Greenhouse trials were conducted to evaluate graminicidal resistance of selected ornamental grasses. Blue fescue cultivars ‘Blue Glow’, ‘Sea Urchin’, ‘Spring Blue’, and ‘Superba’ were resistant to 1× (medium use rate) and 2× rates of fenoxaprop, fluazifop-P, quizalofop, and sethoxydim, whereas fountain grass, ravenna grass, and switchgrass were sensitive. Minor (<20%) visible phytotoxicity was observed on some fescues treated with the 2× rate of fluazifop-P at 14 but not at 69 days after treatment (DAT). Fountain grass, ravenna grass, and switchgrass exhibited severe (>70%) phytotoxicity from all herbicides 69 DAT. Mortality of non-fescues ranged from 55% (fountain grass) to 96% (ravenna grass).

Atrazine metabolism was studied in four warm-season forage grasses to determine if metabolism was the basis for differential atrazine tolerance among the grasses. Big bluestem and switchgrass are atrazine tolerant while indiangrass and sideoats grama are atrazine susceptible in the seedling stage. Metabolism of atrazine in big bluestem and switchgrass occurred primarily by glutathione conjugation. The major metabolic product isolated from indiangrass and sideoats grama was the N-deethylated metabolite of atrazine. Glutathione conjugation by big bluestem and switchgrass occurred at a faster rate than N-dealkylation of atrazine in indiangrass and sideoats grama. Differential tolerance to atrazine among the grasses studied was probably due to the metabolic route by which they detoxify atrazine and the rate of metabolism for that specific route. Intraspecific differences in atrazine tolerance in indiangrass were due to the amount of metabolite produced in relationship to the amount of parent atrazine remaining in the shoot tissue. The more tolerant indiangrass lines had a higher metabolite to parent atrazine ratio than susceptible lines. This study confirmed differences in seedling atrazine tolerance of four indiangrass lines observed in previous greenhouse studies.

Experiments were conducted near Scottsbluff, NE in 1991 and 1992 to evaluate the selectivity of imazethapyr for weed control in blue grama, intermediate wheatgrass, little bluestem, Russian wildrye, switchgrass, and western wheatgrass. Imazethapyr reduced weed biomass in all seedings and injured all perennial grasses 12 days after treatment (DAT). Imazethapyr reduced the height of intermediate wheatgrass, Russian wildrye, and switchgrass 35 DAT. Russian wildrye, and switchgrass biomass 50 DAT was reduced by imazethapyr. Weed biomass in new seedings of intermediate wheatgrass and western wheatgrass were reduced more than that of the other grasses.

Switchgrass (Panicum virgatum cv. Alamo) standing hay was cut and offered to 16 rams. The rams were randomly allocated to one of the following levels of feeding: 0·5; 1·0; 1·5 and 2·0 ✕ maintenance. The forage was offered twice a day to the animals; no supplements were given. The animals were individually penned and fitted with faeces collection bags. After 8 days for adaptation, in vivo dry matter apparent digestibility (DMD) and proportion of blades and stem + sheath of the consumed forage were measured for 8 days. DMD varied from 0·310 (0·5) to 0·391 (2·0) and the proportion of the blade fraction in the diet from 0·44 (0·5) to 0·78 (2·0). The short-term intake rate (STIR) of rams was measured for 5 days. The animals were divided randomly into four blocks, with one ram of each treatment in each block. After 4 h without food and 15 min intervals between blocks, the amount of forage consumed during 4 min of active eating was measured. The amounts consumed were (in g DM per min per 50 kg live weight): 0·5: 8·2; 1·0: 7·8; 1·5: 5·3 and 2·0: 5·3 (0·5 = 1·0 > 1·5 = 2·0; P < 0·01). The results show that offer rate of P. virgatum affects the blade: stem + sheath ratio of intake and, therefore, the nutritive value of the diet. Level of feeding before measuring STIR influences the amount of forage consumed during the test.