Spring is coming–I hope.  The calendar says it’s March next week, but it still feels like December.  One way we know spring is actually coming isall the lawncare trucks (especially those clean LawnAmerica trucks) driving around, with all the little lawncare flags sticking up along home lawns.  Your 2010 lawn starts in February, with a pre-emeregent weed-control treatment applied.  This really does set the stage for successful weed-control in a home lawn.  So how do they work anyway?  And, if a pre-emergent is supposed to stop weeds, why do weeds come up anyway during the season? 

Pre-emergents have come along way in the 26 years I’ve been applying them.  Back in the 80’s, we had products such as Balan, Betasan, and Surflan to name a few.  As is the case in all pest-control products, the new chemistry is so much better, safer, more effective, and with lower use rates.  They often are more expensive also, but I’ll take that if they work better and safer.

Any pre-emergent can be appied in the granular or liquid form.  Most homeowners apply a granular, which has been coated with a pre-emergent.  Professional companies, such as LawnAmerica, will mix the product into a liquid solution, while adding other products andeven fertilizer to the mix.  The liquid is then sprayed in a drench application over the lawn.  With either method, the pre-emergent needs to be watered into the soil within a few day, where it binds to the soil surface, and stays active for several months.  Once in the soil, as small weed seeds such as crabgrass germinate late in spring, the weeds are killed as they shoot up through the herbicide barrier. 

Three  keys to good crabgrass control are:

1. Use a quality product.
2. Apply it properly at the right time, at the proper rate.
3. Water in the product.

At LawnAmeirca, we use the best pre-emergent available–Barricade.  This product can be purchased in the granular form at garden centers, along with other products.  The chemical name is Prodiamine, so if you’re doing your own lawncare, look for a product with this chemical.

This young crabgrass would not have germinated if a good pre-emergent would have been applied earlier.

In Tulsa, pre-emergents need to be applied and into the soil at least a week prior to crabgrass germination.  Crabgrass will germinate when the 4″ soil temperatures stay at about 54 degrees for about four consecutive days, and withadequate soil moisture.  With the winter we’re having, we’re along way from soil temperatures that high, so we have plenty of time left.  We generally have our  customers serviced with their pre-emergent by around March 26thor so.  Very seldom will I see crabgrass germinating before that, unless it’s along a concrete curb, in bare ground, which will heat up faster in the spring.  Even good products such as Barricade will not work though if they are not applied at a good rate, and with a good application covering all areas of the lawn.  Older products often required two applications, since they only lasted about 2-3 months in the soil before breaking down.  Newer products, such as Barricade, will provide weed-control for up to 7 months, as long as the proper rate is used.   Therefore, only one good treatment is required for season-long control of crabgrass and grassy weeds.

One of the things that really chaps me about some of my competitors, especially that big national company that claims how true they are are and how green they are, is that they apply two pre-emergent treatments, with a much lower rate of product (with a lower cost in their tank), in the same time that I apply one!  Some folks think they are getting such a good deal with a cheaper application cost, but they charge double to get the same results we provide with one treatment!  I know–as I’m one of their customers, and I’ve competed against them for years, with their 8-step program.  I’m looking at a card now, that they’ve sent me, showing my first treatment applied last week, and my 2nd (of 6) coming on March 26th–before crabgrass even germinates!  Maybe they just want to make sure that the 2nd guy may hit some of the areas their first guy missed, since he was in such a hurry.  They also do the same technique in fall, apply two fall pre-emergent treatments, when only one is needed to do the job, assuming that one is applied at the full rate.

Barricade won't stop a dandelion and most other broadleaf weeds from germinating. They need to be controlled with a liquid post-emergent spray.

If applied properly, at a good rate, you only need one pre-emergent.  It also needs to be watered into the soil within a few days.  In fact, if it’s not watered in, and we have one of those dry spells that are common in early spring, some of the product will break down from the sunlight.  Therefore, the pre-emergent barrier will not last as long into the summer, leading to more weeds coming up in mid to late summer.

So why do you still have weeds if this fancy pre-emergent was applied you ask?  NO pre-emergent is perfect.  Things happen in nature to break it down quicker (such as months were it rains every day like last spring).  And pre-emergents are only effective on crabgrass and grassy weeds.  Some broadleaf weeds are on the label, but the control is very sporadic at best.  And then, with weeds such as Nutgrass, other specialty types of products are needed, which can act as a pre-emergent. 

With my next post, I’ll talk more about pre-emergent herbicides, and how to get the most out of a pre-emergent treatment.