Surgical experiments were conducted on cultured five-node apical rhizome segments of quackgrass. Removal of scale leaves promoted an initial burst of growth within the axillary buds but did not support the continued growth of buds as effectively as removal of the rhizome apex. Replacement of detached scale leaves over denuded buds temporarily repressed the promotive effect of scale leaf removal. Aqueous extracts of scale leaf material inhibited apical growth in rhizome segments but did not inhibit bud growth. Anatomical sections revealed that removal of scale leaves promoted development of buds: cells enlarged, vascular tissues differentiated, and new nodes began to form within 4 days of the removal of scale leaves. It is suggested that scale leaves contribute to apical dominance by inhibiting the initial development of axillary buds.

Effects of nonchemical weed control on weed and seedbank demography in ridge-tilled fields were simulated to examine long-term effects on weed population dynamics. Ridge tillage entails active seedbank management, including removal of much of the seedbank from the crop growth zone (ridge) to the interridge zone (furrow) at planting, and other seedbank manipulations. Dynamics of simulated yellow foxtail and velvetleaf populations were sharply sensitive to the rate of seed removal from the ridge. Variation in winter seed survival, ridge plant demography (emergence, survival, and seed production), and seed survival in the furrow after removal from the ridge also had strong effects on simulated dynamics. To prevent rapid population growth in a simulated corn-soybean rotation, very effective control of seedlings emerging with each crop was necessary to offset seed production from seedlings emerging after ridge rebuilding in corn years. Dynamics of both species were highly sensitive to cultivation efficiency. Effective “rescue” weed control must be available to prevent sharp increases in weed seedbanks during years when cultivation is ineffective.

The metabolism of three 14C-ring-labeled herbicides, atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], chloramben (3-amino-2,5-dichlorobenzoic acid), and dicamba (3,6-dichloro-o-anisic acid) was studied in the earthworm, Lumbricus terrestris L., taken from plots treated with these herbicides for the past 10 yr and from control plots treated with no herbicides. For the two benzoic acid herbicides, acetone extracts of sand and earthworms from untreated plots contained more unmetabolized herbicide than similar extracts of sand and earthworms from treated plots, indicating a net enhancement of metabolism in worms from treated plots. For atrazine, the amount of unchanged herbicide in the acetone extracts of earthworm and sand were nearly equivalent. Finally, the relative metabolic stability of the three herbicides in decreasing order in earthworms from both control and untreated plots was chloramben>atrazine>dicamba.

Soybean (Glycine max (L.) Merr., ‘Hawkeye 63′) seedling segments from the zone of elongation and corn (Zea mays L., ‘Pioneer 3306) seedling segments were utilized to evaluate the antagonistic interaction of S-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)-acetic acid (2,4-D). EPTC inhibited growth of the soybean and corn tissue, and 2,4-D in combination with EPTC caused an increase in growth compared to EPTC alone. The 2,4-D-enhanced growth in the presence of EPTC was due to an antagonism of the EPTC inhibition. Inhibition of soybean tissue growth by S-ethyl diisobutylthiocarbamate (butylate) also was antagonized by 2,4-D. Preincubation of soybean tissue in EPTC for 4 hr prior to the addition of 2,4-D did not prevent 2,4-D enhancement of growth. Conversely, the rate of growth was inhibited when EPTC was added after 4 hr of 2,4-D-enhanced growth. The addition of uridine to the incubation media with EPTC did not decrease the EPTC-inhibition of soybean tissue growth. This indicated that EPTC did not inhibit the synthesis of pyrimidine precursors. EPTC vapor losses from the incubation media reduced the inhibitory effect of EPTC to soybean tissue. Also, a growth reduction occurred when the amount of soybean tissue per unit of EPTC was increased.

