The synthesis of C14 carbonyl labeled 3–(parachlorophenyl)–1, 1–dimethylurea (CMU) was undertaken to provide a supply of the herbicide for use in studies of its mode of action and of its retention in the soil.

The anatomy and pollination of subterranean cleistogamous flowers of Benghal dayflower (Commelina benghalensis) is described as a contribution to understanding its reproductive biology. Subterranean stems bear one spathe per node, each enclosing a single cleistogamous flower. Only the three anterior stamens produce functional pollen; the posterior three stamens are staminodes. Tapetum is amoeboid and endothecium is present. The three-carpellate superior ovary bears five dimorphic orthotropous ovules. Nearly mature flowers have straight to somewhat curved styles; at maturity, styles elongate and coil. Our observations indicate that coiled style growth causes rupture of anthers and brings pollen into contact with stigmas. Pollen tubes were observed in styles that had previously undergone coiling, located within mucilaginous secretions of the mature stylar canal. The subterranean cleistogamous flowers of Benghal dayflower and their apparently unique mode of pollination, viewed together with reproductive capacity of its aerial chasmogamous flowers, underscore the complexity and flexibility of the reproductive biology of this noxious weed species.

Effects of 2,4–dichlorophenoxyacetic acid (2,4–D), 2,4,5–trichlorophenoxyacetic acid (2,4,5–T), 2–methyl–4–chlorophenoxyacetic acid (MCPA) and 4–(2–methyl–4–chlorophenoxy)butyric acid [4–(MCPB)] on Oxalis latifolia H.B.K. were compared. 2,4,5–T killed leaves and up to 50% bulbs, 2,4–D was slightly less effective while MCPA and MCPB killed or distorted leaves but did not affect bulbs appreciably. Effectiveness of spray was increased by spraying in the evening rather than the morning and by applying nutrient solution for three weeks prior to spraying, but spray additives, sucrose, boric acid or urea gave no significant alteration. Studies with C14–labelled 2,4–D indicated accumulation in rapidly developing organs with less movement to organs of slower development.

Musk thistle is an invasive weed that is widely distributed throughout much of North America, including grasslands in temperate climates of the midwest USA. A series of laboratory and greenhouse experiments were conducted to determine the effect of various environmental factors on germination of musk thistle seeds. In temperature-fluctuation experiments, seed germination was greater than 65% in both alternating (30/20 C) and constant (20 or 25 C) temperature regimes with an 8-h day but less (33%) in warmer regimes (35/20 C). Germination of musk thistle seeds was 37% in alternating temperature regimes of 30/20 C in total darkness, but less than 67% in pots in the greenhouse. Differences of 10 and 15 C between day and night temperatures resulted in 91 and 75% maximum germination of musk thistle, respectively. Increasingly dryer soils reduced germination of musk thistle seeds from 35% (−0.03 MPa) to 0% (−1.2 MPa), whereas saline soils (> 80 mM) reduced maximum germination to less than 10%. Musk thistle seeds collected from populations in a bare-ground area had 96% germination, which was greater than that of seeds collected from populations growing in a perennial grass pasture (71%). A residence time (i.e., period that seeds remained on the parent plant) of 9 to 12 wk after capitulum maturity resulted in seeds germinating more quickly than those dispersed earlier. Overall, reduced light levels, cool and fluctuating temperatures, and amount of time seeds remained in residence are some of the most important factors that contribute to germination of musk thistle seeds. Information on germination dynamics of musk thistle seeds provides an understanding of the interactions that affect this process and underscores the importance of timely management strategies in temperate grasslands.

