Evaluation location: Iowa, United States
A total of 1,167 lines were evaluated in tests consisting of from 1 rep in 1 year to several hundred reps spread over multiple years. Lines were planted in single-row plots consisting of five 3-plant hills (40 inches. between hills) or in single-row plots containing 16 plants (about 10 inches between plants). Rows were spaced by 40 inches.
Usually 6 to 16 plants at midwhorl stage of development were infested with 4 egg masses giving an infestation of approximately 80-100 eggs per plant. In most years 2 masses were placed on plants in each of 2 dates approximately 3-7 days apart when lines were 18-32 inches in extended leaf height. At 3-4 weeks after egg hatch lines were rated for damage on a plot basis.
A 9 class rating scale was used with 1-2 considered highly resistant, 3-4 resistant, 5-6 intermediate in resistance, and 7-9 were highly susceptible.