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K-State Turf and Landscape Blog

Tag: summer annual

More than you ever want to know about preemergent herbicides

(by Jared Hoyle, KSU Turfgrass Research and Extension)

Ever year I write a blog, a newsletter article, send out a tweet and post on Facebook about applying preemergent herbicides for summer annual grass control. We are typically most concerned with crabgrass so I went back and searched through the blog posts and articles and believe it or not it is all still relevant information! Not much has changed, so for this article I am going to spotlight information across these articles and compare from when I originally wrote it.

Crabgrass emerging in bare ground earlier than turf

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Up first, Methods of Predicting Crabgrass Emergence! In this article I go over the different methods to predict when crabgrass emerges; calendar date, soil temperatures, forsythia blooms, growing degree days. Like last year we have had a fluctuating Spring. In the article from March 14, 2017 I stated that it was 80 deg F on the 12th and was snowing just a couple days before. Sound familiar? Refresh yourself on the different methods and know its not too late to get preemergence herbicides out.

https://blogs.k-state.edu/turf/methods-of-predicting-crabgrass-emergence/

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Next article is for all you golf course turfgrass managers. Preemergence Weed Control in Bentgrass Putting Greens. This article was also from March 2017 and I went through what preemergent herbicides are available to use on bentgrass putting greens. The list of herbicides was from the Turfgrass Weed Control for Professionals 2017 Manual (https://mdc.itap.purdue.edu/item.asp?Item_Number=TURF-100). Going through the 2018 edition…. Guess what again? Not much has changed for use on putting greens but I would encourage you to check out the manual and read the “Tips for Herbicide Use on Golf Course Putting Greens” section on page 108.

https://blogs.k-state.edu/turf/preemergence-weed-control-in-bentgrass-putting-greens/


And now one of my favorite quotes from Benjamin Franklin “An ounce of prevention is worth a pound of cure”. This was the lead in for talking about why preemergent herbicides are worth it! This article talks about what weeds preemergent herbicides work on, how they work, and the growth stages of crabgrass. To “round-up” the article I put a list of options out there, the weeds these preemergent herbicides control and some concerns/comments. One thing that I did not list is the combination products. I only listed the single active ingredients.   There are many combination products as well. (Maybe that will be the next blog post – Combination Preemergent Herbicides.)

https://blogs.k-state.edu/turf/an-ounce-of-prevention-is-worth-a-pound-of-cure-by-benjamin-franklin-that-goes-for-preemergence-herbicides-too/

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.***

“An ounce of prevention is worth a pound of cure.” by Benjamin Franklin – (That Goes for Preemergence Herbicides Too!)

(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.

Slide1

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.

http://mesonet.k-state.edu/weather/historical/

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.

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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.

Active Ingredient Weeds Controlled Concerns or Comments
benefin summer annual grasses, annual bluegrass, some-small seeded broadleaves Do not use on golf course greens.
prodiamine summer annual grasses, annual bluegrass, henbit, chickweed, spurge, some-small seeded broadleaves Only apply to well established turfgrass.
bensulide annual grasses, some broad-leaves Do not use on putting greens composed of  > 50% Poa annua.
florasulam broadleaves, dandelion, prickly lettuce, clover Packaged with Dimension 2EW, florasulam great cool temperature activity, Prevents flowering in some broadleaves (dandelions).
dithiopyr summer annual grasses, annual bluegrass, yellow-woodsorrel, some small-seeded broadleaves PRE and early post-emergence activity on crabgrass.
isoxaben broadleaves such as chickweed, henbit, spurge, plantain, others Tank-mix with a grass herbicide for broader spectrum.
pronamide annual bluegrass, perennial ryegrass, other grassy & broadleaf weeds. Do not use on cool-season turf. Restricted use pesticide.
pendimethalin summer annual grasses, annual bluegrass, yellow-woodsorrel, some small-seeded broadleaves Not recommended for turf severely thinned due to winter stress.  Split applications can be made for extended control.
metolachlor annual bluegrass, crabgrass, sedges Do not use on cool-season turf.
simazine summer annual grasses, annual bluegrass, henbit, chickweed, spurge, some-small seeded broadleaves Do not use on cool-season turf.
ethofumesate annual bluegrass, annual grasses, some annual broadleaves See label for reducing annual bluegrass in cool-season turf.
oxadiazon summer annual grasses includinggoosegrass, annual bluegrass, some-small seeded broadleaves Ronstar G and Oxadiazon 2G are only formulations labeled for use on cool-season turf.
indaziflam annual grassy and broadleaf weeds in turf Do not use on cool-season turf.
oryzalin summer annual grasses, annual bluegrass, some-small seeded broadleaves Do not use on cool-season turf except tall fescue.
dimethenamid bittercress, crabgrass, goosegrass, purslane, sedges, spurge 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;

https://blogs.k-state.edu/turf/new-weed-control-publication-for-turfgrass-professionals/ 

 

***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.***

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