Thirteen selections of kochia (Kochia scoparia (L.) Schrad.), self-pollinated for four generations, varied in response to (2,4-dichlorophenoxy)acetic acid (2,4-D) and 3,6-dichloro-o-anisic acid (dicamba). The most susceptible selection was injured more by 0.35 kg/ha of the dimethylamine salt of 2,4-D than the most tolerant by 0.70 kg/ha based on visual injury rating, growth in plant diameter relative to untreated controls, and seed production. The 0.28 kg/ha rate of dicamba injured the most susceptible selection as much as 0.54 kg/ha injured the most tolerant based on visual injury rating and change in plant diameter. Plant size and maturity influenced the response of kochia to herbicides, but the differences in response among selections could not be explained by variations in size or maturity. All kochia selections were tolerant to 4-amino-3,5,6-trichloropicolinic acid (picloram) at 4.28 kg/ha.

Polymerized and conventional (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-trichloro-picolinic acid (picloram) were applied alone and in certain combinations to several brush species. Generally there were no significant differences in effectiveness between conventional and polymerized herbicides on honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockrell), huisache (Acacia farnesiana L. Willd.), Macartney rose (Rosa bracteata Wendl.), live oak (Quercus virginiana Mill.), whitebrush (Aloysia lycioides Cham.), and winged elm (Ulmus alata Michx.). Conventional granular picloram was more effective on yaupon (Ilex vomitoria Ait.) than polymerized formulations.

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.

A field and greenhouse study was conducted to determine the relative effectiveness of preemergence herbicides applied at low volume (9.35 to 37.4 L/ha) and conventional volume (187 L/ha). In the field study 11 preemergence herbicides were applied to plots seeded with seven weed species. Five herbicides were used in the greenhouse study each applied at five rates and two volumes. Both field and greenhouse results indicated that water soluble materials and emulsifiable concentrates which need not be incorporated can be applied at low volume with results comparable to conventional volume application. Field results suggested wettable powders can be applied low volume with success; however, greenhouse results indicated that with present equipment and technique wettable powders are not well suited for low volume application. Incorporated materials were included only in the field study and gave irregular results.

Under greenhouse conditions activated carbon, applied as a slurry at the time of seeding, protected Italian ryegrass (Lolium multiflorum Lam.) seedlings from the toxicity of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) applied preemergence. Plants growing from seeds planted 1.3 cm deep received less protection from diuron than plants growing from seeds planted 0.6, 1.9, or 2.5 cm deep. Sandy loam soil required at least three times more activated carbon than a clay loam soil to obtain the same protection. Activated carbon applied at 130 kg/ha in a 2.5-cm band on the soil surface directly over the seeds provided adequate protection on a clay loam soil. On a sandy loam soil the 130-kg/ha rate was not adequate. Wetting agents added to aid in carbon wetting reduced the protective effect of activated carbon when added at 0.9 or 2.7% (v/v) but had only a slight effect on protection when added at 0.3% (v/v). The soil moisture level at the time of carbon application and the amount of subsequent irrigation did not influence the protection obtained with activated carbon.

Herbicide content in honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell) phloem 48 hr after treatment was higher in stems within 20 cm of the foliage than in those near the soil line. Similar levels of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) occurred from applications of either 0.56 or 1.12 kg/ha, whereas three times as much 4-amino-3,5,6-trichloropicolinic acid (picloram) occurred in plants sprayed with the high rate than in those sprayed with the low rate. Herbicide concentration was highest in June and lowest in August.

Systems of weed control composed of (a) intensive cultivation only, (b) herbicides only, or (c) herbicides plus cultivation controlled weeds in soybeans (Glycine max (L.) Merr.) with acceptable crop tolerance. On Ocilla sandy loam, systems with S-propyl dipropylthiocarbamate (vernolate) as a preplanting treatment and 3[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron) as an early postemergence treatment, followed by either sweep cultivations or directed postemergence applications of other herbicides, controlled yellow nutsedge (Cyperus esculentus L.) satisfactorily and controlled 99 to 100% of the common cocklebur (Xanthium pensylvanicum Wallr.) and Florida beggarweed [Desmodium tortuosum (Sw.) DC.]. As directed postemergence treatment, 2-seobutyl-4,6-dinitrophenol (dinoseb) controlled common cocklebur and Florida beggarweed about as well as 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron). However, for the broad spectrum of weeds encountered on the Greenville soil, linuron was superior to dinoseb, especially on Texas panicum (Panicum texanum Buckl.). Systems containing only cultivation controlled 84 to 98% of the common cocklebur and 78 to 99% of the Florida beggarweed. On Greenville sandy clay loam, several systems of weed control significantly reduced the stand but not the yield of soybeans. Vernolate reduced stands when used as a preplanting incorporated treatment but not when injected at planting. No significant yield differences among the weed control systems were apparent in the 3-year averages. Costs of weed control ranged from $20 to $30/ha for cultivation only, from $55 to $73/ha for herbicides only, and from $45 to $53/ha for herbicides combined with cultivation. Uncontrolled weeds, primarily common cocklebur and Florida beggarweed, in the weedy check plots reduced the average yield of soybeans 74% on the Ocilla soil during the 3-year period. The different systems of weed control did not affect commercial quality of soybean oil.

Floral induction in kochia (Kochia scoparia (L.) Schrad.) was influenced more by light period and temperature than by soil fertility or soil moisture. Floral induction occurred when the light period per 24-hr cycle was shorter than a critical length. However, the critical duration of light per 24-hr cycle at which floral induction occurred varied from about 13 to 15 hr among kochia selections. The time from emergence to flowering varied from 57 to 100 days. The kochia selection from New Mexico required a shorter light period and a longer time after emergence for floral induction than did selections from North Dakota, South Dakota, and Minnesota. Kochia selections from the latter three states varied greatly in flowering date.

