Acetolactate Synthase- (ALS) inhibiting herbicides are important components for the control of ryegrass species infesting cereal-cropping systems worldwide. Although resistance to ALS herbicides in ryegrasses has evolved more than 25 yr ago, few studies have been dedicated to elucidate the molecular mechanisms involved. To this end, we have investigated the molecular basis of chlorsulfuron, sulfometuron-methyl, and imazapyr resistance in AUS5 and AUS23, two ryegrass populations from Australia. Comparison between whole-plant herbicide assays and DNA sequencing results showed that resistance to the nonmetabolizable herbicide sulfometuron-methyl was associated with four different proline mutations at ALS codon position 197 (P197) in AUS23. In addition to three P197 amino acid changes impacting on the efficacies of the two sulfonylurea herbicides, the tryptophan to leucine target-site mutation at ALS codon position 574 (W574L) was present in AUS5, conferring resistance to both sulfometuron-methyl and imazapyr. The samples were also characterized by non target-site-based resistance impacting on the metabolizable herbicide chlorsulfuron only. Interestingly, compound mutant heterozygotes threonine/serine at ALS position 197, and plants with double mutations at positions 197 and 574 were detected, thus reflecting the ability of this outcrossing species to accumulate mutant alleles. Whole-plant dose-response assays conducted on predetermined wild-type and mutant genotypes originating from the same populations allowed for a more precise estimation of the dominant and very high levels of resistance associated with the proline to serine target-site mutation at ALS codon position 197 (P197S) and W574L mutations. The two highly efficient polymerase chain reaction- (PCR) based derived cleaved amplified polymorphic sequence (dCAPS) markers developed here will allow for quick confirmation of 197 and 574 ALS target-site resistance in ryegrass species field samples and also contribute to identify populations characterized by other likely resistance mechanisms in this important weed species.

Mexican sunflower is a native species of North and Central America that was introduced into China early last century, but it has widely naturalized and become a harmful invasive plant in tropical and subtropical regions in South China. Inter-simple sequence repeat (ISSR) markers were employed to assess genetic diversity and variation in Mexican sunflower populations from China and neighboring regions. The karyotypes of populations were also studied. Our research showed high levels of genetic diversity in all populations. The lowest genetic diversity estimates were represented in two populations in Laos, suggesting prevention of new introductions into Laos is critical. Partitioning of genetic variance revealed that genetic variation was mostly found within populations, and unweighted pair group method with arithmetic means (UPGMA) analysis showed that the introductions into China and Laos were independent. There were no obvious correlations between genetic relationships and geographic distance of populations in China, consistent with the human associated dispersal history of Mexican sunflower. Previous cytological data and our chromosome count (2n = 34) and karyotype analysis showed chromosome stability among populations. The high levels of genetic diversity within invasive Mexican sunflower populations could be challenging for its management in China, and further expansion and potential negative effects on ecological systems of this plant should be monitored.

Amicarbazone is a photosystem II (PSII)-inhibiting herbicide in the triazolinone family, which is similar in mode of action to the triazines. Annual bluegrass is a cool-season weed and has shown resistance to some PSII-inhibiting herbicides. The objective was to evaluate triazine-resistant and -susceptible annual bluegrass populations for potential cross-resistance to amicarbazone. Two triazine-resistant (MS-01, MS-02) and triazine-susceptible (AL-01, COM-01) annual bluegrass populations were treated with amicarbazone, atrazine, and simazine at 0.26, 1.7, and 1.7 kg ai ha−1, respectively. All herbicide treatments controlled the susceptible populations greater than 94% 2 wk after treatment (WAT). No visual injury of MS-01 and MS-02 was observed at any time following herbicide treatment. Quantum yield (ΦPSII) of annual bluegrass was measured 0 to 72 h after application (HAA) to determine the photochemical effects of amicarbazone compared to other PSII inhibitors. ΦPSII of triazine-susceptible populations was reduced at all measurement times by all three herbicides. However, amicarbazone decreased ΦPSII of susceptible populations faster and greater than atrazine and simazine at most measurement times. Amicarbazone did not reduce ΦPSII of the MS-01 population. Amicarbazone significantly reduced ΦPSII of the MS-02 population during several measurement timings; however, these reductions were short-lived compared to the susceptible populations and no trend in ΦPSII reduction was observed. Sequencing of the psbA gene revealed a Ser to Gly substitution at amino acid position 264 known to confer resistance to triazine herbicides. These data indicate amicarbazone efficiently inhibited PSII of susceptible annual bluegrass populations; however, triazine-resistant annual bluegrass populations with Ser264 to Gly mutations are cross-resistant to amicarbazone.

