The dipeptidase activity of the cotyledons of the squash (Cucurbita maxima Duch. ‘Hubbard’) increases during germination. Several herbicides inhibited this increase in various degrees. Those herbicides inhibiting the development of dipeptidase activity 70% or more were (2,4-dichlorophenoxy)-acetic acid (2,4-D), 3,6-dichloro-o-anisic acid (dicamba), (2,3,6-trichlorophenyl)acetic acid (fenac), and N-1-naphthylphthalmic acid (naptalam). Those inhibiting dipeptidase activity by 63 to 34% were 4-amino-3,5,6-trichloropicolinic acid (picloram), 2,6-dichlorobenzonitrile (dichlobenil), 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil), 3-amino-s-triazole (amitrole), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 7-oxabicyclo[2.2.1] heptane-2,3-dicarboxylic acid (endothall), and 5-bromo-3-sec-butyl-6-methyluracil (bromacil). Those causing only slight inhibition, 24 to 16%, were N,N-dimethyl-2,2-diphenylacetamide (diphenamid), isopropyl m-chlorocarbanilate (chlorpropham), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin); 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) was essentially the same as the control. However, 2,2-dichloropropionic acid (dalapon), O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)-benzenesulfonamide (bensulide), N,N-diallyl-2-chloroacetamide (CDAA), and 2-chloroallyl diethyldithiocarbamate (CDEC) were somewhat stimulatory. When compared with previously reported herbicide activity on the proteinase activity, those herbicides which inhibited dipeptidase activity did not necessarily affect proteinase activity to the same degree.

Field and greenhouse experiments were conducted during 1984 through 1986 to examine the efficacy of the seed protectants CGA-92194 {α-[(1,3-dioxolan-2-yl-methyl)imino]benzacetonitrile} and flurazole [2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylic acid] for protecting grain sorghum [Sorghum bicolor (L.) Moench.] from alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], and propachlor [2-chloro-N-(1-methylethyl)-N-phenylacetamide] injury. In the field, CGA-92194 and flurazole protected sorghum from injury, stand reduction, and yield loss due to alachlor and metolachlor. In general, sorghum was protected with either antidote, and protected response to alachlor or metolachlor was similar to sorghum subjected to propachlor. Greenhouse experiments were conducted to examine the response of bronze and yellow pericarp color to seed protectants, six sorghum hybrids to these antidotes, and the effects of cool soil temperature on the early seedling vigor of sorghum protected with the antidotes. The response of sorghum with yellow and bronze pericarp color was similar when compared across antidotes. However, there were differences among the sorghum hybrids when compared across protectants. The potential of CGA-92194 and flurazole to protect against alachlor injury was reduced when sorghum was grown in cool soil.

Leaf washing was used to determine relative rates of uptake of 2,4-D and dicamba dimethylamine salts by wheat following field application of a postemergence tank mixture (3:1) of 476 g ae ha-1 at the 4- to 5-leaf growth stage. Foliar herbicide deposits and total acid residues in the crop were determined the day of spraying as well as 2 and 7 d after spraying. Leaf washing of foliage samples collected on the day of spraying indicated that the crop/weed canopy intercepted 51% of the application, and that dicamba was taken up more quickly than 2,4-D. Within a few hours of spraying, approximately 80% of the deposited dicamba and 65% of 2,4-D were taken up by the crop. A 35-mm rain during the first 48 h after application reduced plant surface deposits of both herbicides by more than 98%. During this 2-d period, dicamba residues within the crop were metabolized more quickly than those of 2,4-D. There was little difference in effectiveness among water, 10% methanol, 25% methanol, or 90% methanol in removing plant surface deposits of 2,4-D and dicamba from wheat.

Greenhouse studies were conducted to evaluate the activity of fluometuron [1,1-dimethyl-3-(α-α-α-trifluoro-m-tolyl)urea] and disulfoton [o,o-diethyl s-(ethylthio ethyl) phosphorodithioate] alone and in combination on the height of seedling cotton (Gossypium hirsutum L.) in 10 light-textured soils from the lower alluvial floodplain of the Mississippi River. An antogonistic interaction was demonstrated between the two pesticides in six of the soils studied. The phytotoxic effects of high rates of fluometuron applied preemergence were decreased by granular application of disulfoton. This interaction was repeated in four of the soils and was modified but not eliminated by partial sterilization of the soils, by autoclaving, or by fumigation before treatment. Correlation analyses detected no significant association between the antagonistic interaction and any measurable soil property in the 10 soils. Three field studies failed to demonstrate this interaction. Neither the greenhouse nor the field studies revealed any deleterious interaction between these two chemicals.

