Fall is a critical period when it comes to weed control. In this article, we'll look at some of the characteristics of both winter annual weeds and perennial weeds. We'll also provide growing tips and specific recommendations for choosing the best pre-emergent and post-emergent herbicides.

Preventing Winter Annual and Perennial Weeds

Cooler temperatures trigger the germination of winter annual weeds like describe the imagePoa annua, Chickweed, Mallow and many others. To prevent infestations and maintain healthy turf throughout the fall and winter, it's important to apply pre-emergent herbicide in specific windows. To illustrate this, let's look at a few key facts about Poa annua.

What you should know about Poa annua (annual bluegrass):

  • Light green grassy weed with unsightly seed head. Grows well in moist, compacted soil - TIP: Don’t overwater the turf!

  • Starts germinating in later summer or early fall, as soil temperatures fall below 70 degrees.

  • Is a prolific seed producer – Each plant can produce 100 seeds in as few as 8 weeks, and those will germinate later if not stopped with a pre-emergent herbicide!

  • The best method of control is the PREVENTION of new infestations by applying a pre-emergent herbicide BEFORE weeds germinate – mid-August to mid-September in most areas.

  • NOTE: Pre-emergent herbicide applications made in the spring will NOT control Poa annua or other Winter Annual Weeds. It’s too late!

What about perennial weeds, like Thistle?

Perennial Weeds are those that come back each year from existing roots. In the fall, as temperatures cool, these weeds start storing carbohydrates in their roots. This makes fall a GREAT time to apply a Post-Emergent Herbicide, because the chemical will be carried in the direction of the carbohydrates. In other words, the chemical will carry down to the ROOTS for complete kill.

Suggested Herbicides for Fall

The Best Pre-Emergent Herbicides:

  • Prodiamine (Barricade equivalent) is the longest-lasting, and most economical due to lowest application rates.

  • Isoxaben (Gallery equivalent) prevents a very large list of Broadleaf Weeds. A great tank mix with other Pre-Emergents that prevent mostly Grassy Weeds.

  • Oxadiazon (Ronstar equivalent) is a great granular option – safe in all turf and ornamentals. 

The Best Post-Emergent Herbicides:

  • Roundup ProMax provides trusted down-to-the-root kill of annual & perennial weeds, and is rain-fast in 30 minutes.

  • Roundup QuikPro offers power AND speed, even in cool temperatures, with visible results in 24 hours.

  • Speedzone / Speedzone Southern – Excellent control of Broadleaf Weeds, safe in turfgrass.

If you're looking for an all-in-one solution, TurfGro Combo Fertilizers allow you to feed your turf AND control weeds in one step! Horizon offers formulas with Barricade, Dimension, Viper, Atrazine and Trimec.

Contact your local Horizon store if you need assistance choosing the right pre-emergent, post-emergent herbicide, or fertilizer for the upcoming fall season. You can also review many of the herbicides we have in stock by downloading our Product Catalog.