Placing hydrilla (Hydrilla verticillata Royle) in 2.7 and 5.4 μM solutions of carbon-14-labeled endothali [7-ox = abicyclo(2,2,1)heptane-2,3-dicarboxylic acid] under controlled conditions resulted in a sigmoid-shaped uptake curve for both herbicide concentrations. Apical sections of hydrilla, which included the apical bud, absorbed greater amounts of endothall-14C than sections excised from the center of the plant below the apical bud. Low concentrations of copper as copper sulfate pentahydrate solutions of 0.4 and 2.0 μM in combination with endothall-14C increased the amount of radioactivity found in hydrilla, but copper concentrations of 4.0, 8.0, and 16.0 μM inhibited endothall-14C uptake. The greatest uptake by hydrilla in 5.4 and 2.7 μM solutions of endothall-14C exposed to temperatures of 10, 20, and 30 C occurred in the 20 and 30 C solutions, respectively. Endothall-14C uptake was studied under light intensities of 0, 540, 5400, and 21,500 lux. Uptake of radioactivity from 2.7 and 5.4 μM solutions of endothall-14C was greatest at 540 and 21,500 lux, respectively.

The acetanilide herbicides alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], the ethyl ester of diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine], or H-26910, the isopropyl ester of N-(chloroacetyl)-N-(2-methyl-6-ethylphenyl)glycine, failed to inhibit yellow nutsedge (Cyperus esculentus L. ♯ CYPES) tuber sprouting in petri dishes. At 3.5 and 0.35 μM, all herbicides inhibited growth of newly emerging shoots. There was no significant difference in activity among alachlor, metolachlor, diethatyl ethyl, and R-26910 on yellow nutsedge sprouts grown in petri dishes. In soil, metolachlor and alachlor were equally effective for yellow nutsedge control. Both were more effective than H-26910 at high levels of soil organic matter. Diethatyl ethyl was least effective at all levels of soil organic matter. For all herbicides evaluated, activity decreased with increased levels of organic matter in the soil. For acetanilide herbicides to be effective on yellow nutsedge, they needed to be in the soil zone, above or at the level of the tuber.

Organic cropping systems are characterized by soil-disturbance events that can be diversified over years through crop rotations and within seasons by varying planting dates. The Farming Systems Project at Beltsville, MD, USA, is a long-term experiment that includes three organic rotations, corn (Zea mays L.)–soybean [Glycine max (L.) Merr.], corn–soybean–wheat (Triticum aestivum L.), and corn–soybean–wheat–alfalfa (Medicago sativa L.). Analysis of weed presence and cover over the first 18 yr of this experiment revealed that the tall, erect annual broadleaf weeds smooth pigweed (Amaranthus hybridus L.), common lambsquarters (Chenopodium album L.), horseweed (Erigeron canadensis L.), jimsonweed (Datura stramonium L.), and/or velvetleaf (Abutilon theophrasti Medik.) were most prominent in corn and soybean. Generally, these species exhibited traits adapted to the disturbance regimes, nutrient availability, crop environment and duration, and local meteorological conditions associated with the summer annual corn and soybean crops. Abundance of A. hybridus, D. stramonium, and A. theophrasti were controlled primarily by rotation diversity, whereby presence and cover of these species were highest in the short corn–soybean rotation and lowest in the longer rotations that had more diverse seasonal soil-disturbance regimes. Early-season temperature was the primary factor controlling C. album presence and cover, which were higher at lower temperatures associated with earlier planting dates. Higher early-season precipitation was the primary factor associated with higher presence of annual grass species. The relative abundance of species in organic corn and soybean was determined primarily by the diversity of crops and disturbance operations in rotation, the timing of spring tillage and planting, and annual meteorological conditions driving emergence periodicity.

Greenhouse studies were conducted to determine the influence of spray-solution pH, adjuvant, light intensity, temperature, and glyphosate on the efficacy of saflufenacil on horseweed. Control of glyphosate-resistant horseweed from saflufenacil alone was greatest with a spray-solution pH of 5, compared with pH 7 or 9. However, when glyphosate was added to saflufenacil, similar GR50 values were measured with spray solutions adjusted to pH 5 and 9, and horseweed control at pH 9 was 38% greater than at pH 7. The efficacy of saflufenacil on horseweed was 36% greater when crop oil concentrate was used as an adjuvant compared with nonionic surfactant, regardless of the addition of glyphosate or the sensitivity of the horseweed population to glyphosate (resistant vs. susceptible). The addition of glyphosate to low rates of saflufenacil increased control over saflufenacil applied alone on glyphosate-susceptible and -resistant horseweed. Saflufenacil activity was greater under low light intensity (300 μmol m−2 s−1) than high light intensity (1,000 μmol m−2 s−1). Although initial horseweed control was greater under high temperature (27 C) compared with low temperature (10 C), by 21 d after treatment horseweed dry weight was similar from saflufenacil applied under high and low temperatures.