Basal bark treatment of invasive trees is an approach designed to limit damage to non-target vegetation in the vicinity, but non-target injury is still documented. No study of basal bark treatments has examined the release of herbicide residues from roots of treated plants and resulting non-target impacts. Studies were conducted in Alaska interior and coastal boreal forests on basal bark treatments with aminopyralid and triclopyr on active-growth and dormant invasive chokecherry (Prunus padus L.). The study assessed non-target damage and soil herbicide residue using a combination of visual evaluations, bioassays, and soil residue analyses. Non-target damage from herbicide residues were identified in 40% of treatments containing aminopyralid with triclopyr, 60% of treatments containing aminopyralid alone, and 5% of treatments containing only triclopyr. Laboratory studies of aminopyralid treatments to saplings isolated the effects of herbicide exudation from roots, which was found to be significant, and the magnitude was dependent on dose. Herbicide soil residues in field and laboratory experiments were quantified with analytical detection and plant bioassays. Aminopyralid soil residues were identified in 57% of field treatments receiving 8 to 60 ml of herbicide solution (2% ai) and 70% of laboratory treatments receiving 10 µl of herbicide solution (2% to 16% ai). Triclopyr residues were found from one field treatment following dosage with 28 ml of herbicide solution (18.5% ai). Anatomically, plants grown in soils associated with herbicide-treated trees, both in the field and lab, grew less dry mass than non–herbicide treated controls. This study provides the first evidence that root exudation of herbicide following basal bark treatments contributes to non-target damage of adjacent vegetation and to accumulation of soil herbicide residues. This is an important new factor for integrated pest management within basal bark treatment systems and has implications for other herbicide application types such as injections and frill, as well as determining whether root exudation is species or herbicide specific.

Dicamba was labeled in dicamba-resistant cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.] in 2017, resulting in a record number of off-target complaints. To address off-target movement via volatilization, experiments were conducted to evaluate the effectiveness of potassium tetraborate tetrahydrate (KBo) as a volatility-reducing agent (VRA) with dicamba. Low-tunnel experiments examined: (1) whether KBo functions as a dicamba VRA, (2) the relationship between KBo concentration and dicamba volatilization, (3) the effectiveness of KBo compared with potassium acetate as a VRA, and (4) the impact of KBo on dicamba volatilization with and without glufosinate. In a large-scale trial (0.4-ha plots), the effectiveness of KBo in reducing dicamba volatilization was quantified relative to a commercial dicamba application labeled for use in 2020. The addition of KBo to dicamba reduced volatility over dicamba alone and a dicamba plus potassium acetate premix. As KBo concentration increased in the dicamba spray solution, volatilization was exponentially reduced. Dicamba volatilization with the addition of KBo at 0.01 M was comparable to dicamba plus potassium acetate at 0.05 M. Potassium tetraborate tetrahydrate was more effective than potassium acetate at reducing volatility of a dicamba plus glufosinate mixture. In large-scale experiments over a 30-h period, the addition of KBo to a diglycolamine plus glyphosate mixture lowered dicamba volatilization 82% to 89% over the herbicide mixture alone. Overall, the addition of KBo to dicamba appears promising as a VRA compared with what is commercially available.

In undrained soil or solution cultures of oats or barley, the effects of hours of exposure and concentration of 2,2-dichloropropionic acid (dalapon) on height and fresh weight were equivalent. Dalapon was shown to be a growth inhibitor in corn coleoptile and pea stem sections but was inactive in oat coleoptile sections. Dalapon was antagonistic to IAA induced growth in corn coleoptile sections and 2,4-D induced growth in pea stem and oat coleoptile sections. The antagonism was reversible in pea and oat tissue, but was competitive in pea stem sections. Dalapon was shown to be an anti-auxin.

Foliage applications of 2,4–dichlorophenoxyacetic acid (2,4–D) to marabú (Dichrostachys nutans), a woody weed found in Cuba (3), generally give complete defoliation with varying amounts of stem kill. The older, more basal areas are not killed and the roots are rarely damaged by single applications of 2,4–D. Presumably therefore, little if any of the herbicide moves downward after these applications.

Halogenoalkylcarboxylic acids such as monochlorocetic acid, trichloroacetic acid, dichloropropionic acid and 2,3–dichloroisobutyric acid, have well known herbicidal activities upon monocot plants. However, they are not effective in killing the seeds of weeds. This may be due to their inability to penetrate the seed coats.

Shoot growth and morphology of sicklepod responded to distance of sicklepod from the soybean row and relative time of emergence of crop and weed. Sicklepod was added to soybean as either uniform stands of 26 individuals m−2 or as widely spaced individuals. Sicklepod shoot height, number of main-stem nodes, number of primary branches, and shoot dry weight were decreased at 12 wk after emergence when plants were situated closer to a soybean row. Sicklepod that emerged 7 d later than soybean were shorter statured and had fewer main-stem nodes. Virtually all sicklepod overtopped the soybean, but proximity to the soybean row or later emergence reduced shoot dry weight up to 60%. A doubling in branches originating at lower main-stem nodes on sicklepod 25 cm from the row, compared to those in the row (upper branch numbers were unchanged), was associated with a 67% increase in leaves. Sixty to 90% of lower branches reached the upper canopy and thus contributed to the number of leaves above the soybean. Early-season effects of soybean interference on sicklepod reduced lower branches and, as a consequence, leaf production above the soybean late in the season, when sicklepod has the greatest impact on soybean yield.