The allelochemicals 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 6-methoxy-benzoxazolin-2-one (MBOA) in wheat are considered to have a role in plant defense against weeds. This study explored the effect of proximity to two weeds, wild oat and flixweed, on DIMBOA/MBOA production in wheat seedlings under hydroponic culture to identify whether the breeding of modern wheat varieties with higher concentrations of these compounds could ensure plant-mediated weed control. MBOA was detected and was noted to exert a significant response; its exudation by some wheat seedlings was significantly increased irrespective of whether the roots were in contact with or separate from those of the weeds. The weeds were a source of biotic stress to wheat when grown in proximity to it, and the stress resulted in production of higher levels of MBOA in wheat seedlings, although the concentration varied with the wheat cultivar. Therefore, the synthesis and exudation of DIMBOA/MBOA in wheat seedlings appears to be an active metabolic process influenced by the environment, particularly the presence of weeds.

Greenhouse and laboratory studies were conducted to confirm and quantify glyphosate resistance, quantify pyrithiobac resistance, and investigate interaction between flumiclorac and glyphosate mixtures on control of Palmer amaranth from Mississippi. The GR50 (herbicide dose required to cause a 50% reduction in plant growth) values for two glyphosate-resistant biotypes, C1B1 and T4B1, and a glyphosate-susceptible (GS) biotype were 1.52, 1.3, and 0.09 kg ae ha−1 glyphosate, respectively. This indicated that the C1B1 and T4B1 biotypes were 17- and 14-fold resistant to glyphosate, respectively, compared with the GS biotype. The C1B1 and T4B1 biotypes were also resistant to pyrithiobac, an acetolactate synthase (ALS) inhibitor, with GR50 values of 0.06 and 0.07 kg ai ha−1, respectively. This indicated that the C1B1 and T4B1 biotypes were 7- and 8-fold, respectively, more resistant to pyrithiobac compared with the GS biotype, which had a GR50 value of 0.009 kg ha−1. Flumiclorac was antagonistic to glyphosate by reducing glyphosate translocation. The C1B1 and T4B1 absorbed less glyphosate 48 h after treatment (HAT) compared with the GS biotype. The majority of the translocated glyphosate accumulated in the shoot above the treated leaf (that contains the apical meristem) in the GS biotype and in the shoot below the treated leaf in the resistant biotypes, C1B1 and T4B1, by 48 HAT. The C1B1 biotype accumulated negligible shikimate levels, whereas the T4B1 and GS biotypes recorded elevated levels of shikimate. Metabolism of glyphosate to aminomethylphosphonic acid was not detected in either of the resistant biotypes or the susceptible GS biotype. The above results confirm multiple resistance to glyphosate and pyrithiobac in Palmer amaranth biotypes from Mississippi and indicate that resistance to glyphosate is partly due to reduced absorption and translocation of glyphosate.

