Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 6.7 kg/ha, twice the recommended rate, stunted early-season growth of ‘Jubilee,’ ‘Commander,’ and 'Stylepak’ sweetcorn (Zea mays L.) 9 to 15%, reduced plant populations of Commander and Stylepak 12 to 15%, reduced the kernel yield of Jubilee and Stylepak 14 to 16%, and delayed ripening of Jubilee and Stylepak by 2 or 3 days. Alachlor at 3.4 kg/ha slowed early-season growth of Jubilee and Stylepak, but reduced yield and delayed ripening of only Jubilee. EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloracetamide) and vernolate (S-propyl dipropylthiocarbamate) + R-25788 at 4.5 + 0.4 or 9.0 + 0.8 kg/ha did not reduce the growth, yield, or quality of the three sweetcorn cultivars. Planting date did not influence the response of sweetcorn to the herbicides. In these experiments, none of these herbicides injured sweetcorn severely, as has sometimes occurred in commercial fields.

Translocation and metabolism of 14C-2,4-D [(2,4-dichlorophenoxy)acetic acid] and effects of 2,4-D on protein synthesis were compared in ‘T–68’ (2,4-D tolerant) and ‘Viking’ (susceptible) birdsfoot trefoil (Lotus corniculatus L.) in an attempt to elucidate some tolerance mechanisms. After 14C-2,4-D was applied to upper trifoliate leaves, significantly less 2,4-D was found in stems, in leaves below the treated leaves, and in roots of T–68 compared to Viking. More 2,4-D was bound to alcohol-insoluble cellular constituents of T–68 leaves, stems, and roots. When alcohol-soluble components were fractionated, slightly more 14C water-soluble compounds were found in T–68, indicating further inactivation by glycosylation. No amino acid-2,4-D conjugates were found. The rate of 14CO2 evolution from 14C-2,4-D treated seedlings in T–68 was five times that in Viking. Protein synthesis appeared to be more rapid in T–68 but the relationship to 2,4-D was not clear. In part, 2,4-D resistance in T–68 may result from its ability to inactivate 2,4-D by differential binding and conjugation and by side chain breakdown as indicated by 14CO2 release.

In closed vapor exposure chambers, foliar injury on tobacco (Nicotiana tabacum L. ‘Speight G-28’) seedlings was caused by vapors arising from soils in which technical grade benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) or its commercially-formulated emulsifiable concentrate had been incorporated. The emulsifier alone did not cause injury. Dosages of the herbicide ranged from 0.84 to 6.72 kg/ha or 13.1 to 104.8 ppmw in the concentration in soils, and the lowest dosage was sufficient to induce the foliar injury. Leaves which developed during the exposure were markedly shortened, narrowed, and thickened, distorted in shape, and had an extremely poor lamina expansion and abnormal venation pattern. Severity of the foliar injury increased as the herbicide dosage and soil moisture increased, and as the soil organic matter content decreased. Leaves which were partially expanded before the exposure were affected much less. When exposed to vapors of 14C-benefin, plant seedlings readily absorbed radioactive materials by its entire foliage including the stem tip with a few tiny developing leaves. More than half of the 14C absorbed and adsorbed during a 3-day exposure was recovered by CHCl3 wash of leaves and appeared to be retained by the wax and cutin layers, and also by lipoidal secretion substances of the numerous trichomes on the leaf surface. There was a small fraction of unabsorbed or loosely retained 14C material on the surface of the leaves and stem tip, which was removed by water. That not recovered from H2O and CHCl3 washes appeared to be distributed in the internal tissues. Little acropetal translocation appeared to occur from the expanded leaves toward the stem tip. There was no translocation of 14C-benefin into roots of plants where only a single leaf was exposed to the radioactive vapors.

An experiment to investigate tillage practices for producing safflower (Carthamus tinctorius L.) and controlling weeds was conducted from 1963 to 1965. Three tillage intensities designated excessive, moderate, and minimum, depending on the number and kind of tillage operations performed prior to planting, were used. Three different tillage tools used as the primary implement in preparing the seedbed were sweep machine, oneway, and moldboard plow.

