Fall panicum (Panicum dichotomiflorum Michx.) and Texas panicum (Panicum texanum Buckl.) were grown in the greenhouse under flooding treatments of 0, 6, and 9 days in 10 for 1 month. Fall panicum was more tolerant of flooded soil than was Texas panicum. Root development of Texas panicum was reduced by 50% under all flooding treatments. Herbage and root growth of fall panicum with flooding was similar to that on well-drained soil. Fall panicum root diameter was greater than that of Texas panicum, but both species increased under flooding. Tolerance of fall panicum to flooding may partially explain why it competes so well with crop plants during wet periods.

Soybean (Glycine max (L.) Merr., ‘Hawkeye 63′) seedling segments from the zone of elongation and corn (Zea mays L., ‘Pioneer 3306) seedling segments were utilized to evaluate the antagonistic interaction of S-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)-acetic acid (2,4-D). EPTC inhibited growth of the soybean and corn tissue, and 2,4-D in combination with EPTC caused an increase in growth compared to EPTC alone. The 2,4-D-enhanced growth in the presence of EPTC was due to an antagonism of the EPTC inhibition. Inhibition of soybean tissue growth by S-ethyl diisobutylthiocarbamate (butylate) also was antagonized by 2,4-D. Preincubation of soybean tissue in EPTC for 4 hr prior to the addition of 2,4-D did not prevent 2,4-D enhancement of growth. Conversely, the rate of growth was inhibited when EPTC was added after 4 hr of 2,4-D-enhanced growth. The addition of uridine to the incubation media with EPTC did not decrease the EPTC-inhibition of soybean tissue growth. This indicated that EPTC did not inhibit the synthesis of pyrimidine precursors. EPTC vapor losses from the incubation media reduced the inhibitory effect of EPTC to soybean tissue. Also, a growth reduction occurred when the amount of soybean tissue per unit of EPTC was increased.

Three-day-old soybean (Glycine max (L.) Merr., ‘Hawkeye 63′) hypocotyl segments (0.5 to 1.5 cm below the cotyledons) were utilized to evaluate the effects of the antagonistic interaction of S-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)acetic acid (2,4-D) on growth and nucleic acid synthesis. EPTC inhibited growth and RNA synthesis in soybean tissue. The addition of 2,4-D with EPTC was antagonistic to EPTC inhibition of growth and caused an increase in total RNA synthesis. Analysis of soybean tissue nucleic acids by methylated-albumin-kieselguhr(MAK) column chromatography showed that EPTC inhibited ribosomal-RNA (r-RNA), DNA like RNA (D-RNA), and tenaciously-bound-RNA (TB-RNA) synthesis. The combination of 2,4-D with EPTC caused an increase in D-RNA and TB-RNA synthesis compared to the EPTC treatment alone. The 2,4-D-enhanced synthesis of D-RNA and TB-RNA in the presence of EPTC appears to be the basis of the antagonism between EPTC and 2,4-D. Preliminary analysis of r-RNA indicated that EPTC preferentially inhibited the synthesis of 18S r-RNA more than 25S r-RNA and that 2,4-D had no effect on this selective inhibition.

Over a 3-year period, pigweed (Amaranthus sp.) was successfully controlled in grain sorghum (Sorghum bicolor (L.) Moench) with preemergence aerial application of 2-chloro-4, 6-bis(isopropylamino)-s-triazine (propazine) and postemergence application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) in 4.7 to 47 L/ha of various carriers. Equally good pigweed control was obtained with ground application of the herbicides with as little as 37 L/ha carrier. Liquid formulations of the two herbicides gave results comparable to an 80% wettable powder formulation.

Delayed planting or “stale seedbed” for weed control in close-drilled (20-cm rows) soybeans [Glycine max (L.) Merr. ‘Amsoy’] was evaluated for 3 years. The system combined final seedbed preparation 3 to 6 weeks before planting with herbicide application at planting time. The best control of six weed species and highest soybean yields were obtained by a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) application at the time of seedbed preparation followed by 3-(3,4-dichlorophenyl)-1-methylurea (linuron) application at planting and by linuron application at planting without the early trifluralin application. Applications of 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) at planting, either with or without trifluralin treatments, resulted in less weed control and lower soybean yields than comparable treatments with linuron. However, even the best treatments failed to provide the weed control necessary to prevent substantial soybean yield reduction in heavy infestations of weeds that emerge in large numbers after planting, and that resist the phytotoxic action of the herbicides.