Three herbicides, 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and 3-tert-butyl-5-chloro-6-methyluracil (terbacil), applied annually at 0.45, 0.90, and 1.80 kg/ha for 2 or 3 years to establish forage alfalfa (Medicago sativa L. ‘Ranger’), effectively controlled downy brome (Bromus tectorum L.), tumble mustard (Sisymbrium altissimum L.), and prickly lettuce (Lactuca serriola L.). However, downy brome control decreased to less than half and broadleaf control ceased 18 months after the final herbicide application. Atrazine injured alfalfa most. Usually, annual applications of 0.45 kg/ha did not reduce yield. Greenhouse and field bioassay data indicated that the herbicides leached below the 0 to 32.5 cm soil zone and persisted. Residues were absorbed by roots of crops planted 2 to 3 years after the last application. Injury was similar whether the last application was made 18 or 30 months previously. The order of crop tolerance was sweet corn (Zea mays L. ‘Rugosa’) > potatoes (Solarium tuberosum L. ‘Norgold’) > winter wheat (Triticum aestivum L. ‘Nugaines’) > bush beans (Phaseolus vulgaris L. ‘Humilis’) ≅ sugar beets (Beta vulgaris L. ‘U. & I. hybrid No. 8′).

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.

The compound α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) inhibited mitosis in onion (Allium cepa L. ‘Yellow Globe’) and wheat (Triticum aestivum L. Thorn’) root tips. Photomicrographs showed that trifluralin affected mitosis in the same manner as colchicine. Arrested metaphases, c-pairs, micronuclei, amoeboid nuclei, and polyploidy were observed at various times after treatment. An increase in the percentage of arrested metaphases and a decrease in anaphase and telophase figures after 3 hr showed that mitosis was being blocked at metaphase. Prophase did not appear to be affected. Centrifugation of treated root tips displaced the chromosomes of arrested metaphases indicating that the spindle apparatus was disrupted.

Growth-chamber studies were conducted to determine the effect of p-chlorophenyl-N-methylcarbamate (PPG-124) and 1-naphthyl N-methyl carbamate (carbaryl) on the response of safflower (Carthamus tinctorius L. ‘Gila’) and common buckwheat (Fagopyrum esculentum Moench.) to isopropyl m-chlorocarbanilate (chlorpropham). Addition of PPG-124 or carbaryl did not increase the sensitivity of safflower, a resistant species, to chlorpropham and affected buckwheat, a susceptible species, only at the lowest dosage level.

Isopropyl m-chlorocarbanilate (chlorpropham) at 6.7 kg/ha applied in mid April controlled dodder (Cuscuta campestris Yunck. and Cuscuta indecora Choisy) that emerged in May but did not consistently control dodder that emerged in June. Mid March applications sometimes controlled dodder that emerged in May but did not control that which emerged in June. When p-chlorophenyl N-methylcarbamate (PCMC), an inhibitor of microbial enzyme activity, at 1.7 kg/ha was applied with chlorpropham at 6.7 kg/ha in mid March or mid February, dodder that emerged in May and June was controlled consistently. A reduced rate (4.5 plus 1.1 kg/ha) of the combined materials applied in mid March also consistently controlled dodder that emerged in May and June.

Volunteer castorbean (Ricinus communis L.) was most effectively controlled by preemergence application of 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) at 1.1 to 2.2 kg/ha in grain sorghum (Sorghum bicolor (Moench) L.) and by 1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea (fluometuron) at 1.7 to 2.2 kg/ha in cotton (Gossypium hirsutum L.). Preplant applications of propazine were not as effective as preemergence treatments. Efficacy of soil-applied herbicides was greatest when 1 to 2 cm of rain occurred within 7 to 10 days after application. Effective postemergence treatments on castorbean seedlings with two to eight true leaves were 2-chloro-4(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) at 1.1 to 1.7 kg/ha, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) at 0.9 kg/ha, or 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) at 0.9 kg/ha.

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.

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.

The effect of timing of preemergence application of N,N-dimethyl-2,2-diphenylacetamide (diphenamid) on phytotoxicity to pepper (Capsicum annuum L.), efficacy of weed control, and damping-off incidence was studied in greenhouse and field experiments. Delay of application from day of sowing to close to emergence reduced phytotoxicity to pepper while only partially reducing herbicidal action. Addition of a mixture of the contact nonresidual herbicides 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat) and 1,1′-dimethyl-4-4′-bipyridinium ion (paraquat) to a late preemergence application of diphenamid resulted in control of weed seedlings which emerged after sowing of pepper and significantly increased the yield. The increase of Rhizoctonia damping-off incidence due to diphenamid was also reduced by delayed application.

Tillering, flowering, and rhizome formation of johnsongrass (Sorghum halepense (L.) Pers.) started approximately 2 months after planting seeds or single-node rhizome fragments in the warm season. The minimum temperature for rhizome formation was between 15 and 20 C. Inflorescences were produced only from May to November. No causal relationship was found between flowering and rhizome formation. The bud activity of new rhizomes, as assessed by sprouting of single-node fragments, ranged between 48 and 100%. Sprouting was nil at 10 C, slow below 20 C, and maximum at 28 C. Seed germination required a temperature about 10 C higher than rhizome sprouting. While the initial leaf production of seedlings was more rapid than on plants produced from rhizomes, other differences in growth and development between seedlings and rhizome plants were of only limited practical significance.

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.