Germination and emergence assays represent the most notable examples of time-to-event data in agriculture and related disciplines. In spite of the peculiar characteristics of this type of data, there has been little effort to establish a specific and comprehensive framework for their analyses. Indeed, a brief survey of the literature shows that germination and emergence data, along with other phenological measurements such as flowering time, have been analyzed through myriad approaches, giving rise to confusion and uncertainty among scientists and practitioners as to what may represent the best statistical practice. This lack of coherence in statistical approach may reduce the efficiency of research, while making the communication of results and the cross-study comparisons extremely challenging. Here, we attempt to provide a coherent framework and protocol for the analyses of germination/emergence and other time-to-event data in weed science and related disciplines, together with a software implementation in the form of a new R package. We propose a similar approach to biological assays in ecotoxicology, based on: (1) fitting a time-to-event model to describe the whole time course of events; (2) comparing time-to-event curves across experimental treatments, and (3) deriving further information from the fitted model to better focus on some traits of interest. The most appropriate methods to accomplish this procedure were carefully selected from the framework of survival analysis and related sources and were modified to comply with the specific needs of weed, seed, and plant sciences. Finally, they were implemented in the new R package drcte. In this article, we describe the procedure and its limitations by way of providing examples of several types of germination/emergence assays. We highlight that our proposed procedure can also serve as the first step of data analyses, with its output subsequently submitted to traditional or meta-analytic approaches.

Several triazines exhibit high phytotoxicity towards many species of higher plants and are being extensively studied as possible herbicides. Moreland et al. and Exer reported that 2-chloro-4,6-bis(ethylamino)-s-triazine, simazine, inhibited the photochemical activity of isolated chloroplasts. Exer also presented evidence that the inhibited reaction involved the photochemical reduction of DPN, diphosphopyridine-nucleotide. Gast has shown that in Coleus Blunei Benth. simazine blocked starch production in the light and that this effect was overcome by the addition of sucrose to starch-free leaves in the dark. These results indicated interference of photosynthetic CO2 fixation by simazine. Roth reported that simazine inhibited photosynthesis in Elodea but had a stimulating effect on respiration. In light of these findings a study of the effect of simazine and certain related triazines on the photosynthetic CO2 fixation of red kidney bean was undertaken.

Field infestations of a seed-feeding insect developed from overwintered populations reduced viability of velvetleaf seed to 17.5 and 15.5% at two locations in central Missouri, compared to 95.5 and 87.5% at insect-free sites. Insect feeding enhanced the proportion of seedborne microorganisms in seed up to 98% compared to the average fungal infection of 8% for seed not exposed to the insect. There was a strong negative correlation between fungal infection associated with insect feeding and percent velvetleaf seed viability. The insect transmits microorganisms externally just as pollen is carried by various other insect species and not by ingestion and regurgitation. The effectiveness of the insect on reducing seed viability and seed production in central Missouri is mainly limited by the time required to build up populations capable of significantly affecting early-season velvetleaf seed production.

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] residue analysis of soil samples showed greater amounts of residue extractable at soil pH 6.7 than 4.6. Metribuzin leaching increased with increasing soil pH. Metribuzin disappearance from soil followed pseudo first-order kinetics. The half-life of metribuzin decreased as soil pH increased and increased at all soil pH levels as depth of sampling increased. The decreased activity and decreased rate of metribuzin dissipation at lower soil pH is apparently due to protonation and increased adsorption.

In greenhouse studies, 11 cultivars of potato (Solanum tuberosum L.) responded differently to foliar applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5-(4H)one] at rates of 0.14 to 1.12 kg/ha. The first symptoms of metribuzin injury varied among cultivars. When measured 14 days after treatment, the dry weight was reduced more than the height or the vigor. Height was least affected. When metribuzin was applied at 0.14 kg/ha, the height of ‘Norchip,’ the vigor of ‘Norland,’ ‘Norchip,’ and ‘White Rose,’ and the dry weight of ‘Red La Soda,’ ‘Cascade,’ ‘Norchip,’ and ‘White Rose’ were reduced significantly 14 days after treatment. Plant vigor and dry weight of all of the cultivars were reduced significantly by metribuzin applied at 1.12 kg/ha. ‘Nooksack’ and ‘Norgold’ were the most tolerant to foliar applications of metribuzin, and ‘Norchip’ and ‘White Rose’ were the most susceptible.