A higher population of common purslane (Portulaca oleracea L.) developed on a smooth seedbed than a rough seedbed. Purslane germinated best when the seed were placed on the soil surface, and the percentage germination decreased progressively as depth of seed placement increased. Growth of common purslane was greater at elevated nutrient levels and was dependent on adequate phosphorus in the nutrient media. High soil temperature requirements for optimum germination make common purslane a middle to late-growing season weed in the central United States. Often preemergence herbicides which are effective on common purslane have become ineffective by the time the common purslane population has developed, and postemergence herbicides which do not injure the individual crop species must be relied on for common purslane control.

Field experiments were conducted to study the competitive ability of green foxtail (Setaria viridis (L.) Beauv.) with wheat (Triticum aestivum L.) and the feasibility of using a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) for the selective control of green foxtail in wheat. Rates of 0.56 to 0.84 kg/ha of trifluralin gave 90 to 100% control of foxtail when growing in competition with wheat. Wheat tolerated rates of trifluralin up to 2.24 kg/ha, the maximum rate used, without injury or reduction in crop yield, when the herbicide was applied and incorporated to a shallow depth 1 day after seeding. A semidwarf and a tall variety of wheat were not affected by trifluralin treatments. Green foxtail had a relatively low competitive ability, and wheat plants suppressed foxtail to a marked degree under normal growing conditions. However, suppressed plants still produced sufficient seed to insure a dense infestation of foxtail plants in the succeeding year. Further, when wheat was grown under less competitive situations, green foxtail resulted in significant reductions in crop yield. It was concluded that green foxtail is an “opportunist-type” weed.

Injury from 2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine (terbutryn) was greater on winter wheat (Triticum aestivun Vill. ‘Host’) grown at high soil temperature than on that grown at low soil temperature. The injury was more severe when the herbicide was incorporated into the soil close to the root system. In postemergence applications 2-week-old plants were more susceptible to terbutryn injury than 4-week-old plants. High soil water content (75% to 100% of field capacity) favored the uptake of terbutryn through the root system. Terbutryn caused greatest damage under high transpiration rates and in sandy soils.

Mortality rates of Geyer larkspur (Delphinium geyeri Greene), a poisonous plant, were determined after spraying with (2,4-dichlorophenoxy)acetic acid at various stages of plant development in 1967 to 1969. Sprays of 2,4-D at 2.2 kg/ha were more effective at early than at late stages of development, but seldom exceeded 40% mortality. Uneven-aged stands and early drying (dormancy) of small non-flowering plants often prevented the exposure of all plants to a single application of spray; treated plants contorted but continued growth for 5 to 8 weeks after spraying; residual seed provided a source of new plants; and previously dormant rootstock buds gave rise to new shoot and root growth the year after spraying. These characteristics and escape mechanisms direct attention to possibilities of improving effectiveness by spraying two or three times in a single season.

The effects of weed species on the anatomy of roots of cabbage (Brassica oleracea L.) and tomato (Lycopersicum esculentum Mill.) were studied. One crop seed was placed on agar in a test tube to germinate in association with four additional seeds of a weed species. All the weed species caused abnormal changes in the anatomy of cabbage and tomato roots. Jimsonweed (Datura stramonium L.) inhibited cell elongation and caused disruption of epidermis and disorganization of the root tissue in cabbage. Green foxtail (Setaria viridis (L.) Beauv.) also caused disruption of cabbage roots. Mustard (Brassica kaber DC.) and velvetleaf (Abutilon theophrasti Medic.) induced enlarged parenchyma cells of cabbage roots. The combination of tomato and jimsonweed resulted in disorganized root tissue or large roots with large parenchyma cells.

Uptake of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) as influenced by adjuvants to the treatment medium was studied using both excised leaf sections and leaves of intact plants. Uptake of the 14C-atrazine label by yellow foxtail (Setaria glauca (L.) Beauv.) leaf sections was higher at 35 than at 5 C and at pH 3 and 9 than at 5 or 7. The rapid uptake of 14C-atrazine label by corn (Zea mays L.) leaf sections was attributed to a high rate of atrazine metabolism. However, atrazine metabolism did not explain the greater uptake by common lambsquarters (Chenopodium album L.) leaf sections than by yellow foxtail. Atrazine 14C-label uptake by yellow foxtail leaf sections from exogenous solution was influenced by light, phospholipase D or water pretreatment, atrazine concentration, and oil. The 14C-label of atrazine in the leaf distal to the treated spot was greater when the treatment contained an oil than when applied in only water even though the area of the spot was kept constant. Further, greater uptake of the label occurred at a high than at a low temperature regardless of the application medium.