Smutgrass is an invasive warm-season perennial bunch-type grass native to tropical Asia. The two varieties of smutgrass prevalent in Florida are small smutgrass and giant smutgrass. Laboratory seed germination experiments were conducted on both smutgrass varieties to determine the effect of various environmental factors on germination and emergence. The average germination rate for both varieties was 88% at 30/20 C day/night temperatures. Seed germination for both varieties was greater under simulated temperature flux than at constant temperatures. Seed of both varieties germinated at four simulated Florida temperature fluxes (22/11, 27/15, 33/24, and 29/19 C day/night), although the germination of small smutgrass and giant smutgrass was reduced at 33/24 and 22/11 C, respectively. Germination of small and giant smutgrass under dark conditions was 27 and 53%, respectively. Both smutgrass varieties germinated over a wide range of pH values. Small and giant smutgrass germination was inhibited at water potentials below −0.2 MPa and when small smutgrass seed was placed below the soil surface. Emergence of giant smutgrass seed did not occur below 3 cm. Both smutgrass varieties germinated over a broad range of environmental conditions, indicating their capability of year-round germination; however, germination is only likely to occur under field conditions during the summer growing season when rainfall is prevalent. These results indicate that both species have the ability to germinate over a wide range of environmental conditions but that germination is inhibited by moisture stress and depth of burial. Considering that giant smutgrass prefers higher temperatures than small smutgrass, the advent of rainfall from June through September is conducive for germination. Practices that focus on the germination pattern of smutgrass could lead to better long-term management of smutgrass in Florida.

Natural dissemination of johnsongrass seeds as well as the effect of combine harvesting on this process were studied in corn fields. The estimation of natural dispersal was carried out by two different methods, collecting seeds throughout the season using seed traps and sampling soil–surface seed abundance before harvest using a vacuum device. Both methods showed the same dispersal pattern. A minimum of 84.6% was dispersed in the first 2 m from the focus and a maximum of 1.6% was dispersed beyond the first 5 m. An average of 76.3% of these dispersed seeds were lost or buried after shedding but before harvest. Seed dispersal by the combine harvester was estimated from the difference between soil–surface seed abundance in the same sites pre and postharvest. Although the quantity of seeds dispersed by the combine was similar to those dispersed by natural factors, dispersal distances were significantly higher. Around 90% of the dispersed seeds were found in the first 5 m forward and backward of the combine direction from the infestation source, and 1.6% of the seeds were found beyond 22 m forward and 10 m backward of the combine direction from the infestation source. A large proportion of the seeds dispersed were dormant or not viable. It is concluded that the major role of sexual reproduction in johnsongrass population dynamics may be to spread the risks, promoting dispersal in time and space.

In addition to being a strong competitor with cotton and other row crops, Palmer amaranth has developed resistance to numerous important agricultural herbicides, including glyphosate. The objective of this study was to determine if the glyphosate-resistance trait can be transferred via pollen movement from a glyphosate-resistant Palmer amaranth source to a glyphosate-susceptible sink. In 2006 and 2007 glyphosate-resistant Palmer amaranth plants were transplanted in the center of a 30-ha cotton field. Susceptible Palmer amaranth plants were transplanted into plots located at distances up to 300 m from the edge of the resistant pollen source in each of the four cardinal and ordinal directions. Except for the study plots, the interior of the field and surrounding acreage were kept free of Palmer amaranth by chemical and physical means. Seed was harvested from 249 and 292 mature females in October 2006 and 2007, respectively. Offspring, 14,037 in 2006 and 13,685 in 2007, from glyphosate-susceptible mother plants were treated with glyphosate when the plants were 5 to 7 cm tall. The proportion of glyphosate-resistant progeny decreased with increased distance from the pollen source; approximately 50 to 60% of the offspring at the 1- and 5-m distances were resistant to glyphosate, whereas 20 to 40% of the offspring were resistant at the furthest distances. The development of resistance was not affected by direction; winds were variable with respect to both speed and direction during the peak pollination hours throughout the growing season. Results from this study indicate that the glyphosate-resistance trait can be transferred via pollen movement in Palmer amaranth.