Retention, absorption, translocation, and volatility of foliarly applied diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy) phenoxy] propanoate} were compared in barnyardgrass [Echinochloa crus-galli (L.) Beauv.], a susceptible grass; proso millet (Panicum miliaceum L.), a moderately susceptible grass; longspine sandbur [Cenchrus longispinus (Hack.) Fern.], a tolerant grass; and soybean [Glycine max (L.) Merr. ‘Hark’] and cucumber (Cucumis sativus L. ‘Green Star’), both tolerant broadleaf plants. On a jug/plant basis, the order of diclofop-methyl spray retention was cucumber > soybean > proso millet > longspine sandbur = barnyardgrass. On a μg/mg dry weight basis, proso millet retained 3 to 10 times more diclofop-methyl than all other species. One day after treatment (DAT), absorption of 14C-diclofopmethyl was 14 to 18% less in longspine sandbur than in the other species, 3 DAT absorption in cucumber was 8 to 14% greater than in the other species, and 5 DAT absorption in soybean was 3 to 12% less than in other species. Translocation of 14C-diclofop-methyl did not differ among species, with 98% of the applied radioactivity located in the treated leaf. An average of 11% of radioactivity applied to the surface of intact, living plants and excised, dried leaves of cucumber, soybean, and barnyardgrass, as well as glass cover slips, was lost by evaporation. None of the parameters measured showed differences large enough to be implicated as primary selectivity mechanisms.

The effect of Russian thistle density and duration of interference on spring wheat was investigated in two 3-yr field studies. In the density study, the best fit regression equation predicted a loss in spring wheat yield of 0.5, 0.5, and 0.6% in 1983, 1984, and 1985, respectively, for each percent of the total biomass contributed by Russian thistle. In 1985, when rainfall was 46% below normal, the highest weed density produced greater than 70% of the total plant biomass and reduced yields more than 50%. In contrast, in 1984 when rainfall was 65% above normal, the highest weed density produced less than 20% of the total plant biomass and reduced yields 11%. In the duration study, the predicted yield loss was 2.3 and 0.7% for 1983 and 1984, respectively, for each week of interference. In 1985, yield was not significantly reduced until after 6 weeks of interference. In both studies, spikes/m of row had the highest correlation with yield and were affected the most by weed interference.

Field studies were conducted in 1986, 1987, 1988, and 1989 to determine the stability of crop loss functions across site by year environments. Environment was a significant source of variation for the soybean crop loss function as influenced by velvetleaf, but not as influenced by tall waterhemp and common sunflower. Weed density was a highly significant source of variation for all weed species studied. Regressions between percent soybean seed yield reductions and weed populations were linear. The velvetleaf interference regression equations were divided into two groups, those with high soybean-yielding intercepts and those with low-yielding intercepts, to explain the variance observed across environments. The regression equation for the high-yielding intercept group was Ŷ = 4.24X while the low-yielding group was Ŷ = 2.14X, where Y is percent soybean yield reduction and X is weed density per 10.7 m of soybean row. Tall waterhemp and common sunflower regression equations were determined to be Ŷ = 1.37X and Ŷ = 6.52X, respectively. Confidence intervals were used to account for the variance associated with the mean regression equation for each model and to develop economic threshold models that include risk aversion principles.