Excessive, moderate, and minimum tillage plots averaged 342, 374, and 413 lb/A of safflower and 72, 73, and 63 lb/A of weeds, respectively. The sweep machine plots produced the highest safflower yields and lowest weed yields at all intensities with the oneway and moldboard plow about the same. Yields produced from the best treatments in the experiment (minimum tillage with the sweep machine and seeding with the shoe drill) averaged approximately 300 lb/A more than commercial fields and weed control was effective.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil) had no effect on germination but reduced growth of emerging shoots of orchardgrass (Dactylis glomerata L. ‘Virginia Common’) more than Kentucky bluegrass (Poa pratense L. ‘Merion’). Fresh weight gain and transpiration were reduced in orchardgrass seedlings at 0.125 ppmw of bromacil whereas 1.0 ppmw were required for reductions in bluegrass. Photosynthesis was inhibited in both plants; however, bluegrass recovered in 6 days. Water soluble carbohydrate content was greater and was not reduced as much by bromacil in bluegrass compared with orchardgrass. Absorption of 2-14C-bromacil from solution and translocation to shoots was directly related to transpiration rate. Bromacil was translocated acropetally from sheath and foliar treatments. Higher metabolic conversion of 2-14C-bromacil occurred in bluegrass compared to orchardgrass. Metabolites detected in plant extracts were 5-bromo-3-(2-hydroxy-1-methylpropyl)-6-methyluracil and an unknown. Traces of 3-sec-butyl-6-methyluracil and 5-bromo-3-sec-butyl-6-hydroxymethyluracil were also detected. Bluegrass tolerance involved high carbohydrate levels in tissues, hydroxylation of bromacil, and recovery of photosynthesis.

Nitrogen (N) management markedly affects weed competition with crops. The effect of N availability on plant competition varies with a plant's abilities to capture and use N. Accordingly, we expected the N effect on plant competition to change with the relative emergence time of competing individuals. This hypothesis was tested by growing corn and velvetleaf plants in target and neighbor roles and comparing their N responses. Sowing times were varied, so that target plant emergent dates were constant, whereas neighbor plants were sown to emerge 7 d before, with, or 7 d after targets. Seedlings were fertilized daily with 2.5 mmol (“low N”) or 10.0 mmol (“high N”) ammonium nitrate (NH4NO3). Corn had greater total weight, leaf area, and root-to-shoot ratio (RSR) than velvetleaf. Different dry weights may have reflected seed weights; corn seed weight was greater than velvetleaf. Regardless of role, corn and velvetleaf dry weight and leaf area were greater with high N than low N; in contrast, RSR was lower with high N than low N. The RSR response to N availability suggested plant resources were shifted from N foraging, toward competition for photosynthetically active radiation (PAR). In target plants of each species, dry weight and leaf area increased linearly with time between target and neighbor emergence. Conversely, dry weight and leaf area of neighbor plants decreased with time between target and neighbor emergence. The N response of neighbor plants increased with time of emergence between target and neighbor emergence. Larger plants likely required more N to sustain growth than smaller plants; plants that emerged earlier likely had greater daily N requirements than those that emerged later. These results support factoring in emergence when predicting N effects on plant competition. Optimal N provisioning for integrated weed management may differ with emergence times of competing plants.

