The objective of this study was to evaluate the response of hairy beggarticks plants to different doses of glufosinate ammonium and the range in sensitivities of the plants and their progenies to the herbicide. Three studies were conducted, all in a greenhouse and repeated at different times. In the first study, two experiments were conducted to examine the dose–response curve, and the treatments were seven different doses of the herbicide glufosinate ammonium (0, 50, 100, 200, 400, 800, and 1,600 g ai ha−1), with four replications each. In the second study, which examined the range in sensitivity of hairy beggarticks to glufosinate ammonium, 44 plants were sprayed with a dose of 200 g ai ha−1 of the herbicide. Finally, in the third study, the range in sensitivity of the progeny of hairy beggarticks to glufosinate ammonium was investigated; in this experiment, the progenies of seven of the previous plants were sprayed with 200 g ai ha−1 of herbicide. The ammonium contents in the tissues were measured and percent injury wase visually assessed. Ammoniun content in hairy beggarticks leaves was increased more than seven times by glufosinate application and the maximum ammonium content was observed for the highest dose of the herbicide. Variability existed in the ammonium content among the individuals of the population of hairy beggarticks; however, the behavior was not replicated in the same way in the progenies. The survival of the plants after application of the herbicide allows the production of progenies with wide variability in their sensitivity to the product, independent of the behavior for the progenitor plants.

Early maturity allows weedy rice (Oryza sativa L. f. spontanea) to persist by escaping harvest in paddy fields. A shorter grain-filling period contributes to the early maturity of weedy rice. However, the differences in morphology and endosperm development in the caryopsis between weedy and cultivated rice are largely unexplored. Here, we selected four biotypes of weedy rice and associated cultivated rice (ACR; Oryza sativa) from different latitudes to conduct a common garden experiment. The endosperm development process of the caryopsis was observed by optical microscopy and electron microscopy. Endosperm cell division and starch accumulation rate during grain filling were also measured. The grain development progress in weedy rice was more rapid and earlier than that in ACR. The endosperm development progress of weedy rice was 6 to 8 d earlier than that of ACR. The endosperm cells of weedy rice cellularized earlier and more rapidly than those of ACR, and the starch grains of weedy rice were more sharply polygonal and compactly arranged than those of ACR. The active endosperm cell division period in weedy rice was 4 to 7 d shorter than that in ACR, while the active starch accumulation period of weedy rice was 2 to 8 d shorter than that of ACR. The rapid development of endosperm cells and starch grains leads to the shorter grain-filling period of weedy rice. weedy rice.

Complaints of control failures with acetolactate synthase (ALS)- and protoporphyrinogen oxidase (PPO)-inhibiting herbicides on redroot pigweed (Amaranthus retroflexus L.) were reported in conventional soybean [Glycine max (L.) Merr.] fields in North Carolina. Greenhouse dose–response assays confirmed that the Camden County and Pasquotank County populations were less sensitive to ALS- and PPO-inhibiting herbicides compared with susceptible A. retroflexus populations, suggesting the evolution of resistance to these herbicides. Sanger sequencing of target genes determined the Camden County population carried a Trp-574-Leu mutation in the ALS gene and an Arg-98-Gly mutation in the PPX2 gene, while the Pasquotank County population carried a His-197-Pro mutation in the ALS gene (first documentation of the mutation in the Amaranthus genus), but no mutation was detected in the PPX2 gene. Single-nucleotide polymorphism (SNP) genotyping assays were developed to enable efficient screening of future control failures in order to limit the spread of these herbicide-resistant populations. In addition, preliminary testing of these assays revealed the three mutations were ubiquitous in the respective populations. These two populations represent the first confirmed cases of PPO-inhibiting herbicide-resistant A. retroflexus in the United States, as well as the first confirmed cases of this particular herbicide-resistance profile in A. retroflexus inhabiting North America. While no mutation was found in the PPX2 gene of the Pasquotank County population, we suggest that this population has evolved resistance to PPO-inhibiting herbicides, but the mechanism of resistance is to be determined.