A technique using CaCl2 solutions for separating seed of approximately equal size and/or shape by relative density was developed using nine hard-seeded weed species and four soybean [Glycine max (L.) Merr.] cultivars having an average density of 1 g/ml or above. Relative seed densities were determined by the water displacement method. From a seed mixture of nine weed species and soybeans, three groups were obtained: Group I, sicklepod (Cassia obtusifolia L.) and smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb]; Group II, hemp sesbania [Sesbania exaltata (Raf.) Cory], tall morningglory [Ipomoea purpurea (L.) Roth], cypressvine morningglory (Ipomoea quamoclit L.), and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.]; and Group III, soybeans, balloonvine (Cardiospermum halicacabum L.), and velvetleaf (Abutilon theophrasti Medic). Ipomoea lacunosa L. was divided between Group II and Group III due to the range of seed density within the seedlot. The minimum relative CaCl2 solution densities required to separate these seed were 1.38, 1.30, and 1.25 g/ml for Group I, Group II, and Group III, respectively. Further separation into individual species within a group was accomplished by screening in some cases. Sicklepod was separated effectively with this technique from seed screenings obtained from a commercial seed processing plant. There was no effect on germination from soaking weed seed or soybean for 40 min in the CaCl2 solution.

Uptake, translocation, and metabolism of propham (isopropyl carbanilate) were ascertained for wheat (Triticum aestivum L., ‘Neepawa’) sugarbeet (Beta vulgaris L., ‘HH-10’), and alfalfa (Medicago sativa L., ‘Cherokee’) when grown in either liquid culture or in soil. Three-week-old wheat and 5-week-old sugarbeet and alfalfa plants were treated with 14C-propham in liquid culture for 1, 2, and 4 days. Other plants were placed in treated soil at 10 weeks after germination and grown for 15 weeks. Wheat absorbed 98%, sugarbeet 93%, and alfalfa 81% of the propham from solution after 4 days. Propham was translocated in all species. Under liquid culture, three polar metabolites of propham were isolated from wheat and alfalfa extracts and one was isolated from sugarbeet extracts. The agylcone moiety of the two most polar wheat metabolites was isopropyl-4-hydroxycarbanilate and that of the least polar metabolite was isopropyl-2-hydroxycarbanilate. The aglycone of all alfalfa and sugarbeet polar metabolites was isopropyl-4-hydroxycarbanilate. Only one polar metabolite was isolated from all soil-treated plants. The aglycone moiety was determined to be isopropyl-4-hydroxycarbanilate. Of the propham absorbed 95, 91, 89, and 36% was metabolized by sugarbeet roots, sugarbeet leaves, wheat leaves, and alfalfa leaves, respectively, after a 4-day liquid culture treatment. Propham was 100% metabolized when applied to plants via soil application.

Barnyardgrass (Echinochloa crusgalli (L.) Beauv.) seeds which did not germinate because of low temperature, insufficient moisture, or seed dormancy were exposed to concentrations of ethyl N,N-di-n-propylthiolcarbamate (EPTC) lethal to emerging barnyardgrass seedlings. After different periods of exposure, seeds were removed from the EPTC-treated environments and germinated in untreated soil. Seed germination was not reduced by EPTC and there was no permanent injury to the seedlings. It was concluded that rates of EPTC used for selective weed control do not injure barnyardgrass seeds prior to germination.

Watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] grafting is commonly used for management of diseases caused by soilborne pathogens; however, little research exists describing the effect of grafting on the weed-competitive ability of watermelon. Field experiments determined the response in yield, fruit number, and fruit quality of grafted and nongrafted watermelon exposed to increasing densities of Palmer amaranth (Amaranthus palmeri S. Watson). Grafting treatments included ‘Exclamation’ triploid (seedless) watermelon grafted on two interspecific hybrid squash rootstocks ‘Carnivor’ and ‘Kazako’, with nongrafted Exclamation as the control. Weed treatments included A. palmeri at densities of 1, 2, 3, and 4 A. palmeri plants per watermelon planting hole (0.76-m row) and a weed-free control. Increasing A. palmeri densities caused significant reductions (P <0.05) in marketable watermelon yield and marketable fruit number. Watermelon yield reduction was described by a rectangular hyperbola model, and 4 A. palmeri plants planting hole−1 reduced marketable yield 41%, 38%, and 65% for Exclamation, Carnivor, and Kazako, respectively. Neither grafting treatment nor A. palmeri density had a biologically meaningful effect on soluble solids content or on the incidence of hollow heart in watermelon fruit. Amaranthus palmeri seed and biomass production was similar across weed population densities, but seed number per female A. palmeri decreased according to a two-parameter exponential decay equation. Thus, increasing weed population densities resulted in increased intraspecific competition among A. palmeri plants. While grafting may offer benefits for disease resistance, no benefits regarding weed-competitive ability were observed, and a consistent yield penalty was associated with grafting, even in weed-free treatments.

