A sample of the weed's closest native U.S. relatives is also treated. A high-tech filtration system also keeps tiny, floating particles and airborne spores from leaving the greenhouse. To further ensure that nothing escapes the facility, a waste disposal system sterilizes any effluent generated. This includes water from plant beds, toilets, and showers where scientists and technicians wash off any seeds, pollen, or spores. Putting Pathogens Through the Paces One method of checking a weed pathogen's virulence is counting the number of pustules or lesions that pepper a plant's leaves.
Scientists also measure plant height, weight, growth rate, mortality, and seed production.
They also determine the environmental conditions under which pathogens are most likely to grow best and cause disease. For example, a weed pathogen or insect can vanish after it's been released, only to reappear in force months or even years later. Classic biocontrol is generally slower acting than chemical pesticides, so noticeable results may take several years. But once those results generally kick in and are observed, they're permanent. One exception is if a weed marshals a natural defense against the pathogen recruited to fight it, though evidence of potential resistance is usually noted in greenhouse evaluations.