In many cases, the logical presentation of scientific results masks the actual unfolding of experimental progress. Our work to identify the mechanisms by which chemicals break red rice seed dormancy is presented as an example. Doing the simplest experiments first, allowing the data to drive subsequent work, frequent and aggressive study of published literature, and examination of potentially key findings using multiple, interlocking strategies have been the keys to defining the relationship between the structure and action of dormancy-breaking chemicals. Our experiments show that chemical activity is dependent upon the lipophilicity as well as the nature and position of functional groups. However, the chemical that is applied to a dormant seed is not necessarily the chemical that actually breaks dormancy. A combination of approaches using structure–activity studies, metabolic inhibitors, and physiological measurements indicate that alcohols must first be metabolized to carboxylic acids to elicit germination of red rice. This report summarizes these findings as a personal account, illustrating the importance of logic, luck, and imagination in scientific discovery, as well as to highlight some important lessons about conducting research.

Striga hermonthica reduces cereal yields in large areas of sub-Saharan Africa. Recent research has shown that transplanting maize seedlings that are more than 15 d old reduced Striga emergence and improved crop yields. Field experiments were conducted in 1998 and 1999 to determine whether maize varieties with different maturity periods and susceptibility to Striga parasitism respond similarly to transplanting. There was a considerable difference in Striga emergence between varieties in direct-seeded maize, but transplanting clearly reduced Striga emergence for all varieties. Transplanting of maize in plastic tubes gave the best Striga control until 8 wk after transplanting, whereas transplants from nurseries provided better season-long control. Transplanting improved grain yields 50 to 100% compared with direct seeding for three of the four varieties tested. Only the early-maturing variety ‘Morogoro’ had lower yields with transplanting than with direct seeding, indicating that transplanting caused more stress on the plants than was alleviated by the lower Striga infestation. The two varieties (‘Pioneer 3251’ and ‘H622’) most susceptible to Striga parasitism profited the most from transplanting, and the concomitant reduction in Striga induced stresses. Increases in productivity because of transplanting were associated with increases in biomass or harvest index. Transplanting of different maize varieties under rain-fed conditions has proven to be a biologically efficient method to improve maize yield and reduce Striga infestation within one season.

Landscape-induced differences in soil variability and other parameters have potential effects on herbicide sorption, persistence, degradation, and, ultimately, efficacy. This study examined the spatial variability of herbicide efficacy across an eastern South Dakota field in continuous corn. Atrazine and alachlor had been applied for the previous 10 yr. The spatial variability observed in weed control was compared with herbicide sorption (Kd), mineralization rate, and first-order half-life (t1/2), and field herbicide dissipation rates (DT50). Spatial structure was present in atrazine mineralization, weed biomass, and corn biomass data. The amount of atrazine and alachlor sorbed to soil collected from the summit position of the field was 10 and 20% less, respectively, than the amounts sorbed to backslope or toeslope soils. Generally, both herbicides had faster mineralization rates and shorter t1/2 in summit than in backslope or toeslope soils. Weed biomass was correlated positively with elevation and total amount of atrazine mineralized, whereas corn biomass was correlated negatively with these parameters. These findings suggest that weed control can be improved by accounting for the landscape positional effects on differential herbicide mineralization and dissipation in fields.

In the San Joaquin Valley of California the presence of preemergence herbicides in runoff water from citrus orchards during winter rainfall can cause surface water and groundwater contamination. In 1999 and 2000 this study was conducted in a citrus orchard to evaluate the effect of irrigation incorporation with rotor sprinklers on simazine losses in runoff water. Four treatments included the application of simazine at 2.0 kg ai ha−1 without irrigation incorporation and the application of simazine at 2.0 kg ai ha−1 with three levels of irrigation incorporation (0.5, 1.25, and 1.75 cm of water). Simulated rainfall with 3.5 cm of water was then applied on the plots to generate surface runoff. Simazine concentrations in runoff water from the first simulated rainfall event averaged 0.85, 0.77, 0.45, and 0.30 mg L−1 for treatments without irrigation incorporation and for those receiving 0.5, 1.25, and 1.75 cm of water incorporation, respectively; simazine concentration in runoff water from the second event applied 1 wk later averaged 0.42, 0.38, 0.21, and 0.16 mg L−1, respectively. Total simazine mass recovered in runoff water from both simulated rainfall events was estimated to be 6.5, 6.0, 3.6, and 2.5% of the application for treatments without irrigation incorporation and for those receiving 0.5, 1.25, and 1.75 cm of water incorporation, respectively. Applying sufficient water for herbicide incorporation into the soil matrix is a practical approach to mitigate off-site movement from the soil.

