hot weather and herbicide

Discussion in 'Pesticide & Herbicide Application' started by RigglePLC, Aug 28, 2014.

  1. RigglePLC

    RigglePLC LawnSite Fanatic
    Messages: 13,678

    I was thinking of the early years when some inexperienced, but well meaning, applicators sprayed some crabgrass escape plants with MSMA by aiming the nozzle at the center of the plant while holding the nozzle about 4 inches high. They probably shouted, "Take that!" before releasing the trigger. 48 hours later we had calls about some kind of disease spot. Easy to diagnose--there was a dead crabgrass plant in the center of each spot.
    I am not saying it never happened to me--I've done it.

    What I mean is move the nozzle across the weedy spot--in a manner similar to the motion when you calibrated your hand sprayer. Do not sweep the nozzle back and forth. Not accurate--its approximate.
    Since my test used trigger sprayers. I used one squirt and tried to cover a half sqft. (9.6" diameter circle). (Then three times; then five times over)--(only for purposes of the phytotoxicity test).

    I am not worried about dandelions. I never liked to be called back for resprays on oxalis, veronica, ground ivy, spurge and wild violets. I found these weeds tough to kill, particularly when in the tough mature growth stage.
  2. Skipster

    Skipster LawnSite Bronze Member
    Messages: 1,076

    Still not sure what you're talking about here. When my spray nozzle moves across weedy spot, it's because I walked it across. That motion is similar to my calibration because my calibration follows the standard for a single-nozzle application: GPA = (GPM * 5940)/(MPH * W).

    When you say "spot spray," are you just standing still and pushing the spray wand forward with only an arm motion? Does anybody really do that? That is precisely the behavior that all the university extension materials, pesticide applicator exams (the "Applying Pesticides Correctly" manual in many states), and many herbicide labels expressly say to avoid.

    In the world of "spot" applications to turfgrass areas, there are only two main techniques. One involves using a hand-held sprayer (backpack, etc) as I described -- where you hold the wand steady an still with your hand and the only motion it has in space is done by the operator walking with it. The other is a spray-to-wet method, where the applicator waves the wand in multiple directions with his arm over a weed until the weed leaves are uniformly wet and stops just short of the point of product runoff. A good way to tell which application technique a label is recommending is how the rate is described. Labels describing rates (amount of product per unit area) are calling for broadcast treatments to a small area. Labels describing concentrations (amount of product per volume of completed spray mix) are intended to be applied in spray-to-wet fashion.

    This is usually covered in certified applicator training manuals.
  3. RigglePLC

    RigglePLC LawnSite Fanatic
    Messages: 13,678

    I do not spray to wet--unless I am applying fungicides or insecticides.
    I think we agree on the herbicide spot spraying, Skip. Whether I am walking or standing still--having just discovered a dandelion--the nozzle must be moving--otherwise there is a risk of over dosing and injuring the turf.
  4. Skipster

    Skipster LawnSite Bronze Member
    Messages: 1,076

    Many herbicide labels give explicit instructions on how applications should be made. Let’s consider T-Zone:

    If you’re standing still and using your arm to move the wand (even if only in a forward direction), you have no way to be sure of your speed and direction, thus you are making an imprecise application that is potentially damaging or potentially ineffective.

    On the other hand, some labels give explicit instructions for spray-to-wet applications:

    Tribute Total
  5. americanlawn

    americanlawn LawnSite Fanatic
    from midwest
    Messages: 5,954

    Seems like Riggle and I usually think along the same lines, and this is no exception.

    1) "Waiving the spot sprayer wand back & forth" -- nearly every newer applicator I have ever had does this. The reason they do this is because they mean well and are trying their best to do a good job. These hard working guys certainly do not lack effort >> just lack of training. And this is my fault.

    2) Spot spraying "heavy" >> I do it all the time when it comes to difficult weeds. Ground Ivy & Rugle's Plantain come to mind, but there are "summer annual" broadleaf weeds that require a "hard hit" too. knotweed, spurge, purslane, etc.

    3) Herbicide rates: Right now, we are applying about 15% less product than herbicide labels allow. This is illegal in my state, but not in most other states. So shoot me just cuz we don't apply more pesticides. :laugh:

    4) Some factors that affect herbicide weed uptake.
    a) Humidity
    b) Heat
    c) Growing conditions

    my 2 cents
  6. RigglePLC

    RigglePLC LawnSite Fanatic
    Messages: 13,678

    Here are the photographs showing 4 herbicides sprayed on Bermuda grass. I used (estimated): label rate, three times over and 5 times over. The test was supposed to show the differences at high temperatures--but it has been a cool year; the predicted 90 degree temperature fell to about 85 and the following days had highs of about 80.
    After 6 days, only T-Zone caused visible injury, at the high rate. Surge, Speedzone, and a 3-way caused none or very slight injury even at the high (five times) rate. All treatments except the generic three way (RTU) contained surfactant.





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