Hot weather and lawn weed killers, called herbicides, do not mix well. Spraying a lawn with an herbicide when temperatures are too high can damage or even kill your grass.
Most herbicide labels include a warning like this: “Do not use this product when temperatures are expected to be 85°F or higher.”
Knowing when to use herbicides is important and correct timing is key.
Weeds that are growing now are summer weeds. And winter weeds are not growing yet. Right now, winter weeds are still seeds waiting for cooler weather before they begin to grow. It’s the summer weeds that are in our lawns now.
Some common summer weeds that are visible now in lawns include crabgrass, goosegrass, spurge, Florida pusley, doveweed, sandbur and poorjoe. Some common winter weeds that come up and grow in fall and winter include annual bluegrass, chickweed, henbit, hop clover, lawn burweed, and wild geranium.
To prevent winter weeds, apply a preemergence herbicide for lawns during October when nighttime temperatures stay between 55°F and 60°F for several nights in a row. This is just before winter weeds begin to grow.
To prevent summer weeds, apply a preemergence herbicide during February when daytime temperatures stay between 65°F and 70°F for four or five days in a row. This is just before summer weeds begin to grow.
Do not spray herbicides on summer weeds while the weather is still hot. You may kill the weeds, but you could also damage your lawn. Instead, keep mowing your grass and let the first hard frost or freeze kill the summer weeds. Then, plan to apply a preemergence herbicide in February to help stop them from growing again.
If your lawn usually has winter weeds, plan to apply a preemergence herbicide in October to help stop them from growing.
When used correctly, a preemergence herbicide forms a barrier on the soil surface. This barrier keeps annual weed seeds from growing, helping break the weed’s life cycle.
For season-long weed control, you may need a second application of preemergence herbicide 6 to 9 weeks after the first one.
Before using any pesticide, including herbicides, read and follow all label directions and safety precautions.
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