Atrazine kills weeds within 14–21 days after application. During this time period, the Atrazine infiltrates plant systems through the roots, then travels to the leaves where the chemical blocks photosynthesis, killing the weeds.
In addition to killing actively growing weeds in 2–3 weeks, Atrazine also works as a pre-emergent. It will remain in the soil for up to 6 weeks, killing new seeds as they attempt to germinate. It’s important to keep in mind that even though you may not see Atrazine at work, it’s halting weeds before you see them.
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Signs Atrazine is Working
Within 14–21 days after spraying Atrazine, plants affected by the weed killer will begin to yellow, wilt, and develop dry, brown areas on their leaves. This is because Atrazine travels from the roots to the leaves, where it kills plants by preventing them from turning sunlight into energy. The effects of Atrazine are:
- Brown, dry areas on leaves
- Yellowing and wilting
- Leaf curling
The leaves of plants attacked by Atrazine often begin to curl at the edges as the herbicide does its work. If the weeds in your yard are showing these symptoms then your Atrazine application is working.
How Long Does Atrazine Last?
One application of Atrazine typically remains active in the soil for 6 weeks, killing weed seeds as well as the mature weeds in your lawn. Over the course of these 6 weeks, Atrazine is absorbed by plant roots and is gradually washed out of the soil by watering and precipitation.
- Typically active for 6 weeks.
- Gradually removed from soil by water and plant root uptake.
- Trace amounts of Atrazine may remain in the soil for 3–6 months.
- Apply Atrazine no more than 2 times per year to prevent overloading the soil.
Trace levels of Atrazine may remain in the soil for one growing season (3–6 months), but typically it has broken down long before then. In order to make certain you do not introduce too much of this popular herbicide into your lawn, which could be deadly for desirable plants, apply Atrazine no more than 2 times per year.
What Grasses Can be Safely Sprayed with Atrazine?
Only spray Atrazine on your lawn if you have St. Augustine, Zoysia, or Centipede Grass. Almost all other turf grasses will be harmed or killed by Atrazine.
- Atrazine-Safe Grasses: St. Augustine, Centipede Grass, Zoysia
- Grasses Killed by Atrazine: Bermuda, Fescue, Ryegrass, Bentgrass, Kentucky Bluegrass, Buffalo Grass
Review all manufacturer guidelines for Atrazine application and rates. Do not apply Atrazine to a turfgrass that is not specified as Atrazine-safe on the product label. Additionally, avoid over-applying Atrazine, as excessive exposure may harm even Atrazine-safe grasses.
Atrazine on Bermuda Grass
Atrazine will harm and even kill Bermuda grass. This is great news if you have invasive Bermuda in your St. Augustine yard that you want to get rid of, but terrible news if you have a Bermuda yard you’re trying to maintain. Take caution and do not apply Atrazine on Bermuda grass you wish to keep healthy.
Will Atrazine Kill Emerged Weeds?
Atrazine’s primary function is to kill mature, emerged weeds. Whether it’s clover or foxtails you’re trying to kill, Atrazine will attack it, starting from the roots.
- Atrazine attacks mature weeds by infiltrating root systems.
- Atrazine also stops weeds from sprouting by attacking seedling roots.
Because Atrazine is a rare weed killer that attacks through the roots, it also kills underground seedlings as they germinate and send forth their first roots. Atrazine is capable of killing both grassy and broadleaf weeds as they sprout.
Does Atrazine Kill Crabgrass?
Atrazine can be effective at controlling or slowing the spread of crabgrass, but it is not an effective crabgrass weed killer. If you want to attack crabgrass, use a Quinclorac-based weed killer that will kill crabgrass but leave your grass unharmed.
When Should You Apply Atrazine to Your Lawn?
The best time to apply Atrazine is in spring, typically as lawns begin to green up. Depending on your region, this may be anywhere between February and April.
- In spring, at lawn green-up.
- Typically between February and April
- Apply when temperatures are 65–90℉ (18–32℃). Atrazine is not effective outside this range.
The best time to apply Atrazine is when daytime temperatures are 65–90℉ (18–32℃). Atrazine will not be effective if applied outside of this range. If spring daytime temperatures are exceptionally hot, apply Atrazine in the morning, when temperatures are cooler.
How to Use Atrazine
When using pure Atrazine, first make sure to dilute the concentrate in the label-specified number of gallons of water. For instance, Hi-Yield Atrazine should be mixed at a rate of 4.3 ounces per gallon of water. The resulting mixture is enough to cover 500 square feet of lawn.
- Dilute Atrazine with the amount of water specified on the product label.
- Apply properly diluted Atrazine at specified rates using a sprayer or hose-end system.
- Do not mix Atrazine with any other chemicals.
Use your backpack sprayer, handheld sprayer, or hose-end sprayer with dilution controls to spray your lawn with the Atrazine mix. Always apply at the rates and volumes recommended by the manufacturer. Additionally, do not mix any other chemicals with Atrazine. Because it penetrates the soil and attacks through the roots, Atrazine should not be mixed with a surfactant.
How Long Does it Take Atrazine to Dry?
Atrazine will become rainfast in as little as 1 hour after application. For best results, apply on a day with no rain in the forecast.
- Atrazine will resist rain 1 hour after application.
- Apply on a day with no forecasted rain, when possible.
- Apply on low-wind days, to prevent overspray and evaporation.
Always spray Atrazine on days with little or no wind. This prevents overspray from being carried onto other plants and keeps the Atrazine from evaporating before it can penetrate the soil.
How Long Does it Take for Atrazine to Kill Weeds?
Atrazine kills weeds completely within 14–21 days. It does so by first penetrating the roots, then traveling to the leaves and disrupting photosynthesis. Atrazine remains in the soil for approximately 6 weeks, where it is taken in by plant roots and kills seedlings as they sprout.
By applying Atrazine on grasses that are safe for Atrazine exposure, you can wipe out existing weeds and stop new weeds from sprouting for an entire spring season. This leads to a greener, fuller yard with less competition for your grass.