A technique was developed for seeding rangelands which are too steep or too rocky to seed by current methods. Hardinggrass (Phalaris tuberosa L. var. stenoptera (Hack.) Hitchc.) and subclover (Trifolium subterraneum L.) were established by seeding immediately after spraying the resident vegetation with 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat). Tested for seeding in sod were single-disk, double-disk, and hoe-type drill openers. The double disk was best adapted to the clay soils most common in the area. A heavy-duty rangeland drill was modified with custom-made, heavy, double-disk openers and equipped with a spray system which sprays either bands or full coverage. The resulting planter will kill weeds, plant seeds, and spread fertilizer any place where a crawler tractor can pull it. Weed-free bands of 6 and 12 inches were compared with full spray coverage. No hardinggrass was established without some weed control. In only 5 of 16 tests over a 5-year period was full-spray coverage superior to the 6-inch band. The 12-inch band or full spray may be preferable on shallow soils or soils of low water-holding capacity. Spraying helped establish subclover but, unlike with hardinggrass, was not critical. Grazing or mowing during the establishment period improved stands of both hardinggrass and subclover. Prolonged weed control made paraquat superior to cultivation by giving better weed control and a firmer seedbed.

The uptake, translocation, and fate of (2,4-dichlorophenoxy)acetic acid (2,4-D) were compared in nightflowering catchfly (Silene noctiflora L.) and common lambsquarters (Chenopodium album L.), resistant and susceptible species, respectively. Nightflowering catchfly leaf sections absorbed more 2,4-D from 5 × 10-4 M and 5 × 10-6 M 2,4-D solutions at pH 3.0 than did leaf sections of common lambsquarters. Intact plants of both species accumulated 2,4-D in the stems and leaves below the treated leaf. At 72 hr after treatment, nightflowering catchfly released 2,4-D through the roots into the nutrient solution while common lambsquarters continued to accumulate 2,4-D. Nightflowering catchfly metabolized 2,4-D and the metabolite was recovered in the roots 24 hr after treatment, whereas common lambsquarters did not metabolize 2,4-D.

Laboratory experiments were conducted to determine the effects of temperature, light, cold stratification, dry storage, solution pH, solution osmotic potential, and planting depth on germination and emergence of dame's rocket. Maximal germination (> 80%) of fresh seeds occurred at alternating temperatures ≥ 25/15 C in both alternating light/dark and continuous darkness. However, < 10% of seeds germinated at or below 20/10 C, with lower germination in the presence of light than in darkness. Cold stratification at 4 C for 4 to 16 wk enhanced germination at low alternating temperatures (≤ 20/10 C), but depressed germination at warm temperature regimes (≥ 25/15 C). After 1 yr of dry storage (after-ripening), germination exceeded 94% and did not differ significantly among temperature regimes. Germination exceeded 60% in solutions with pH 3 to 10. Germination was reduced below 50% in solutions with osmotic potentials below −0.6 MPa. Percent emergence was greater than 56% at burial depths in soil of 0 to 5 cm, with maximal emergence (93 to 99%) at 0 to 2 cm. Dame's rocket seeds possess non-deep physiological dormancy at maturity, but when dormancy is alleviated, the seeds are capable of germinating in a variety of climatic and edaphic conditions.

Native polyacrylamide gel electrophoresis was used to identify polymorphisms in α- and β-esterases loci and electrophoresis in starch gel to identify polymorphism in malate dehydrogenase (MDH; EC 1.1.1.37) and acid phosphatase (ACP; EC 3.1.3.2) isozymes loci in leaf tissues from samples of horseweed and hairy fleabane populations to determine genetic diversity and population structure. Similar or differential genetic divergence between the two species may guide specific use of herbicides. For samples of plants with high genetic similarity it is possible to adopt similar mechanisms and processes for their control. The proportion of polymorphic loci was 57.14, 50.0, and 53.6%, in samples of horseweed and hairy fleabane, for EST, MDH, and ACP isozymes, respectively. A comparison of the diversity parameters in the two species showed that the number of alleles is similar in the horseweed and hairy fleabane plants. The estimated heterozygosity in horseweed and hairy fleabane was also very close. A relatively low level of population differentiation was detected between horseweed and hairy fleabane (FST = 0.0199), which suggests a substantial genetic exchange among the two species. Accordingly, estimate of gene flow was high (Nm = 12.3172) for the alleles of the loci Est, Mdh, and Acp. The Nei's identity (I) values also was high (I = 0.9561) indicating very high similarity between the two Conyza species. AMOVA showed higher genetic variation within (95%) than among (5%) the two samples. The low genetic structure and high value of genetic identity was an important indication that alleles are exchanged between horseweed and hairy fleabane populations, and provides additional evidence of occurrence of outcrossing between populations or dispersion of samples of one for other site.