Field experiments were conducted for 2 yr to determine the influence of picloram (4-amino-3,5,6-trichloropicolinic acid) and a commercial mixture of picloram plus 2,4-D [(2,4-dichlorophenoxy)acetic acid] (1:16, w/w) on control of wild oats (Avena fatua L. # AVEFA) with four postemergence herbicides. The phytotoxicity to wild oats of barban (4-chloro-2-butynyl m-chlorocarbanilate) or difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) in 1981 and diclofop {2-[4-(2,4-dichlorophenoxy)-phenoxy] propanoic acid} or flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] in 1981 and 1982 was reduced when these herbicides were applied in a mixture with picloram plus 2,4-D. Consequently, the use of these mixtures for broad-spectrum weed control in one spray operation is not recommended. Picloram applied at a rate equivalent to the amount present in the picloram plus 2,4-D mixture did not influence the control of wild oats obtained with any herbicide, indicating that the antagonism was due to the 2,4-D component of the picloram plus 2,4-D mixture.

A clean-up procedure for soil and plant samples utilizing a non-ionic exchange resin column followed by treatment with lead acetate was developed for determining microgram quantities of hexaflurate (potassium hexafluoroarsenate) spectrophotometrically. The method is sensitive to 0.45 ppm with a standard deviation of 0.09 ppm with a recovery of better than 85%. Samples high in organic matter require this treatment to remove interfering substances. Soil samples containing little or no organic matter could be analyzed by using either the lead acetate treatment or the non-ionic exchange resin column. Soil and plant samples analyzed 5 to 7 yr following treatment of south Texas soils for pricklypear (Opuntia spp.) control were found to contain trace quantities of hexaflurate. Downward movement of hexaflurate is either very slow or plants continually assimilate the ion and redeposit it on the soil surface through decomposition of plant parts. The tri- and pent-oxide forms of arsenic did not interfere with analysis of the hexaflurate ion using the clean-up procedure.

Increasing plant density of grain sorghum [Sorghum bicolor (L.) Moench.] from 57100 to 114300 plants/ha had no significant effect on grain yields, but significantly increased Striga hermonthica (Del.) ‘Benth’ # STRHE shoot yields by 49% in S. hermonthica infested soil of the Sudan. Addition of urea at 43, 86, and 172 kg N/ha increased grain yields by 14, 25, and 45%, respectively, above the control and S. hermonthica shoot yields were reduced by 14, 21, and 35%, respectively, below the control. Although average grain yields in 1981 were 77% less than in 1980, S. hermonthica shoot yields were significantly increased by about sixfold. Grain sorghum yields of pure stands were not consistent over both years. In 1980, the cultivar ‘Ariana’ outyielded ‘Tetron’, but in 1981 the reverse occurred. However, in both years, the 50:50 mixture of both cultivars gave intermediate grain yields. While pure stands of Tetron’ sustained the lowest infestations of S. hermonthica and ‘Ariana’ had the greatest, the mixture had intermediate infestations which were on average 31% less than those of ‘Ariana’. Thus, the results suggest that the cultivation of equiproportional mixtures of relatively resistant and susceptible grain sorghum varieties, coupled with the use of high rates of nitrogenous fertilizer and wider inter- and intra-row spacing, may be a better cultural practice under dense striga infestations.

The objective of this study was to define further the environmental requirements for safe sites for germination of diffuse knapweed achenes (seeds). Germination temperature profiles were developed for diffuse knapweed seeds collected from sites in the Great Basin and Colorado. Each profile consisted of seeds germinated at 55 constant or alternating temperatures from 0 through 40 C. The resulting germination was used to develop quadratic response surfaces with regression analysis. Some germination occurred from 71 to 96% of the temperature regimes, depending on the accession being tested. Maximum observed germination ranged from 85 to 98%. Optimum germination, defined as the maximum observed minus one half the confidence interval at the 0.01 level of probability, occurred at a wide range of temperatures from cold periods of 0 through 20 C, alternating with warm periods of 10 through 35 C. The temperature regimes that most frequently supported optimum germination were 5/25 C (5 C for 16 h and 25 C for 8 h in each 24-h period) and 10/25 C. Germination of diffuse knapweed seeds was generally higher at alternating than constant temperatures.

