Yes, and the tree never has to catch a single drop for it to happen. Two routes carry weed killer to plants you meant to protect. One route runs through the soil into roots. The other rides the air onto leaves. Root uptake is the route homeowners miss, and it causes plenty of herbicide damage to trees standing in or beside a treated lawn. Neither route is ranked as the bigger threat.
I noticed the maple at the fence line where the gravel meets the lawn, deformed new leaves over the turf and clean growth over the gravel. Nobody had sprayed that tree. The grass under it had been treated with a dicamba product, and dicamba moves in soil, so the roots below pulled it in and sent it up the trunk.
That is the soil route, and it works because roots do not stop at the trunk. They spread out under the lawn well past the branch tips, so the grass you treat sits on top of a feeding network. Trees and shrubs are sensitive to dicamba, since the product stays mobile in soil instead of locking in place. Most dicamba tree damage starts under the turf.
The air route splits into two things people mix up. Herbicide drift is spray blowing off target while it leaves the nozzle, so you can see it and stop. Volatilization happens later. The product lands where you aimed, then turns to vapor and moves onto whatever grows nearby. Heat is the trigger. Run the sprayer on a day hotter than the label allows and a growth regulator is more likely to volatilize and hit sensitive plants.
The rates that cause trouble are small. Penn State Extension puts the deforming rate at 1 ounce (28 g) per acre for growth regulators such as 2,4-D and dicamba. Tobacco, grapes and tomatoes sit on that sensitive list. You would struggle to see that much product in a full tank. Over broadleaf ornamentals the same two actives are not safe as a general rule, so azaleas and roses count as targets rather than bystanders.
Damage rarely shows up while you are standing there with the sprayer in your hand. Root-taken product has to move up the trunk before anything odd appears on new growth. That gap is why people blame drought or a bad planting job instead of the weed killer they put on the lawn.
- Change the product: Keep dicamba off turf that sits over tree and shrub roots, and those roots run far past the branch tips.
- Watch the thermometer: Spray inside the labeled temperature window, since heat is the documented driver of volatilization.
- One sprayer, one job: The only way to be certain a sprayer is clean is to never put a harmful herbicide in it, so keep one dedicated to weed killers.
- Pull weeds by hand in planted beds and get the roots out, because many weeds regrow from the underground parts you leave behind.
The fix on the turf side is a swap, not a technique. Pick a broadleaf product without dicamba for grass that sits over tree and shrub roots, then accept slower results on the tough weeds. Spot-treat the patches you can point at instead of blanket-spraying the whole yard.
In vegetable beds I skip the sprayer. Hand weeding stays part of the work there, and you have to extract the roots or the plant comes back from what is left underground. It takes longer than a spray pass. It also cannot drift onto your tomatoes, and tomatoes deform at rates you can barely measure.
Read the full article: How to Choose a Weed Killer That Actually Works
