Best Time to Apply 2,4-D to Kill Weeds in Your Yard

For best results applying 2,4-D weed killer on your yard, spray during these conditions:

  • Temperatures between 60 and 85℉ (15–30℃).
  • Wind speed below 5 mph (8 kph).
  • No rain in the forecast for at least 24 hours.
  • Lawn should be dry of rain and dew.
  • Allow at least 2 days after mowing before applying 2,4-D.
  • Apply 2,4-D weed killer in early spring or fall.

By following these simple rules you will ensure the greatest effectiveness of your 2,4-D Amine herbicide. Optimal temperatures and dry, windless conditions will guarantee that the 2,4-D is absorbed by weeds before it evaporates or is washed away. Meanwhile, waiting to spray a few days after mowing ensures there is enough leaf material present to be coated with weed killer, allowing the herbicide to attack invasive plants. Finally, by applying 2,4-D in early spring or in fall you will attack weeds when they’re most vulnerable, resulting in a larger percentage of dead weeds.

Best Time to Apply 2,4-D to Kill Weeds in Your Yard

Can You Spray 2,4-D on Wet Grass?

You should always apply a 2,4-D weed killer on dry grass. If applied to wet grass, 2,4-D can be washed away before it has a chance to penetrate plant systems and get to work killing weeds.

A study by the Farming Smarter Association discovered that weed killers perform best when sprayed at midday. This may be in part because weed-killing sprays applied at this time cannot be diluted or washed away by morning dew. By choosing to spray 2,4-D in the middle of the day, when your grass is typically at its driest, you will get the best results from your weed killer.

How Long Does 2,4-D Need to Be on Before Rain?

2,4-D Amine should be allowed to dry for 24 hours before being exposed to rain or lawn irrigation. This ensures the 2,4-D adequately infiltrates plant systems and kills weeds.

When you are planning to apply 2,4-D to your yard, make sure there is no rain in the forecast for 24 hours, at a minimum. Also, turn off all lawn irrigation and sprinklers for 24 hours. By protecting your 2,4-D application and allowing it to thoroughly dry and attack weeds, you’re getting the best value on the dollar for your weed killer. Given a 24-hour drying time, 2,4-D will effectively kill the broadleaf weeds in your lawn.

Applying 2,4-D After Rain

If you are applying 2,4-D after recent rain, allow time for your lawn to dry completely before application. While it’s perfectly fine if the ground is still moist during the 2,4-D application, make sure that grass blades and weed leaves are free of water droplets and are dry to the touch.

Water present on the lawn can dilute 2,4-D and render it less effective. The goal during the 2,4-D application is to mist weed leaves with a thin layer of weed killer spray. Water present on leaves and stems can form a barrier against weed killer. This will lead to more weeds surviving your 2,4-D application.

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Does Rain Affect 2,4-D?

Rain negatively affects 2,4-D if the weed killer isn’t allowed to properly dry first. Rainfall within 24 hours after 2,4-D application can dilute your herbicide, limiting its effectiveness. For this reason, it’s important to make sure there is no forecasted rain for at least 24 hours when applying 2,4-D.

If there is rainfall more than a day after applying 2,4-D it shouldn’t have any negative impact on the effectiveness of the herbicide. By that time, the 2,4-D will have infiltrated broadleaf plant systems and begun to kill the weeds. You should begin to see visible effects of 2,4-D on weeds (such as leaf browning and wilting) within 48 hours of application.

Man spraying 2,4-D on a dandelion weed in the yard

Best Temperature for Spraying 2,4-D

2,4-D should be sprayed at temperatures 60–85℉ (15–30℃). Air temperatures should be at least 60℉ because the majority of weed species are actively growing at this temperature and 2,4-D is most effective against actively growing plants. Air temperatures should not exceed 85℉ because excessively hot temperatures may cause your 2,4-D spray to evaporate too quickly, losing some of its effectiveness.

How Warm Does it Have to Be to Spray 2,4-D?

For the most effective application, spray 2,4-D at temperatures 60–85℉ (15–30℃). 2,4-D is less effective outside of this temperature range, meaning you will kill fewer weeds and get less value from your weed spray.

According to the Iowa State University Extension, weed killers are most effective in fall (mid-September–November). To kill the most weeds in your yard, plan to spray in fall, once summer temperatures have begun to drop off. The second-best time to spray is in spring before summer temperatures have peaked.

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Will 2,4-D Work in Cold Weather?

2,4-D will not be very effective in cold weather. Like most weed killers, 2,4-D works best on actively growing plants. You will attack the largest variety of weeds by applying 2,4-D when temperatures are at least 60℉ because these temperatures trigger most weeds to grow.

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Can You Spray 2,4-D at Night?

Nighttime application of weed killers is more effective than application at dawn, but midday is typically the best time of day to spray for weeds. If, however, you live in a region with strong daytime winds that make spraying difficult or impossible, nighttime can be an excellent choice for spraying 2,4-D.

Can You Spray 2,4-D After Mowing?

Wait 2–3 days after mowing before applying 2,4-D. Like most weed killers, 2,4-D works by coating weed leaves and attacking the plant. If you have recently mowed, some weeds may have been mowed-over and stripped of leaves. This will make them more resistant to 2,4-D application. It’s actually best to allow weeds to sprout a few new leaves after mowing, then spray 2,4-D.

Additionally, wait 3–4 days after 2,4-D application before mowing. This gives time for the 2,4-D to do its work and kill weeds. Mowing too early after application can prevent complete absorption of 2,4-D and allow some weeds to survive.

Best Time to Apply 2,4-D

2,4-D is most effective when sprayed at midday, either in early spring or fall, when weeds are actively growing and temperatures are between 60 and 85℉ (15–30℃). Make sure your lawn is dry, that there is no rain in the forecast, and that there is little or no wind before applying 2,4-D. Dry, still conditions allow 2,4-D to best coat leaves and kill weeds. Choose an optimal day at least 2–3 days after mowing to spray 2,4-D. This will guarantee you get the most out of your weed killer, wiping out weeds and leaving grass unharmed.

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