Answer: The good new is that yellow star thistle is an annual plant. The bad new is that it's not very pleasant to deal with because of the sharp spines on the stems. Since it's an annual, it spreads by seed. If you can keep the plants cut down so they don't develop flowers and set seeds, you can control the population of yellow star thistles. The first line of defense is to survey the yard every few days and cut down to ground level any weeds you find. Eventually the roots will run out of energy and won't be able to produce new shoots. Any weeds that have already grown to flowering size should be cut down before the flowers set seeds. This is labor-intensive but very effective, and safe for the rest of the landscape. A second method of control is flaming, where you pass a flame over the weeds - not to incinerate them but to heat the fluid within the tissues just enough to burst the cells. Most flamed weeds will die within 24 hours.
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