I know it’s still officially winter, and turning your irrigation system on or dragging the hose out is not high on your priority list. However, if you have had a pre-emergent treatment to your lawn, it does need to be watered into the soil within about 5 days for best results. We are actually in somewhat of a drought in Oklahoma now, going back to our dry fall. We typically don’t get much rainfall in winter, and the snow has been nowhere to be found again this winter. So even without the need to water in your pre-emergent, your trees, shrubs, and even the lawn would benefit from some irrigation.
All pre-emergent herbicides need to be watered into the soil in order to be activated and do their job in preventing weeds. Barricade, or Prodiamine, is our choice of products, and the very best on the market. Once waterered in, Baricade adheres to soil particles close to the surface, and will kill grassy weed seedlings as they try to germinate. Barricade does not last forever by design though, just long enough to last through the crabgrass weed germinating season of spring and into summer.
There are factors that can cause the pre-emergent to break down sooner than it should or to negate the effectiveness of the product. One of them is sunlight, which can break down the product with longer exposure than just a few days. Some of the Barricade when sprayed on the lawn adheres to grass blades, stems, and the very top layer of the soil. So this needs to be watered into the topsoil, where it is protected from the degrading sunlight. If Barricade just sits on the turf or top surface for a week or more without any significant rainfall or watering, some of the product will just dissipate.
Only about 1/4″ of watering is fine to move the pre-emergent into the soil and activate it. So It does not take much watering to wash the product off the turf and into the soil. We normally don’t recommend light hand watering, but even this would be better than nothing. And too much water can also be a factor in degrading the pre-emergent sooner than normal. If the soil stays saturated for weeks at a time, such as can sometimes happen during a rainy spring, or with over-irrigation, this will also cause the pre-emergent to break down sooner than normal.
And we can’t forget our old friend the mole. Disruption of the soil surface, such as mole activity, digging, or even aeration, can also break the pre-emergent barrier in the soil, leading to increased crabgrass and weed problems later in the season. So many things can affect the success of a pre-emergent. Watering in the treatment within a few days of application is one that a homeowner can control, so please do so to help enjoy a more weed-free and crabgrass-free lawn this season.