Approximately 80% of the johnsongrass (Sorghum halepense (L.) Pers.) rhizomes produced in clay soil were in the top 7.5 cm, but 80% of the rhizomes in sandy loam occurred in the top 12.5 cm. Distribution of rhizomes within the top 20 cm of soil was more uniform in sandy loam than in clay; yet, 5% of the rhizomes produced in clay occurred deeper than 20 cm, but only 1% of the rhizomes in sandy loam occurred deeper than 20 cm. Incorporation of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-/7-toluidine (trifluralin) in soil at 0.84 kg/ha reduced rhizome production approximately 50% throughout the soil profile but reduced rhizome production most in the top 6 cm. More plants emerged from rhizomes when planted in sandy loam than in clay. More plants emerged from short rhizomes (76 mm) than from long rhizomes (152 mm) when planted at depths to 7.6 cm, but the opposite trend was obtained when rhizomes were planted deeper. Percentage germination of rhizome buds increased as rhizomes were cut into smaller pieces. Exposure of rhizomes to temperatures of 50 to 60 C killed buds within 1 to 3 days. Rhizomes usually survived temperatures of −3 to −5 C for only a few hours.

Anionic herbicide transport properties of lipids were measured using the Schulman model of liquid-liquid membrane and parenchymateous tissue from potato (Solarium tuberosum L. ‘Russet’) tubers. The more polar lipids, lecithin and monogalactosyl dilinolenate, increased (2,4-dichlorophenoxy)acetic acid (2,4-D) exchange from the hydrophilic phase (buffered H2O:2,4-D solution) to the lipophilic phase (n-pentanol) more rapidly than the less polar triglycerides: tristearate, trioleate, and trilinolenate. The rate of 2,4-D exchange decreased with increased acidity of the hydrophilic phase indicating that polar lipids increased exchange of anionic herbicides through the liquid-liquid interface in the dissociated form. Potato tuber slices treated with lecithin accumulated more 2,4-D than did tissue receiving no lecithin, indicating that lecithin treatments increased 2,4-D accumulation by parenchymateous tissue when compared with untreated tissue.

Experiments were conducted at Lincoln and North Platte, Nebraska, during 1967 and 1968 to determine the effect of early preplant applications of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) on sorghum [Sorghum bicolor (L.) Moench ‘Nebraska 505′] and weed yields. Atrazine at 2.24 kg/ha was applied on separate plots preplant and incorporated about April 15, April 30, and May 15, and also preemergence without incorporation about May 17, after sorghum was planted. Sorghum grain yields were highest on plots where atrazine was applied preemergence rather than preplant due mainly to better weed control. Sorghum planted with planter units equipped with furrow openers, set to remove 2.5 to 5 cm of surface soil, had better sorghum stands and smaller weed yields than sorghum planted without removing surface soil. Sorghum population was the lowest following the April 30 atrazine application due to stand loss at North Platte, but grain yields were not significantly different from other preplant treatments since stand loss was compensated for by more heads per plant, larger heads, and larger seed.

Cucumber (Cucumus sativus L. ‘Chicago pickling’) and wheat (Triticum aestivum L. ‘Manitou’) seeds were germinated in various concentrations of (2,4-dichlorophenoxy) acetic acid (2,4-D), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram). The nucleic acid and protein levels in the roots of the two species were determined 4 days after germination and compared on a per root basis. All four herbicides increased the DNA and protein of both cucumber and wheat roots with the increase in cucumber being higher than in wheat. The greatest difference between the tolerant wheat and susceptible cucumber was the effect on the RNA levels. As the concentration of all four herbicides increased, a progressive decrease of RNA levels occurred in wheat. In contrast, in cucumber the herbicides at high concentrations (10 and 100 ppmw) increased the RNA levels by more than 200% over the water controls. When the protein levels in both species were compared on a per unit RNA basis, there was an inverse relationship. In wheat the protein/RNA ratio was higher than the control whereas in cucumber the ratio was lower. A differential alteration of RNA species and interference with protein synthesis is suggested as the basis for selectivity.