Spreading dogbane is a common perennial weed in wild blueberry fields. It is highly competitive and spreads rapidly once established. Herbicides can provide effective control of spreading dogbane, but application timing is important. The emergence pattern, ramet height, and flowering time of spreading dogbane were observed in 2008 and 2009, and thermal-based emergence, growth, and development models were developed and used to estimate optimum herbicide application timing. Spreading dogbane emergence and height were described with a three-parameter, sigmoid, nonlinear regression model, whereas flowering was described with a four-parameter, Weibull, nonlinear regression model. Spreading dogbane ramets initiated emergence soon after the biofix date of April 1. Peak emergence tended to occur at 420 growing degree days (GDD). Spreading dogbane reached its peak height by about 558 GDD. The maximum number of flowers per plant was reached at approximately 750 GDD. This study suggested that POST herbicides should be applied between 486 and 535 GDD to maximize efficacy. This time frame occurs after peak emergence and during early floral bud development.

Goatsrue is an introduced perennial plant which has proven to have great invasive potential, leading to its classification as a noxious weed in many states and at the federal level. Very little research has been done on its basic biology. Physical dormancy of mature goatsrue seed was tested through scarification with sulfuric acid for up to 60 min resulting in 100% germination. Comparison of dormancy for 26-yr-old and 6-mo-old goatsrue seed indicated that aged seeds had reduced dormancy levels compared to newly harvested seeds. Maximum germination was similar among the 6-mo old and 26-yr-old seed lots, suggesting no loss of viability had occurred in seed stored dry for 26 yr. Goatsrue seedling emergence was inversely related to burial depth, and decreased as burial depth increased. Emergence of seed buried at 0.5 to 3.0 cm soil depth was 93 to 87%, respectively, and no emergence occurred from 12 and 14 cm. When the soil seed bank of five goatsrue-infested areas was sampled, the largest density of seeds found was 74,609 seeds m−2 while the lowest was 14,832 seeds m−2. Viability and dormancy of seeds recovered from the soil seed bank survey ranged from 91 to 100% and 80 to 93%, respectively. Management, which reduces the soil seed bank and controls emerging seedlings, is as essential as control of mature goatsrue plants in order to avoid seedling establishment and reinvasion of a location.

Soldier thistle [Picnomon acarna (L.) Cass.] is widely distributed throughout rainfed fields across western Iran, where it decreases crop yields and interferes with harvest operations. This study was conducted to determine the influence of different factors on seed germination and seedling emergence of P. acarna. Freshly harvested seeds were dormant and required an after-ripening period for breaking dormancy. Seed germination was greatly promoted by light. Germination occurred over a wide spectrum of constant and fluctuating temperature regimes, ranging from 5 to 35 C, with highest germination at constant (74%) and fluctuating (94%) temperatures of 20 and 20/10 C. Seed germination of P. acarna was tolerant to osmotic potential, while salt stress significantly inhibited its germination percentage. pH was not an inhibiting factor for germination of P. acarna seeds. Seedling emergence decreased exponentially with an increase in seed burial depth in the soil; at soil burial depths of 4 cm or greater, no seedlings were able to reach the soil surface. The results suggest that significant seed germination of P. acarna in rainfed fields is possible, and the weed has great potential to spread throughout rainfed systems in western Iran. Based on these results, effective control of P. acarna can be achieved by applying interrow cultivation in row crops and deep tillage at seedbed preparation.