Three herbicidal ionic liquids (HILs)—alkyldi(2-hydroxyethyl)methylammonium (2,4-dichlorophenoxy)acetate, dialkyldimethylammonium (2,4-dichlorophenoxy)acetate, and alkyltrimethylammonium (2,4-dichlorophenoxy)acetate—were synthesized and their activity against broad-leaved weeds was investigated under field conditions. HILs as [cation][2,4-D] used in winter wheat were much more active compared to 2,4-D-dimethylammonium salt and demonstrated efficacy similar to 2,4-D 2-ethylhexyl ester. HILs exhibited desirable surface properties such as low contact angle of droplets and low surface tension. Moreover, the HILs may be safer to operators and neighboring plants due to their nonvolatile nature. HILs at 450 g ha−1 of 2,4-D did not injure wheat.

ρ-Cymene was one of the major components of volatiles released by croftonweed. The allelopthy of ρ-cymene on the growth of upland rice seedlings was performed. Hydrogen peroxide generation, malondialdehyde (MDA) content, proline content, total ascorbate (ascorbate/dehydroascorbate), reduced/oxidized glutathione, and the levels of induction of antioxidant enzyme were studied in the seedlings of upland rice. ρ-Cymene inhibited the growth of upland rice seedlings. Exposure of upland rice seedlings to ρ-cymene increased levels of H2O2, MDA, and proline, indicating lipid peroxidation and induction of oxidative stress. Activities of the antioxidant enzymes superoxide dismutase, catalase, peroxidase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase were significantly elevated during the treatment period (7–15 d) compared with enzymes in the upland rice seedlings unexposed to ρ-cymene, thereby indicating the enhanced generation of reactive oxygen species (ROS) upon ρ-cymene exposure. These results suggest that activation of the antioxidant system by ρ-cymene led to the formation of ROS that resulted in cellular damage and decreased growth of upland rice seedlings.

Silverleaf nightshade is a widespread, deep-rooted, summer-growing perennial that significantly reduces production in Australian crop and pasture systems. It has an extensive root system, which competes both directly and indirectly with summer and winter pastures and crops through depletion of soil moisture and nutrients. Long-distance dispersal of seeds is an important mechanism for its spread and management. A range of experiments was conducted to determine the factors influencing seed production and seedbank dynamics. Seed production ranged from 1,814 to 2,945 m−2. Diurnally fluctuating temperatures of 25/15 C provided the optimal thermal conditions for germination, with germination not affected by light. Osmotic stress reduced germination, with no germination occurring at −1MPa. Germination was reduced to 5% at 160 mM NaCl, suggesting some salt sensitivity. Germination occurred over a pH range of 4 to 10, but declined with increasing acidity. Viability of buried seed declined to around 20% after 3 yr, with seed buried at 10 cm remaining the most viable. The prolonged seed persistence in the soil indicates a long-term control program is necessary for depleting the soil seedbank.

Common beggar's-tick is an annual weed commonly found in citrus groves in Florida. A series of laboratory and greenhouse experiments were conducted to determine the germination response of common beggar's-tick to various environmental factors that influence seed survival, germination, and dormancy. The results suggest that common beggar's-tick germinated over a wide range of temperatures (15 to 40 C) and in both alternating light and dark and dark conditions. New seeds (collected in 2010) germinated better than the old seeds (collected in 2007) at 15/10 C; however, at temperatures above 35 C, the old seeds germinated better. The highest germination was 95% at 25 to 30 C with old seeds compared to 78 to 86% at 20 to 30 C with new seeds. Germination of common beggar's-tick was inhibited at osmotic potential above −0.6 MPa and salt concentrations of 320 mM. Highest germination in common beggar's-tick was found under neutral conditions (pH 7); germination decreased sharply under increasing acidity and alkalinity. Emergence decreased as depth of sowing increased, with greatest germination (89 to 91%) occurring when sown at the surface (0 cm) regardless of seed age. No germination was observed when seeds were buried at 10 cm. Results of this study suggest that favorable temperature and soil pH, and adequate moisture in Florida ensures the germination and continued presence of common beggar's-tick.

