Great Googily Moogily The Lilacs Are Blooming!!!!

Discussion in 'Pesticide & Herbicide Application' started by Bret Austin, May 10, 2001.

  1. Bret Austin

    Bret Austin LawnSite Member
    Messages: 14

    I don't even have to go outside to see the lilacs are blooming, my phone rings constantly. Little old ladies (bless their heart they are a large part of my business) calling to tell me that it's too late to apply Pre-M. How do we put these concerns to rest once and for all? The way I understand it is the Crab Grass seed germinates when the soil temperature is 60 degrees at 2 inches deep. I'm not sure if that's average daily temp or a one time shot. However, I don't believe it has anything to do with the darn lilacs.

    Anyone got the real answer?

  2. greens1

    greens1 LawnSite Senior Member
    Messages: 352

    To the best of my knowledge lilacs have little or nothing to do with crabgrass. The rule of thumb is 5@50, 5 days where the soil temps remain at 50 degrees or above.
    Jim L
  3. GroundKprs

    GroundKprs LawnSite Bronze Member
    Messages: 1,969

    What they are referring to is that crabgrass will germinate as the lilac blooms fade. They have probably just learned this from observation during their lives, or they may have been enlightened by phenology at some time in their lives. Phenology = The relationship between a periodic biological phenomenon and climatic conditions.

    While there is no causal relationship between lilacs and crabgrass, there is a phenological relationship. Since most of nature responds to cumulative temperatures during the season, some things in nature can be used to predict totally unrelated events in nature. Nature does not read the calendar, or actually measure the temperature, it is just a built in mechanism for the survival of plants and animals. Insects and disease also follow temperature trends much more closely than calendar dates.

    Growing Degree Day (GDD) models are used to predict activity in nature rather well, but GDD calculations for a given region may be way off from the microclimate of the site you are managing in that region. Thus, instead of collecting temperature data on each site, you use plants on the site as your GDD indicators. The budding, and especially the flowering of certain species are used frequently for these phenologic predictions.
  4. greens1

    greens1 LawnSite Senior Member
    Messages: 352

    I am not sure I agree with grounds on this one.
    Blooms times on flowering shrubs and plant disease can be affected by far different variables than temperature.

    This summer in SE lower MI is a perfect example. We have had much warmer temps than normal (+25 degrees on many days) and very little rainfall. The limited rainfall has produced a late blooming season for many of the flowering shrubs, including Lilacs. I was seeing crabgrass as early as April 10th and the Lilacs are blooming now.

    It takes very little time to take soil temps, 2 min at most. I would not use broad area data, rather gather your own. The microclimates in your area should stay fairly consistent and you can adjust your data accordingly from year to year, this will cut down on scouting time.

    There is a reason that the turf schools teach students to use Degree Day Models, they work.

    Jim L
  5. GroundKprs

    GroundKprs LawnSite Bronze Member
    Messages: 1,969

    The fallicy above of seeing crabgrass before the blooming of lilacs to disprove the use of phenology is incomplete. Now if one saw the crabgrass sprouting under the lilac, before the lilac bloomed, only then could you disprove the lilac-crabgrass relationship noted above. The lilac in the shady back yard could truly bloom after the crabgrass germinates on the sunny treelawn cooking next to the asphalt roadway.

    The answer to the original question stands: the old ladies are correct. In the general flow of nature, crabgrass germinates shortly after lilacs flower.
  6. greens1

    greens1 LawnSite Senior Member
    Messages: 352

    I am not trying to disprove phenology, simply stating that it is not always accurate. That I saw crabgrass germinating before the lilacs bloomed is a statement of fact, and therefore not fallible.

    The premise is " when lilacs bloom crabgrass germinates"
    I saw crabgrass germinating when no lilacs were blooming.
    The above fact makes the premise false and therefore the argument is false.

    The material point is- if you apply PreM until the lilacs bloom, in my area, you will be throwing away money and chemical. You can avoid this if you use Degree Day Models and scouting. When I apply pesticide I am interested in accuracy not generalization.

    If phenology works for you then terrific. If I see a steady and consistant correlation with other phenomina, be it plant or somthing else, in my area I will be more than happy to use it.

    Jim L
  7. BRL

    BRL LawnSite Bronze Member
    Messages: 1,211

    :blob3: Great googily moogily, what a great discussion. I just had to write that, and doesn't that blue guy make you think of that phrase too? LOL I thought I remembered reading somewhere at some point in my life that flowering trees & shrubs base their flowering schedules more on the amount of light they are receiving than temperatures. For example, once the daylight becomes 14 hours Mrs. Lilac starts to bloom, whether its been a very cool spring or a very warm spring, with temperatures affecting that schedule only slightly. Any truth to that? Now using the DDM for the weeds emerging makes sense because their schedule is based on soil temps. Also, according to its label, Dimension PreM says it has post emergent effects as long as the crab grass is in only its first or second tillering (I don't have the label in front of me so you'd have to check it), so that product is an option for late treatments.
  8. GroundKprs

    GroundKprs LawnSite Bronze Member
    Messages: 1,969

    Sorry, Jim greens1, you are trying to elevate phenology to a broader range than it is intended. Also it is mainly used to predict insect activity on ornamentals. The lilac - crabgrass analogy is just a way to explain the ideas of the old ladies in the original post. And phenology is actually based on growing degree days. If you wish to discuss further, let's do it by email.

    And Bret, educate them a little more. The crabgrass germination just begins when lilacs bloom. There can be continued germination for another two months or so, so pre-em is still useful. And calm them by telling them that you can easily control any that has germinated with professional products(Acclaim or Drive).

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