Preemergent herbicides are a form of chemical weed control which prevent germinated weed seedlings from becoming established.
In some areas of the world, they are used to prevent crabgrass from appearing in lawns.[1] Preemergent herbicides are applied to lawns in the spring and autumn, to prevent the establishment of weed seeds. They will not affect any established plant. In the spring, they should be applied when air temperatures reach 65–70 °F for four consecutive days. In the autumn, they should be applied when nighttime lows reach 55–60 °F for four consecutive nights.[2]
"Weed and feed" products which contain both preemergent herbicide and fertilizer in a single product should not be used on southern lawns or warm-season grasses. If applied when preemergent herbicide is needed, the fertilizer may burn or stress the lawn. If applied after the lawn "green-up", weed seeds will have already germinated and the herbicide will be ineffective.[3] Preemergants do not prevent seeds from germinating, they prevent cell division, and prevent vital parts of the weed from forming
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Pre-emergent Herbicides
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How To Apply Pre-Emergent Herbicide Weed Killers
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Soybean Pre-Emerge Herbicides #977 (Air Date 12-25-16)
Transcription
As a landscape professional your number one defense against weed germination comes in the form of pre-emergent herbicides. Whether going into the spring or fall season, you'll want to have a pre-emergent heribicde in your arsenal to help you control weeds. pre-emergents inhibit successful germination by creating a chemical barrier between the seed and the soil. A few of the pre-emergents that you can commonly find include Dithiopyr, Prodiamine, and Pendimethilin. Spring-applied pre-emergents provide excellent control of summer annual weeds like crabgrass, goose grass, and foxtail. Many provide protection against several broadleaf weed species as well. Just be sure to check the label for effectiveness against the weeds common to your location. Most pre-emergent herbicides will not have an effective spray after weed establishment so prepare application timing is critical, ideally, you'll want to apply a spring pre-emergent before soil temperatures warm up to 55 degrees on average over a three to four day period. If winter annual weeds are an issue in your area, a fall application maybe necessary as well. Application timing can vary significantly by geography, so do a little research to determine the easiest way to closely monitor your soil temperature. You can easily test the temperature of your soil with a simple thermometer, or look online for a weather data library for your region. Your local university would be a great place to start. If you happen to miss your application window you can still use products containing Dithiopyr which have early post-emergent activity. For example, if soil temperature are already at 65 degrees average in your area and your crabgrass has not begun tillering, you will still get excellent control by applying these products. It's important not to aerate or cultivate after making your application, as this can interfere with the process by breaking down the barrier. If you're planning to overseed your lawn, do not use a pre-emergent, as it will interfere with germination. Dry pre-emergent herbicides are water-activated so you need to irrigate immediately after application. On the other hand, liquid products are diluted in water and applied using a pump sprayer. Therefore, irrigation following application is not necessary. I can't stress enough how important it is to read the product label and follow the manufacturer's directions before you use any herbicide. Each product is a little different, so knowing the prepare method for its application and safe use will help you get the best results. If you need help finding the pre-emergent herbicide best suited for your needs, stop into one of our local Ewing branches and one of our service professionals will be more than happy to help. You can also learn more by visiting us online at ewingirrigation.com.
Brands
| Brand | Ingredient | Prevents | Notes |
|---|---|---|---|
| Barricade | prodiamine | crabgrass | [4] |
| Dimension | dithiopyr | crabgrass | [4] |
| Dimension 750 | dimethyl tetrachloroterephthalate | ||
| Pendulum | pendimethalin | crabgrass | |
| Pestanal | dimethyl tetrachloroterephthalate | ||
| Surflan | oryzalin | crabgrass | |
| Tupersan | siduron | crabgrass |
Crabgrass
To prevent growth of crabgrass, preemergent herbicides must be applied at a critical time. If they are applied to the soil too early, they get washed too deep into the soil or washed away by rainwater. If they are applied too late, the key enzyme inhibited is no longer active. The best control requires a second application about 6–8 weeks later. This provides coverage in mid-late summer when crabgrass can still germinate. Depending on location, one rule of thumb is to apply when the local forsythia blooms are wilting. In the northeast, they need to be applied before azaleas bloom.
References
- ^ Wright, Robert (April 20, 2010). "The Dandelion King". New York Times. Retrieved 2010-04-21.
- ^ Williamson, Joey. "Managing Weeds in Warm-Season Lawns".
- ^ Tyson, Jenion. "When to apply preemergent herbicides".
- ^ a b "Time is right to prevent crabgrass from sprouting". Osawatomie Graphic. April 7, 2010. Retrieved 2010-04-21.
This page was last edited on 13 December 2023, at 02:36