Glyphosate-resistant (GR) volunteer corn has emerged as a problematic weed in corn:soybean rotational systems, partly because of the rapid increase in adoption of corn hybrids that contain traits for both glyphosate and insect resistance. Volunteer GR corn can decrease soybean yields. The objectives of this study were to quantify the impact of volunteer corn on soybean growth and yield and determine how volunteer corn densities affect western corn rootworm (WCR) emergence. Volunteer corn seed was hand-planted at targeted densities of 0.5, 2, 4, 8, 12, and 16 seeds m−2 at soybean planting and 21 d after planting to evaluate both early- and late-emerging cohorts. WCR emergence was assessed with the use of field emergence traps placed over individual corn plants in the 0.5- and 16-plants-m−2 plots in 2008 and 2009. In 2010, WCR emergence traps were also placed over individual and clumped volunteer corn plants at densities of two and eight plants m−2. Soybean yield reductions ranged from 10 to 41% where early-emerging volunteer corn densities ranged from 0.5 to 16 plants m−2. No soybean yield loss occurred with the late-emerging cohort of volunteer corn. Twice as many adult WCRs emerged from a single volunteer corn plant growing at densities of 8 and 16 plants m−2, compared with plots containing 0.5 and 2 plants m−2. These results demonstrate that controlling volunteer corn will not only prevent soybean yield loss, but also may reduce the risk of WCR larval survival after exposure to Bt (Bacillus thuringiensis Berliner derived) corn.

Leafy spurge seeds are responsive to alternating temperature rather than constant temperature for germination. Transcriptome changes of dry leafy spurge seeds and seeds imbibed for 1 and 3 d at 20 C constant (C) and 20 : 30 C alternating (A) temperature were determined by microarray analysis to examine temperature responsiveness. Principal component analysis revealed differences in the transcriptome of imbibed seeds based on the temperature regime. Computational methods in bioinformatics parsed the data into overrepresented AraCyc pathways and gene regulation subnetworks providing biological context to temperature responses. After 1 d of imbibition, the degradation of starch and sucrose leading to anaerobic respiration were common pathways at both temperature regimes. Several overrepresented pathways unique to 1 d A were associated with generation of energy, reducing power, and carbon substrates; several of these pathways remained overrepresented and up-regulated at 3 d A. At 1 d C, pathways for the phytohormones jasmonic acid and brassinosteroids were uniquely overrepresented. There was little similarity in overrepresented pathways at 1 d C between leafy spurge and arabidopsis seeds, indicating species-specific effects upon imbibition of dry seeds. Overrepresented gene subnetworks at 1 d and 3 d at both temperature regimes related to signaling processes and stress responses. A major overrepresented subnetwork unique to 1 d C related to photomorphogenesis via the E3 ubiquitin ligase COP1. At 1 d A, major overrepresented subnetworks involved circadian rhythm via LHY and TOC1 proteins and expression of stress-related genes such as DREB1A, which is subject to circadian regulation. Collectively, substantial differences were observed in the transcriptome of leafy spurge seeds imbibed under conditions that affect the capacity to germinate.

Parthenium weed, an annual herb native to tropical America, causes severe economic, human, and animal health and environmental impacts in Australia and in many countries in Asia, Africa, and the Pacific. There is little known about variation in reproductive output in naturally occurring populations of this weed. This information is vital to develop plant population models, devise management strategies to reduce seed output, and formulate parthenium weed pollen-induced human health (e.g., dermatitis and hay fever) risk assessment. Here, the variations in the number of capitula produced by the parthenium weed at two sites in Queensland, Australia, over a 4-yr period are reported. Under field conditions, parthenium weed produced up to 39,192 capitula per plant (> 156,768 seeds per plant), with majority of the plants (≈ 75%) producing between 11 and 1,000 capitula, and less than 0.3% of the plants producing more than 10,000 capitula (> 40,000 seeds per plant). The number of capitula per plant in the field (297 ± 22) was much lower than those reported from glasshouse and laboratory studies. Plant biomass contributed to 50 to 80% of the variation in capitulum production between plants within plots at each site, and weed density accounted for 62 to 73% of the variation in capitulum production between plots within each site. As plant size is directly correlated with reproductive output, plant size distributions in parthenium weed can be used to estimate effective population size. Information on variation in reproductive output will be used to implement management strategies to reduce parthenium weed seed output, resulting in reduced soil seed bank and weed seed spread.