Redroot pigweed (Amaranthus retroflexus L.) and slender amaranth (Amaranthus viridis L.) are considered emerging problematic weeds in summer crops in Australia. An outdoor pot experiment was conducted to examine the effects of planting time on two populations of A. retroflexus and A. viridis at the research farm of the University of Queensland, Australia. Both species were planted every month from October to January (2017 to 2018 and 2018 to 2019), and their growth and seed production were recorded. Although both weeds matured at a similar number of growing degree days (GDD), they required a different number of days to complete their life cycles depending on planting date. The growth period was reduced and flowering occurred sooner as both species experienced cooler temperatures and shorter daylight hours. Both species exhibited increased height, biomass, and seed production for the October-sown plants compared with other planting times, and these parameters were reduced by delaying the planting time. The shoot and root biomass of A. retroflexus and A. viridis (averaged over both populations) was reduced by more than 70% and 65%, respectively, when planted in January, in comparison to planting in October. When planted in October, A. retroflexus and A. viridis produced 11,350 and 5,780 seeds plant−1, but these were reduced to 770 and 365 seeds plant−1 for the January planting date, respectively. Although the growth and fecundity of these species were dependent on planting time, these weeds could emerge throughout the late spring to summer growing season (October to March) in southeast Australia and could produce a significant number of seeds. The results showed that when these species emerged in the late spring (October), they grew vigorously and produced more biomass in comparison with the other planting dates. Therefore, any early weed management practice for these species could be beneficial for minimizing the subsequent cost and energy inputs toward their control.

Automated guidance systems have advanced precise interrow hoeing in narrowly spaced cereals. Compared with other direct mechanical strategies, hoeing provides superior weed control and improved yields. However, weeds in the uncultivated intrarow zone may survive and compete intensely with the crop, causing yield loss. Therefore, improved intrarow weed management strategies in hoed cereals must be investigated. In spring barley (Hordeum vulgare L.), the effect of crop density was assessed at four levels (200, 300, 400, and 500 plants m−2); interrow spacing at two levels (15 and 20 cm), relevant to the abilities of current automated equipment to hoe between narrowly spaced rows; and weed management treatment at three levels (no additional controls, herbicide, and preemergence tine harrowing). All treatments received interrow hoeing, and a surrogate weed (white mustard, Sinapis alba L.) was sown and monitored throughout experiments. The manipulation of crop density was a reliable method for suppressing the growth of intrarow weeds. As barley density increased from the target 200 to 500 plants m−2, percent reduction in intrarow surrogate and ambient weed biomass (g m−2) increased from 49% to 82% and 53% to 99%, respectively. Increasing crop density caused a decrease in grain bulk density (kg hl−1) both years, and grain protein (%) and 1,000-kernel weight (g) in one year; whether these changes constitute a loss in grain quality depends upon end use. While row spacing had no effect on intrarow weeds, crop yields were 7% to 8% lower at 20 cm compared with 15 cm, incentivizing narrow row sowing. Barley yields were unaffected by increasing crop density, and the effect of preemergence tine harrowing was inconsistent. In one year, harrowing reduced surrogate and ambient weed biomass and increased barley yield; however, in another year, ambient weed biomass increased, and harrowing did not affect yield or surrogate weed biomass.

It was discovered in 1952 that 3–amino–1,2,4–triazole (amitrole) possesses defoliating and regrowth inhibiting properties in cotton. Subsequent study has shown that its most dramatic effect is in the inhibition of chlorophyll formation. Since it is readily absorbed by roots, is translocated throughout the plant, is a general growth inhibitor, and is effective in low concentrations, it is a potentially valuable systemic herbicide. It has been used successfully in the control of quackgrass, nutsedge, Canada thistle, and such woody plants as poison ivy.

(The paper to which this is a supplement appeared in Weeds 3:241–253. The following explanation of the table is repeated from that issue:

“The chemicals are arranged alphabetically according to Chemical Abstracts' nomenclature.

“Density is given at 20°C referred to water at 4°C. Specific gravities are at the indicated temperatures. The melting point is of the commercially used material unless otherwise specified. −H2O. indicates loss of water.

“The pH value is for 5% solutions in water or alcohol unless otherwise indicated.”

