No. A homemade weed killer mix belongs in the tank at the strength printed on the bottle, and that number is not a suggestion. The pesticide label is the law, so the herbicide label rate is your ceiling and your target at the same time. Pouring in extra product will not rescue a spray that already failed.
A tank that failed is worth checking against the thermometer and the calendar before you blame the measuring cup. Post-emergent broadleaf products want air between 65°F and 85°F (18°C and 29°C). When it gets hotter than that, more of the spray turns to vapor and drifts onto plants you meant to keep, so the weed lives and a nearby tomato takes the damage.
Doubling the dose does not double the kill. A weed takes up what it can hold and the rest sits on the leaf or runs into the soil, where it can linger long enough to bother the next thing you plant. Your grass has limits too, and it feels a hot mix as fast as the weed does. None of that touches the real cause, which is often a weed the product was never rated for.
The missing ingredient is usually not more herbicide. Penn State Extension reports that more than 70% of all herbicides recommend one or more adjuvants in the spray mixture. An adjuvant is a helper, and the common kind is a surfactant that thins the droplet so it spreads across a waxy leaf instead of beading up and rolling off. A weed with a slick coating can shed most of a spray that has no surfactant behind it.
Get the weed killer dilution right and you have done the bulk of the job. Use a marked measuring cup, not a bottle cap and not your eye, and mix only what you plan to spray that day. Leftover mix sitting in a warm shed is a hazard and a waste.
Mow or trim the weeds a few days before you spray. That step alone can lower the amount of herbicide you need.
Wait for a mild day inside the temperature window the label gives. Heat pushes the spray into vapor and sends it where you did not aim.
Fill a marked cup and hit the rate on the label exactly. There is no bonus for rounding up, and there is real risk in it.
If the label calls for a surfactant or a crop oil, add it at the listed amount. That is the legal way to make a spray work harder.
Mark a sprayer for weed killers and use it for nothing else. Rinsing gives you no guarantee, so a dedicated tank is the only sure answer.
The reason for that dedicated tank shows up in how small the numbers get. Growth-regulator herbicides can deform sensitive crops such as tobacco, grapes or tomatoes at 1 ounce (28 g) per acre. That is a trace across a whole field, which tells you how little residue it takes to warp a plant you never sprayed.
Before you mix again, write down what went in the tank, the date, and how warm the air was. Two failed passes with the same product on the same weed tell you far more than any change in strength ever will. A weed that comes back from its roots may need a second pass on a later date instead of a heavier one, and the calendar settles that question, not the measuring cup.
So fix the timing first, then add the adjuvant the label names. The amount in the measuring cup stays fixed through all of it. If a correct spray fails you twice on the same patch, you are holding the wrong product for that weed, and a hotter tank will never fix that mismatch.
Read the full article: How to Choose a Weed Killer That Actually Works
