lawn13Pre-emergent herbicides have a tendency to destroy newly germinated weed seeds by attacking the tender shoots and roots before they have an opportunity to develop.

Pre-emergent does not stop seed germination actually. However, it may pose as a potential barrier on the ground. If the seeds do not germinate, they may remain temporarily dormant in the soil and escape the effectiveness of the pre-emergent only to reveal themselves later.

Many of the weeds that plague your lawn throughout the summer germinate in late fall and early spring as soil temperatures rise above 50 degrees.  

In such a situation a properly timed pre-emergent application becomes really critical to the successful suppression of weeds. If applied too early in the season, pre-emergent will degrade into a useless product before weeds germinate, if applied too late, weed seedlings will get the upper hand by becoming established beyond the ability for the pre-emergent to destroy them.

You may apply the pre-emergent in granular or liquid form. Granular products are coated solid particles which release the pre-emergent into the soil surface layers when properly irrigated. Over-irrigation will dilute the effectiveness of the pre-emergent while insufficient watering may not move enough of the product into the soil to provide a protective barrier. Properly applied liquid pre-emergents may have the advantage of not requiring irrigation immediately after being applied.

You may also encounters situations as a result of pre-emergents application in the form of turf aeration, heavy foot traffic and digging may disturb the barrier and allow some weed seedlings to dodge contact with the herbicide and grow to maturity. These fugitives along with winter annual weed seeds can take advantage of fall soil temperatures by germinating late in the year so mid-September is another good time to apply pre-emergents.

In case of perennial weed seeds may be checked by pre-emergents, their parent plants have established root systems and are not adversely impacted. It will largely depend on the nature of your landscape. These invaders may require a selective post-emergent application sometime before they become strongly established later in the season.

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