Bamboos are perennial grasses which exhibit great variation in culm height and diameter and are among the most widespread and useful plants in the tropics. More than fifty bamboo genera have been recognized, and the total number of described species and varieties throughout the world is probably near 1000. In India, this plant is considered the poor man's timber, and it is an irreplaceable basic material for millions of people in the Orient and in South and Central America. Many species are extremely vigorous, however, and become pests when they invade cultivated areas such as coffee farms, lawns, pastures, and sugarcane fields. In some localities, bamboo growth is so rampant as to interfere with the reproduction or development of valuable tree species, and measures must be taken to keep it in check.

A field experiment was conducted at the research farm of the University of Tehran to evaluate the effect of cover crops and herbicide (nicosulfuron) dosage on corn (Zea mays L.) productivity. Cover crops suppressed weed biomass and density during the fallow period; however, there was no significant effect on weed biomass or weed density in the subsequent corn crop. A mixture of cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.) was the most weed-suppressive cover in the fallow period. Nicosulfuron applied at different amounts suppressed weed biomass and density in corn when compared with weedy plots. Application of 40 g ai ha−1 of nicosulfuron was as effective on weed control as the recommended application. Cover crops did not affect corn growth; however, corn yield improved with herbicide application.

Glyphosate-resistant (GR) horseweed [Conyza canadensis (L.) Cronquist; syn.: Erigeron canadensis L.] interference can substantially reduce corn (Zea mays L.) yield. The complementary activity of 4-hydroxyphenylpyruvate dioxygenase (HPPD) and photosystem II (PSII) inhibitors has been investigated for the control of several weed species, and in many cases has been synergistic; however, there is little information on the interaction of HPPD- and PSII-inhibiting herbicides for postemergence control of GR C. canadensis in corn. Four field trials were studied over 2 yr (2019, 2020) in Ontario, Canada, in commercial corn fields with natural infestations of GR C. canadensis to evaluate the level of GR C. canadensis control with three HPPD-inhibiting herbicides (mesotrione, tolpyralate, and topramezone) and three PSII-inhibiting herbicides (atrazine, bromoxynil, and bentazon) applied individually and in tank-mix combinations, and to document the interaction of the three HPPD inhibitors tank mixed with the three PSII inhibitors. Mesotrione, tolpyralate, and topramezone controlled GR C. canadensis 83%, 84%, and 72%, respectively, at 8 wk after application (WAA). Bromoxynil and bentazon controlled GR C. canadensis 71% and 79%, respectively, while atrazine provided only 31% control at 8 WAA. The joint application of atrazine, bromoxynil, or bentazon with mesotrione increased GR C. canadensis control from 83% to 100% at 8 WAA. Tolpyralate tank mixed with atrazine, bromoxynil, or bentazon controlled GR C. canadensis 96%, 98%, and 98%, respectively, which was comparable to the mesotrione tank mixes at 8 WAA. Topramezone plus atrazine, bromoxynil, or bentazon controlled GR C. canadensis 91%, 93%, and 95%, respectively, at 8 WAA. Interactions between HPPD and PSII inhibitors were synergistic for all combinations of mesotrione or tolpyralate with atrazine, bromoxynil, or bentazon. The interaction between topramezone and PSII inhibitors was additive. All nine tank mixes controlled GR C. canadensis >90%. This study concludes that bromoxynil or bentazon, instead of atrazine, can be co-applied with mesotrione, tolpyralate, or topramezone without compromising GR C. canadensis control in corn.

I AM most happy to signal the opening of the eighth meeting of the Weed Science Society of America, the first under our new name. Let me welcome you to New Orleans and to several days of stimulating meetings and discussions with your colleagues from Canada, Latin America, and the United States.