Picloram (4-amino-3,5,6-trichloropicolinic acid) did not influence germination but differentially regulated postgermination growth of range grass seedlings. Radicle elongation of buffalograss (Buchloe dactyloides [Nutt] Elgelm.), sideoats grama (Bouteloua curtipendula [Michx.] Torr.)3, and switchgrass (Panicum virgatum L.) in petri dishes was reduced by 125 ppb picloram, whereas shoot elongation was not retarded by 1,000 ppb. Buffalograss, sideoats grama, and switchgrass seedlings, germinated in soil containing 500 ppb picloram, were usually not reduced in topgrowth production. However, topgrowth production of Arizona cottontop (Digitaria californica [Benth.] Henr.) and vine mesquite (Panicum obtusum H. B. K.) was reduced by 125 to 250 ppb of picloram in soil. Relative tolerance to picloram was ranked buffalograss, sideoats grama>switchgrass>vine mesquite, Arizona cottontop.

Birdsfoot trefoil (Lotus corniculatus L.) was direct-seeded into five different grass sods after treatment with dalapon (2,2-dichloropropionic acid), glyphosate [N-(phosphonomethyl)glycine], or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at varying rates for vegetation control. During establishment, the stands of birdsfoot trefoil were acceptable in all treated- and untreated-sod grass sods except 1 yr in untreated tall fescue (Festuca arundinacea Schreb.) and timothy (Phleum pratensis L.) and 1 yr in tall fescue receiving 3 kg/ha of dalapon. Herbicide treatments resulted in a more rapid development of a significant legume component in the sward and an increase in forage yield over the untreated plots. Minimum herbicide application rates for best return for grass sod control were 0.5, 1, and 5 kg/ha respectively for paraquat, glyphosate, and dalapon.

An oats (Avena sativa L.) – no-till soybean [Glycine max (L.) Merr.] ecofarming system was evaluated through four, 2-yr rotations during 1978 through 1982. Herbicides were applied to oats, to oat stubble, and to no-till soybeans for maximum weed control throughout the 2-yr rotation. The treatment sets also included conventional tillage of oat stubble for weed control and preparation of a soybean seedbed. Several herbicides gave effective weed control in oats with minimal crop injury; however, grain yield was not increased by any of the treatments. No recropping problems were encountered when planting no-till soybeans 14 months after application of chlorsulfuron {<2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide)}. Soybean yield under ecofarming was greater 1 yr and equal to that with the conventional-tillage system the other 2 yr.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) at 1.1 and 2.2 kg/ha and paraquat + dinoseb (2-sec-butyl-4,6-dinitrophenol) at 1.1 + 0.7 kg/ha controlled redroot pigweed (Amaranthus retroflexus L.) and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] in hops (Humulus lupulus L. ‘Yakima Cluster’) without reducing hop yield or the alpha and beta acid content of the hop cones. Three applications at about 3-week intervals were required to control weeds until harvest. Two applications controlled hop sucker growth. Paraquat at more than 0.6 kg/ha in the third application caused excessive reduction in hop sucker growth.

Early-preplant herbicide application for uncultivated production of soybean [Glycine max (L.) Merr. ‘Williams’] slot-seeded into untilled oat (Avena sativa L. 'Stout’) stubble was studied. Foliar- and soil-active herbicides were applied to stubble of recently harvested oats to control weeds without tillage so that soil moisture could accumulate during the fallow period. The following spring, five herbicide treatments were applied 0, 2, 4, and 6 weeks prior to soybean planting as well as preemergence to control weeds selectively in uncultivated soybeans. Broadleaf weeds were more effectively controlled than grass weeds, but both were controlled adequately with several herbicide combinations and at all five application times. Selective control of weeds was sufficient to eliminate yield loss of uncultivated soybeans seeded into untilled oat stubble. This production method could provide the Great Plains soybean producer with an effective weed control system while conserving soil, soil moisture, labor, and fuel.