Redroot pigweed (Amaranthus retroflexus L.) is a dominant weed in soybean [Glycine max (L.) Merr.] fields in Heilongjiang Province, China. High selective pressure caused by the extensive application of the protoporphyrinogen oxidase (PPO)-inhibiting herbicide fomesafen has caused A. retroflexus to evolve resistance to this herbicide. Two susceptible and two resistant populations (S1, S2, R1, and R2) were selected in this study to illustrate the target-site resistance mechanism in resistant A. retroflexus. Whole-plant bioassays indicated that R1 and R2 had evolved high-level resistance to fomesafen, with resistance factors of 27.0 to 27.9. Sequence alignment of the PPO gene showed an Arg-128-Gly substitution in PPX2. The basal expression differences of PPX1 and PPX2 between the S1 and R1 plants were essentially nonsignificant, whereas the basal expression of PPX2 in R2 plants was slightly lower than in S1 plants. Compared with the PPX1 gene, the PPX2 gene maintained higher expression in the resistant plants after treatment with fomesafen. An enzyme-linked immunosorbent assay showed a similar basal PPO content between the susceptible and resistant plants without treatment. After fomesafen treatment, the PPO content decreased sharply in the susceptible plants compared with the resistant plants. Furthermore, after 24 h of treatment, the resistant plants showed increased PPO content, whereas the susceptible plants had died. The PPO2 mutation resulted in high extractable PPO activity and low sensitivity to fomesafen along with changes in PPO enzyme kinetics. Although the mutant PPO2 exhibited increased Km values in the resistant plants, the Vmax values in these plants were also increased. Changes in the properties of the PPO enzyme due to an Arg-128-Gly substitution in PPX2, including changes in enzyme sensitivity and enzyme kinetics, are the target-site mechanism of resistance in A. retroflexus.

Shortly after 1934 when Kögl and co-workers found that indole–3–acetic acid is a substance which has cell elongation activity in plants, many attempts were made to find other chemicals showing an indole–acetic–acid-like activity. It is 25 years now since Zimmermann and Wilcoxon found that naphthyl–1–acetic acid and some other aryl-acetic acids are active plant regulating compounds also. With these experiments it could be shown that the indole-nucleus is not essential for a plant growth regulator. The findings of Irvine showed that 2-naphthoxy-acetic acid is equally active as a phytohormone. This indicates that the acetic acid has not necessarily to be linked to the naphthalene ring directly. Thenaphthoxy-acetic acid was further modified chemically and became the starting point for the most widely used phytohormones: 2,4-D, MCPA and 2,4,5-T.

Because nut grass is a weed problem, there is need for knowledge of the factors affecting the sprouting of tubers following conditions in which they are dormant. Similarly an understanding of the mechanisms involved in the control of dormancy along with information on the metabolism of tubers at different stages of growth is needed. The purpose of this series of studies was to obtain information on some of those problems. The purpose of the present study was to determine the response of nut grass to several oxygen levels as measured by germination habits and respiration of tubers.

Optimum temperature for bud activity and shoot growth of quackgrass (Agropyron repens (L.) Beauv.) occurred between 20 and 27 C. CO2 and O2 gas concentrations normally occurring in soil air were not found to affect bud activity and shoot growth appreciably.

Internal dormancy (the state of internally arrested growth) in western ironweed (Vernonia baldwini Torr.) buds consisted of a recurring annual cycle of high and low activity with transition periods. Trends in sprouting activity were similar regardless of whether activity was measured by sprouting of buds following removal of stems in the field, or by sprouting of rhizome section buds in moist sand. Bud activity measurement was quantitatively different by the two methods, however, and the apparent period when internal dormancy developed also differed. A number of interdependent factors modified activity. At various points in the cycle, the stem apex inhibited bud growth; the stem alone inhibited bud growth; a transient block due to immaturity occurred in some buds; and two temperature-related blocks occurred. Bud age and location on the rhizome had little effect on activity. During the period of internal dormancy, sprouting of buds apparently stimulated activity of adjacent buds. Temperature greatly affected expression of internal dormancy; prolonged moist cold treatment eliminated it.

Leafy spurge is a perennial weed that is found in almost every state north of the fortieth parallel and in the southern portions of most Canadian provinces. Heaviest infestations are found in Minnesota, the Dakotas and the Prairie Provinces.

Thirteen-day-old common cocklebur (Xanthium pensylvanicum Wallr. # XANPE) plants were treated with 15 μg glyphosate [N-(phosphonomethyl)glycine] applied to the lowermost true leaves. Growth was inhibited rapidly following treatment. About 56% of applied 14C-glyphosate was taken up within 8 h. Within 4 days after treatment, diffusive resistance increased in treated leaves but did not change in untreated leaves. Glyphosate had little effect on nonstructural carbohydrate content of leaves, but soluble carbohydrate levels of stems and roots had increased by 130 and 180%, respectively, by 56 h after treatment. The uptake of 33P into roots was unaffected by the herbicide, but transport of P to the aerial tissues was severely inhibited. Effects such as inhibition of P movement could result from inhibition of protein synthesis.

The girdling of apple trees by field mice (Microtus spp.) is a common problem in most areas where this fruit is grown. Since these species of mice will seldom cross a bare area to feed, it is desirable to remove all vegetation at the base of the trees to help reduce the possibility of girdling. Many growers maintain such a bare area by slow and costly hand methods. Such methods are frequently employed in late fall, increasing the possibility that the newly exposed trunk area may incur winter injury.