Root development and the associated acquisition of water and nutrients are an important part of weed competitiveness. Characterization of root morphological development, however, is inherently problematic because of the complexities of soil–plant interactions. In this study, we used hydroponically grown plants and digital imaging to examine root characteristics of Glycine max and the competing weeds Senna obtusifolia and Amaranthus palmeri. The purpose was to define inherent differences in root length and surface area that would contribute to growth responses during the establishment phase in the field. The methodology involved growing plants for 16 to 22 d, dissecting and staining root segments, mounting subsamples on slides, and imaging using a stereomicroscope and digital camera. Microscopy was required because of the small diameters of a significant proportion of the weed roots. With plants of similar root fresh weights (4.5 to 5.0 g), counting of individual roots revealed that 5. obtusifolia and A. palmeri had 2 and 3.7 times more roots than G. max (4,616 and 7,781 vs. 2,120, respectively). The imaging analyses indicated that roots of S. obtusifolia and A. palmeri had 2.9 and 5 times more length than G. max (10,042 and 17,192 cm vs. 3,418 cm, respectively). Furthermore, the analysis of length in different root diameter classes indicated that weed roots were noticeably finer then those of G. max. Approximately 84% of S. obtusifolia root length was contributed by roots in the 0.1- to 0.25-mm range, whereas 45% of the G. max roots were in the 0.1- to 0.25-mm range and 48% were in the 0.25- to 0.75-mm range. In contrast, 68% of A. palmeri length was contributed by roots smaller than 0.1 mm in diameter with 26% in the 0.1- to 0.25-mm range. Based on the expression of root characteristics observed here, root systems of these weed species would have finer roots with much greater length that would occupy a much larger volume of soil than those of G. max. Presumably, this would result in a competitive advantage in the acquisition of water and nutrients, especially when availability is limited.

Field studies were conducted to determine how the spatial arrangement of weed populations influences interspecific competition. We studied the influence of regular, random, and clumped distributions of barnyardgrass on growth and yield of direct-seeded tomato planted at different densities. Increasing aggregation increased intraspecific competition in barnyardgrass. At the same time, interspecific competition experienced by tomato from barnyardgrass decreased. Differences in the amount of shading of the tomato canopy by barnyardgrass contributed to yield loss differences for the various spatial arrangements. Clumped barnyardgrass caused significantly less average shading than barnyardgrass in regular or random arrangements. At a typical planting density of 10 tomato plants m−1 of row, yield losses ranged from 10 to 35% (1993) or 8 to 50% (1994) when competing with a clumped arrangement of barnyardgrass. At the same tomato density, yields were reduced from 20 to 50% (1993) or 11 to 75% (1994) for the regular and random arrangements for the same barnyardgrass densities. Predicted single-season economic threshold densities for barnyardgrass at a typical tomato planting density of 10 plants m−1 would be one barnyardgrass plant per 25, 19, or 15 m of crop row, respectively, for regular, random, and clumped spatial distributions.

Japanese foxtail is one of the most common and competitive annual grass weeds of wheat in China. Whole-plant dose-response experiments were conducted with fenoxaprop and pinoxaden to confirm and characterize resistant and susceptible Japanese foxtail populations and to elucidate the basis of resistance to these herbicides. The resistant Japanese foxtail population was 49-fold resistant to fenoxaprop and 16-fold (cross) resistant to pinoxaden relative to the susceptible population, which was susceptible to both fenoxaprop and pinoxaden herbicides. Molecular analysis of resistance confirmed that the Ile1781 to Leu mutation in the resistant population conferred resistance to both fenoxaprop and pinoxaden. This is the first report of cross resistance of Japanese foxtail to pinoxaden in the world and of a target site mutation that corresponded to resistance to both fenoxaprop and pinoxaden in Japanese foxtail. Prior selection pressure from fenoxaprop could result in evolution of resistance to fenoxaprop and cross resistance to pinoxaden in Japanese foxtail population.

The potential of preventing seed production and reducing seed viability of weeds that commonly grow taller than soybeans [Glycine max (L.) Merr. ‘Williams 82’] was evaluated. Chlorflurenol (2-chloro-9-hydroxy-9H-fluorene-9-carboxylic acid), chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide}, and glyphosate [N-(phosphonomethyl)glycine] were evaluated against sparse stands of velvetleaf (Abutilon theophrasti Medik. # ABUTH) and giant foxtail (Setaria faberi Herrm. # SETFA) growing in soybeans. Simulated-roller applications of all three herbicides significantly reduced seed production and germination of both weeds, although glyphosate was more effective than were the other two. Applications during early flowering of velvetleaf and early heading of giant foxtail reduced seed production more than later applications when some seeds were present. With the early application of glyphosate, 99% prevention of velvetleaf and 96% prevention of giant foxtail seed production were attained. With the early glyphosate application, germination of seeds produced was reduced by 50% in velvetleaf and by 95% in giant foxtail. Soybean yields were not reduced by either glyphosate or chlorflurenol but were drastically reduced by chlorsulfuron.

