One of the most common questions we get every spring is:
“I just put down Prodiamine and then a massive downpour or “gully-washer” rolled through! Is my pre-emergent ruined? Do I need to reapply?”
Short answer:
No, your prodiamine application is not ruined, and you do not need to reapply.
Why Prodiamine is Tougher than You Think
Prodiamine (found in products like Barricade, Prodiamine 65 WDG, and many granular “crabgrass preventer” bags) binds very quickly to soil particles. It only needs about ½ inch of water to be activated and locked into the top layer of soil where weed seeds germinate. Even in a heavy rain, the vast majority of the product stays put and remains effective.
Years of real-world use by both homeowners and professional lawn companies prove that prodiamine holds up remarkably well, even when Mother Nature throws a tantrum right after application.
Should you reapply after heavy rain?
No, and here’s why: You have no way of knowing exactly how much (if any) product was lost. Reapplying risks over-application, which can:
- Harm your grass
- Increase costs unnecessarily
- Potentially cause regulatory issues in some areas
The safest and smartest approach is to trust the first application and move on.
The best protection against rain: Use the “Split Application” strategy!
This is why top lawn experts, including our very own Allyn Hane (The Lawn Care Nut), strongly recommend splitting your spring pre-emergent into two lighter applications:
First app: When soil temps cross 50–55°F (puts down the initial barrier)
Second app: 6–8 weeks later, when soil temps hit 65–70°F (acts as insurance)
If a torrential rain hits after round 1 → round 2 has your back.
If the monsoon hits after round 2 → round 1 is already working.
In fall and winter, cold naturally kills any breakthrough weeds, so you’re covered year-round.
Bonus: The same rules apply to dithiopyr (Dimension)
Everything above also applies if you’re using dithiopyr-based pre-emergents; heavy rain rarely washes them away, and there is no need to reapply.
Bottom Line
A big rain right after applying prodiamine is usually no big deal.
No need to reapply! Over-applying is riskier than under-applying.
Use the proven split-app method for total peace of mind.
Your lawn (and your wallet) will thank you!
For more information on this, please see the video below:
https://www.youtube.com/watch?v=myALhB3SVGk&list=PLJxvMuB9D3vtqCmWs5rT7i-QSKUthD5by&index=6
Click HERE for our FREE Pre-Emergent Guide
Want to know when to put Prodiamine down on your lawn? Download our FREE Yard Mastery app for timing recommendations based on your soil temperatures and geographical location.
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