|Abstract:||Studies were conducted (1) to determine H. glycines egg hatch and emergence of second-stage juveniles (J2) from cysts exposed to soybean root leachate in vitro and under field conditions, (2) to determine effect of six soil-applied herbicides on hatch and emergence, (3) to clarify the distribution of H. glycines races in Illinois. Cysts of H. glycines were exposed to root leachate of H. glycines-resistant Fayette soybean and H. glycines-susceptible cultivars A2575, A3127, and Williams 82 in vitro for different numbers of days. Field populations of H. glycines eggs were monitored at two sites. Leachate from 8-week-old Williams 82 and A3127 plants stimulated the most hatch and emergence. There was no apparent relationship between leachate from a cultivar and the population that developed on that cultivar. A2575 stimulated more hatch and emergence and Fayette less when cysts were exposed to leachate from soybeans as the plants developed 7-59 days after planting. Hatch and emergence was greatest during the initial 12 days of the experiment. Leachate from A2575 grown in autoclaved soil and Fayette grown in nonautoclaved soil stimulated the most hatch and emergence. Numbers of eggs decreased at both field sites though few differences among treatments were observed. Soil-applied herbicides alachlor, imazaquin, metolachlor, metribuzin, trifluralin, and vernolate were evaluated under laboratory conditions at concentrations of 0.0, 1.0, 3.0, 5.0, and 10.0 ppm of active ingredient in root leachate of 7-day-old Williams 82 soybean. Herbicide treatments and the root leachate control did not differ except for alachlor (10.0 ppm). Metribuzin (1.0 ppm) and (3.0 ppm) stimulated the most hatch and emergence, whereas alachlor (5.0, 10.0 ppm) stimulated the least hatch. Race determinations of 44 populations of H. glycines from 23 Illinois counties were done using Lee 68 and Williams 82 as the susceptible standards. Twenty-eight populations were race 3, twelve were race 1, two were race 5, and there was one each of race 2 and 4. Populations of race 3 and 1 were widely distributed in the state. Only two tests differed according to the choice of susceptible standard, indicating that Williams 82 can be used if seed of Lee 68 is not available.