Chief researcher J.H. Tumlinson said the findings highlight the complexity of plant-insect interactions underlying plant defense responses to herbivorous insect attacks. Rhizobacteria live on or within a few millimeters of roots. As roots grow through the soil oozing juices in their wake, the microbes feed on the substances. These trigger cells of some plants to produce excessive hormones. Weeds weakened by DRB toxins are less able to compete with other plants, such as field crops and forage plants, for soil nutrients, moisture and sunlight.
Wimpier weeds are also more vulnerable to other controls.
Leafy spurge, a Eurasian native, infests at least 29 states. So far, Kremer and colleagues have tested thousands of strains of DRB at the agency's Cropping System and Water Quality Research Unit. About 30 percent are highly toxic to leafy spurge. Many have reduced root growth in preliminary field tests. Some DRB may prove better suited than others for mass production and commercial use.