Increased seed cost of glyphosate tolerant (GT) compared to non-GT alfalfa (Medicago sativa L.) raises questions about reducing seeding rates. Th e objective of this study was to determine if alfalfa stand density, yield, and forage quality are compromised in the later years of the stand when reduced seeding rates, in combination with glyphosate application, were used during establishment. At seven locations in the United States, GT alfalfa was seeded into conventionally tilled seedbeds at 6.7, 11.2, 15.7, and 20.2 kg ha -1 pure live seed (PLS) in the spring of 2006. Stand density, yield, and forage quality were determined for each seeding rate under three herbicide treatments: (i) glyphosate [N-(phosphonomethyl)glycine], (ii) non-glyphosate herbicide, and (iii) no herbicide. For the third through fi ft h years of the alfalfa stand, there was no herbicide treatment × seeding rate interaction. Higher seeding rates resulted in higher plant densities. Th e 11.2 and 15.7 kg ha -1 seeding rates had greater alfalfa and total forage (alfalfa + weeds) yields than the 6.7 kg ha -1 seeding rate. Herbicide treatments had no eff ect on alfalfa plant density but produced cumulative (over the duration of the study) alfalfa yield in the following order: glyphosate > non-glyphosate > no herbicide. Cumulative total forage yield was less when no herbicide was used compared to using a herbicide. While forage fi ber content was generally unaff ected by seeding rate or herbicide treatments, using glyphosate to control weeds during alfalfa establishment increased forage crude protein content of older alfalfa stands compared to no weed control.

The ability to predict when a cool‐season forage grass cultivar will begin inflorescence emergence under different ecogeographical conditions would allow plant breeders, agronomists, and grass‐seed marketers to better position that cultivar into a forage production system. Our objective was to determine the ecogeographical factors (longitude, latitude, elevation, day of year when average daily temperature exceeds 0°C for five consecutive days [DOY at 0°C], cumulative growing degree‐day [GDD], photoperiod, and cumulative photosynthetic active radiation [PAR]) that have the greatest effect on grass maturation in the spring. Inflorescence emergence was monitored in established cultivars of festulolium (× Festulolium spp.), orchardgrass (Dactylis glomerata L.), ryegrass (Lolium perenne L. and Lolium multiflorum Lam.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.) at eight locations in North America during the spring of 2004 and 2005. As latitude increased, the day of year when grasses reached 1% inflorescence emergence (DOY) also increased, while cumulative GDD and PAR decreased. Latitude, cumulative PAR, and DOY at 0°C were more closely correlated (r2 ≥ 0.67) to the onset of inflorescence emergence than the other variables. Latitude combined with the inverse transformation of PAR provided the best prediction of when these grasses would initiate inflorescence emergence (validation R2 for all species ≥ 0.83).

Commercial seed of glyphosate‐tolerant alfalfa contains small percentages of seeds, called nulls, that do not posses the herbicide trait. Differential competitiveness of glyphosate‐tolerant seedlings compared with null seedlings may be detrimental to alfalfa stand density if delayed glyphosate application allows the null and tolerant seedlings to compete with each other. Our objective was to determine if delayed glyphosate application affects plant density of glyphosate‐tolerant alfalfa stands. Commercially available glyphosate‐tolerant alfalfa was seeded at 17 and 29 kg/ha, plots were treated with glyphosate one month (3‐ to 6‐trifoliate leaf stage) or one‐year after planting and plant density was monitored throughout the study. Regardless of seedling rate an average of 6.5 and 5.5% of the alfalfa plants died when glyphosate was applied one month and one year after planting, respectively, but plant density remained unchanged during the same time periods when glyphosate was not applied. Planting alfalfa at 17 kg/ha resulted in lower seedling density, but also lower plant mortality during the seeding year than planting at 29 kg/ha. We conclude that delaying glyphosate application to glyphosate‐tolerant alfalfa until one year after planting does not alter the percent of glyphosate‐tolerant and non‐tolerant plants.