The U.S. Department of Agriculture World Collection of Flax Germ Plasm was screened for resistance to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine). A single plant selection of CI 719 was the most resistant. It produced dry matter equaling 33% of the control in soil treated with atrazine at 1 lb/A while Amy produced 10%. In another experiment, the selection of CI 719 produced 44% as compared to only 11% for Koto. The atrazine-resistant selection was not resistant to 2-chloro-4,6-bis(ethylamino)-s-triazine [simazine]. Seed of this selection of CI 719 have been entered in the World Collection and assigned the number CI 2484.

Shortly after we had completed several studies of the effect of the new herbicide, dalapon, (2,2–dichloropropionic acid), on enzyme systems, it became apparent that high concentrations of this compound inhibited a variety of different enzymes in a noncompetitive fashion. Furthermore, transparent solutions of enzymes frequently became quite turbid when this inhibitor was added. Such behavior suggested that 2,2–dichloropropionic acid was acting as a protein precipitant.

Live oak (Quercus virginiana Mill. # QUEVM) on the Texas Coastal Prairie was treated with herbicides using ground and aerial application methods. Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} and pellets of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} at 2.2 kg ai/ha were the most effective herbicides, killing 60 to 95% of the live oak. Tebuthiuron pellets 3.2 mm in diam were more effective than the wettable powder at 1.1 kg/ha. Bay Met 1486 {N-[5-(ethylsulfonyl)-1,3,4-thiadiazole-2-yl]-N,N′-dimethylurea}, Dowco 290 (3,6-dichloropicolinic acid), hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H, 3H)-dione], and picloram (4-amino-3,5,6-trichloropicolinic acid) reduced the live oak canopy at 2.2 kg/ha whereas 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} were ineffective. Foliage-active herbicides generally were most effective in reducing the live oak canopy during the year of application. The soil-active herbicides generally were most active 1 or 2 yr after herbicide application. All herbicides reduced the live oak cover sufficiently to allow an increase in grass cover 2 to 4 months after treatment. Tebuthiuron at 2.2 kg/ha maintained a high degree of grass cover at least 2 or 3 yr after treatment.

Average monthly rooting of saltcedar (Tamarix pentandra Pall.) stem cuttings collected weekly for a year and planted on a mist-bed was 96–100% from early February through May arid decreased to 77% in November. Accompanying shoot formation reached a concurrent maximum of 96–100%, with an October low of 10%. Bud dormancy of October-November cuttings was reduced by cold treatment, but June-July cuttings were not responsive. A rooting compound reduced shoot and root formation.

In tests conducted at Prosser, Washington, during 1955 and 1956, DCB (orthodichlorobenzene), alone or in combination with xylene, showed considerable promise for controlling submersed aquatic weeds when introduced into irrigation channels. The first objective of the experiment reported herein was to determine whether irrigation water treated with DCB or DCB-xylene mixtures would injure certain crop plants. In other tests amitrol (3–amino–1,2,4–triazole) and sodium salt of dalapon (sodium 2,2–dichloropropionate) were effective in controlling certain emergent aquatic and ditchbank weeds. Frequently, the application of herbicides to control such weeds results in inadvertent or unavoidable contamination of water used to irrigate crop plants. Consequently, a second objective of this investigation was to determine the approximate quantities of amitrol and sodium salt of dalapon required to injure certain crop plants when applied in irrigation water, and to study the symptoms of injury.

Black henbane (Hyoscyamus niger L.) has invaded cultivated land, pastures, and disturbed areas in east central Saskatchewan. This species flourishes during cycles of abundant moisture and disappears during dry cycles, surviving in Saskatchewan only in moist depressions or disturbed areas. Summerfallow, fall tillage, and competition from vigorous perennial grasses provide effective control of the weed. Black henbane is not likely to become a serious deterrent to crop production in Saskatchewan.

