Dithiopyr vs Pendimethalin (Lawn Herbicide Comparison)

There are many different things to think about with lawn care maintenance, and keeping weeds at bay is probably one of the most important. It is not as simple as picking up any herbicide from your local garden store, drenching those weeds in said herbicide, and then sitting back and watching as they shrivel away, never to be seen again.

You need to ensure you are using the correct herbicide to achieve the desired outcome without it being detrimental to your lawn. Two common herbicides are Dithiopyr and Pendimethalin. In this article, I will break down each one of them in a way that helps you decide whether either one of them, or both, are the herbicides you need as part of your lawn maintenance plan.

What’s the Difference: Dithiopyr vs Pendimethalin

Keeping it nice and simple, Pendimethalin is a selective herbicide used in pre-emergence and post-emergence applications to control annual grasses and certain broadleaf weeds. Annual grasses are those species that grow from seed each year and die off at the end of the growing season.

Dithiopyr is a broad-spectrum herbicide that focuses on killing broadleaf and grass-like weeds, specifically summer annuals, in the pre-emergence phase only.

Comparing Dithiopyr vs Pendimethalin in More Depth

Now you know at a basic level what each of these herbicides does, let’s compare Dithiopyr vs Pendimethalin in more depth and drill down into how they work, how quickly you can expect results, and what their safety profile is like.

How Are They Applied?

Dithiopyr Application

Once Dithiopyr is mixed with water (to the ratios in the instructions) you can apply it with a watering can, knapsack or a small handheld spray can. Because Dithiopyr’s primary function is the prevention of growth, the best time for application is in early spring. The reason for doing this is because you want to affect the weeds before they sprout, and Dithiopyr when applied correctly, can control weeds for up to 16 weeks.

Pendimethalin Application

The fact that Pendimethalin is selective means that you can be a little more liberal with its application. That is, of course, once you have read and made sure that it will not harm the plants and grasses you wish to keep.

An application can be done with a knapsack, or for those of you with a large lawn, you could use a lawn tractor with a boom sprayer. Again, ensure those grass species you want to keep will not be affected by Pendimethalin. Targeting weeds at the pre-emergence stage means the best time for application is in early spring. The treated area will need to be watered in afterward, to ensure the herbicide is drawn up through the roots. The soil should then not be disturbed for at least 2 to 3 weeks.

What Weeds Will They Kill?

Dithiopyr Target Species

Dithiopyr can kill a large variety of weeds as well as some grass species, so it is imperative to consult the instructions provided with the herbicide. With regards to lawn care, the more common species that Dithiopyr is used for are crabgrass, goosegrass, chickweed, and annual meadow grass.

Pendimethalin Target Species

As mentioned earlier, Pendimethalin is a selective herbicide, so it only targets certain weed and grass species. That does not mean that it only kills one type of weed, simply that it is more specific in its performance.

A few examples of grasses would be Signalgrass, Crowfootglass, Foxtail, Goosegrass, Johnsongrass, and Witchgrass.

Some broadleaf weeds that it will kill are Burweed, Clover, Chickweed, Pusley, Spurge, Woodsorrel, and Velvetleaf.

How Do They Work?

Dithiopyr Method

Dithiopyr prevents growth in targeted pre-emergent weeds. It does this by disrupting the growth of the roots, which we all know are a vital component of any plant’s development. Dithiopyr also interferes with the formation of microtubules which are a major component of plant growth.

Pendimethalin Method

Pendimethalin works similarly to Dithiopyr, in that it prevents the growth of the plant’s roots and shoots, leading to the overall death of the plant. Pendimethalin is an inhibitor of plant cell elongation and cell division.

How Fast Do You See Results?

Dithiopyr Results

As a pre-emergence herbicide, the effects of Dithiopyr may not be visible after a few days, but it can control weeds for up to 16 weeks when applied at the right time. Hence any emergence of known target species such as crabgrass 2 – 4 weeks after Dithiopyr application can be taken as a sign that the herbicide was not effectively applied.

Pendimethalin Results

Using Pendimethalin as a pre-emergence application means that results will only be noticeable after a few weeks, in the form of stunted growth and death of the targeted weeds. Pendimethalin can be used as a post-emergence herbicide on certain species and those results can be noticed within 10 to 14 days of application.

Is One Safer Than the Other?

Dithiopyr Safety Profile

Dithiopyr is safe for use on residential lawns as it is not toxic for humans and animals, and has no cancer-causing properties. It can cause slight skin irritation and moderate eye irritation so suit up with the appropriate safety equipment before mixing it.

It does, however, pose a highly toxic risk to aquatic animals and should not be applied directly to water sources.

It binds easily with organic matter in the soil and does not leach easily. It also biodegrades in soil over time from sunlight exposure, soil microbe activity, and in the presence of oxygen.

Pendimethalin Safety Profile

Pendimethalin is slightly toxic when ingested orally but not by dermal (skin) exposure or inhalation. It potentially has carcinogenic properties, and displays skin irritant tendencies. However, the risk of harmful exposure is so low that the recommended safety protocols are wearing long-sleeve clothes, pants, shoes, and socks. I always err on the side of caution with safety goggles and gloves when I mix chemicals, even supposedly safe ones. So really, the baseline attire for Pendimethlin is to be fully clothed and to use your common sense.

In terms of the comparison of Dithiopyr vs Pendimethalin, both are fairly safe to work with, but if it were a race for wellbeing Dithiopyr would come out just ahead.

When is Dithiopyr a Good Option?

If you already have a well-established lawn but would like to keep new seasonal grasses and weeds from germinating in it, a well-timed application of Dithiopyr in Spring will save you a lot of walking for spot treatments later on.

When is Pendimethalin a Good Option?

Grab the Pendimethalin when you have a recurring problem with one of the weed species that it is known to control. If you have an unruly patch of pigweed on the plot next door, then an application of Pendimethalin once or twice a year will keep any of those pesky weedlings from invading your turf, even after they have already germinated.

Can I Mix Dithiopyr and Pendimethalin?

Yes, Dithiopyr and Pendimenthalin can be mixed. Dithiopyr is a broad-spectrum herbicide and Pendimenthalin has post-emergence capabilities, so by combining them you can cover a broader range of weed species over a more flexible time frame.

Summary

The main advantage of Pendimethalin vs Dithiopyr, is that it works as a post-emergent treatment of problem weeds as well as a pre-emergent. So if your to-do list gets away from you and you only get to spraying your lawn later than intended, it will still take care of those weeds that have already sprouted.

If your annual lawn maintenance day is already planned and booked in your calendar, then Dithiopyr is a slightly safer option and more gentle on the surrounding environment.

Both Pendimethalin and Dithiopyr will not take care of established weeds though, so don’t get caught napping this spring, as it will only create more yard work for you in the summer heat.