--- title: 5 Reasons Why Preemergence Herbicides Sometimes Fail description: It’s disheartening when you’ve applied a preemergence herbicide, only to see unwanted grasses break through in spring and early summer. Ewing’s Pat Gross discusses five reasons behind preemergence herbicide failure. image: https://ewingirrigation-20200354.hs-sites.com/hubfs/Imported_Blog_Media/ewing-irrigation-five-reasons-pre-emergents-fail-1.jpg --- ### Resources [![Ewing Outdoor Supply Logo V 4 Color](https://ewingirrigation-20200354.hs-sites.com/hubfs/Ewing%20Outdoor%20Supply%20Logo%20V%204%20Color.png) ](https://www.ewingoutdoorsupply.com/) [![Login/Register](https://no-cache.hubspot.com/cta/default/20200354/5d045e9a-574a-4a92-a8cc-1ce2a4352784.png)](https://cta-redirect.hubspot.com/cta/redirect/20200354/5d045e9a-574a-4a92-a8cc-1ce2a4352784) 0 You have no items in your shopping cart ### Shop Products Shop Products # Irrigation & Landscape supply Blog # 5 Reasons Why Preemergence Herbicides Sometimes Fail [Pat Gross](https://ewingirrigation-20200354.hs-sites.com/author/pat-gross) on January 26, 2022 Share - [**](https://twitter.com/share?source=https://ewingirrigation-20200354.hs-sites.com/five-reasons-why-pre-emergent-herbicides-sometimes-fail&text=5%20Reasons%20Why%20Preemergence%20Herbicides%20Sometimes%20Fail%20-%20https://ewingirrigation-20200354.hs-sites.com/five-reasons-why-pre-emergent-herbicides-sometimes-fail) - [** ](https://www.facebook.com/sharer/sharer.php?u=https://ewingirrigation-20200354.hs-sites.com/five-reasons-why-pre-emergent-herbicides-sometimes-fail&title=5%20Reasons%20Why%20Preemergence%20Herbicides%20Sometimes%20Fail&picture=https://20200354.fs1.hubspotusercontent-na1.net/hubfs/20200354/Imported_Blog_Media/ewing-irrigation-five-reasons-pre-emergents-fail-1.jpg&description=It’s%20disheartening%20when%20you’ve%20applied%20a%20preemergence%20herbicide,%20only%20to%20see%20unwanted%20grasses%20break%20through%20in%20spring%20and%20early%20summer.%20Ewing’s%20Pat%20Gross%20discusses%20five%20reasons%20behind%20preemergence%20herbicide%20failure.) - [**](http://www.linkedin.com/shareArticle?mini=true&url=https://ewingirrigation-20200354.hs-sites.com/five-reasons-why-pre-emergent-herbicides-sometimes-fail&title=5%20Reasons%20Why%20Preemergence%20Herbicides%20Sometimes%20Fail&summary=It’s%20disheartening%20when%20you’ve%20applied%20a%20preemergence%20herbicide,%20only%20to%20see%20unwanted%20grasses%20break%20through%20in%20spring%20and%20early%20summer.%20Ewing’s%20Pat%20Gross%20discusses%20five%20reasons%20behind%20preemergence%20herbicide%20failure.) - [**](https://ewingirrigation-20200354.hs-sites.com/five-reasons-why-pre-emergent-herbicides-sometimes-fail) ![](https://ewingirrigation-20200354.hs-sites.com/hubfs/Imported_Blog_Media/ewing-irrigation-five-reasons-pre-emergents-fail-1.jpg) It can be frustrating to see break throughs of crabgrass and goosegrass in the spring and early summer after a preemergence herbicide was applied earlier in the year. Here are the top five reasons why applications of preemergence herbicides sometimes fail to prevent weed growth. ### 1. Improper Timing The germination of crabgrass and goosegrass are highly correlated to soil temperature. Conventional models for crabgrass recommend applying preemergence herbicides when soil temperature at the 1-inch depth is 55F or above for five consecutive days. Not getting the herbicide down early enough will allow crabgrass and goosegrass to get a head start and make the herbicide ineffective. ### 2. Improper Application Rate This is mainly a problem of not properly calibrating equipment prior to application. Before each application, it is important to check the label for recommended rates and calibrate sprayers and spreaders to make sure they are applying the proper amount of preemergence herbicide. ### 3.Not Watering-In the Product Preemergence herbicides need to be watered into the turf to activate the herbicide and form a barrier to prevent weed growth. Consult the label to verify how much water needs to be applied and when watering must be done after application. ### 4. Skips or Misses This is simply an application error and easy to do when making applications to irregular-shaped areas. Skips and misses are usually visible in strips or triangulated shapes consistent with an application pattern. ### 5. Weed Resistance Weed resistance can develop with repeated use of an herbicide with the same mode of action. Several preemergence herbicides are in the dinitroaniline (DNA) family, including Pendulum and Barricade. While Dimension is in the pyridine family, the mode of action is the same as the DNAs, leading to some confusion over chemical rotation. There is one that falls outside this group and that is Ronstar, which is in the oxadiazole family. If allowed by the herbicide label and the law, it is recommended to alternate between the use of Ronstar and the other DNA herbicides to avoid weed resistance. If you have any questions about turfgrass management, irrigation or water use efficiency, feel free to email them to me at [**pgross@ewingos.com**](mailto:pgross@ewingos.com). 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