Alfalfa was grown hydroponicalHy in 0, 0.6, and 4.8 millimolar K in order to determine the influence of tissue level of K on photosynthesis, dark respiration, photorespiration, stomatal and mesophyll resistance to CO2, photosystem I and II activity, and synthesis and activity of ribulose 1,5-bisphosphate carboxylase (RuBPc).A severe (0.0 millimolar) and mild (0.6 millimolar) K deficiency, compared to plants grown at 4.8 millimolar K, produced a significant decrease in photosynthesis and photorespiration, but an increase in dark respiration.Both deficient K levels increased hydrophyllic resistance to C02, but only the severe deficiency increased stomatal resistance. Photosystem I and II activity of isolated chloroplasts was not affected by K deficiency. The apparent activity of a crude RuBPc preparation was significantly reduced in severely deficient plants. Activity of the enzyme could not be restored to normal rates by the addition of K to the reaction medium.The specific activity of RuBPc isolated from severely K-deficient and K- K deficiency has been shown to reduce the rate of photosynthesis in numerous higher plants (2,10,12,13,18,19). Cooper et al. (3) attributed the decrease in photosynthesis of K-deficient alfalfa to a decrease in stomatal number and aperture size. Reduction in photosynthesis of K-deficient corn was attributed to increased stomatal resistance (4, 9). A combination of increased stomatal and mesophyll resistance to CO2 was thought to reduce photosynthesis in K-deficient sugarbeets (20, 21). Since K is the major solute in turgid guard cells (6), it is reasonable to suggest that K deficiency will result in stomatal closure. In the presence of Na, low K increased stomatal resistance less, but mesophyll resistance remained high (21). These results suggest that the role of K in regulating photosynthesis may be within mesophyll cells. (NO3)2 was 6.5, 6.2, and 4.6 and that of CaCl2 was 0, 0.3, and 2.4 mm for the 0, 0.6, and 4.8 mm K solutions, respectively. One plant per crock was established and the crocks were arranged in a completely randomized block design with eight replications. Crocks were subirrigated every 2 h during the day and every 4 h at night. Nutrient solutions were changed every 2 weeks. The temperature in the greenhouse was 25/20 ± 5 C day/night, and the average daily solar radiation was approximately 310 cal cm-2 day-'. Plants were cut back to a 5-cm stubble when they reached the 'ho bloom stage and had attained approximately 20 days of regrowth (early bud stage) at the time of measurement.Gas Exchange. Photosynthesis, transpiration, dark respiration, and stomatal and mesophyll resistance to CO2 diffusion were measured on 20 individual attached leaves (fourth fully expanded leaf from the top) per treatment using an air-sealed leaf chamber (26)

Long-term control of downy brome with an integrated approach is needed in order to sustain range productivity. Studies were conducted to study the effectiveness of a combination of downy brome control practices. In two studies, glyphosate and paraquat were evaluated at various rates for up to three successive years for control of downy brome in rangeland. A third study evaluated the competitiveness of perennial cool-season grasses against downy brome in the absence of herbicides. Glyphosate, at 0.55 kg/ha, and 0.6 kg/ha paraquat provided selective downy brome control on rangeland when applications were combined with intensive grazing. Downy brome control was greater than 90% following two sequential years of 0.6 kg/ha paraquat at either the two- to eight-leaf stage or bloom stage at both study locations. At one study location, 0.55 kg/ha glyphosate provided 97% control after the first application at both growth stages. In the second study, control averaged greater than 92% following three sequential applications of glyphosate. When perennial cool-season grasses were seeded in the spring following fall tillage (no herbicides) and allowed to establish for three growing seasons, three of the five species were effective in reducing the reestablishment of downy brome. ‘Luna’ pubescent wheatgrass, ‘Hycrest’ crested wheatgrass, ‘Sodar’ streambank wheatgrass, ‘Bozoisky’ Russian wildrye, and ‘Critana’ thickspike wheatgrass controlled 100, 91, 85, 45, and 32% of the downy brome, respectively. Yields of perennial grass dry matter were 1,714, 1,596, 1,135, 900, and 792 kg/ha. Replacing noncompetitive annual grasses with competitive cool-season perennials will provide a longer term solution to a downy brome problem than the use of herbicides alone or with intensive grazing.

