We have gotten some much appreciated rain but the grasses will come to the end of their life cycles soon. Some have already turned brown. The impulse to cut them down is understandable. Let me give you an excuse to procrastinate if you are plagued with yellow star thistle. I am sure you know of what I speak. It can be eradicated with timely mowing. YST is an annual, growing anew each year from seeds. Most of the other weeds are annuals, too, but their life cycles have a useful difference. The majority of the weeds will produce seeds and die soon, earlier than the star thistle. Traditionally, YST does not comes to full bloom until the Fourth of July.
When YST is in full bloom and its flowers are bright yellow, you want to make your attack. The plants have put their best effort into making those flowers. Cut it then and you will vastly reduce its ability to produce a large volume of seeds that will sprout next year. YST has an amazing ability to regenerate and will flower again but they will be smaller, inferior flowers that produce fewer viable seeds. If you can, cut them again. I use a lawnmower but a string trimmer will work. I like the lawnmower because it chops the plants up into a mulch that covers the other seeds, and reduces the opportunity for the thorns to get you.
By waiting until after the other plants have gone to seed, they will be ready to germinate next season and fill the space, which will help crowd out YST. YST is not a good competitor and does not do well in the shade. You may want to augment the seeds from the other weeds with something like cereal rye. It does very well without cultivation or irrigation. It grows tall and thick, leaving the YST no room and in the shade. Join the Campaign Against Star Thistle and roll back the invasion.