No abstract

Summary The effects of intensity, duration and spectral quality of light were investigated on the germination of Galium spurium L. Light inhibited germination and the degree of this inhibition was related to the intensity and duration of exposure to light beyond the initial 36‐h imbibition period. Subsequent dry storage for up to 7 weeks and reincubation in the dark did not remove this inhibitory effect, indicating that a secondary dormancy was induced by continuous exposure to light. Germination was completely inhibited with intermittent 1‐h exposures of light every 3, 7 or 11 h for 8 days. Red, far‐red and blue light inhibited germination and the degree of inhibition was related to the duration of exposure. Far‐red light was more inhibitory than red or blue light. Green light promoted germination slightly. Nitrate salts in the medium during light exposure did not prevent the onset of light‐induced dormancy. In subsequent dark incubation, light‐induced dormancy was overcome by the addition of nitrates and, to a lesser extent, by kinetin and GA3.

The long-term effect of repeated late-fall versus early-spring imazethapyr, hexazinone, terbacil, metribuzin, dichlobenil, or chlorsulfuron treatments, when applied on dormant stands of alfalfa was investigated at three sites for weed management of alfalfa grown for seed. Dichlobenil applied at 1.2 to 2.4 kg ha−1and chlorsulfuron applied at 11 to 22 g ha−1in fall or spring were the only herbicides to injure alfalfa at one location. Hexazinone provided the most consistent weed control of the herbicides evaluated. Average control of Canada thistle, catchweed bedstraw, dandelion, perennial sowthistle, quackgrass, Russian pigweed, and scentless chamomile was 80%. When averaged over three sites, weed control by hexazinone resulted in a 33% increase in seed yield.

During the establishment of alfalfa, POST applications of imazethapyr at 50 g/ha, following PPI applications of trifluralin at 1,100 g/ha, consistently provided ≥ 80% control of wild oat, volunteer canola, and shepherd's-purse with no crop injury. POST applications of the same rate of imazethapyr without PPI applications of trifluralin provided similar volunteer canola and shepherd's-purse control, but ≥ 80% wild oat control was achieved only 25% of the time. Imazethapyr, alone or following trifluralin, did not control common groundsel. Broadleaf weed control from imazethapyr at 50 g/ha tank mixed with fluazifop-P at 125 g/ha or sethoxydim at 200 g/ha was not reduced compared to imazethapyr alone. However, the probability of controlling wild oat by ≥ 90% was reduced from 83% to 0 when the same rate of imazethapyr was tank mixed with fluazifop-P, compared to fluazifop-P alone. Tank mixtures of imazethapyr at 50 g/ha and sethoxydim controlled wild oat only slightly less than sethoxydim alone. First cut and total herbage yields, obtained 1 yr after alfalfa establishment, increased where treatments effectively controlled broadleaf weeds and wild oat, compared to check plots. Second cut herbage and seed yields, also obtained 1 yr after alfalfa establishment, were not affected by any of the treatments.

Can.