During thermal weed control a high temperature medium exterminates weeds and culture plants without distinction. The problem of preserving germinating plants from thermal extermination therefore arises. Stable foam can be used to protect germinating agriculture plants from the thermal extermination. Using 100C water steam for weed control for the sprouted carrot crop, till 40 days after the sowing, was investigated, and it was found that it is necessary to use preservatives. Extermination of carrots without preservatives depends upon the carrots' development stage. It is advisable to use stable foam for plant protection from extermination, when biometric parameters of weeds and agricultural plants are similar. Sprouting agricultural plants covered with a stable foam layer are completely protected from thermal extermination, when 100C water steam is sprayed at a distance of 8 cm to the plant. In the foam covered plant medium the temperature reached 39C+4.2.