weeding is not necessarily burning the plant, but rather causing a lethal wilting by denaturing proteins in the weed. Similarly, hot air weeders can heat up the seeds to the point of destroying them. Flame weeders can be combined with techniques such as stale seedbeds (preparing and watering the seedbed early, then killing the nascent crop of weeds that springs up from it, then sowing the crop seeds) and pre-emergence flaming (doing a flame pass against weed seedlings after the sowing of the crop seeds but before those seedlings emerge from the soil—a span of time that can be days or weeks). Hot foam causes the cell walls to rupture, killing the plant. Weed burners heat up soil quickly and destroy superficial parts of the plants. Weed seeds are often heat resistant and even react with an increase of growth on dry heat. Since the 19th century soil steam sterilization has been used to clean weeds completely from soil. Several research results confirm the high effectiveness of humid heat against weeds and its seeds.<ref>Research report of DLR Rheinlandpfalz, September 2010: [http://www.soil-steaming-steam-boiler-blog.com/wp-content/uploads/2010/10/steaming-research-results_dlr2010.pdf Weed control in seed cultures, especially arugula], Author: Dr. Norbert Laun, Institute "Queckbrunnerhof", Schifferstadt (Germany). Viewed on 14. February 2011.</ref> Soil solarization in some circumstances is very effective at eliminating weeds while maintaining grass. Planted grass tends to have a higher heat/humidity tolerance than unwanted weeds. Lasers In precision agriculture, novel agricultural robots and machines can use lasers for weed control, called "laserweeding". Their benefits may include "healthier crops and soil, decreased herbicide use, and reduced chemical and labor costs". Seed targeting In 1998, the Australian Herbicide Resistance Initiative debuted. gathered fifteen scientists and technical staff members to conduct field surveys, collect seeds, test for resistance and study the biochemical and genetic mechanisms of resistance. A collaboration with DuPont led to a mandatory herbicide labeling program, in which each mode of action is clearly identified by a letter of the alphabet. The key innovation of the Australian Herbicide Resistance Initiative has been to focus on weed seeds. Ryegrass seeds last only a few years in soil, so if farmers can prevent new seeds from arriving, the number of sprouts will shrink each year. Until the new approach farmers were unintentionally helping the seeds. Their combines loosen ryegrass seeds from their stalks and spread them over the fields. In the mid-1980s, a few farmers hitched covered trailers, called "chaff carts",