Laboratory studies were conducted to evaluate 14C-flumetsulam mobility in two Mississippi soils of varied texture and organic matter content following delays in irrigation. Mobility was evaluated using packed soil columns, 25 cm deep, under unsaturated–saturated flow conditions. Irrigation timings included 0, 3, and 5 d after flumetsulam application. Flumetsulam mobility (defined as the amount collected in leachate) decreased from 45% to no more than 20% of the applied in the Prentiss sandy loam soil when irrigation was delayed 3 or 5 d. With the Okolona soil, flumetsulam recovery in the leachate was 21, 14, and 6%, respectively when irrigation occurred 0, 3, and 5 d after application. Flumetsulam proved to be mobile when irrigation immediately followed application, with 6 to 45% recovered in the leachate from all soils evaluated. The Prentiss soil retained 6% of the applied flumetsulam in the upper 5 cm and the Okolona soil retained 22% when irrigation immediately followed flumetsulam application. When the irrigation interval was delayed at least 3 d, the Okolona soil retained 40% in the upper 5 cm, whereas the Prentiss soil retained 10%. Flumetsulam mobility was dependent on irrigation timing and soil type.

Yellow rocket (Barbarea vulgaris R. Br.) was effectively controlled in established alfalfa (Medicago sativa L.) by September 15 applications of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 3-tert-butyl-5-chloro-6-methyluracil (terbacil), and 2-sec-butylamino-4-ethylamino-6-methoxy-s-triazine (hereinafter referred to as GS 14254). White cockle (Lychnis alba Mill.) was more difficult to control, but simazine was the most effective herbicide. Herbicide applications in early October reduced reserve nonstructural carbohydrate accumulations in roots of yellow rocket by November 15 but not in white cockle. Alfalfa yields were not reduced by two consecutive autumn applications of the herbicides at rates that provided adequate control of yellow rocket and white cockle.

Yellow toadflax is an introduced ornamental perennial that has become a serious weed in Wisconsin peppermint production. Glyphosate is the only labeled herbicide that controls yellow toadflax in peppermint. Other control strategies, either mechanical or cultural, have little effect on the weed in solid stands of peppermint. Previous research has suggested that the root mining moth Eteobalea serratella Tr. (Lepidoptera: Cosmopterigidae) may provide effective biological control of yellow toadflax. Therefore, experiments were conducted to determine the host specificity of E. serratella and to quantify E. serratella root mining of yellow toadflax. In larval and adult no-choice tests, E. serratella attacked only yellow toadflax. Other plant species collected from E. serratella's natural range were not attacked, neither those closely related to yellow toadflax in the family Scrophulariaceae, nor those closely related to peppermint in the family Labiatae. Root mining by E. serratella reduced root biomass an average of 20% compared to nontreated plants. Peppermint competition alone or in conjunction with root mining by E. serratella reduced root biomass 52 and 65%, respectively, compared to nontreated plants under noncompetitive conditions. E. serratella is host specific for yellow toadflax and demonstrates potential as a biological control agent by contributing to the reduced competitive ability of yellow toadflax in peppermint.

Translocation, distribution, and metabolism of 14C-carboxy-labeled dicamba (3,6-dichloro-o-anisic acid) in western bracken [Pteridium aquilinum (L.) Kuhn var. pubescens Underw.] were determined in field and greenhouse trials by liquid scintillation radioassays, autoradiographs, and paper chromatography. Absorption and translocation of 14C readily occurred from 14C-labeled dicamba applied to frond buds, pinnae of new leaves, and rhizome tissue. The translocated 14C tended to accumulate in opened fronds or if fronds had not emerged, in frond buds and rhizome apices. Dicamba applied to living tissue of a quasi-dormant rhizome in the field in spring was translocated to rhizome apices and metabolized to 5-hydroxy-3,6-dichloro-o-anisic acid and 3,6-dichlorogentisic acid 10 days after application.