Heavy infestations of johnsongrass (Sorghum halepense (L.) Pers.) reduced the yield of six soybean (Glycine max (L.) Merr.) varieties 23 to 42% with both hand-harvesting and mechanical-harvesting over a 3-year period. ‘Davis', ‘Lee’, and ‘Bragg’ varieties produced significantly higher yields than did ‘Semmes', ‘Jackson’, or ‘Hardee’ when grown in weed-free plots, but ‘Bragg’ produced significantly higher yields than all other varieties when grown with johnsongrass. Less regrowth of johnsongrass occurred in plots of ‘Bragg’, ‘Davis', and ‘Semmes' than in plots of ‘Lee’, ‘Jackson’, and ‘Hardee’. Common cocklebur (Xanthium pensylvanicum Wallr.) reduced the average yields of six soybean varieties 63 to 75% when plots were hand-harvested. ‘Semmes' showed the lowest percentage yield reduction from common cocklebur competition when hand-harvested, and ‘Semmes' and ‘Bragg’ showed 53% to 57% reduction respectively when machine harvested.

Phytotoxicity of 2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine (terbutryn) on winter wheat (Triticum aestivum Vill. ‘Host’) was investigated in a controlled environment. Highly significant differences in foliage dry weight were caused by different light intensities and rates of terbutryn. Injury symptoms appeared much earlier in plants under high light intensity. Carbon dioxide uptake by wheat plants was reduced by terbutryn at high light intensity. At low light intensity the reduction was less severe and developed later. Respiration (CO2 evolved in the dark) was reduced only by the highest rates. Terbutryn was significantly less toxic to wheat than 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). The difference was more noticeable at low rates under high light intensity. At low light intensity no injury was observed with terbutryn.

Studies were conducted to determine the stage of growth at which curly dock (Rumex crispus L.) and broadleaf dock (Rumex obtusifolius L.) can propagate vegetatively from a rootstock. Curly dock plants were grown from seed in the greenhouse and phytotron under long-day conditions. Curly dock seedlings were capable of regrowth from a rootstock 47 days from seeding in the greenhouse. Some of the phytotrongrown plants attained this capacity 31 to 38 days after seeding; while all demonstrated this ability at 41 days. Broadleaf dock produced flower stalks within 38 days in phytotron studies but was not capable of regeneration during this same period of time. Broadleaf dock was capable of regrowth from a rootstock approximately 51 days after seeding in the phytotron.

Canada thistle (Cirsium arvense (L) Scop.) includes many regional races that are heritable, distinct ecotypes. When cultured at Bozeman, Montana a group of these ecotypes varied in phenological, morphological, and anatomical characteristics. These ecotypes also responded differently to (2,4-dichlorophenoxy)acetic acid (2,4-D) and 3-amino-s-triazole (amitrole). Stomatal frequency and area on leaves also differed among ecotypes studied. Although stomatal frequency and stomatal area differed among the ecotypes studied, there was no correlation with herbicide response. Apparently, stomata were not a significant portal of entry of 2,4-D into the upper surface of Canada thistle leaves.

The following herbicides were evaluated for relative phytotoxicity to cotton (Gossypium hirsutum L. ‘Acala SJ-1′), purple nutsedge (Cyperus rotundus L.), and yellow nutsedge (Cyperus esculentus L.) under greenhouse conditions: 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl)acetanilide (CP-53619); 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (VCS-438); 4-chloro-5-(dimethylamino)-2-α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone (San-6706); 2-(α naphthoxy)-N,N-diethyl-propionamide (R-7465); and S-isopropyl 5-ethyl-2-methyl-piperidine-1-carbiothioate (R-12001). Herbicides were incorporated 6.35 cm deep, at rates of 1.12, 2.24, and 4.48 kg/ha, into a fine sandy loam prior to planting. All treatments except the low rate of alachlor and VCS-438 controlled yellow nutsedge for 8 weeks. R-7465 and R-12001 at 1.12 kg/ha and San-6706 at 2.24 kg/ha controlled purple nutsedge for 8 weeks. Alachlor and CP-53619 were somewhat less effective against purple nutsedge than yellow nutsedge, but their intermediate rates suppressed purple nutsedge for 4 weeks. Even the high rate of VCS-438 was ineffective against purple nutsedge. Cotton, in terms of fresh shoot weight, exhibited considerable tolerance to 1.12 and 2.24 kg/ha of VCS-438 and CP-53619 and 1.12 kg/ha of R-7465. Applications of 2.24 kg/ha of CP-53619 and 1.12 kg/ha of R-7465, however, suppressed the development of lateral roots of cotton. Other rates of these herbicides and all rates of alachlor, R-12001, and San-6706 moderately to severely injured cotton in most of the experiments.