Preemergence herbicide applications for crabgrass, goosegrass, foxtail, and other annual grasses are underway. Here are some bullet points to consider to increase the efficacy of the herbicide you use.
Maintain turf density and mow higher. Good turf density resulting from proper cultural practices for the grass you’re managing reduces encroachment of all weeds, including annual grasses. Mowing at the higher end of the recommended range has consistently shown significantly lower populations of crabgrass and other annual grasses than mowing at lower mowing heights.
Apply before emergence. Not all annual grass species emerge at the same time. For example, goosegrass emerges later than crabgrass. However, even within a species, emergence of new seedlings occurs throughout spring and summer. With most preemergence herbicides, when seedlings have emerged, they will not effectively control those plants. However, the application will control emergence of grasses beyond that date. Dithiopyr (Dimension) does provide control of crabgrass that has emerged but has not begun to produce tillers.
Use effective strategies to guide application. Calendar dates, soil temperature, flowering of ornamentals, and other strategies are all used to help guide applications and maximize herbicide residual during the period annual grasses emerge. Here are a couple of articles related to this subject:
Apply uniformly. Uniform application is critical – just like distributing paint evenly over your house is aesthetically pleasing. If you leave a section of the house unpainted, it’s clearly visible. Good annual grass control requires uniform application; if an area is not treated, it’s likely you’ll seed weed emergence there. Uniform application is achieved by proper spreader or sprayer calibration, colorants that indicate areas that have been treated with liquid products, and applying the product in two directions (half rate in each).
Split applications. Preemergence herbicides generally provide better suppression of annual grasses when applications are split (1/2 rate each application), usually 6 to 8 weeks apart. This allows a higher level of herbicide presence on the soil surface, which will minimize weed emergence. Here’s an article from Purdue on this subject:
Water in after application. For preemergence herbicides to be activated and ensure uniform distribution on the soil surface, irrigation (or rainfall) after application is needed.
Find more information on weed control by clicking on the tags on the blog (left column), such as “weed control,” “crabgrass,” etc., or search by category on the right side of the page.
***Mention of trade names or commercial products in this article is solely for identification purposes and does not imply recommendation or endorsement, nor is criticism implied of similar products not mentioned by Kansas State University.***
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Crabgrass emergence was evident last weekend – at least in Olathe, KS (picture below).
Crabgrass seedlings (inside white border) emerging on April 19, 2020 in Olathe, KS.
This was on bare soil next to a paved sidewalk. It can take a few weeks longer for crabgrass to emerge within areas of thin turf due to cooler soil temperatures (see article on timing herbicide applications here: Flowering Ornamentals and Crabgrass Emergence). So, on a lawn of acceptable quality (and no bare areas), you should still have time to get a preemergence herbicide out. Once you see crabgrass such as this emerging within a lawn, consider using a preemergence herbicide that has postemergence activity, such as dithiopyr (Dimension) or mesotrione (Tenacity). Of course, there are also a number of postemergence herbicides that can be used for crabgrass control as well.
Always remember to READ THE LABEL for the correct rate, turfgrass tolerance, and specific instructions before application!!!
***Mention of trade names or commercial products in this article is solely for identification purposes and does not imply recommendation or endorsement, nor is criticism implied of similar products not mentioned by Kansas State University.***
(By Jared Hoyle, KSU Turfgrass Research and Extension)
This morning when I cranked my truck up and headed to the office it was 25 deg F. Just a couple days ago it snowed. Just before that it was 80 deg F. What is going on with the weather? (Every time I make that statement, someone says “Welcome to Kansas!”) With the fluctuating weather and temperatures I get the question “What date do I need to put my preemerge herbicide out on?”
Well this is a trick question because there is no correct answer for it. Here are some of my thoughts on preemerge timing.
As soon as that first warm front comes through everyone gets excited and ready to work in their lawn. I have even heard the comment that spring and summer are going to come early this year. Are they right? I don’t know but it is something to think about.
But as soon as we get excited about the warm weather we have another cold snap. So we got all excited and talked about weeds germinating early and needing to get out our preemergence herbicides because the forsythias are blooming. But what happens when it gets cold? Any crabgrass that “might” have germinated is now dead because of the cold temperatures. So this brings up a lot of discussion between myself and some colleges. Here are just some of the questions we are asked and a couple of comments.
Why do we recommend around April 15th for most of Kansas to put out a preemerge in our lawns?
– April 15th is about the time that we have our “last” frost/freeze. (This also shifts to April 30th in Western/North Western KS and to April 1 in Eastern/South Eastern KS.) This goes along with our concept that I was talking about before. Even though it may be getting warm we are still might have a cold snap that would end up killing the crabgrass if it emerged. This is the same concept of why we don’t plant crops until after this date as well. (Something I don’t know anything about but that is what I figure…..)
Should we use soil temperature at 1″ to predict when to put out preemergent herbicide applications?
