The response of net photosynthetic rate to temperature and light, the rate of photorespiration, the compensation concentration for CO2, and the pathway of CO2 fixation in smooth pigweed (Amaranthus hybridus L.) were investigated using infrared gas analysis and 14CO2. Maximum net photosynthetic rates of whole shoots were 45 mg CO2 dm-2 hr-1 at 30 C and 7.8 klux. Intact whole shoots were not light saturated at 10 klux. The optimum temperature for net photosynthesis was between 30 C and 40 C. Photorespiration was low and the CO2 compensation concentration was 7 ppm. After a 5-sec exposure to 14CO2 in the light, label was detected in oxaloacetate, malate, and aspartate. It was concluded that smooth pigweed has the gross photosynthetic characteristics and CO2 fixation pathway typical of C4 or Hatch-Slack plants.

Rates of trifluralin (α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and vernolate (S-propyl dipropylthiocarbamate) were compared with and without 45 kg/ha of nitrogen for 2 yr on soybeans [Glycine max (L.) Merr.]. Nodulation was the only factor affected significantly by nitrogen. Nodule weight was 65% greater where nitrogen was not applied. Nodulation was suppressed by trifluralin, but not by vernolate. Delays in emergence, stunting, plant injury, and yield reduction were associated with preplant incorporated treatments of trifluralin at 1.12 kg/ha and with incorporated vernolate at 2.24 and 4.48 kg/ha. Trifluralin incorporated at 0.56 kg/ha and vernolate injected at 2.24 and 4.48 kg/ha had essentially no effect on plant injury and did not reduce yields significantly. Soybeans were injured more by incorporated vernolate than by trifluralin. Average yields of weed-free soybeans for 2 yr were reduced 10.5, 8.6, and 14.0%, respectively, by (a) trifluralin at 1.12 kg/ha and (b) incorporated vernolate at 2.24 and 4.48 kg/ha. However, injected vernolate (compared to other treatments) significantly increased soybean emergence, reduced plant injury, and increased yields.

Wild oat (Avena fatua L.) seedlings were exposed to vapors arising from soil treated with triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate]. Vapor from the liquid triallate formulation inhibited seedling growth more than vapor from the granular formulation, and the degree of inhibition was least in Fargo clay, intermediate in Hecla sandy loam and greatest in washed sand. Growth inhibition from vapors of soil-applied liquid or granular triallate increased as soil moisture content and soil temperature increased. The site of effective vapor action on wild oat seedlings was below the soil surface.

In greenhouse studies, 11 cultivars of potato (Solanum tuberosum L.) responded differently to foliar applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5-(4H)one] at rates of 0.14 to 1.12 kg/ha. The first symptoms of metribuzin injury varied among cultivars. When measured 14 days after treatment, the dry weight was reduced more than the height or the vigor. Height was least affected. When metribuzin was applied at 0.14 kg/ha, the height of ‘Norchip,’ the vigor of ‘Norland,’ ‘Norchip,’ and ‘White Rose,’ and the dry weight of ‘Red La Soda,’ ‘Cascade,’ ‘Norchip,’ and ‘White Rose’ were reduced significantly 14 days after treatment. Plant vigor and dry weight of all of the cultivars were reduced significantly by metribuzin applied at 1.12 kg/ha. ‘Nooksack’ and ‘Norgold’ were the most tolerant to foliar applications of metribuzin, and ‘Norchip’ and ‘White Rose’ were the most susceptible.

The control of winter annuals in dormant bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] has not been consistent with available herbicides. Experiments were conducted to evaluate rates and number of glyphosate [N-(phosphonomethyl)glycine] applications for control of winter annuals growing in dormant bermudagrass. Glyphosate applied as a single treatment at 0.6 kg/ha consistently controlled more parsley-piert (Alchemilla microcorpa Boissier Reuter), corn speedwell (Veronica arvensis L.), and henbit (Lamium amplexicaule L.) than paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or combination treatments of 2,4-D [(2,4-dichlorophenoxy)acetic acid) + mecoprop 2[(4-chloro-o-tolyl)oxy] propionic acid + dicamba (3,6-dichloro-o-anisic acid). There was no difference between glyphosate and paraquat control of annual bluegrass (Poa annua L.) and common chickweed [Stellaria media (L.) Cyrillo]. Glyphosate treatments did not injure the bermudagrass the following spring.

Broadleaf species such as tanoak [Lithocarpus densiflorus (Hook. & Arn.) Rend.] and pacific madrone (Arbutus menziezii Pursh) reduced conifer growth on previously logged or burned areas of the northern California and southwest Oregon coast range. Cut-surface applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and picloram (4-amino-3,5,6-trichloropicolinic acid) into tanoak and pacific madrone growing as overstory to Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] were found to provide acceptable control for 10 years following application. Increment cores obtained from Douglas fir in treated and non-treated plots revealed substantial stem enlargement as a result of tanoak and pacific madrone control.