Does anyone have any experience with a chemical that does not work if sprayed on a heavy dew?.
Same. We usually always try to rule of thumb an hour of dry leaves for us. We aim for atleast if spray is on 1 hour before rain and after dew.If spraying roundup wait for dew to burn off and plants to dry before spraying. Heavy dew will dilute droplet concentration and can cause run off on plants. Have had poor results with roundup and wet plants
I may have to have another look at that, funny thing is although I don't intentionally spray in the rain unless its atrazine I find it takes a lot more than just having the windscreen wipers on. My knowledge on this stems from spraying in the early nineties with a lay farming system. We were typically spraying roundup on large plants later in the season for knockdown. Now I am disappointed if I see ryegrass tillering, meaning I got there too late. These days the weather when we are spraying knockdown (glysophate) it's earlier in the season and there seems to be less dew. Maybe also bigger boomsprays mean we are getting to the paddock a little later.(getting slacker)There's a big difference between plants wet due to a rain and plants wet due to condensation (dew). Plants wet with rain water tend to have large drops of water on them and when they are hit with spray, they tend to roll off the feaf taking much of the chem with it. Dew, OTOH tends to cover the whole leaf with a mass of micro drops and when the spray hits the leaf, the chem spreads over the whole surface of the leaf and does not create a runoff situation. This improved dispersal is why I think most chemicals work as good or better on a dew which is why I asked the question "which chemicals DON'T work". What nig71 describes is what I experience with rain water but not dew. After a rain, I will give a plant a light flick with a finger, if the water runs off, don't spray, if it hangs on, good to go. Not the best test and I would sure like to hear of some better ones.
My rule of thumb is that when the hood is all wet, it's time to shut 'er down. The amount of rain in the window is irrelevant as you are driving into the rain so more rain hits the window (per square inch) than the ground and it's not enough for the plants to get a bit wet, it has to WASH the chem off. That takes quite a bit. Of course, some chemicals I shut 'er down if it only LOOKS like it might rain.funny thing is although I don't intentionally spray in the rain unless its atrazine I find it takes a lot more than just having the windscreen wipers on.