The dynamics of the host–parasite relationship between tomato cv. Brigade and Egyptian broomrape is temperature-related. This relationship was utilized for the development of an equation on the basis of thermal time (as measured by growing degree days, GDD, C) to predict the parasitism dynamics of Egyptian broomrape in tomato. To obtain a reliable prediction from thermal time values, studies based on a wide range of temperatures are essential. Four temperature-regime treatments and five levels of infestation with Egyptian broomrape seeds were tested in a multiclimate greenhouse (phytotron) and a temperature-controlled greenhouse, respectively. The day/night temperature regimes were 20/12 C, 23/15 C, 26/18 C, and 29/21 C and the infestation levels were 0 (noninfested control), 1, 5, 10, and 25 mg of Egyptian broomrape seeds per liter of soil. As expected, increasing temperature or infestation levels resulted in faster appearance and higher rate of attachments, respectively. The relation between development of attachments and GDD was described as a three-parameter logistic curve. In both temperature-regime and infestation-level experiments, the development of attachments began 200 GDD after planting and the maximal number of attachments was recorded 800 GDD after planting. A significant reduction in the aboveground biomass of the tomato plants due to increased Egyptian broomrape biomass was recorded only for the 26/18 C and 29/21 C day/night treatments and the three highest infestation levels (5, 10, and 25 mg L−1 soil). The ability to predict the start of parasitism can be used to develop a climate-based system for Egyptian broomrape control with herbicides.

Maize dwarf mosaic (MDM) stunts corn growth, delays development, and is the most prevalent viral disease of sweet corn grown in many regions of North America and Europe. Although some weeds escape control in most sweet corn fields, the extent to which MDM influences the weed suppressive ability of the crop is unknown. Field studies were conducted over a 3-yr period to characterize the influence of variable MDM incidence in sweet corn on growth, fecundity, and germinability of wild-proso millet, a common weed in the crop. Treatments included five levels of MDM incidence (0, 25, 50, 75, and 100% of plants infected) in two MDM-susceptible hybrids differing in weed suppressive ability. Previous research showed that hybrid ‘Legacy’ had greater weed suppressive ability than ‘Sugar Buns’. Wild-proso millet biomass and fecundity depended largely on the hybrid in which the weed was growing. Wild-proso millet growing in Sugar Buns weighed 45 to 117% more than wild-proso millet in Legacy. Incidence of MDM in sweet corn affected wild-proso millet biomass and fecundity, but only under high weed population densities. When wild-proso millet was observed at 122 plants m−2, weed biomass increased 9 g m−2 for each additional 10% incidence of MDM of sweet corn. Weed suppressive ability of the competitive and less competitive hybrids were influenced to the same extent by MDM. Coupled with a lack of resistance to MDM in two-thirds of commercial sweet corn hybrids, the disease could be an additional factor perpetuating weed growth and fecundity in sweet corn, particularly in fields with high population densities of wild-proso millet.