A weed survey was conducted on 134 Palmer amaranth (Amaranthus palmeri S. Watson) populations from Mississippi and Arkansas in 2017 to investigate the spread of resistance to protoporphyrinogen oxidase (PPO) inhibitors using fomesafen as a proxy. Fomesafen resistance was found in 42% of the A. palmeri populations. To investigate the resistance basis of different PPO inhibitors, we further characterized 10 representative populations by in planta bioassay in a controlled environment and molecular characterizations (DNA sequencing and TaqMan® gene expression assay). A total of 160 plants were sprayed with a labeled field rate (1X) of fomesafen or salfufenacil and screened for the presence of three known resistance-endowing mutations in the mitochondrial PPX2 gene (ΔGly-210, Arg-128-Gly, Gly-399-Ala). To compare the potencies of fomesafen and saflufenacil, dose–response studies were conducted on two highly resistant and one sensitive populations. The interaction of the two herbicides with the target protein harboring known PPX2 mutations was also analyzed. Our results showed that: (1) 90% of the fomesafen- or saflufenacil-resistant plants have at least one of the three known PPX2 mutations, with ΔGly-210 being the most prevalent; (2) saflufenacil is more potent than fomesafen, with five to nine times lower resistance/susceptible (R/S) ratios; (3) fomesafen selects for more diverse mutations, and computational inhibitor/target modeling of fomesafen suggest a weaker binding affinity in addition to a smaller interaction volume and volume overlap with the substrate protoporphyrinogen IX than saflufenacil. As a result, saflufenacil shows reduced sensitivity to PPX2 target-site mutations. Results from current study can help pave the way for designing weed management strategies to delay resistance development and maintain the efficacy of PPO inhibitors.

Bermudagrass and goosegrass are problematic weeds with limited herbicides available for POST control in creeping bentgrass. Metamifop effectively controls these weeds with greater selectivity in cool-season grasses than other ACCase inhibitors. The objectives of this research were to determine the physiological basis for metamifop selectivity in turfgrasses. In greenhouse experiments, metamifop rate required to reduce shoot biomass 50% from the nontreated (GR50) at 4 wk after treatment was > 6,400, 2,166, and 53 g ai ha−1 for creeping bentgrass, Kentucky bluegrass, and goosegrass, respectively. The GR50 for bermudagrass treated with diclofop-methyl or metamifop was 2,850 and 60 g ha−1, respectively. In laboratory experiments, peak absorption of 14C-metamifop was reached at 48, 72, and 96 h after treatment (HAT) for goosegrass, creeping bentgrass and Kentucky bluegrass, respectively. Grasses translocated < 10% of the absorbed radioactivity out of the treated leaf at 96 HAT, but creeping bentgrass translocated three times more radioactivity than goosegrass and Kentucky bluegrass. Creeping bentgrass, Kentucky bluegrass, and goosegrass metabolized 16, 14, and 25% of 14C-metamifop after 96 h, respectively. Goosegrass had around two times greater levels of a metabolite at retention factor 0.45 than creeping bentgrass and Kentucky bluegrass. The concentration of metamifop required to inhibit isolated ACCase enzymes 50% from the nontreated (I50) measured > 100, > 100, and 38 μM for creeping bentgrass, Kentucky bluegrass, and goosegrass, respectively. In other experiments, foliar absorption of 14C-metamifop in bermudagrass was similar to 14C-diclofop-methyl. Bermudagrass metabolized 23 and 60% of the absorbed 14C-diclofop-methyl to diclofop acid and a polar conjugate after 96 h, respectively, but only 14% of 14C-metamifop was metabolized. Isolated ACCase was equally susceptible to inhibition by diclofop acid and metamifop (I50 = 0.7 μM), suggesting degradation rate is associated with bermudagrass tolerance levels to these herbicides. Overall, the physiological basis for metamifop selectivity in turfgrass is differential levels of target site inhibition.

