No matter how much I do to prevent spring weeds in my grass and garden, I always have some. So what do I do? Well, the tough news is that with Poa annua all I can do is kill it and everything else around it with Roundup or hand pull it. Regardless, the best prevention is a fall application of pre-emergent herbicide. Now for weeds like dandelion and wild onions or garlic, I can kill these and many other spring weeds with a product containing 2,4-D, like Weed-B-Gone. Spray directly onto the plant according to label directions. It has been my experience that repeated application may be necessary. While you might think you can dig or pull these, in both cases you will not get all the roots of dandelion or all the bulbs of wild garlic or wild onions. It is almost impossible to do. Here is one additional tip. I add a teaspoon of liquid dish washing detergent per gallon of mixed herbicide to help the solution stick to the plants better. Never spray when temperatures are expected to go above 85 degrees the day you spray it. Now go out and kill those weeds before they seed.