Growth chamber and field experiments were conducted to assess the potential of Pseudomonas syringae pv. tagetis (Pst) as a biocontrol agent for Canada thistle. Silwet L-77, an organosilicone surfactant, was required to facilitate Pst penetration into Canada thistle leaves. Growth chamber experiments indicated that maximum Pst populations inside leaves were obtained with a Silwet L-77 concentration of 0.3% (v/v) or greater. High Pst populations (109 colony-forming units [cfu] per gram fresh weight) were found in leaves 48 h after treatment with 108 or 109 cfu ml−1 Pst plus Silwet L-77 (0.3%, v/v). In growth chamber experiments, foliar application of Pst (109 cfu ml−1) plus Silwet L-77 (0.3%, v/v) on 4- to 5-wk-old Canada thistle reduced shoot dry weight by 52% (measured 14 d after treatment) and chlorophyll content of emerging leaves by 92% (measured 10 d after treatment). In field trials conducted in 1999 and 2000, Pst (109 cfu ml−1) plus Silwet L-77 (0.3%, v/v) were applied at 700 L ha−1, and the method of application (paint gun, backpack sprayer, boom) and the number of applications (one or two separated by 14 d) were examined. Averaged over 2 yr, two applications with a backpack sprayer resulted in 67% disease incidence (apical chlorosis) of treated plants measured 4 wk after the initial treatment (WAIT). At the time of flower bud formation (8 WAIT), there was little or no disease incidence, 31% reduction in plant height, 81% reduction in number of flower buds, and 20% reduction in shoot survival during 1999 but no effect on survival in 2000.

Dormancy is a critical factor for the survival and persistence of weedy species. Contemporary approaches can be used to identify genes that regulate dormancy directly or indirectly to elucidate key mechanisms, signals, and pathways. Several domesticated plant species have been used as model systems to mark quantitative trait loci (QTL) that affect dormancy in seeds and vegetative propagules directly. A few weedy species have also been used to mark QTL and to determine dormancy genes using microarray analysis. Given the number of serious weeds worldwide and the role that dormancy plays in their persistence, developing fundamental knowledge on dormancy is an important step toward developing new strategies for weed management. This paper describes current research and outlines some weeds that might be candidates for dormancy investigations using molecular genetic and genomics approaches. An underlying theme in the selection of weeds for dormancy investigations is their relation to crop species and the ability to adapt existing resources to investigate dormancy in weedy plants.

The genetic variation of quackgrass as a species and the array of environments in which it is found indicate that selection in these different environments could lead to differentiation among quackgrass populations. Yet, a highly diverse environment might not promote the genetic divergence of quackgrass if it poses contradictory selection pressures. To assess the extent of divergence among quackgrass populations, this study compared the morphology of populations of quackgrass for 1 yr in Rosemount, MN, in a “common garden” study. The quackgrass was initially collected from three different farming systems in southeast Minnesota: corn–soybean (CS), oats–hay–corn (OHC), and permanent pasture (PP). The systems represent pasture or arable land and differ in cropping rotations and levels of disturbance. Although no differences among farming systems were detected in multivariate or univariate comparisons, a significant farming system effect was detected between CS and PP systems when the most diversified system, OHC, was excluded from the analysis. Consistent with this result, a principal components analysis suggested that plants from two of the three farming systems exemplified contrasting modes of perennial plant growth. Relative to each other, the CS plants showed more features of the “guerrilla” growth mode (longer intra-ramet distances, sparse, large patches), whereas PP plants showed more “phalanx” mode features (short intra-ramet distances, dense, smaller patches). Plants from the most diversified system, OHC, did not fit into either growth form, and for this farming system, the variation among populations was the highest. The results suggest that the CS and PP systems selected for distinct growth forms, whereas the diversified OHC system did not. This is consistent with the hypothesis that diversification of a farming system and weed management decreases the risk of evolution of a weed population highly adapted to control measures used in that farming system.

Clomazone dissipation was examined in four soils in field experiments. Field half-lives were 6 to 59 d (average of four field sites was 35 d) for ferrosol (clay loam), kurosol (loamy sand), sodosol (silt loam), and vertosol (light clay). The Hoerl equation provided a better fit to the measured field concentration at all four sites than did a first-order equation. The order of clomazone dissipation rate was ferrosol > sodosol > kurosol > vertosol. Clomazone desorption varied with soil type, with apparent Kd values of 3.6, 1.7, 1.8, and 2.4 for ferrosol, sodosol, kurosol, and vertosol, respectively. Clomazone residues became more strongly sorbed with time, as indicated by desorption hysteresis, but detectable concentrations were present in all soils 1 yr after application. The data indicate that the potential for carryover injury to crops is greatest in the kurosol and least in the ferrosol.