It is believed that the abbreviations, tabled in the previous paper, are clear without repetition. Ed.)

Smooth bromegrass, Bromus inermis, and red fescue, Festuca rubra, were sown in 1952 on a fertile soil severely infested with yellow toadflax, Linaria vulgaris Mill., in the Peace River section of Alberta. Annual applications of 2,4-dichlorophenoxyacetic acid (2,4-D) were made at late flower-bud stage at nil, 1, 2, 3, and 4 lb/A acid equiv. In 1958, the average per cent of toadflax in the brome was 1, 0.5, 0.5, 0, and 0, respectively. Red fescue had 6 to 0.1% of toadflax. All rates of 2,4-D prevented seed production. The sods were broken in 1959, and toadflax re-established strongly on all plots from dormant seed and residual plants. In 1961, the brome, rejuvenated by breaking, strongly suppressed toadflax, while fescue failed to compete with it.

Most seed of broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. & Rusby] and threadleaf snakeweed [G. microcephala (DC.) Gray] were dormant when collected soon after maturity, requiring 4 to 6 months of storage at room conditions to break dormancy. An alternating temperature regime of 10 C (16 h) and 20 C (8 h) favored snakeweed germination during the afterripening period, but germination was greatest under alternating temperatures of 20 C (16 h) and 30 C (8 h) after 24 months of storage. After 6 months of storage, maximum germination (70% or more) of threadleaf snakeweed seed occurred at continuous temperatures of 15 to 25 C; whereas, broom snakeweed seed germinated best at 15 and 30 C. Germination of both species in darkness was half or less of germination with daily 8-h periods of light. Germination of seed lots containing a high proportion of dormant achenes was enhanced by preimbibition storage at 50 C; after dormancy was naturally broken, exposure to 50 C prior to germination decreased early seedling vigor and growth but not germination.

Improved methods of weed control through use of herbicides offer important means of reducing production costs and labor requirements in irrigated cotton. The use of pre-emergence herbicides has proved to be an effective tool for annual-weed control in cotton in the humid southeastern cotton region of the United States. Research in Arizona has shown that certain herbicides applied at layby (immediately after the last cultivation) are effective for the control of late-season annual weeds in cotton.

Several herbicides were used for control of weeds in Jersey Orange sweet potato plantings on a sandy loam soil at Hammonton, New Jersey, during 1960, 1961, and 1962. The treatments were applied preemergence to the weeds at transplanting of the crop. Data included crop injury scores, level of weed control, effects on yield, influence on internal root color and flavor, and effects on sprouting.

Excellent control of germinating annual weeds was obtained with 3-amino-2,5-dichlorobenzoic acid (amiben), 2,6-dichlorobenzonitrile (dichlobenil), N,N-dimethyl-2,2-diphenylacetamide (diphenamid), and dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA). These herbicides had no adverse effects on yield, quality factors, or growth.

A truck sprayer for applying herbicides to brush is described. It consists of a three-section, hydraulically controlled boom capable of spraying about a 22-ft swath on brush up to 12 ft tall. The spraying system is mounted on a ⅓-T truck equipped with additional lights for night spraying. Plots 22 ft wide by 50 to 200 ft long are sprayed.

Selected herbicides were evaluated for control of large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.] in planted ‘Tifway’ bermudagrass (Cynodon sp.). The most effective treatment technique was sequential treatments of DCPA (dimethyl tetrachloroterephthalate) at planting followed with two applications of MSMA (monosodium methanearsonate) + 2,4-D [(2,4-dichlorophenoxy) acetic acid] which controlled 95% of the weeds and permitted bermudagrass to form a 96% ground cover in 22 weeks. Other treatments, listed in order of decreasing effectiveness were a single application of oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one], pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl)-benzamide] applied in two applications and MSMA + 2,4-D in two applications.

Seeds of false cleavers (Galium spurium L.) grown in mid-May germinated 12 to 14 days after planting in central Alberta. The plants flowered from early July to late August and developed fruits from mid-July to early September. Plants from the late-June sowing date developed fruits until early October unless early fall frost killed the plants. Plants from seeds sown after mid-July remained in a vegetative state until late September and did not flower. Seedlings that emerged in August and September survived a mild prairie winter and resumed growth the following spring. Under greenhouse conditions, plant height ranged from 77 to 113 cm and the number of branches at first node ranged from 6 to 14, as plant density decreased from 16 to 1 plant/pot. Shoot dry weight decreased by 50% as plant population doubled, 46 days after emergence. The number of seeds produced/plant decreased from 3500 to 175 as plant density increased from 1 to 16 plants/pot. In growth chamber studies, plant growth was greatest at 20 compared to 16 or 24C.