A population of shepherd's-purse suspected to be resistant to the triazinone herbicide hexazinone, a photosystem II (PS II) inhibitor, was collected from an alfalfa field in 2007 in Oregon. A whole-plant, dose–response assay confirmed that the putative-resistant population was highly resistant to hexazinone. The resistant population was 22-fold more resistant to hexazinone than the susceptible population. However, the hexazinone-resistant population was susceptible to other PS II-inhibiting herbicides, including atrazine, diuron, and terbacil. DNA sequence analysis of the chloroplast psbA gene encoding the D1 protein of PS II, the target site of PS II inhibitors, identified a point mutation from Phe to Ile at position 255 in the hexazinone-resistant population. Single- and double-point mutations at position 255, which is located in the QB binding niche of the D1 protein, were previously reported in Chlamydomonas reinhardtii, Synechococcus species, and Synechocystis species after site-directed mutagenesis and were associated with decreased binding of PS II inhibitors. To our knowledge, this is the first report of a mutation of the psbA gene at Phe255 in a field-selected, herbicide-resistant plant.

The sulfentrazone is regularly applied to sugarcane crop harvest residue for PRE control of weedy species, especially in the dry season during the year, but little is known about how rainfall timing or crop residue mass affect the release of sulfentrazone into the soil and its subsequent effectiveness. Two experiments were conducted to examine the effects of sugarcane residue mass (5, 10, 15, and 20 t ha−1) and rainfall timing (1, 30, and 60 d after herbicide application) on sulfentrazone retention. Rainfall volumes were simulated at 2.5, 5, 10, 20, 35, 50, and 100 mm. A 20-mm rainfall volume was simulated at 7 and 14 d after the first simulated event. The water passing through the straw was collected after each rainfall simulation. The concentration of sulfentrazone was measured by liquid chromatography and mass spectrometry. The initial 20 mm of rain released the maximum mass of sulfentrazone from the sugarcane residue. The mass of sugarcane residue affected the amount of sulfentrazone recovered. The amount of sulfentrazone released from the residue was significantly reduced by the persistence on the residue surface for long periods before the occurrence of rain. During periods of low rainfall, recommendations for sulfentrazone rate must take into account losses that occur when applied over the harvest residues to design a weed-management plan that does not compromise efficacy and duration of the residual effects.

Hoop structures bedded with crop residues are becoming increasingly popular for swine production in the northcentral United States. Compost made from bedding materials and swine manure can be used as a soil amendment. A 3-yr field experiment was conducted in Boone, IA, to determine how composted swine manure affected selected soil characteristics and nutrient uptake, growth, and seed production of corn and three weed species (giant foxtail, velvetleaf, and common waterhemp) grown in mixture with corn. Two soil management systems, designed to provide equivalent amounts of N to corn, were compared: one that received composted manure and an average of 118 kg N ha−1 as synthetic fertilizer and another that received no composted manure and an average of 143 kg N ha−1 as synthetic fertilizer. Soil organic matter, P, K, and early-season NO3-N levels were greater in the (+) compost system. The N concentration of velvetleaf shoots, the P concentration of giant foxtail and common waterhemp shoots, and the K concentration of shoots of all three weed species also were greater in the (+) compost system. Compost application consistently increased common waterhemp height, common waterhemp biomass, and velvetleaf height, but increased velvetleaf biomass in only 1 yr and had no effect on giant foxtail height or biomass. Measurements of weed seed production, conducted in the final year of the study, showed that compost increased velvetleaf and common waterhemp seed production but had no effect on giant foxtail seed production. Compost consistently increased corn height and leaf K concentration but generally had no effect on corn yield. Results of this study indicate that large differences can exist among crop and weed species in their response to soil amendments. Depending on the weed species present, use of composted swine manure may increase requirements for weed management in corn production systems.

