A pre-emergent herbicide is an excellent addition to your lawn and garden care arsenal.
Correct use of these chemical weed control products can help make weed control an easy task. But if you don’t apply the product at the right time, you’ll be washing your money into the dirt.
This article presents ten frequently asked questions about the correct use of pre-emergent herbicides.
10 Question Pre-Emergent Herbicide Use Q&A
1. What is the best soil temperature to apply pre-emergent herbicide?
When using pre-emergent herbicides, time your application very carefully for the best results.
Apply this type of herbicide the day soil temperatures rise to 50°-55° degrees Fahrenheit. If you allow several warm days to pass, weed seeds will begin to germinate.
2. Why is temperature important in pre-emergent herbicide application?
Suppose you wait until after soil temperatures have risen consistently to 55° degrees or above. In warm soil temperatures, summer weed seeds (e.g., crabgrass) germinate after five or more days.
If you wait until these seeds have germinated, you will no longer be able to catch them “pre-emergence.” They will have emerged.
3. How can you tell the temperature of the soil?
One easy way is to bury the bulb of an indoor/outdoor thermometer about 1″ inch deep in your soil.
This shallow level is good because the top inch of the ground will warm sooner than deeper levels. Weed seeds in the top inch of soil will sprout much sooner than those buried deeper.
4. How can you apply pre-emergent herbicide to deeply buried weed seeds?
When the temperature of the top 1″ inch of the soil rises to 50°-55° degrees, apply your pre-emergent herbicide. Water it thoroughly.
This timing will cause it to soak more deeply into the soil and come in contact with weed seeds buried at a deeper level.
5. Should you apply pre-emergent herbicide before soil temperatures rise to 50° degrees Fahrenheit?
When you apply a pre-emergent herbicide, it gets broken down by soil microbes and exposure to light. This process starts the moment you use the herbicide.
If you apply it too early, it may not be very effective when soil temperatures rise to 50° degrees Fahrenheit.
6. How long does pre-emergent herbicide stay effective?
A quality product will remain effective in the soil for 3-5 months; however, this varies depending on weather conditions.
Lots of rain and sun will speed up the loss of effectiveness.
7. Exactly when should I apply pre-emergent herbicides?
It isn’t easy to provide exact month/day instructions. This varies depending upon your location and climate.
Generally, it’s good to apply this herbicide twice a year – late summer to mid-autumn and again early in the springtime.
8. What if weeds have already started growing?
You should apply an herbicide containing Pendimethalin, Prodiamine, or Dithiopyr if this happens.
Follow packaging instructions carefully and water the product thoroughly immediately after application.
9. Should you use a pre-emergent herbicide on a newly seeded lawn?
This act is rarely a good idea. But, some herbicides containing Siduron as their main ingredient may be safe on newly seeded lawns. Read and follow packaging instructions carefully.
10. If you use pre-emergent herbicide correctly, do you need post-emergent herbicide?
Keeping weeds under control requires a well-stocked arsenal. Having a comprehensive collection of tools in your toolbox will help you stay on top of the challenge.
Successful weed control involves:
- Diligence
- Hand pulling
- Natural weed control methods
- Close attention to lawn care and maintenance
- Judicious use of both pre and post-emergent herbicides