Search

Field experiments were established on September 7, 1968, and Hay 13 and July 16, 1969, by seeding three rates (on pure live seed basis [PLS]) of several companion grasses with a constant rate of Kentucky bluegrass (Poa pratensis L.). Mixtures were irrigated and clipped to 1- and 2-in. sod residues. Objectives were to determine which mixture or mixtures could provide rapid initial establishment. with subsequent high quality, permanent turf. The improved perennial ryegrasses (Lolium perenne L.) (NK-100 and Pelo) were no more competitive in the seedling stage toward Kentucky bluegrass (Poa pratensis L.) than annual ryegrass (Lolium multiflorum L.), but they provided as rapid initial cover. However, their persistence provides a means for bluegrass encroachment during the seedling year. Seedling competition was not due to any excretions from ryegrass seeds or seedlings. Turf quality of the improved perennials was superior to annual ryegrass, but slightly lower than pure bluegrass, because of frayed leaf tips. Redtop (Agrostis alba L.) and creeping red fescue (Festuca rubra L.) were less competitive to bluegrass than the ryegrasses, but they provided little advantage in ground cover; however, turf quality was similar to pure bluegrass. It was concluded that mixtures should be designed to obtain designated populations of companion and other seedlings that are needed for sufficient initial cover. The 5% PLS in this study was higher than normally recommended on a weight basis; therefore there was no advantage from higher seeding rates. Fall seeded mixtures generally contained the most Kentucky bluegrass, and the summer seedings had the least. Low clipping reduced competition from companion grasses, especially the improved perennial ryegrasses, which allowed a uniform transition toward bluegrass dominance with turf of average quality. Sod strength was best for the pure bluegrass turf, but root development of the improved perennial ryegrasses was best. Master of Science

The effectiveness of 5-bromo-3-sec-butyl-6-methyluracil (bromacil) for the selective removal of orchardgrass (Dactylis glomerata L.) from Kentucky bluegrass (Poa pratensis L.) turf and some physiological responses of the grasses to bromacil were evaluated in field studies. Bromacil reduced photosynthesis to a greater extent in orchardgrass than Kentucky bluegrass turf. Foliage carbohydrates were depressed initially in bluegrass followed by recovery in 2 weeks to 1 1/2 months following bromacil application. Orchardgrass, however, did not recover. Application of 0.56 kg/ha bromacil each summer and fall for 2 years gave the best control of orchardgrass. During the second year, increase in foliage crude protein was observed in treated bluegrass. Bluegrass foliage yields were equal to or greater than the controls. Orchardgrass yields were drastically reduced by bromacil. Effective seedling orchardgrass control was obtained with minimal bluegrass injury at 0.14 to 0.28 kg/ha of bromacil. Bromacil treated areas were effectively fall-seeded with bluegrass approximately 8 weeks after a 0.56 kg/ha application, Rooting of bluegrass sod was not inhibited at the rates used for selective control of orchardgrass in bluegrass turf. In controlled environmental growth chamber studies, bromacil had no effect on germination of Merion Kentucky bluegrass or Virginia Common orchardgrass, but reduced the growth of emerging shoots of orchardgrass more than bluegrass. Fresh weight gain, root growth, and transpiration were reduced in orchardgrass plants at 0.125 ppmw bromacil whereas 1.0 ppmw gave reductions in bluegrass. Photosynthesis was inhibited initially in both grasses, however, bluegrass recovered in 6 days. Foliage carbohydrate content was greater and was affected less by bromacil treatment in bluegrass than orchardgrass. Root absorption and translocation of 2-¹⁴C-bromacil to the shoot was directly related to transpiration in both grasses. Bromacil was absorbed and translocated acropetally in sheath and foliar treatments in both grasses. Higher metabolic conversion of 2-¹⁴C-bromacil occurred in bluegrass as compared to orchardgrass with 1.0 ppmw treatment. The major metabolites were 5-bromo-3-(2-hydroxy-1-methylpropyl)-6-methyluracil and an unknown. Trace amounts of 3-sec-butyl-6-methyluracil and 5-bromo-3-sec-butyl-6- hydroxymethyluracil were also detected. Bluegrass tolerance to bromacil involves high carbohydrate levels in tissues, hydroxylation of bromacil, and rapid recovery of photosynthesis. Ph. D.