How Long Does 2, 4-D Take to Work and Kill Weeds?

2, 4-D, (2,4-Dichlorophenoxyacetic acid) is an effective herbicide that controls a large number of broadleaf weeds in lawns and crop fields. It is quickly absorbed by the target plants and starts to work immediately by changing the way cells grow and develop. So, how long will it take to see results after applying 2, 4-D on weeds?

2, 4-D takes 14 days to work, but weeds will start to show signs of dying, such as wilting, leaves turning brown, stunted growth, and dying 48 hours after application. If you apply 2,4-D with a surfactant, the results may show sooner because it will be absorbed more effectively by the target plants.

How Long Does 2, 4-D Take to Kill Weeds

Although 2,4-D is an effective broadleaf weed killer, it can take 7 to 14 days to see the signs that the weeds are dying. For some tough weeds that 2,4D kills, a month may elapse before the weeds actually die. You may need to spray two times to make 2,4-D kill some perennial weeds faster.

After application, 2, 4-D herbicides remain in the soil for 7 to 10 days and will break down depending on the moisture level, temperature, and aeration of the soil.

When it is too wet, the esters and salts in 2,4-D break down rather fast, meaning the efficacy of the herbicide may reduce and the expected time of action may also increase.

To ensure 2,4-D does not take too long to kill weeds in your lawn or crop field, observe the following:

• Spray 2,4-D weed killer when the weeds are still young and growing actively.
• Spray when there’s less wind to reduce drift and injury to other plants.
• Apply when temperature is below 90 F.
• Apply 2,4-D when there’s less rain to increase absorption rate.
• Observe the recommended mixing ratio for 2,4-D

Even with all these factors, you can start to observe signs of weed destruction as soon as 48 hours after applying 2,4-D.

The weeds will start to wilt, discolor (weeds start to turn brown), and grow slower than usual due to the action of the herbicide. These are signs that the target plants are dying in your lawn, allowing your turfgrass to outgrow them.

Note: 2,4-Dichlorophenoxyacetic acid works by mimicking the plant hormone auxin. It triggers abnormal growth and eventually causing death in susceptible or targeted weeds. The effectiveness of 2,4-D may vary at times due to type of formulation, rate of application, and the environmental conditions. As a result, time 2,4-D takes to kill weeds may vary depending on weed species, growth stage, and weather conditions.

How long does 2 4 D need to be on before rain?

The rule of the thumb is to apply 2,4-D at least 24 hours before it rains to allow for maximum absorption of the herbicide by the weeds. 2,4-D amine formulations have a rainfast period of 6-8 hours, while the ester formulations become rainproof within one hour.

Keep in mind that the rainfast periods may differ for different products on the market. Therefore, it is important to read the label to determine after how long 2,4-D needs to be on before it rains or before you water your lawn.

If you water your lawn before the rainfast period elapses, you’ll need to spray 2,4-D again within 48 hours to improve its efficacy in killing lawn weeds.

Do the same if it rains unexpectedly before the herbicide becomes rainproof, as indicated on the label to improve the chances of killing tough lawn weeds such as dandelion and plantain.

How long after spraying 2,4-D can I plant grass?

You should wait at least 30 days after spraying 2,4-D before planting grass seed. Although it is a broadleaf weed killer, 2,4-D can reduce the germination rate of grass seed. For new grass, wait at least after the third mowing before spraying 2,4-D to kill broadleaf weeds in your lawn.

After how long can you mow your lawn?

After applying 2,4-D herbicides, you can mow your lawn after 3 days when the weed killer has been absorbed by the plant adequately. Avoid mowing your lawn 3-4 days before application because you want to allow enough leaf surface for the absorption of the herbicide.

Ideally, I would recommend that you allow a week before and after applying 2,4-D to mow your grass. Mowing immediately will reduce the effect of the broadleaf weed killer because some of the weed leaves will be chopped off with herbicide being translocated in them.

See also: When to apply crabgrass preemergent on your lawn

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How many hours does 2,4-D need to dry?

2,4-D herbicides take 1 to 8 hours to dry, depending on the type of formulation. Esters dry faster than amines, so it is important to determine which type of 2,4-D herbicide you’re using to control weeds on your lawn.

If you’re using dust applications, you may need to apply it on wet grass for better performance. In some cases, it is recommended that you water down 2,4-D dust applications for the weed killer to be absorbed.

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From my experience, you can get the best results with 2,4-D weed killers when you watch the sprayed area for any regrowth and new emergents. Two applications of 2,4-D herbicide are usually the best for controlling weeds effectively because new plants can emerge as soon as you finish spraying.

The soil may remain temporarily sterile for a little while after the application, but how long that will last depends on the amount of 2,4-D you applied and the weather conditions after that.

Precautions

• Do not forage or harvest hay until after 7 days of 2, 4-D application.
• Do not allow the herbicide to spread to nearby plants. It will cause severe injury.
• Proper usage and following the instructions (on the label) is important to avoid environmental hazards.

Sources + References

• Gwen Stahnke, Oregon State University Extension: Influence of Cultural Practices on Weed Encroachment
• W. A. Harvey, W. W. Robbins, University of California Agricultural Extension Service: 2,4-D as A Weed Killer
• Alligare: 2,4D Amine Weed Killer Label