herbicide temp restrictions

Discussion in 'Pesticide & Herbicide Application' started by americanlawn, Jul 15, 2011.

  1. americanlawn

    americanlawn LawnSite Fanatic
    from midwest
    Posts: 5,854

    Most labels say 85 degrees is the upper limit for applying most pesticides, but I got Q's: (full sun vs shade)

    American meteorologists in Greenland recently measured the "air" temperature in shade vs sun. 20 degrees in the shade/ 80 degrees in the sun.

    I had a thermometer in the cab of my truck 3 weeks ago. It registered 114 degrees, but the current (airport) reading was only 76 degrees. Then I see chemical companies saying we need to "quit spraying at 85".

    We also have thermometers at our office. One is in the shade. One is in direct sunlight. The direct sunlight thermometer typically measures about 30 degrees warmer than the "shade" thermometer.

    2 Q's:

    1) Why do the meteorologists measure the hot summer temps in the SHADE, yet they measure "wind chills' in the winter? :confused:

    2) If I wake up in the morning when it's 74 degrees in the shade/92 degrees in the sun...do I not need to shut my business down for several months? Or maybe I can only treat turf which grows in the shade? :confused:

    rscp, thanks
  2. mdlwn1

    mdlwn1 LawnSite Silver Member
    Posts: 2,443

    Are you joking or do you really not understand?
  3. ted putnam

    ted putnam LawnSite Platinum Member
    Posts: 4,539

    :laugh: My grandpa told me he used to walk back and forth to school. He said it was uphill both ways. How can that be? Is that possible??
  4. White Gardens

    White Gardens LawnSite Fanatic
    Posts: 6,776

    I see your point AmericanLawn.

    I just did 2 acres today, and 80% of it was in the shade. The temps topped out at 85, but I felt that the shaded areas were going to be less susceptible to get burned in the heat. It was a had to be done sort of thing as we are going into a heat warning Sunday through next Friday. So the window to spray was going to get slammed shut.

    Did all my other spot-spraying yesterday.

    So I was thinking the same thing today. What if it's too hot, would you still go do shaded areas.

    Personally I say no. Even the lawn I treated today had minimal weeds in the shade, so I'm guessing it's not worth the turf burn to try it.

    Ultimately, any other lawn on a program this year doesn't have but a couple of weeds in them anyways, so my spraying will be shutdown until fall.

  5. ted putnam

    ted putnam LawnSite Platinum Member
    Posts: 4,539

    Temp "restrictions" are more like recommendations. They inform you that if you apply in temps higher than that upper threshold, you risk damage to turf. It's pretty much a "liability waiver" for the chem company. Right now it is 78F at 7AM here. It is 90F by 10 AM. I am spraying along with every other LCO around here.
    Common sense and past experience goes a long way in avoiding turf injury. Y'all must have some deep pockets and very understanding customers to shut off spraying weeds for weeks when temps hit 85F.
  6. Ric

    Ric LawnSite Fanatic
    Posts: 11,956



  7. dgw

    dgw LawnSite Bronze Member
    from OH
    Posts: 1,008

    if the lawn is healthy and on a watering schedule i will spray in the heat
  8. Wright48

    Wright48 LawnSite Member
    Posts: 242

    READ THE LABEL !!!!!! i have a product called Q4 for all weeds and crabgrass the label says 90 degrees or less trick is to spray light not heavy in hot weather. If the label says 2 oz per gallon maybe got 1.5. Use your brain wherever that may be.
  9. ChiTownAmateur

    ChiTownAmateur LawnSite Senior Member
    Posts: 386

    1) Temperatures are always measured in the shade because the "air temperature" is so inconsistent in the sun that the only reliable measure that can be taken is in the shade. It is absolutely true that in the arctic they can measure sub freezing temperatures in the shade, and at the same time wear a t-shirt and shorts in the sun because the sun is warming the air and ground in that particular spot. The measure is the air temperature, not the ground temperature or the air temperature in the sun just above the ground.

    1a) As you suggest, in the sun, a 80 degree day may well be 100 or 120 at the ground level in the sun. This should be taken into account when applying treatments.

    1b) Windchill does have an opposite, which is the heat index. Windchill and heatindex ARE NOT TRUE TEMPERATURE MEASUREMENTS. They are formulas which take into account other factors. For windchill, the wind speed is put into a table and referenced against the temperature to give a HUMAN FEEL READING. So if it's 32 with no wind, the chill is 32. If it is 32 with 20 mile an hour winds, the FEEL to a human is much colder, and hypotermia occurs at a rate much faster which is why people are informed about windchill.

    1c) Heat index takes into account the humidity level in order to inform a HUMAN FEEL to the temperature. As you well know in warm areas, 90 with very low humidity FEELS much more comfortable than 85 with very high humidity. This is again, not a temperature measurement but an index that can be used to inform people about their relative chance of overheating in the sun.

    2) The guidance not to apply certain treatments above 85degrees (just like the guidance to NOT apply RoundUp in low temperatures) is just guidance, but it is referring only to the temperature, not to the heat index. As you infer, if it is bright sun and 90 degrees out, the temperature at the ground level by the turf is quite likely 110+. Experience is the only guide here but the gist is that applications should be done as early or late as possible to avoid the hotter parts of the day. Ideally, a time of day without sun shining would be the best situation because then the temperature reading you see on tv or on your home thermometer is the true temperature at the ground level (+ or - for the soil temperature which will have some variance).

    VARMIT COMMISSION LawnSite Senior Member
    Posts: 547

    2) The guidance not to apply certain treatments above 85degrees (just like the guidance to NOT apply RoundUp in low temperatures) is just guidance.

    Yes it is just guidance. I apply roundup when the temp is in the mid 30's, and get the same results as if I had sprayed it in 85 degree temps. Just much much slower.
    Me personally I quit adding any sticker/surfractant when the temps get above 90 and I do keep spraying just like everyone else. I sprayed some MSMA three days ago in 100 plus temps, and last week and the week before. Heck it has been over 100 for three weeks here.

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