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Preparing for the Next Poa Control Season
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Welcome to The Turf Zone podcast. This episode features the article “Preparing for the Next Poa Control Season” by Scott McElroy, PhD – Professor, Department of Crop, Soil, and Environmental Sciences, Auburn University and and Travis Gannon, PhD – Professor, Department of Crop and Soil Science, North Carolina State University.
Quote – “When did Noah build the Ark? Before the Rain.” – Robert Redford in “Spy Game”
It is the end of Poa annua’s life span here in the southeast. As this article is being written in late May, Poa is struggling to produce that last bit of seed it can before it dies, perpetuating whatever traits it carries into the future. Likely, if you have been trying to control Poa, you are looking down at a population that has been selected for some form of resistance to the herbicides you have been using. The short-time traveler seeds are going to greet you next November-ish. As warm-season grasses are sliding into dormancy, or at least a state of slowed or diminished growth, those seeds carrying those herbicide-defying traits are going to make their appearance, potentially thwarting whatever attempt you used last year yet again.
Before you start making decisions about your management program next year, you need to test your Poa population. Two populations from this year were showing signs of Kerb resistance until we brought them into the lab and realized that it was not resistance, but most likely enhanced degradation due to overuse. Email Dr. McElroy at resistancelab@auburn.edu and get a better picture of what your population is resistant to. For most herbicides, you can get an answer in six weeks.
For the southeastern US, there are three distinct application periods for Poa control. This is for bermudagrass and zoysiagrass golf, sports fields, professional lawn care, and general use. Golf and sports fields are the most complicated because they receive the most traffic and use, therefore the greater turfgrass damage, which leads to greater weed invasion. The application scenarios we talk about here are more likely to be used in golf than in other areas, but applicable to all situations except sports, which require special attention to not reduce rooting and traction.
The Pre Application- The Basis of Control.
In all situations, you want to start off with a general preemergence herbicide. If in golf and non-sports turfgrass areas, this is Specticle (indaziflam) or a standard pre like Barricade (prodiamine), Pendulum (pendimethalin), or Dimension (dithiopyr). In our opinion, this is the optimal application timing for Specticle (indaziflam). Specticle should not be used on sports fields, it is a root inhibitor and can result in poor-performing turfgrass. Regardless of which herbicide, the initial pre application is the basis of all Poa control programs. Skipping the pre puts greater pressure on follow-up postemergent applications. Even if pre-applications only reduce the Poa population by 50%, that is still 50% fewer weeds that follow-up applications have to deal with. Later applications are much more likely to fail if you put all the pressure on follow-up post applications.
Adding in a postemergent herbicide at this time is not a bad idea, but it needs to have some residual and some root uptake because your pre needs to be watered in. Monument (trifloxysulfuron) is possible because it can be foliar absorbed, but Revolver (foramsulfuron) has limited root uptake. Others are using Sencor (metribuzin) in this timing.
The Winter Transition: Key to Resistance Management.
The early winter, or early winter transition application, is the most critical. Skipping this application leads to too much pressure being placed on the initial pre application which can expedite resistance development. This application needs to yield acceptable control in two to three weeks, which eliminates any resistant survivors that may be present and provides further preemergence control.
The key to the transition application is choosing multiple herbicides with a minimum of three different modes of action, with at least two having preemergence and postemergence activity. To clarify- Three modes of action with two having both pre and post activity. Triazines – atrazine and simazine – are the starting point for this control. Think of these as your Post/Pre herbicides, they are primarily post but give you some pre activity. Sencor (metribuzin) is also an option, although not as consistently effective as atrazine or simazine. If these herbicides are not available for use or if you have extensive confirmed resistance, ALS inhibitors such as Revolver (foramsulfuron), Monument (trifloxysulfuron), or Katana (flazasulfuron) are useful, as is Scepter (imazaquin).
Next, you need a Pre/Post in the mix – a herbicide that gives you primarily pre action but adds in some post control. Kerb (pronamide/propyzamide) and Sureguard (flumioxazin) are good choices at this timing. A second application of Specticle also has potential in this situation, although it has less post activity than the two listed above. Ronstar (oxadiazon) applied as a liquid to provide post activity also has potential in this timing.
Last in the mix you need something that can aid control and help prevent resistance. Glyphosate is the obvious choice in this mixture. If you are not completely dormant, a low rate at 5 fl oz/a (of a 4 lb ai gallon) can add some benefit, but if confident in the dormancy, use a full labeled rate on dormant turfgrass. Finale (glufosinate) is a good substitute if glyphosate resistance is present or developing. Neither glyphosate or glufosinate are recommended for zoysiagrass, adding in a Revolver, Katana, or another ALS inhibitor is a better choice due to potential damage from non-selective herbicides.
The Spring Transition – Control Any Escapes and Spring Crabgrass Control.
Combining any further Poa annua control with spring crabgrass and goosegrass control is an easy way to maximize efficiency. This pushes the herbicide application into late February to early March for the majority of the southeastern United States (time applications to your specific area based on local weather patterns and soil temperatures). Dormancy questions and spring greenup of bermudagrass or zoysiagrass complicate this application timing. Some herbicides are simply too harsh on greenup to be used in this period.
First, the standard pre herbicides should be used at this time – Barricade (prodiamine), Pendulum (pendimethalin), Dimension (dithiopyr), or Ronstar (oxadiazon, granular is not dormant, but liquid can be used if still dormant). While Specticle is more effective for Poa annua control and summer annuals such as goosegrass and doveweed, it is equivalent to the standards for crabgrass control.
Second, post herbicides that can be used in this transition period are few. ALS-inhibitors mentioned before are definitely safe, but resistance is extensive, thwarting their use. Triazines can delay greenup and cause transition injury. Non-selectives such as glyphosate and glufosinate are out due to spring injury.
Final Thought.
Herbicides are primary technology we have today to control weeds. We live in a chemical technological age. Unfortunately, weeds, especially Poa annua, have evolved resistance to these herbicides. Our thoughts and ideas we provide herein are meant to reduce the potential for resistance development and all herbicide options are not discussed for brevity. These multi-herbicide strategies now are necessary because herbicide resistance has become so prevalent and it is our goal to strategically use these herbicides to prevent further resistance development and protect herbicide technology for future use.
Note: Always read and follow the complete herbicide label before mixing, handling, or applying any product, as the label provides legally required directions for safe, effective use, application rates, precautions, and site-specific restrictions.
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