 200,000 - 250,000 seeds per pound and it gets seeded normally at the 4 - 6 lb. rate per 1,000 sq. ft.  That's a lot of seed!    Having said all this, it is not critical to add mulch.  If areas don't come in well, simply seed those areas again.   It helps a lot if you are doing a late seeding (e.g., early October), but if you are seeding in early July, I think it could be detrimental because it will hold too much water once the seed germinates.  My recommendation would be to not use if for a July seeding.  By the way, in looking at your photo of your lawn, I see that hedge bordering it.  You will need to be especially careful along that edge with watering as it will be in a lot of shade and higher humidity.  That area is much more likely to get damping off.  Good luck.

responder: The Question Asker Replied July 07, 2023, 8:41 AM EDT
response: Hi Brian. A quick follow up on my yard renovation project. Got all the seed down but ran in to damping off on several places throughout the yard. The last couple weeks have been unusually hot here and I think between the heat and me trying to keep the seedlings moist I have over watered and created a poor condition for the new seedlings. With that being said, I know I have fungus on/in the turf, can I replant at some point? Since we're in the middle of summer I thought it would be good to hold off on replanting until late August or September. Can you help me on two questions? First, when is the soil acceptable to replant seed and second, how does late summer planting work with application of Dimension 2EW for potential poa?Thank you for your help again.Chet WilsonMedford OR-----------------------------------------From: "Ask Extension" To: "Chester Wilson"Cc: Sent: Wednesday May 10 2023 11:32:50AMSubject: Re: Help Removing Poa Annua (#0099023)

responder: Brian McDonald Replied July 07, 2023, 5:05 PM EDT
response: Hello Chester,  Yes, damping off can be an issue when trying to plant this time of year.    It is difficult to keep the plants from dying  from drought while not getting damping off.   You have three options.   Option 1 is to reseed those areas and hope for cooler weather in the couple of weeks it takes for the new seedlings to establish.   You can repeat this process as many times as you like.  Option 2, is to apply Subdue GR, which is a granular fungicide that will control damping off.   You would simply apply it before seeding.  If the weather continues to be hot, you could make a second application in 7 to 14 days.   This product should be watered in with at least 0.25" of water (See the label for exact instructions).  You can make a third application, if you think the weather is conducive, but do not make more than 3 applications per year on the same turf.   There is a generic version of Subdue GR, but it only comes in a liquid formulation that you would have to spray.  Option 3 is to wait until fall which does cause an issue with timing of your Dimension application.  You would have to wait for your new seedlings to be established before applying Dimension.  The label tells you how long to wait after seeding to apply it, but I can't remember what that is off the top of my head.   Look on the Dimension label.    Of course, the problem with waiting is that the poa can be germinating at the same time as your new grass is germinating.  But if you are planting perennial ryegrass, you could have a professional applicator apply Prograss SC herbicide at the 1 leaf stage of the perennial ryegrass.  That will kill the newly emerging Poa.  I hope this helps.  Good luck.