Bean plants (Phaseolus vulgaris L. var. Black Valentine) pretreated with gibberellic acid (hereinafter referred to as GA) absorb and accumulate considerably more N-1-naphthylphthalamic acid (naptalam) than untreated plants. All concentrations of GA from 2.9 × 10−6 to 8.6 × 10−4M were effective; peak influence occurred at 6 × 10−4M. Plants pretreated with this concentration took up 58% more naptalam than untreated plants. When the different parts of the plant were analyzed for naptalam separately, the leaf area (on a per g dry weight basis) was influenced most by GA pretreatment. The leaf area of bean plants pretreated with 2.9 × 10−4M contained 212% more naptalam than the leaf area of untreated plants. The leaf area also included all stem and petiole tissue above and including the first true leaves.

The incidence of puncturevine (Tribulus terrestris L.) carpels and viable seed recovered from soil samples varied inversely and linearly with depths to 24 cm. Soil type and texture and method of tillage influenced the gradients of carpel distribution and their rate and degree of vertical migration. Evidence for enforced, induced, and innate dormancy in puncturevine seed is presented. Most seed germinated from depths of less than 4 cm in cultivated, sandy loam and clayloam soils. The intra-carpel pattern of seed germination was such that seed located nearest the stylar end of two, three, and four-seeded carpels tended to germinate first, with the other seed tending to follow in order of their position in the carpel from the stylar to the receptaclar end. However, all possible combinations of intra-carpel germination patterns occurred under field conditions.

The physiological responses of corn (Zea mays L. ‘Goldencrossbantam′) and pea (Pisum sativum L. ‘Alaska′) to sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one} were investigated. Sethoxydim did not affect excised pea root growth at 1 × 10−4 M but inhibited excised corn root growth at concentrations of 1 × 10−8 M and above. Treating corn impeded root growth with 1 × 10−7 M sethoxydim within 4 h after treatment; however, little histological change of the roots was observed at 48 h. At 1 × 10−6 M, growth nearly stopped within 4 h after treatment, and clear cytological changes of the roots were observed at 24 and 48 h. Sethoxydim inhibited both mitosis and DNA synthesis of excised corn root tips between 4 and 48 h after treatment. Respiration of corn roots measured by oxygen uptake and the TTC (2,3,5-triphenyltetrazolium chloride) test was not affected by the herbicide directly. Sethoxydim (1 × 10−4 M) inhibited IAA-induced cell elongation of corn coleoptile and pea epicotyl by 37 and 12%, respectively. Sethoxydim selectively inhibited the growth of excised root tips of susceptible corn by affecting cell division rather than cell enlargement, and the inhibition mechanism of cell division (inhibition of mitosis) by the herbicide was not by direct inhibition of DNA synthesis or by effects on respiration.

Survival and growth of five collections of big sagebrush were compared in reciprocal transplant gardens. The study was designed to further the understanding of seedling ecology of this important rangeland plant. Survival of transplanted seedlings was not tied to their origin, but antagonism for collection site in survival was apparent for some collections. The site with the highest environmental potential as indexed by native plant community, soil development, and precipitation had the poorest seedling survival. The site with the lowest environmental potential produced seedlings that had the highest survival across all reciprocal gardens. The average mortality level after 3 yr was 11%, indicating that seedlings of big sagebrush can be transplanted successfully. In dry years, the collection from the driest location had the highest amount of juvenile biomass accumulation. However, during a season with much above-normal precipitation this was reversed and the amount of growth for this source was below levels observed for the dry years. The relation between subspecies of big sagebrush and survival or growth of the collections used in this study was not clear. Because collections were made on arid extremes of the subspecies they may reflect introgressive populations among subspecies.

Fumitory (Fumaria officinalis L.) achenes were subjected to various treatments to induce germination and to study dormancy. Complete pericarp removal, partial seed coat removal, puncturing the seed coat, heat treatment, red and far-red light treatments, and germination temperature treatments did not break dormancy. Low-temperature after-ripening for 60 days at 4 C dormant fumitory achenes resulted in 90 to 95% germination. Water leaching of fumitory achenes increased the time required for successful after-ripening and the water leachate stimulated Avena coleoptile cylinder elongation. Wild oat (Avena fatua L.) embryo germination was inhibited by high concentrations of fumitory achene leachate and stimulated slightly by lower concentrations. High concentrations of the leachate inhibited epicotyl and radicle growth of pre-sprouted lettuce (Lactuca sativa L.) seedlings and lower concentrations markedly stimulated radicle growth.