Grounds Keeper, pre-emergent thoughts

Discussion in 'Pesticide & Herbicide Application' started by Forever Green Lawn, Feb 11, 2001.

  1. Forever Green Lawn

    Forever Green Lawn LawnSite Senior Member
    Messages: 282

    I read your post about pre-m effecting an established lawn and found it interesting that the pre emergent would cause the problem. As C3 grasses have the majority of their root growth in the fall, the pre emergent will have long been broken down, or maybe something else going on? I never seen a pre-m have that effect, unless it was way over applied. Maybe lawns that have some disease/insect damage should not recieve a pre-m until they have been aerated/overseeded and are healthy again. Something for us to think about. Any thoughts?

    P.S. Thanks for the interesting post!!

  2. GroundKprs

    GroundKprs LawnSite Bronze Member
    Messages: 1,969

    In the post mentioned , my recent experience with Dr W's lawn was that turfgrass rooting will be inhibited for almost 24 months after the last pre-em application. Here a single app of pre-em is usually applied by mid-April. In closely watching root growth over 6 years on this lawn, healthy rooting was finally observed 22.5 months after the last pre-em application. This was not a single event; a small part of the lawn was done one year earlier, and the same effect was observed.

    While it is common knowledge that root growth in C3 (cool season) grasses is basically a fall function, root growth is actually a year-round function. The fall flush of root growth is to replace those lost from summer stress. However, there are many other environmental reasons, unrelated to climate and calendar, that can trigger root growth. Among these are reduced N in surface soil, reduced water in surface soil, mechanical removal of existing roots, etc. Try planting some sod in early Aug, give it proper care, then see what the root growth is over next 2 weeks. (And for a real test, put a pre-em on a small area of your sod, and see how many roots you don't have.)

    Also, even though the root inhibiting pre-ems have degraded significantly by fall, they have not completely disappeared. Could these pre-ems, or some of them, actually have a more stressful effect on roots of desireable grasses than on weeds? Maybe that is why, in my experience, the desireable grasses took almost 2 years to recover, but crabgrass will break through sometimes just 2 months after application.

    As far as disease and insects, during the 3rd year of Dr W's ordeal, we had dollar spot so bad that an 800 ft² area was completely brown. As I said red thread and summer patch were also rampant. Since eliminating root inhibiting pre-ems, there has been no need to treat dollar spot or red thread, and summer patch has disappeared. This is mainly because of proper grass rooting. The only cultural practice that was changed was the cessation of pre-em use. We do have a significant grub problem in our area. On a number of my properly maintained lawns, I have not discovered heavy grub density until aerating in late Sept, early Oct, when the aerator rolls up the turf. The grass was recovering itself by re-rooting. But would this be possible if the area was loaded with annual pre-em apps?

    Elimination of pre-em is definitely not for everyone, contractors and customers. The lawns must be getting all the proper cultural practices, and even then there will be a learning curve. I would have drowned in crabgrsss if apps had been stopped across the board. You will have to think way outside the rules, and to support your extra work, clients will have to think outside their wallets. As in Dr W's lawn, it's not easy to manage 23,000 ft² of sunny turf with no pre-emergents, but in the long term results are rewarding for both of us.

    [Edited by GroundKprs on 02-12-2001 at 09:12 AM]
  3. I will bet you a dollar to a doughnut that dr. w's turf was taken "care" of by big "green" for the 3-5 years prior to Jim's tenure.

    You guys need to be aware to educate the former big green customer (that is now yours) that by the constant broadcast applications of pre and post emegrent herbicide with urea the turf will take TWO years to regenerate.

    The first issues you need to deal with is the inches of thatch (bluegrass lawns) formed over the years of abuse by big green. You see big green does not remove thatch. Usually the thatch is so bad you have power rake and bag the lawn at least three times in the first year alone.

    You have to inform prior big green customers up FRONT that the renovation process with be long and costly.
  4. Forever Green Lawn

    Forever Green Lawn LawnSite Senior Member
    Messages: 282

    Your right, Larry. Tru-Green's excessive use of N will cause excessive thatch which causes moisture stress which in turn leads to a host of problems. Jim is also right that C3 grasses do grow roots to a certain degree all year as long as the soil is not frozen, just that most growth takes place in the fall and some in the spring. Environment does play a huge roll as we know.

    Could be that simply aerating broke up enough thatch to let the lawn recover? As far as pre-m's being more stressful on grass roots as opposed to weeds, I'll e-mail my old professor at Purdue and get his thoughts on that one.

    Thanks guys!!

  5. Island Lawn

    Island Lawn LawnSite Senior Member
    Messages: 632

    I'm interested what your ole prof says about this one.

    Be sure to give us all an update when you get the info.


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