3-Amino-1,2,4-triazole (amitrole) sprayed on annual grassland infested with medusahead (Elymus caput-medusae L.) at 1/2 to 4 lb/A when medusahead was in the boot or soft dough stage reduced viable caryopses from 60 to 100 percent, and seed production the following year from 75 to almost 100 percent. 1,2-Dihydropyridazine-3-6-dione (maleic hydrazide) and 2,2-dichloropropionic acid (dalapon) reduced viability of medusahead seeds, but were less effective than amitrole. Viable caryopses of soft chess (Bromus mollis L.) were reduced and the year following treatment soft chess was decreased in the stands by early application (boot stage of medusahead) but not by late application of herbicides, when the soft chess heads were dry.

Photocontrol of weeds requires knowledge about the response of weeds to light and its changes over time. Thus, littleseed canarygrass germination, as an important weed in winter crops, in response to the light environment was evaluated in seeds retrieved from different burial (10, 20, and 40 cm, under irrigated or nonirrigated conditions) or storage (room temperature 25 C and cold 3 C) conditions for 1 yr. Seeds buried in the soil showed a cyclical germination behavior when tested at 20 C, with high germination percentages (68%) occurring in August, October, and December and low percentages (12%) in February and April, with another late germination in June. Germination percentages were mostly higher for seeds incubated in light than in darkness and seeds were more likely to positively respond to light in June than at the other retrieval dates, with differences as great as 60% having been observed under irrigated conditions and at depths of 20 and 40 cm. The most outstanding effect of light as a germination stimulus was observed for seeds stored at room temperature where germination in light was always 20 to 35% higher than that in darkness. The viability of seeds did not change over time in seeds kept at room or cold temperature. However, the proportion of surviving seeds was reduced by 35 to 65% when buried in the soil. Littleseed canarygrass seeds tended to survive more when buried 40 cm deep and the differences between irrigated and nonirrigated conditions were only detectable at 10 cm deep, with higher seed mortalities under irrigated conditions. Information gained in this study would be useful in developing weed control programs for this species.

Postemergence application of isopropyl N-(3-chlorophenyl) carbamate (CIPC) killed small seedlings or redroot pigweed (Amaranthus retroflexus L.), large crabgrass (Digitaria sanguinalis L.), and pale smartweed (Polygonum lapathifolium L.). However, the apparent mode of action in redroot pigweed and large crabgrass was different from that in pale smartweed. The first two species showed injury symptoms 1 to 2 days after spraying, while the effect of the herbicide on pale smartweed was slow and no growth inhibition was observed until about 2 weeks after application. Injury symptoms of smartweed were different from those of the other two species. Tolerance of redroot pigweed and large crabgrass to CIPC increased rapidly with age.

Studies on respiration, C14O2 fixation, and chlorophyll content showed that the fast action in redroot pigweed and large crabgrass was accompanied by a reduction in photosynthesis, decrease in chlorophyll content, and increase in respiration. In pale smartweed, where slow action of CIPC took place, there was no change in carbon dioxide fixation, chlorophyll content, or oxygen uptake until about 2 weeks after spraying, when symptoms of this type of action were first observed.

Mugwort (Artemisia vulgaris L.) was controlled by soil applications of potassium azide at 100 lb/A and equimolecular amounts of sodium azide in greenhouse studies. Rooted Artemisia plants exposed to exponential concentration ranges of these herbicides in ¼ strength Knops nutrient solution showed lethal effects at 10-3 M of either the potassium or sodium azide. Vapors of the potassium and sodium azides caused leaf injury at relatively low rates. Bioassays indicated dissipation of 100 lb/A of the azides in the soil in 6 weeks under greenhouse conditions.

During the vegetative phase of barnyardgrass (Echinochloa crusgalli (L.) Beauv.) development, the leaves, axillary buds (tillers) and permanent root system were initiated and developed. First adventitious roots appeared on the 6th day after germination. Internode elongation, which was coincident with a change from a vegetative phase to a reproductive phase of the plant, was observed in the field about 30 days after germination. At this time the main stem had 4–5 maturing leaves. Typically, barnyardgrass formed 8 leaves on the main axis from primordia which were initiated during the first two weeks after germination. The first tiller primordium appeared in the axil of either the 1st or 2nd leaf on the day of emergence from the soil. In the field, tillering was observed from the twelfth day. Heading began on the 40th day and the first mature seeds were formed about 64 days after germination.