Lawn Care Tips And Tricks: When To Apply Dithiopyr

When pre emergent season arrives, Dithiopyr is one of the top choices for annual weed control. It can be found both as an active ingredient in weed and feed granules, and as a concentrate product, under the brand name Dimension. 

Dithiopyr is a popular choice as a late spring pre emergent for crabgrass, dallas grass, and other seed-sprouting weeds. It’s designed to control both grassy weeds and broadleaf weeds and is safe on all turf grass types. Dithiopyr also has some post-emergent effects on early-stage crabgrass.

Pre Emergent Herbicides

Quali-Pro Dithiopyr 40 WSB (Dimension) Herbicide

Pre emergent herbicides like Dithiopyr can be applied in late winter, in spring, and in fall to prevent weeds from sprouting. This allows your grass to grow in without competition for space and resources, resulting in a thicker lawn. Dense turf itself provides a barrier for weed growth later in the year, reducing the number of treatments you’ll have to apply. 

Dithiopyr is well known as a crabgrass preventer since it’s so effective against the weed. When crabgrass takes hold, it spreads easily and mixes in with your lawn, making it difficult to target. Pre emergent herbicides are applied before the seeds germinate and prevent their establishment in the first place. 

Pre emergent herbicides remain in the upper inch or two of the topsoil, creating a chemical barrier that prohibits germinating seeds from growing roots. Dithiopyr, and the similar pre emergent herbicide Prodiamine, are known as root inhibitors. They prevent the roots of newly germinating seeds from growing so the seed isn’t able to develop or sprout. 

Dithiopyr Or Prodiamine?

Dithiopyr and Prodiamine act in similar ways and have similar effects on germination. The difference comes in how “sticky” each formula is. Prodiamine tends to hold on longer and is less affected by rain. This makes it a good early spring applicant, while Dithiopyr does well in the later spring when it can have its post emergent effects on both seeds and the early stage crabgrass sprouts.

Quali-Pro Prodiamine, Pre-Emergent Herbicide, 5 lbs, Yellow Granules

Dithiopyr’s penetrative nature makes it a good choice for clay soils, which might have a harder time absorbing a Prodiamine application. For sandy soils that drain well, Dithiopyr might be rinsed away more quickly than Prodiamine would be.

Post Emergent Properties Of Dithiopyr

One of the reasons Dithiopyr is a popular herbicide is that its root-targeting formula can have an effect on the newly developing roots of sprouted crabgrass. Since seeds will germinate and sprout at different points over the several weeks of spring and fall when temperatures are between 55 and 70, a split application of Dithiopyr in early and late spring can keep suppressing seeds that haven’t yet germinated, as well as catch some that have freshly begun to sprout.

Does Dithiopyr Need To Be Watered In?

Pre emergents like Dithiopyr and Prodiamine need to be watered into the soil so the solution disperses and creates a barrier that will prevent seeds from growing. The water activates the active ingredient that prevents the roots from developing, but too much water can rinse it away. The amount of water needed will vary by the rate you apply, but it generally needs about an inch to an inch and a half of water to get it into the soil. Be sure to apply it when you’re not expecting rain for a few days so the barrier doesn’t get too diluted before it can settle in.

What Month Should I Apply Pre Emergent?

Seed germination is driven by the soil temperature, which changes at different times of the year depending on your location. Crabgrass seeds germinate when temperatures are between 55 and 70 degrees, so applying a pre emergent herbicide just before temperatures enter this range will suppress seeds from sprouting. 

Between Prodiamine and Dithiopyr, it’s recommended to apply Prodiamine when soil temperatures are around 50 degrees, and Dithiopyr when temperatures have reached 55. If you don’t get a pre emergent down before the 55 degree point, you won’t be too late to apply a pre emergent until temperatures are over 70 degrees regularly. 

How To Apply Dithiopyr 

How To Apply Dithiopyr 

If you’re applying Dithiopyr WDG (water dispersible granule), you have three options to schedule your applications:

  • Full application of Dithiopyr when soil temperatures reach the 55 degree mark in spring, or 70 degree mark in Fall
  • Split application of Dithiopyr in the early cool season and again halfway through
  • Split application of Prodiamine in early cool season and Dithiopyr halfway through

If crabgrass is a particular problem in your yard, a split application is likely your best choice to keep the unwanted plant growth under control. 

If you apply a Dithiopyr herbicide in the form of a weed and feed fertilizer, be sure to do a soil test first so that you’re not overapplying any nutrient. Normally, phosphorus and potassium are delivered in early spring and early fall fertilizer applications, but overapplication of either of these can inhibit the absorption of other nutrients, like iron or nitrogen. If your lawn doesn’t need nutrients, or you aren’t ready to put any fertilizer down, consider the herbicide-only option.

When you apply Dithiopyr in a handheld or backpack sprayer, it’s important that the solution is fully dissolved in the appropriate amount of water. Always follow the ratio directions on the label, which will tell you how many grams or ounces per gallon of water is necessary per 1,000 square feet. A fan nozzle will give a wide, fine spray for an even application. When you apply Dithiopyr, wear long sleeves, long pants, and gloves for protection; it may irritate the skin.

Be sure to not overapply pre emergent since the root inhibitor that is successful in suppressing weed germination can, in excessive amounts, damage your grass roots as well. Don’t apply pre emergent in the same season that you overseed your lawn, as the herbicide will prevent grass seeds from sprouting as well.