-Soil temperatures are a great way of determining when to apply your preemerge herbicide. Scientists say when soils reach a daily average of 55 deg F for about 5 days at a 1″ soil depth then it is time to put out your preemerge. Well say you go out and measure your soil temperature at 1″ you are not going to get a daily average, you are getting a single point in time. Does that really represent what is going on? What if you are maintaining many different properties. It is not practical to obtain that information. Good news is that KSU has a website (http://mesonet.k-state.edu) that you can click your closest weather station and get daily maximum and minimum soil temperatures where you can then calculate a daily average. Bad news it only give you a 2″ or a 4″ soil temperature. But using the 2″ soil temperatures are going to give you a better idea of the daily averages then going and taking one measurement.
The forsythias are blooming but my redbuds aren’t. Do I still put my preemergent herbicide out?
– This is called phenology – the study of cyclic and seasonal natural phenomena, especially in relationship to climate, plant and animal life. Many people believe that when the forsythias are blooming then crabgrass is germinating. That is not 100% true. When forsythias are in full bloom then we need to be getting “ready” to get our preemerge applied. Even though we see that this is a good indicator, Dr. Fry and others reported in a study that ornamental plant flowering is not always a good way to predict crabgrass germination and emergence. (Fry, J., S. Rodie, R. Gaussoin, S. Wiest, W. Upham, and A.Zuk. 2001. Using flowering ornamentals to guide application of preemergence herbicides in the Midwestern U.S. International Turfgrass Soc. Res. J. 9:1009-1012.) There are some things to consider when utilizing phenology for crabgrass germination and emergence. Not all forsythias will bloom at the same time. It determines where that plant is located in the landscape. There are micro climates in the landscape. Think about plants located in roadway medians. They are typically warmer due to cars and the concrete and asphalt in close proximity. The same thing goes with crabgrass germination. Crabgrass will germinated sooner in areas that are warmer, for example (next to sidewalks, bare ground, etc.).
Crabgrass emerging in bare ground earlier than turf
I have heard about growing degree days to predict crabgrass germination. What is that?
– Growing degree days (GDD) use air temperatures instead of soil temperatures within a formula to get a cumulative number of growing degree days. Using base 50 deg F, once you get to about 200 GDD then crabgrass will start to germinate. Don’t want to calculate GDDs, don’t worry there is a website that will do it for you. http://www.gddtracker.net Just enter your area code and click on crabgrass germination on the right side and it will give you the total GDD. It will also show you a prediction for the next couple of days too. GDD do not go backwards, they only accumulate.
So to put this all in perspective using the prediction methods mentioned above this is what we got;
Today is March 14th so using the calendar model for Manhattan we would not put our preemerge out until closer to April 15th for Manhattan.
Using the 2″ soil temperature method because that is what is available to us our daily average soil temperatures (Deg F) have been;
9-Mar
47.6
10-Mar
45.4
11-Mar
43.65
12-Mar
41.15
13-Mar
39.65
With this method we would assume the 1″ soil temperature is higher but we are not to the 55 deg F mark yet. So we are getting close to putting out our preemerge herbicide.
In my back yard my forsythias are blooming. So that means if I am using the phenology method I need to be getting ready to apply my preemergence.
Lastly, using the GDD model we are at 85 GDD. So I still have some time but getting close. Remember though that you can get more than one GGD in one calendar day and if I look at the future (prediction on the GDD Tracker website) on March 20th Manhattan will be at 111 GDD. So just in 6 days we would have gained 26 GDD.
Now these rules, concepts, ideas are not bullet proof but it is something to think about when planning your lawn care program. There is not magic date for anything that you do to you lawn. You need to make sure you keep up with the temperatures, soil temperatures, precipitation, etc. The more you know what is going on with your turfgrass the better you will be able to predict crabgrass preemergent applications. Use more than one method. This is going to give you the best idea of what to do!
Now by this weekend we are going to get a little warmer but again looking at the 10 day forecast it might get cold again…. Just something to think about. I hope this got you thinking as a turfgrass manager and how this is going to help you choose products if you are going to have to get applications out earlier or even later after crabgrass has emerged.
Always remember to READ THE LABEL for the correct rate, turfgrass tolerance, and specific instructions before application!!!
***Mention of trade names or commercial products in this article is solely for identification purposes and does not imply recommendation or endorsement, nor is criticism implied of similar products not mentioned by Kansas State University.***
(By Jared Hoyle, KSU Turfgrass Research and Extension)
“An ounce of prevention is worth a pound of cure” – Benjamin Franklin
When I start talking about pre-emergent herbicides this quote from Benjamin Franklin always pops in my head. Although, Ben was giving fire-fighting advice to Philadelphians because fires were a dangerous threat at that time it does apply to many things we are dealing with right now, including spreading wild fires. (I won’t comment on that because I have no idea how to manage wild fires.) But I will talk about Pre-remergent herbicides.
Pre-emergent (PRE) herbicides prevent summer annual weed (For Example, crabgrass, goosegrass, annual sedges, and spurge) seeds from developing into mature plants. The reason we use PRE herbicides for summer annual weed control is because these summer annuals come back every year from seeds. So if we can stop the seed from growing then we don’t have to deal with the weeds later in the season.
