To Let Wither
To Kill A Plant, To Let Something Dry Up
transitive verb, godan verb
You learned 枯れる (to wither), but this is when you're the one making a plant wither, so it means to let wither or to kill a plant.
枯らす literally means to let something dry up, usually by neglect or lack of water (though too much water can also 枯らす plants). It's often used when someone accidentally lets plants die, but it can also describe intentionally killing plants with a herbicide. You'll also see it used figuratively, like 声を枯らす (to lose one's voice).
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You already learned this reading when you learned 枯れる, so you should be able to read this word as well.
水をやりすぎて、サボテンを枯らしてしまいました。
I gave the cactus too much water and killed it.
パパが水やりを忘れて、ママの大切なお花を枯らしちゃったの。
Dad forgot to water the plants and ended up letting Mom's precious flowers die.
農家は除草剤で雑草を枯らし、作業の効率化を図っています。
Farmers kill weeds with herbicides to make their work more efficient.
「声を枯らして訴えた」という言葉通り、彼女は全力で訴え続けました。
True to the phrase "shouting herself hoarse," she continued to appeal with all her might.