A 3-yr experiment and a 1-yr experiment in continuous winter wheat (Triticum aestivum L. ‘Newton’) and two 3-yr experiments in continuous grain sorghum [Sorghum bicolor L. (Moench.) ‘Co-op SG-10’ or ‘DeKalb DX-42Y’] were conducted to evaluate selected foliage-applied herbicides for control of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt # AMPAL]. Glyphosate [N-(phosphonomethyl)-glycine] applied at 3.4 kg ae/ha, glyphosate plus dicamba (3,6-dichloro-2-methoxybenzoic acid) applied at 1.7 plus 0.6 kg ae/ha, and glyphosate plus 2,4-D [(2,4-dichlorophenoxy)acetic acid] applied at 1.7 plus 1.1 kg ae/ha in summer between harvesting and planting winter wheat and in spring prior to planting grain sorghum effectively reduced honeyvine milkweed regrowth 1 yr after initial application in both cropping systems. One or two additional annual applications did not provide complete control in either cropping system. Applications of 2,4-D at 2.2 kg ae/ha dicamba at 1.1 kg ae/ha and 2,4-D plus dicamba at 1.1 plus 0.6 kg ae/ha were effective if applied consecutively for 3 yr in continuous winter wheat but not in continuous grain sorghum.

A study was made on the absorption and translocation and of the effects of perfluidone [1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl) phenyl] methanesulfonamide] on the morphology and anatomy of cotton (Gossypium hirsutum L.) and yellow nutsedge (Cyperus esculentus L.). Concentrations of 1 μM to 10 μM perfluidone added to the nutrient solutions retarded growth of both species. Necrotic spots appeared on the lamina of cotton leaves which were expanded previous to the treatment. Cotton plants resumed normal growth within 11 days after removal of the herbicide. Yellow nutsedge plants remained stunted 18 days after removal of the herbicide. After 6 days, cotton and yellow nutsedge had absorbed 5.4% and 1.7%, respectively, of the 14C-perfluidone (uniformly labeled in the toluidine ring) added to the nutrient solution. Of the 14C absorbed by the plant, cotton and nutsedge translocated 20% and 30%, respectively, to the shoots. A 10-fold higher concentration of 14C was found at the leaf tips of nutsedge than in the other shoot tissues. In cotton shoots the 14C was distributed evenly. Perfluidone inhibited the mitotic indexes of cotton and nutsedge roots 78% and 100%, respectively, in 5 days.

Waterhemp (Amaranthus tuberculatus [Moq.] Sauer) escapes are common in midwestern U.S. soybean [Glycine max (L.) Merr.] fields due to the continued rise in herbicide-resistant (HR) populations. In a conventional harvesting system, weed seeds are harvested with the crop grain and spread back on to the field. Harvest weed seed control methods such as chaff lining concentrate weed seed-bearing crop and weed chaff into a narrow row (chaff line). These chaff lines (30- to 50-cm wide) are undisturbed the following growing seasons, under the assumption that the chaff line creates an environment less favorable for weed seed germination and survival. Field experiments were conducted in a soybean–corn (Zea mays L.) rotation in 2020 and 2021 in Ames, IA, and Roland, IA, to quantify the effectiveness of chaff lining for managing A. tuberculatus seeds. About 70% of the A. tuberculatus seeds were retained on the mother plant at soybean harvest in 2020. The chaff lining system concentrated more than 99% of the A. tuberculatus seeds exiting the combine into the chaff line. Although A. tuberculatus population density in 2021 was 76% higher inside the chaff line than outside the chaff line, A. tuberculatus aboveground biomass was 63% lower inside the chaff line than outside the chaff line at 12 wk after corn planting. Similarly, A. tuberculatus inside the chaff line had delayed emergence compared with A. tuberculatus outside the chaff line. Application of preemergence herbicides in corn inside the chaff line delayed A. tuberculatus emergence by more than 2 wk compared with A. tuberculatus outside the chaff line. Additionally, a follow-up postemergence herbicide application in corn was needed only inside the chaff line to manage A. tuberculatus, suggesting the possibility of lower overall herbicide use. These results support implementing chaff lining in soybean-based crop systems of the U.S. Midwest to help manage HR A. tuberculatus seedbanks.

The herbicide 0-(2,4-dichlorophenyl) 0-methyl isopropylphosphoramidothioate (DMPA) applied either as a preemergence spray or in mixture with the alkanolamine salt of 4,6-dinitro-orthosec-butylphenol (DNBP) at the “ground-cracking” (emergent) stage increased the yield of peanuts from 1960 to 1965. Average yield increases from DMPA treatments for the 5-year period were highly significant statistically if DMPA treated peanuts were compared with peanuts either cultivated, handweeded, or sprayed with standard herbicide mixtures.