Growth chamber studies and field trials were conducted to evaluate the toxicity of glyphosate [N-(phosphonomethyl)glycine] and certain other herbicides to wild garlic (Allium vineale L.). Toxicity to wild garlic increased with increasing rates up to 6 kg/ha. Glyphosate was more toxic to wild garlic when applied in spray volumes of 125 to 500 L/ha than in greater volumes. Addition of surfactant did not increase toxicity or absorption rates of 3 kg/ha of glyphosate, but did increase the advantage of 2 kg/ha of glyphosate over 2,4-D [(2,4-dichlorophenoxy)acetic acid]. When glyphosate was sprayed on wild garlic plants at 3 kg/ha, then washed off after 2, 4, 8, 16, and 32 h, absorption of a biologically significant amount of glyphosate required 8 h, and toxicity increased through the 32-h exposure. Injury, which increased as mowing was delayed up to 12 days after application, indicated that significant quantities of glyphosate were translocated between 3 to 12 days after treatment in a field test. Glyphosate; 2,4-D; 2,4-D + mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} + dicamba (3,6-dichloro-o-anisic acid); and VEL-4207 [N-phenyldiethanolamine-bis-(2-methoxy-3,6-dichlorobenzoate)], applied in a sequence of either spring-fall-spring or fall-spring, were compared for wild garlic control. All herbicides tested controlled wild garlic, but glyphosate was more effective than 2,4-D after spring-fall-spring applications. All spring-fall-spring treatments except 2,4-D + mecoprop + dicamba significantly reduced the number and weight of hardshell bulbs present 8 weeks after the last treatment. The initial treatment in the spring-fall-spring sequence was necessary to reduce hardshell bulb populations the second spring. One year after treatment wild garlic reinfested all plots.

Terminal fluorescence (FT) was monitored following root or foliar uptake of metribuzin in soybean, velvetleaf, and smooth pigweed seedlings grown in solution culture. These species are known to be tolerant, moderately susceptible, and susceptible, respectively, to metribuzin under field conditions. The indirect monitoring of herbicide metabolism by fluorescence is complicated by several factors (particularly photoinhibition) and is difficult to interpret when plants are kept in the light. Rapid declines in FT at metribuzin concentrations causing high photosystem II reaction center inhibition were interpreted, in conjunction with fresh weight and injury data, as resulting from photoinhibition in velvetleaf and smooth pigweed, and from a combination of photoinhibition and herbicide metabolism in soybeans. At lower concentrations, FT declines were apparently not affected by photoinhibition but were probably representative of herbicide metabolism. These results suggested a significant rate of metribuzin metabolism in soybeans, a minor degree of metabolism in smooth pigweed beginning after 12 h, and no detectable metabolism in velvetleaf. FT monitored over a 24-h dark period following foliar absorption showed declines in soybeans indicating a modest degree of metribuzin metabolism (at intermediate herbicide doses) but no FT declines attributable to herbicide metabolism in velvetleaf or smooth pigweed. Results indicate that the inhibition of a high percentage of photosystem II reaction centers is required before photoinhibition and photooxidative leaf damage can result from photosystem II inhibitor herbicides such as metribuzin.

Ripgut brome has a quantitative response to vernalization in relation to flowering. In greenhouse studies, cold treatment (5 ± 2 C) of 2, 4, or 6 wk shortened the vegetative period, but longer exposure did not further decrease the time required to flower. Plants vernalized as imbibed seeds for 8 wk took 17 d to flower following transfer from cold treatment to the greenhouse. Unvernalized controls flowered 53 d after planting in the greenhouse. Greatest total seed dry weight and vegetative shoot dry weight were produced by unvernalized plants, whereas lengthening periods of vernalization from 2 to 8 wk decreased both parameters. The percent of total seed dry weight to total shoot dry weight was significantly greater for vernalized plants than unvernalized controls. In field studies, ripgut brome plants established in the fall flowered sooner after resumption of growth in the spring than those planted in the spring. Plants seeded after April failed to flower until the following spring.

Experiments were conducted to determine the efficacy, absorption, and translocation of nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron on barnyardgrass, green foxtail, longspine sandbur, and large crabgrass. In the greenhouse, nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron were applied at 0.0625, 0.125, 0.25, 0.5, 0.75, 1, and 2 times their label rates of 35, 13, and 26 + 13 g ai ha−1, respectively, on 5- to 10-cm plants. Three weeks after treatment (WAT), barnyardgrass was the most susceptible species to all three herbicides, and large crabgrass was the least susceptible. The nicosulfuron, rimsulfuron, or nicosulfuron + rimsulfuron rates causing 50% visible injury (GR50) for barnyardgrass were 10.9, 4.8, and 6 + 3 g ai ha−1, respectively. Similarly, the GR50 for large crabgrass were 25.6, 9.9, and 14.3 + 7.2 g ai ha−1, respectively, 3 WAT. Absorption of nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron was greater in barnyardgrass than in large crabgrass. Absorption of nicosulfuron + rimsulfuron in barnyardgrass and large crabgrass was 74% and 57%, respectively, 7 d after treatment (DAT). In addition, translocation of nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron out of the treated leaf was 14, 12, and 14% higher, respectively, in barnyardgrass than in large crabgrass. The differential response of these weed species to nicosulfuron, rimsulfuron, and nicosulfuron + rimsulfuron might be due to differences in herbicide absorption and translocation.