More than 70% of all 14C-bentazon absorption occurred within 4 h after herbicide application regardless of adjuvant Moisture stress reduced 14C-bentazon absorption by common cocklebur and velvetleaf. Mature (second true leaf) and moisture-stressed leaves of velvetleaf had 50 and 17 μg cm−1 more epicuticular wax (ECW) than did juvenile and unstressed leaves, respectively. Common cocklebur had less 14C in the ECW and lower total 14C in treated mature leaves compared to juvenile leaves. The use of 28% urea ammonium nitrate (UAN) or crop oil concentrate (COC) increased 14C in ECW samples of both plant species, regardless of leaf age or moisture stress. More 14C in the ECW did not always correlate with more 14C in the leaf tissue. Adjuvants increased 14C-bentazon absorption into leaves of plants that had been stressed.

Sociologists define a wicked problem as one without clear causes or solutions, and thus difficult or impossible to solve. Herbicide resistance is the epitome of a wicked problem: the causes are convoluted by myriad biological and technological factors, and are fundamentally driven by the vagaries of human decision-making. Weed scientists for decades have conducted research and developed educational programs to prevent or mitigate evolution of herbicide resistance, yet resistance is more prevalent today than ever before. If we expect to achieve success in herbicide resistance management, different approaches will be essential. The second Herbicide Resistance Summit focused on “doing something different,” bringing in rural sociologists, agricultural economists, weed scientists, and crop consultants to discuss the decision-making process itself, community-based approaches to resistance management, economics of resistance management, potential regulatory and incentive programs, new approaches to educational programs, diversification of weed management, and a call to action for everyone involved in the decision-making process.

Wild cucumber (Sicyos angulatus) and cultivated cucumber (Cucumis sativus) were treated with carboxyl-labeled C142,4–D (2,4–D*) and 2,4,5–T (2,4,5–T*) and autoradiographs developed. The distribution pattern of 2,4–D* was achieved in 24 hours and changed little by the end of 4 or 8 days. The pattern of 2,4,5–T* translocation continued to change during an 8-day period, indicating a highly mobile compound. Metabolic studies indicated that considerably more 2,4–D* than 2,4,5–T* was absorbed by these species but 75% of the absorbed 2,4–D* was converted into two major metabolites within 24 hours. The absorbed 2,4,5–T* formed only traces of these metabolites even after 8 days. Evolution of C14O2 was approximately 10 times greater from 2,4–D*-treated plants than from 2,4,5–T*-treated plants. The greater phytotoxicity of 2,4,5–T on these species seems to be related to the inability of the plants to detoxify this compound as rapidly as 2,4–D.

Seeds of five crop and 17 weed species were germinated with 0, 3, 6, and 10-bar water solutions of polyethylene glycol to simulate drought. With simulated drought, most weed species germinated better than soybeans (Glycine max L. ‘Hampton 266A’) but were not equal to pearlmillet [Pennisetum typhoides (Burm.) Stapf. and C. E. Hubb ‘Millex 23’] or sorghum-sudangrass [Sorghum bicolor (L.) Moench x S. sudanense (Piper) ‘SX-16’]. Prickly sida (Sida spinosa L,), sicklepod (Cassia obtusifolia L.), and Ipomoea lacunosa L. were the most tolerant weed species to simulated drought. Four species were intermediate in tolerance and four species germinated poorly under simulated drought. Hemp sesbania [Sesbania exaltata (Raf.) Cory] was the least tolerant and was similar to soybean.

Experiments to determine effects of chlorimuron, clomazone, and imazaquin applied the year before planting corn, cotton, and sorghum were conducted at three locations in Georgia. Corn injury was <20% in 1987 and 1988 and yield was not affected. In 1988, imazaquin applied at a high rate or sequentially the previous year to late-planted soybeans injured corn more than applications to the early-planted soybeans. Cotton was the most sensitive crop to herbicides applied the previous year. However, seed cotton yield was not decreased due to herbicides applied the previous year. Sorghum growth and yield 8 weeks after planting was not affected by soybean herbicide application the previous year. Sicklepod, corn, and wheat bioassays did not detect any of the herbicides in soil samples obtained the season after treatment. Bioassays accurately predicted potential injury in corn and sorghum but not cotton.