Annual bluegrass (Poa annua L.) emergence under different residue management practices in perennial ryegrass and determination of resistant and susceptible annual bluegrass germination under controlled temperature and moisture

Graduation date: 2000With the loss of field burning the amount of crop residue that remains in\ud perennial ryegrass fields has increased. As the amount of crop residue remaining in the\ud field increases so does annual bluegrass. This has resulted in the increased use of\ud herbicides to control annual bluegrass. However, this increased use has also resulted in\ud herbicide-resistant annual bluegrass. Field experiments were initiated in 1997 to\ud investigate residue management options available to growers and their impacts on\ud annual bluegrass emergence. Two sites, Glaser and Wirth, were established with three\ud residue management treatments replicated four times. The treatments included full-straw,\ud bale/flail, and vacuum sweep. Perennial ryegrass seed yield and annual bluegrass\ud seed contamination were evaluated. The vacuum sweep treatment had lower annual\ud bluegrass emergence than the full-straw or the bale/flail treatments during the 1997-98\ud growing season, for both sites. The fall of 1998 was much drier than the fall of 1997.\ud Annual bluegrass emergence in all plots was lower in 1998 than in 1997 because of the\ud dry conditions. Fall emergence in 1998 was higher in the vacuum sweep treatment than\ud in the other two treatments, which may have been the result of better soil-seed contact\ud in the vacuum sweep treatment. Lower emergence in the spring at the Wirth site\ud compared to the Glaser site may have been due to narrow crop row spacing and cultivar\ud selection, which shaded the annual bluegrass. When growing seasons were combined,\ud there were no treatment differences. However, more emergence was observed in the\ud spring at the Glaser site compared to the Wirth site. Yield was highest for the vacuum\ud sweep treatment at the Glaser site in the 1998-99 growing season. However,\ud competition from volunteer perennial ryegrass in the full-straw and bale/flail treatments\ud could have accounted for this increase. No other differences in yield and no difference\ud in contamination among treatments were observed. However, contamination at the\ud Glaser site was higher in the 1998-99 growing season than in the 1997-98 growing\ud season.\ud Experiments were conducted in growth chambers to determine how differing\ud environmental conditions affect seed germination of diuron-susceptible and diuron-resistant\ud annual bluegrass. Cumulative germination for the susceptible-biotype\ud decreased from 96% to 88% while the resistant-biotype remained above 95% as\ud temperature decreased from 3 0/20 C to 10/2 C. The susceptible-biotype germinated\ud sooner than the resistant-biotype regardless of temperature. The susceptible-biotype\ud had a higher rate of germination than the resistant-biotype at 30/20 C, but not when the\ud temperature decreased to 10/2 C. Germination response to differing matric potentials\ud did not vary much within a biotype for a given soil type and temperature. Therefore,\ud parameters estimated at -1.03 MPa were chosen to contrast susceptible- and resistant biotypes,\ud and soil types, for each temperature. Maximum cumulative germination was greater than 96% for all treatments. When germination on a given soil type was\ud contrasted, differences were only seen for the susceptible biotype vs. resistant biotype\ud on Dayton soil; and the resistant biotype on Dayton soil vs. resistant biotype on\ud Woodburn soil at both temperatures. The lag in onset of germination was shorter for\ud the susceptible biotype on Dayton soil and resistant biotype on Woodburn soil than the\ud resistant biotype on Dayton soil at 30/20 C. At 18/5 C, the lag in onset of germination\ud was shorter for the susceptible biotype on Dayton soil and resistant biotype on\ud Woodburn soil than the resistant biotype on Dayton soil (P = 0.000 1 and 0.0001,\ud respectively). But the rate of germination was faster for the resistant biotype on Dayton\ud soil than both the susceptible biotype on Dayton soil and resistant biotype on Woodburn\ud soil at 18/5 C (P = 0.02 and 0.0004, respectively). The rate of germination did not\ud differ at 3 0/20 C. When just the soils were contrasted, at 18/5 C all annual bluegrass\ud seeds on the Woodburn soil germinated sooner and the rate of germination was higher\ud than on the Dayton soil. These results indicate that the hydraulic properties of the soils\ud may influence germination. However, this was not observed at 30/20 C. The results\ud suggest that the susceptible-biotype was more sensitive to temperature while the\ud resistant-biotype was more sensitive to moisture. Changing crop management in ways\ud that will reduce annual bluegrass emergence and establishment is needed. By altering\ud management strategies, growers may obtain more efficient and effective use of\ud herbicides, while reducing the selection of herbicide-resistant annual bluegrass