Those super pesky patches of unwanted growth that mar your manicured lawn and create an endless series of headaches for you.

Weeds are not only unsighly, but they can have a devastating effect on an entire landscape if they are allowed to spread. Weeds compete with grass for sunlight, water, and essential nutrients robbing your turf. Once they overtake what was once a healthy lawn, it can quickly turn into a wasteland of troublesome weeds.

And when it comes to pre-emergent weed control, timing is everything. Pre-emergent herbicides are only effective if applied before the annual grass weeds emerge. Apply too late and the pre-emergent herbicide will be totally ineffective.

How Pre-Emergent Herbicide Works

To get a better idea of how pre-emergent works, let’s look at 3 key principles of pre-emergent weed control.

#1 Pre-emergent herbicides are designed to control germinating weed seeds.

As its name suggests, pre-emergent is targeted towards weeds that have not yet emerged from the soil. To get the best results and to avoid wasting time and labor cost down the road, the weeds shouldn’t be visible above ground at the time of application.

Important: Pre-emergent is not designed to control existing weeds or weed seeds.

The weed will only be killed when it begins to sprout from the seed and hits the herbicide barrier. It is possible for seeds to remain dormant and not be harmed by the pre-emergent herbicide application. This is why weed control is a constant process. There will always be seeds under the surface and a portion will germinate each season. Annual applications must be made to significantly reduce large infestations.

Remember, pre-emergent herbicide can affect desirable plants. That includes turf. Caution must be taken if you’re applying pre-emergent and seeding the turf in the same season. Seed first, then apply pre-emergent at least 6 weeks later to allow for lawn establishment. Or seed at least 3 months after the pre-emergent has been applied.

#2: Pre-emergent must be mixed correctly and applied evenly over the target area for best results.

Pre-emergent herbicides need to be mixed correctly for the spray solution to be at the appropriate strength. Take the time to read the manufacturer’s recommendations and don’t forget to calibrate your sprayer!

Thorough coverage is key. Think of pre-emergents like a blanket – you need to cover an entire area through which the weed seeds cannot germinate. Spot spraying achieves nothing, as there is plenty of open space for weeds to come through. Manufacturer instructions will indicate how much product to use “per 1000 square feet” or “per acre”, which determines how much herbicide to use for each gallon of water. Note that it usually takes 1 to 2 gallons of spray solution to cover 1000 square feet.

#3: Pre-emergent herbicide must be watered in.

Watering in activates the herbicide, creating a barrier just below the surface. Most products call for 0.5 inches of irrigation or rain within 21 days after application.

If you’re working with a non-irrigated area or a drip zone, apply the pre-emergent just before rain is anticipated.

Applying Pre-Emergent to Different Classifications of Weeds

To know when to apply pre-emergent herbicide, it is important to know how weeds are classified, namely by their life cycles.

Weed Classification: Summer Annuals

Most well-known example: Crabgrass (Crabgrass Germination Map below)
Other examples: Lambsquarters, Mallow, Pigweed, Spurge
Life Cycle: 1 year – Germinate in spring. They flower, produce seed, then die in fall.
Pre-emergent timing: Late winter/early spring

By eliminating the threat of a weed invasion when the weeds are still seeds, you’re literally nipping the problem in the bud. The best way to accomplish this effectively is by implementing a pre-emergent weed control program. First Response Lawn Care offers an efficient 7 step program to feed your lawn and control your weeds.