A waterhemp population from a native-grass seed production field in Nebraska was no longer effectively controlled by 2,4-D. Seed was collected from the site, and dose-response studies were conducted to determine if this population was herbicide resistant. In the greenhouse, plants from the putative resistant and a susceptible waterhemp population were treated with 0, 18, 35, 70, 140, 280, 560, 1,120, or 2,240 g ae ha−1 2,4-D. Visual injury estimates (I) were made 28 d after treatment (DAT), and plants were harvested and dry weights (GR) measured. The putative resistant population was approximately 10-fold more resistant to 2,4-D (R:S ratio) than the susceptible population based on both I50 (50% visual injury) and GR50 (50% reduction in dry weight) values. The R:S ratio increased to 19 and 111 as the data were extrapolated to I90 and GR90 estimates, respectively. GR50 doses of 995 g ha−1 for the resistant and 109 g ha−1 for the susceptible populations were estimated. A field dose-response study was conducted at the suspected resistant site with 2,4-D doses of 0, 140, 280, 560, 1,120, 2,240, 4,480, 8,960, 17,920, and 35,840 g ha−1. At 28 DAT, visual injury estimates were 44% in plots treated with 35,840 g ha−1. Some plants treated with the highest rate recovered and produced seed. Plants from the resistant and susceptible populations were also treated with 0, 9, 18, 35, 70, 140, 280, 560, or 1,120 g ae ha−1 dicamba in greenhouse bioassays. The 2,4-D resistant population was threefold less sensitive to dicamba based on I50 estimates but less than twofold less sensitive based on GR50 estimates. The synthetic auxins are the sixth mechanism-of-action herbicide group to which waterhemp has evolved resistance.

Experiments were conducted in the laboratory and screenhouse to determine the effects of scarification; alternating day/night temperatures; light, salt, and water stress; seed burial depth; and rice residue on seed germination and seedling emergence of threelobe morningglory, and to evaluate the response of this weed to commonly available POST herbicides in the Philippines. Germination was stimulated by seed scarification, suggesting that inhibition of germination in this species is mainly due to the hard seed coat. Germination of the scarified seeds was not influenced by the tested temperatures (alternating day/night temperatures of 25/15, 30/20, and 35/25 C) and light. The concentrations of sodium chloride, ranging from 0 to 250 mM, did not influence germination of the scarified seeds of threelobe morningglory. The osmotic potential required for 50% inhibition of maximum germination was −0.35 MPa, although some seeds germinated at −0.6 MPa. Seedling emergence was greatest for the seeds placed on the soil surface (96%), and emergence declined with increased burial depth in soil. The burial depth required for 50% inhibition of maximum emergence was 2.8 cm. No seedlings emerged from a burial depth of 6 cm or greater. Residues of up to 6 Mg ha−1 on the soil surface did not influence seedling emergence of threelobe morningglory. The herbicide 2,4-D at 400 g ai ha−1 provided excellent control of threelobe morningglory when applied at the four-leaf (100%) and six-leaf (97%) stages. However, at the eight-leaf stage, percent control was reduced to 67% and herbicide rate had to be increased twofold to achieve 95% control. The information gained from this study could contribute to developing components of integrated weed management strategies for threelobe morningglory. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence and early application of an effective POST herbicide could serve as important tools for managing threelobe morningglory.

Weedy rice is a serious problem of cultivated rice in most of the rice-growing areas in Asia, causing increased production costs and yield losses in rice. A study was conducted to determine the response of weedy rice accessions from India (IWR), Malaysia (MWR), Thailand (TWR), and Vietnam (VWR) to seed burial and flooding depths. The greatest emergence for each weedy rice accession (97% for IWR, 82% for MWR, 97% for TWR, and 94% for VWR) was observed in seeds placed on the soil surface. Seedling emergence decreased with increase in burial depth. For the IWR accession, 0.5% of the seedlings emerged from 8-cm depth, whereas for the other three weedy rice accessions, no seedlings emerged from this depth. When seeds were sown on the soil surface, flooding depth ranging from 0 to 8 cm had no or very little effect on seedling emergence of different weedy rice accessions. On the other hand, flooding decreased seedling emergence in all weedy rice accessions when seeds were sown at 1 cm deep into the soil. Compared with seedling emergence, flooding had a more pronounced effect on seedling biomass for all weedy rice accessions. A flooding depth of 2 cm reduced seedling biomass by an amount greater than 85% of each weedy rice accession. The results of this study suggest that emergence and growth of weedy rice could be suppressed by deep tillage that buries seeds below their maximum depth of emergence (i.e., > 8 cm for the accessions studied) and by flooding fields as early as possible. The information gained from this study may help design cultural management strategies for weedy rice in Asia.