Knotweed (Fallopia spp.) is an herbaceous perennial from East Asia that was brought to Europe and North America and, despite control efforts, subsequently spread aggressively on both continents. Data are available on knotweed’s modes of sexual and asexual spread, historical spread, preferred habitat, and ploidy levels. Incomplete information is available on knotweed’s current global geographic distribution and genetic diversity. The chemical composition of knotweed leaves and rhizomes has been partially discovered as related to its ability to inhibit growth and germination of neighboring plant communities via phytochemicals. There is still critical information missing. There are currently no studies detailing knotweed male and female fertility. Specifically, information on pollen viability would be important for further understanding sexual reproduction as a vector of spread in knotweed. This information would help managers determine the potential magnitude of knotweed sexual reproduction and the continued spread of diverse hybrid swarms. The potential range of knotweed and its ability to spread into diverse habitats makes studies on knotweed seed and rhizome cold tolerance of utmost importance, yet to date no such studies have been conducted. There is also a lack of genetic information available on knotweed in the upper Midwest. Detailed genetic information, such as ploidy levels and levels of genetic diversity, would answer many questions about knotweed in Minnesota, including understanding its means of spread, what species are present in what densities, and current levels of hybridization. This literature review summarizes current literature on knotweed to better understand its invasiveness and to highlight necessary future research that would benefit and inform knotweed management in the upper Midwest.

Kochia (Kochia scoparia L.), also commonly called fire weed, is one of the most widespread annual weeds in Kansas and the Great Plains region. The origin of the weed in Kansas is obscure but it was introduced into the United States from Europe (1). The plant had been cultivated as an ornamental and apparently much of its present wide distribution is a result of escape from ornamental plantings.

Excellent protection from 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) injury at twice the dose needed for weed control was obtained by dipping the roots of strawberry plants (Fragaria grandiflora Ehrh.) in a 10% slurry of activated carbon before transplanting. Protection was greater when the roots were dipped in the slurry of activated carbon than when activated carbon was applied in the transplant water. Protection was obtained from three different activated carbons. Protection from injury to varying degrees was observed when several other herbicides were used.

The effects of nitrogen (N) rate and weed interference on the grain yield of four corn genotypes were investigated in 2002 and 2003 at Ikenne (7°38′N, 3°42′E), Shika (11°11′N, 7°38′E), and Samaru (10°24′N, 7°42′E) in Nigeria. Nitrogen (N) at 0, 30, 60, and 90 kg N ha−1 were the main plot treatments. Weed-free (weeded weekly), low (intrarow weeds only), and high (zero weeding) weed pressure were the subplot treatments. Four corn genotypes (ACR8328 BN C7, Low-N-Pool C2, Oba Super II, TZB-SR) were the sub-subplot treatments. Weed density was higher at Shika and Samaru than at Ikenne, and the order of average weed biomass 8 to 10 weeks after planting was Samaru (271 g m−2) > Ikenne (236 g m−2) > Shika (161 g m−2). Corn genotype and N rate had no effect on weed biomass except at Samaru where fertilized treatments had higher weed biomass than the unfertilized treatments. Corn leaf area (LA) increased with increasing N rate at all locations regardless of weed pressure and genotype, except at Shika where ACR8328 BN C7, Oba Super II, and TZB-SR did not show any clear N response; LA was highest in the weed-free and lowest in the unfertilized treatments for all genotypes and locations, and weed pressure treatments. Low-N-Pool C2 had the highest LA, which was 1.3 times larger than in Oba Super II, which had the lowest LA. Nitrogen rate, weed pressure, and genotypes significantly affected corn leaf chlorophyll content. Chlorophyll content was higher in the fertilized treatments than the unfertilized treatments, and higher in the weed-free treatments than the low or high weed pressure treatments. ACR8328 BN C7 and Oba Super II had significantly more chlorophyll than the other genotypes. Low-N-Pool C2 showed a linear grain yield response with the increase in N rates. ACR8328 BN C7 did not respond to N application. Compared with the results in the weed-free treatment, high weed pressure reduced grain yield in all genotypes by more than 65% at Samaru, 50% at Shika, and 35% at Ikenne.