For all that don’t know how a PRE herbicide works here is a very short explanation. They do not keep the seed from germinating but kill the young germinating plant. With few exceptions they have no effect on existing plants, so they must be applied before germination.
But like in everything in life there is an exception. Dithiopyr can kill crabgrass as long as it is young (two- to three-leaf stage, see photo below of three leaf crabgrass) and still have some residual for continued PRE activity. It doesn’t last as long as some of the other PRE herbicides but there is flexibility if you miss your window of opportunity to apply.
So when do I put out the PRE application for summer annual weed control? Well, it depends on many things. What summer annuals you have? Where are you located in Kansas? Many times turfgrass managers center their PRE applications around crabgrass germination. Crabgrass “typically” begins to germinate around May 1 or a little later in KS. April 15 is a good target date for applying a PRE because it gives active ingredients time to evenly disperse in the soil before crabgrass germination starts. The April 15 target works well for most of the state, but for southeast Kansas April 1 is more appropriate, and for northwest Kansas May 1 is best. Additionally, weather varies from one spring to the next (As we can see this year where it is getting warmer earlier!), and with it the timing of crabgrass germination. Some turfgrass managers base their PRE application around the bloom of the Redbuds but other ways can be used as well. Crabgrass germinates when the soil at approximately 1 cm deep reaches 55° F. So watch your soil temperatures to see when the soil consistently reaches 55° F. Here is a great website that will give you soil temperatures for your area.
PRE herbicides do not last forever once applied to the soil. Microorganisms and natural processes begin to gradually break them down soon after they are applied. If some products are applied too early, they may have lost much of their strength by the time they are needed. Additionally, PRE herbicides have different half-life, Koc, water solubility, and vapor pressure. This can determine how fast microbial, chemical and physical decay occurs along with infiltration, volatilization, leaching, and run-off.
Therefore, not all PRE herbicides are created equal. Here is a list of PRE herbicides, the weeds they target and some concerns that you might want to know before applying.
On golf courses: Can be used on cool- and warm-season. Other turf areas: Warm-season only.
siduron
crabgrass, bermudagrass (suppression)
Does not control goosegrass or annual bluegrass.
Information in this table was acquired from “Turfgrass Weed Control for Professionals” by A. Patton and D. Weisenberger, Purdue University (and 11 collaborating states including Kansas). For more information about purchasing this publication see;
***There are many combination PRE herbicides that combine these active ingredients with each other and with other POST-emergent herbicides***
Always remember to READ THE LABEL for the correct rate, turfgrass tolerance, and specific instructions before application!!!
***Mention of trade names or commercial products in this article is solely for identification purposes and does not imply recommendation or endorsement, nor is criticism implied of similar products not mentioned by Kansas State University.***
(By Jared Hoyle and Ward Upham; KSU Research and Extension)
Can you tell the difference? There are two difference weeds in the picture above but they look a lot alike! Not only do they look a lot alike but they both have similar attributes. Below will tell you which one is which.
Many people mistake little barley (Hordeum pusillum) for a little foxtail because the foxtail and little barley seedheads are similar. However, little barley is a winter annual that comes up in late September – October and spends the winter as a small plant. It thrives in the cooler spring temperatures, forms seed heads and dies out usually by July. Foxtail, on the other hand, is a summer annual that does well in hot weather. Also, foxtail will not produce seedheads until mid- to late-summer.
So, why are we talking about little barley now? Because now is the time to control it for next year. The best control for little barley is a thick lawn that is mowed high enough that sunlight does not hit the soil. Little barley seed will not germinate in such conditions. Overseeding now can thicken up a tall fescue lawn and prevent a little barley infestation.
However, if you do not plan to overseed, preemergence herbicides can be used to provide at least partial control of this weed. The only preemergence herbicide that I know is labeled specifically for little barley is Surflan. It is also sold under the name of Weed Impede by Monterey Lawn and Garden. Surflan can only be used on warm-season grasses (bermudagrass, buffalograss, zoysiagrass) and tall fescue grown in warm-season areas such as Kansas. However, Dimension (dithiopyr), is labeled for barley (Herodium spp.) which would include little barley and therefore
can be used to keep this weed under control. Because little barley is a winter annual, apply the preemergence herbicide now and water in to activate. If overseeding, do not apply any preemergence herbicide as it will interfere with the germination of tall fescue.
****Always remember to READ THE LABEL for the correct rate, turfgrass tolerance, and specific instructions before application.****
***Mention of trade names or commercial products in this article is solely for identification purposes and does not imply recommendation or endorsement, nor is criticism implied of similar products not mentioned by Kansas State University.***
(by Jared Hoyle; KSU Turfgrass Research and Extension)
This is an article a friend of mine at UNL wrote a little bit ago but contains some really great information for you Sports Turfgrass Managers. Sorry for the delay in getting it out but I think it contains some good information for Kansas on planning your preemergence and nitrogen applications to sports fiends in this crazy spring we have been having. Enjoy!
