Prodiamine vs Dithiopyr: Which Pre-Emergent Should You Use?

The main difference is that prodiamine is a pre-emergent only with the longest soil residual, while dithiopyr is a pre-emergent that also has early post-emergent activity on young crabgrass. Prodiamine must be applied before crabgrass germinates and then prevents it for up to about 6 months at higher labeled rates. Dithiopyr can be applied slightly later and still kill crabgrass that has already emerged, up to its early tiller stage, but its residual is shorter. Always follow the product label for rates and timing.

Yes, but only young crabgrass. Dithiopyr has early post-emergent activity and can control crabgrass that has germinated up to roughly its early tiller stage, which many labels describe as before it reaches about the 3- to 4-leaf stage. Once crabgrass has tillered and matured, dithiopyr will no longer control it and you would need a dedicated post-emergent crabgrass herbicide. Prodiamine has no post-emergent activity at all and will not kill any weed that is already up. Check the specific product label for the exact growth stage it controls.

Prodiamine is generally the cheaper of the two per 1,000 square feet. Its very low use rate and long residual mean a single early-spring application covers a lot of area for a small amount of product, which is why prodiamine (Barricade) is often the most economical pre-emergent available. Dithiopyr usually costs a bit more per 1,000 sq ft, and granular or on-fertilizer dithiopyr products cost more still. If pure cost per area is the priority and you only need prevention, prodiamine wins.

Prodiamine lasts the longest, up to about 6 months per season at higher labeled rates, which is why it is popular for a single early-spring application. Dithiopyr has a shorter residual, commonly cited around 3 to 4 months. Actual barrier life for both depends on the rate you apply, soil temperature, rainfall, and irrigation, so use the label rate that matches the protection window you want. Higher labeled rates generally extend residual within the allowed range.

No, neither prodiamine nor dithiopyr is meant for use at seeding. Both work by stopping seedlings from establishing roots, so they will prevent your desirable grass seed from establishing just as they prevent weeds. Each label specifies wait intervals before and after seeding, and prodiamine in particular requires waiting until new grass is well established. If you are seeding this season, use a seeding-safe pre-emergent such as mesotrione or siduron per its label, or wait out the residual before applying either of these.