New trait technology incorporating 2,4-dichlorophenoxyacetic acid (2,4-D) resistance in soybean provides an alternative method to control weeds. However, the effect of postemergence treatments of 2,4-D on aryloxyalkanoate dioxygenase-12 (AAD-12) soybean on injury and yield components has not been reported. Our objectives were to characterize the effect of 2,4-D (dimethylamine salt) rates (0, 1,120, and 2,240 g ae ha−1) and soybean growth stage (V5, R2, or V5 followed by R2) on AAD-12 soybean injury and yield components. Less than 3% soybean injury was observed when 2,240 g ha−1 of 2,4-D was applied to R2 soybean, and less than 1% soybean injury was caused by 1,120 g ha−1 of 2,4-D. Seed yield, seed mass, pod number, seed number, seed per pod, reproductive node number, pods per reproductive node, node number, and percent reproductive nodes were not affected by 2,4-D treatments when applied at the V5, R2, or the V5 followed by R2 soybean growth stage. This research demonstrates that soybean transformed with AAD-12 can tolerate foliar applications of 2,4-D at rates up to 2,240 g ha−1 with no effect on soybean grain yield components.

Downy brome is an introduced Mediterranean annual grass that now dominates millions of hectares of western U.S. rangelands. The presence of this grass has eliminated many native species and accelerated wildfire cycles. The objective of this study was to identify soil additives that allowed germination but inhibited emergence of downy brome, while not affecting germination or emergence of the native perennial grass Hilaria jamesii. On the basis of data from previous studies, we focused on additives that altered the availability of soil nitrogen (N), phosphorus (P), and potassium (K). Most water-soluble treatments inhibited downy brome germination and emergence. We attribute the inhibitory effects of these treatments to excessive salinity and ion-specific effects of the additives themselves. An exception to this was oxalic acid, which showed no effect. Most water-insoluble treatments had no effect in soils with high P but did have an effect in soils with low P. Zeolite was effective regardless of P level, probably due to the high amounts of Na+ it added to the soil solution. Most treatments at higher concentrations resulted in lower downy brome emergence rates in soils currently dominated by downy brome than in uninvaded (but theoretically invadable) Hilaria soils. This difference is possibly attributable to inherent differences in labile soil P. In Stipa soils, where Stipa spp. grow, but which are generally considered to be uninvadable by downy brome, additions of high amounts of N resulted in lower emergence. This may have been an effect of NH4 + interference with uptake of K or other cations or toxicity of high N. We also saw a positive relationship between downy brome emergence and pH in Stipa soils. Hilaria development parameters were not as susceptible to the treatments, regardless of concentration, as downy brome. Our results suggest that there are additions that may be effective management tools for inhibiting downy brome in calcareous soils, including (1) high salt applications, (2) K-reducing additions (e.g., Mg), and (3) P-reducing additions.

Experiments were conducted to study absorption, translocation, and activity of clopyralid and tribenuron in perennial sowthistle. Absorption and translocation were compared in perennial sowthistle at the rosette and bud stage over a period of 9 d. Both 14C-clopyralid and tribenuron were absorbed slowly by perennial sowthistle leaves with 60 and 30% absorption, respectively, 216 h after application. Limited movement of the absorbed 14C was observed for both herbicides with less than 28% of either herbicide exported from the treated leaf. Primary movement of 14C-herbicide within the plant was acropetal; however, no more than 18% of either herbicide was recovered in the upper shoot or buds. After 216 h, 4.4% of the applied 14C-clopyralid and 2.5% of the applied 14C-tribenuron were recovered in the roots and secondary shoots of plants at the rosette stage. Application of either herbicide to perennial sowthistle resulted in a decrease in net carbon assimilation and leaf conductance. Transpiration was reduced in rosette stage plants by both herbicides; however, transpiration in plants at the bud stage was not reduced until 216 h after treatment. Plants treated with tribenuron had lower net carbon assimilation, leaf conductance, and transpiration rates than plants treated with clopyralid. Application of clopyralid at 150 and 300 g ha-1 resulted in visual injury ratings of 65 and 95%, respectively. Tribenuron applied at 10 and 20 g ha-1 gave similar results. Dry weight accumulation was reduced at all application rates compared to untreated plants. Limited absorption and translocation along with high herbicidal activity suggests that small amounts of either herbicide are sufficient to inhibit perennial sowthistle growth.