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The Straight Dirt on Moisture Activation

Pre-emergents 101

Timing — with a little help from Mother Nature — is Everything How to get the most out of pre-emergent herbicides

There are two application timing options growers should consider when using a pre-emergent weed control product, spring or fall.

Spring Application Timing
Ideally, you should try to time your pre-emergent herbicide applications early in the spring, ahead of a forecasted rainfall event. The earlier you apply, the more likely you are to catch a spring shower and achieve activation prior to the weed seeds germinating.

After a pre-emergent herbicide is applied in spring, it sits on the soil surface waiting for that early spring rain. The moisture allows the herbicide to form a powerful protective barrier that stops or slows down the growth of germinating weeds.

As we all know, when it comes to weather on the Prairies, it can feel like a gamble applying a pre-emergent herbicide — or any other herbicide for that matter—if dry, windy weather is on the horizon.

So, what happens to your pre-emergent herbicide if that activating rain is delayed by a few days or weeks? The good news is that pre-emergent herbicides will wait for moisture to come and wash it down into the soil, forming a barrier where the weeds are getting set to germinate.

If the moisture activation is delayed, there is a chance of weed escapes.  Germinating weeds can be pulled back and controlled once the pre-emergent herbicide is activated, but only for weeds within a certain size.

Fall Application Timing
Another option growers may want to consider is applying their pre-emergent herbicides post-harvest in late October or November.

With a fall application, you don’t have to worry about getting rain at the right time in the spring and spraying those acres.  Pre-emergent activation will occur from snow melt, mitigating any risk from missing early season rains. This can give you the security in knowing your early weed control is in place – allowing you the time to get your seed in the ground.