Answer:
"The success of the steam application on weed burndown depends on a thorough canopy and stem penetration. For instance, the steam application was found to be relatively ineffective on certain weeds, like pusley, due to their prostrate (creeping) growth nature, which prevents an adequate coverage of steam on the entire plant....some of these weeds are adapted to grow back from the steam burndown." -VSC News
Step-by-step explanation:
I googled it and found this on a news website, so these are not my words. :) I hope this helps.