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When to apply crabgrass preventer?

When to apply crabgrass preventer?


Crab grass is one of those pesky weeds that is an eye sore in an otherwise healthy lawn. Its wide light green leaves stand out in dark green lawns. To worsen matters, it quickly produces tall seed heads, which give the lawn the appearance of never being mowed.

One crabgrass plant can produce 150,000 seeds during a growing season. If you don’t use crabgrass control, this lawn weed can replace lawn grasses. No wonder so many people are interested in preventing crabgrass seed germination.
How do you prevent crabgrass?
Most lawn weed treatment services use a pre emergent lawn treatment to kill crabgrass as the seed germinates. As the seeds begin to germinate, the plant comes into contact with the pre emergent which then kills the seed. This means that you need to apply crabgrass pre-emergent herbicides before the seeds begin to germinate. If applied too late it won’t be able to stop the seeds from forming the plant above ground.
All pre emergents need time to be watered in as well. You can do this on demand by using a sprinkler system. Nonetheless, if relying on rainfall to water in the pre-emergent, it becomes subject to weather conditions. One must allow for sufficient time for a storm to provide the needed water.
The amount of water needed to accomplish this varies among different pre emergents. It often requires a half inch of overhead irrigation to water in the pre emergent. The overhead irrigation should be done shortly after using the product. The timing of the irrigation depends on the product used, ranging from a few hours to a few weeks.
Each herbicide will have a label that specifies the exact details regarding the watering in process. Consider this label as the legal way to use the product. It is also the best way to ensure the product works as intended.
So how do you know when to apply crabgrass pre emergent?
Soil temperatures determine crabgrass seed germination. When soil temperatures reach 55 degrees at a two-inch depth for a few days crabgrass will begin to germinate. In Arkansas, people consider March 15th as the deadline for crabgrass prevention.
Fortunately, pre emergents have a long life in the soil. Some even claim to offer season-long protection.
Some lawn weed control services all pre emergents before freezing temps set in and over winter the product. Because of the lower temperature the herbicide degrades slower.

As mentioned earlier, each herbicide is different. Always consult the label for each product to ensure proper use.


If no sprinkler system is available the product will need to be applied early enough to be worked into the soil by rainfall. If the product isn’t worked into the soil by overhead irrigation before the soil temperature becomes high enough for germination the weed won’t be prevented.


It’s also worth considering that soil doesn’t heat up evenly. Areas with little shade will warm up fast than areas shaded by trees or a home.


Why am I seeing crabgrass along sidewalks and the edge of the house?


If you see crabgrass in these areas it doesn’t mean a complete failure of the pre emergent. These areas often experience heavy stormwater runoff. What this can lead to is an early breakdown of the weed control soil barrier in these locations.

Professional weed and feed services address this in a couple of ways. To address this issue, some pre emergents allow for a split application. Applying two smaller doses instead of one larger dose often maintains the soil barrier longer, extending control.
What if some crabgrass germinates?
Some times despite our best efforts crabgrass will break through. This happens for many reasons but even lawn care experts have to deal with this.
Bare spots in the turf are prone to crabgrass break though. Any area that experiences excess water can experience breakthroughs.
Even when everything cooperates some weeds develop resistance to herbicides over time. You may need post emergent herbicides when this happens.
The are many effective weed killers that are effective at killing crabgrass. This will help eliminate any crabgrass isotypes that have developed resistance to pre emergent herbicides.
Getting rid of crabgrass naturally.
Never underestimate the weed-controlling ability of a dense healthy turf. If a turf is thin and bare weeds will always be a struggle.
Nature does a great job of filling in bare spots. If a lawn is thin address the underlying issue. It could be something as simple as more water or pruning limbs for additional sunlight.
Soil aeration and applying lime can also help improve turf health. Proper mowing habits or sharp blades can make a difference.
The goal is to ensure the lawn is healthy. Once the lawn is healthy it can begin to out-compete and crowd weeds, including crabgrass. This is the best way to reduce herbicide dependence.
Even with the use of herbicides turf health should always be part of the plan for weed control for lawns. In fact it’s part of the reason lawn treatment services use lawn fertilizer as a part of the turf management program.
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