Studies were established near Devil's Tower in Crook County, WY, to determine the potential of 11 grass species to compete with leafy spurge as an alternative to repetitive herbicide treatments. Of the 11 species, ‘Bozoisky’ Russian wildrye and ‘Luna’ pubescent wheatgrass showed the most promise for successful competition with leafy spurge and were selected for further study. Pubescent wheatgrass limited percent canopy cover of leafy spurge to 10 and 15% or less in tilled and no-till plots, respectively, 7 and 10 yr after seeding. Russian wildrye limited percent canopy cover of leafy spurge to 21% or less in tilled and 7 and 27% in the no-till plots, respectively, 7 or 10 yr after seeding. The control plots not seeded to a forage grass averaged 55% leafy spurge canopy cover.

Russian knapweed [Acroptilon repens (L.) DC.] is a creeping, perennial, unpalatable, noxious weed that infests thousands of rangeland and pasture hectares in the western U.S. often forming monocultures. Chemical or mechanical control of Russian knapweed usually is temporary allowing re-invasion of the weed over time. Our objective was to determine whether combining chemical or mechanical methods with seeding of perennial grasses would reclaim Russian knapweed infested areas more effectively than any of the treatments applied alone. Five suppression treatments combined with 5 seeded perennial grasses were evaluated to reclaim Russian knapweed infested site. Two years after suppression treatments were done, clopyralid + 2,4-D + seeded grasses controlled 66 to 93% of Russian knapweed whereas clopyralid + 2,4-D applied alone controlled only 7% of Russian knapweed. Glyphosate + 'Critana' thickspike wheatgrass [Elymus lanceolatus (Scribn. & Sm.) Gould] controlled 36% of Russian knapweed 2 years after treatment (YAT) while glyphosate + 'Hycrest' crested wheatgrass [Agropyron cristatum (L.) Gaertn.], 'Bozoisky' Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski], or 'Sodar' streambank wheatgrass [Elymus lanceolatus (Scribn. & Sm.)] increased Russian knapweed growth 1.5, 2, and 1.6fold, respectively. Glyphosate applied alone tripled Russian knapweed growth. Metsulfuron + streambank wheatgrass controlled 61% of Russian knapweed 2 years after treatments were applied while metsulfuron applied alone controlled 40% of Russian knapweed. Mowing was ineffective and mowing + crested wheatgrass increased Russian knapweed growth about 2-fold. Clopyralid + 2,4-D + streambank wheatgrass yielded 6, 48, and 18 times more seeded grass than metsulfuron treated, mowed, or non-treated control plots seeded with streambank wheatgrass. Clopyralid + 2,4-D + streambank wheatgrass, while expensive ($262 ha-1), was the best treatment combination because it controlled Russian knapweed effectively while the sod-forming grass established well and helped to prevent re-invasion by the weed.

Studies were conducted in the presence of Verticillium wilt (Verticillium albo-atrum) to determine the effect of fall harvesting and grazing over time on plant stand and forage yield of alfalfa (Medicago sativa). Resistant and susceptible cultivars were tested on established and newly seeded fields. In the fall (experiments 1 and 2), cultivars were either: (i) cut (third time); (ii) grazed; (iii) cut and grazed; or (iv) left uncut and ungrazed. Although Verticillium was present, test sites for experiments 2 and 3 were sprayed with a spore suspension of V. albo-atrum immediately following the first cutting of each experiment to standardize disease pressure. In experiment 1, the moderately resistant cultivar Apollo II, harvested twice without a late third cutting or fall grazing, produced the highest forage yield the following year. Fall grazing reduced subsequent yields in both the 2- and 3-cut treatments. In experiment 2, a third cutting decreased plant density and forage yield in both resistant and susceptible cultivars, while grazing had no effect. Neither fall treatment affected incidence of Verticillium wilt. In experiment 3, application of the fungicide benomyl to plant stubble following each harvest decreased Verticillium wilt in Apollo but not in Arrow. Overall, with the resistant cultivar Arrow, harvesting twice annually and grazing after a killing frost in lieu of late fall cutting slowed disease development, prolonged stand life, and maximized forage yield and quality.