MANIPULATING SEASONAL GROWTH DISTRIBUTION AND NUTRITIVE QUALITY OF TIMOTHY AND ORCHARDGRASS USING THE GROWTH REGULATOR IMAZETHAPYR

Other than timely defoliation, management options for cool-season grass forages are limited. The growth regulator, imazethapyr (5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid), was evaluated as an agent for modifying seasonal production and nutritive quality of timothy (Phleum pratense L.) and orchardgrass (Dactylis glomerata L.). In 1986, 1987, and 1988 field plots of Toro timothy and Pennlate orchardgrass were treated with imazethapyr (IM) at rates of 50 and 100 g a.i. ha−1, respectively. Three cutting treatments were imposed, involving a progressive delay of first harvest based on the growth stage of the controls. The 0 Delay, Delay 1, and Delay 2 harvests were made when controls were at early head, anthesis (13-d delay), and post-anthesis (26-d delay), respectively. At 0 Delay, imazethapyr treatment increased timothy in vitro dry matter disappearance (IVDMD) by as much as 80 g kg−1, crude protein (CP) by 27 g kg−1, and reduced neutral detergent fiber (NDF) by as much as 150 g kg−1 (3-yr average). Corresponding changes for orchard-grass were 50, 23, and 100 g kg−1, for IVDMD and CP augmentation and NDF reduction, respectively. Nutritive quality of treated Delay 1 forage was similar to that of 0 Delay controls, while that of Delay 2 forage declined substantially. Although first harvest yield was reduced approximately 50% by imazethapyr treatment, second harvests showed a treatment-related yield enhancement, resulting in similar seasonal production for both treated and control forage. Imazethapyr has potential as a management tool to defer timothy and orchardgrass hay harvest for up to 2 wk without incurring significant losses in yield or quality.Key words: Dactylis glomerata, Phleum pratense, forage production, forage quality, growth regultors