Immediately following postemergence application, similar quantities of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] were retained on the foliage of downy brome (Bromus tectorum L. # BROTE) and winter wheat (Triticum aestivum L.). Three days following treatment, more metribuzin was present on the surface of the foliage of downy brome than of winter wheat and similar quantities of metribuzin had been absorbed into the interior of the foliage of both species. Fourteen days after treatment, metribuzin had disappeared from the surfaces of the foliage of both species but more metribuzin was present in the interior of the foliage of downy brome than of winter wheat. Results from petri dish studies in the field suggested that the amount of unaltered metribuzin available for absorption by leaves was influenced primarily by volatilization and secondarily by photodecomposition. In addition, small quantities of rainfall may have washed metribuzin from leaf surfaces. In 1984, yield of winter wheat was greater in metribuzin-treated plots than in nontreated check plots.

Equipment is described that assists experimental work on controlled-drop application techniques. An electronic tachometer measures centrifugal nozzle rotational speeds in the range 0 to 5000 rpm. Speed control is achieved with a simple regulator incorporated in the tractor electrical system. Both devices are also suggested as worthwhile additions to commercial spray rigs.

The effect of exposing tame oat (Avena sativa L. ‘Hudson’) to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate] during seed imbibition was investigated in a growth cabinet at 21 C in the absence of light. Caryopses were imbibed in 0.0, 1.5, and 3.0 ppmv aqueous dilutions of trifluralin and triallate for up to 10 h, after which germination was continued in distilled water. Germination was not affected following imbibition in either herbicide. Both herbicides produced distinct visual symptoms of herbicide injury during subsequent seedling growth. Coleoptile length of 5-day-old seedlings was reduced following imbibition in a 1.5-ppmv dilution of either herbicide. Triallate at 1.5 ppmv resulted in a reduction in shoot dry weight. Both herbicides were largely excluded from embryos of imbibing caryopses. Seedlings were unaffected when cultured from embryos excised from caryopses imbibed in trifluralin and triallate dilutions. Seedling phytotoxic effects resulted from residual activity of trifluralin and triallate retained by the pericarp and testa of imbibed caryopses. Presence of the hull during imbibition decreased the phytotoxic effect of both herbicides on shoot growth. These findings suggest that germinating seedlings of Avena spp. may be affected by trifluralin and triallate at an earlier stage than previously realized.

Quantifying the level of ecophysiological, biochemical, and agronomical fitness of herbicide-resistant (R) and herbicide-susceptible (S) weeds is useful for understanding the evolutionary development of herbicide resistance, but also for implementing herbicide-resistance management strategies. Although germination is a key fitness component in the life cycle of weeds, germinability of S and R weeds has rarely been evaluated under stressful conditions. Germinability traits of S and non–target site resistant subpopulations of blackgrass (Alopecurus myosuroides Huds.) sharing closely related genetic background were tested under salinity, drought stress, and accelerated seed-aging (i.e., exposed to 100% relative humidity at 45 C from 0 to 134 h) conditions. In addition, the activity of three antioxidant enzymes and protein concentration of accelerated aged seeds of the subpopulations were studied. There were no differences in maximum seed germination (Gmax) and time to 50% germination between the two subpopulations under optimum conditions. However, under salinity, drought stress, and accelerated aging conditions, there were differences between the subpopulations. The salinity, drought, and accelerated aging treatments reducing Gmax of the S subpopulation by 50% were 18 dS m−1, 0.75 MPa, and 90 h, respectively, while for the R subpopulation the corresponding values were 15 dS m−1, 0.66 MPa, and 67 h. No differences were found in the activity of the antioxidant enzymes and the content of protein between non-aged seeds of the subpopulations. The aging treatments reducing the activity of catalase and superoxide dismutase enzymes by 50% were 118 and 82 h for the S subpopulation, respectively, while they were 54 and 58 h for the R subpopulation. In contrast, there were no differences in the effect of the aging treatments on the peroxidase activity and protein content between subpopulations. The results provided clear evidence that the non–target site resistant loci of blackgrass is associated with fitness costs under environmental stress.