The feasibility of visual detection of weeds for map-based patch spraying systems needs to be assessed for use in large-scale cropping systems. The main objective of this research was to evaluate the reliability and profitability of using maps of Johnsongrass patches constructed at harvest to predict spatial distribution of weeds during the next cropping season. Johnsongrass patches visually were assessed from the cabin of a combine harvester in three corn fields and were compared with maps obtained in the subsequent year prior to postemergence herbicide application. There was a good correlation (71% on average) between the position of Johnsongrass patches on the two maps (fall vs. spring). The highest correlation (82%) was obtained with relatively large infestations, whereas the lowest (58%) was obtained when the infested area was smaller. Although the relative positions of the patches remained almost unchanged from 1 yr to the next, the infested area increased in all fields during the 4-yr experimental period. According to our estimates, using a strategy based on spraying full rates of herbicides to patches recorded in the map generated in the previous fall resulted in higher net returns than spraying the whole field, either at full or half rate. This site-specific strategy resulted in an average 65% reduction in the volume of herbicide applied to control this weed.

Chinese sprangletop, a C4 species, is one of the most important grass weeds of seeded rice in Asia. Chinese sprangletop biology was studied by growing it alone and in competition with 4 and 12 rice plants. Rice competition did not affect the height of Chinese sprangletop, and the weed grew taller than rice, regardless of the competition. Compared with Chinese sprangletop grown alone, competition from rice reduced Chinese sprangletop leaf number, leaf production rate, tiller number, tiller production rate, leaf area, shoot biomass, relative growth rate, and net assimilation rate. Leaf area and shoot biomass of Chinese sprangletop when grown in competition with 12 rice plants was only 16% and 13%, respectively, of the leaf area and biomass of the weed grown alone.

Diclofop-resistant Italian ryegrass is widespread in southwestern North Carolina, and growers have resorted to using acetolactate synthase (ALS) inhibitors such as mesosulfuron and pyroxsulam to control this weed in wheat. In the spring of 2007, mesosulfuron failed to control Italian ryegrass in several wheat fields. Seed were collected from six fields in two counties and greenhouse studies were conducted to determine response to mesosulfuron and the acetyl-CoA carboxylase (ACCase) inhibitors diclofop and pinoxaden. All populations were resistant to diclofop and cross-resistant to pinoxaden. Five of the six populations were resistant to diclofop, pinoxaden, and mesosulfuron. An additional study with two biotypes confirmed cross-resistance to the ALS inhibitors imazamox, mesosulfuron, and pyroxsulam. Resistance to mesosulfuron was heritable.

Texasweed is an annual broadleaf plant belonging to the Euphorbiaceae family and is an emerging problem in southern U.S. rice fields. Field studies were conducted in 2008 and 2009 to study the effect of flood depth on Texasweed survival and growth. The trearments were five flood depths: 0, 10, 15, 20, and 30 cm and two Texasweed growth stages: two- to three-leaf stage and four- to five-leaf stage. The experiment was conducted in a completely randomized split-plot design with three replications. Flooding conditions were created by placing potted plants in 1.3 m by 0.7 m by 0.7 m polyvinyl chloride troughs. The effect of flood depth on Texasweed growth and fruit production was evaluated using ANOVA and regression analysis. Texasweed plants were able to survive in floods up to 30 cm; however, growth and fruit production were reduced. Increasing flood depths resulted in increased plant height and greater biomass allocation to stem. Texasweed plants produced adventitious roots and a thick spongy tissue, secondary aerenchyma, in the submerged roots and stem, which may play a role in its survival under flooded conditions. The recommended flood depth for rice in Louisiana is 5 to 10 cm. A 10-cm flood in the present study caused about 30 and 15% biomass reduction in two- to three-leaf and four- to five-leaf stage Texasweed, respectively. The results, thus, suggest that flooding alone may not be a viable option for Texasweed management in drill-seeded rice. However, appropriate manipulation of flooding could enhance the effectiveness of POST herbicides. This aspect needs further investigation.

In 2007, populations of Italian ryegrass were observed surviving applications of glyphosate under field conditions in southeast Arkansas. At least 10 reports of Italian ryegrass escaping glyphosate applications followed in subsequent years in Arkansas. These were unconfirmed reports of resistance from county agents, consultants, and farmers. The objectives of this research were to confirm resistance to glyphosate in a suspected resistant population collected in 2007 (Desha 2007) and to determine the level of resistance of a putative glyphosate-resistant population collected in 2009, both from Desha County, AR. Other objectives were to determine the resistance frequency in these populations, to determine whether the 2009 population was also acetolactate synthase (ALS) or acetyl-CoA carboxylase (ACCase-resistant), and to determine the effect on plant size as it relates to dose–response to glyphosate. The Desha, AR, 2007 population exhibited a low level of resistance to glyphosate. The estimated glyphosate dose that would control this population 50% was 1,260 g ae ha−1, compared with 190 g ae ha−1 for the susceptible check. In 2009, a population of Italian ryegrass (Des03) was identified that survived a glyphosate application of 1,740 g ae ha−1 made in the field, which is twice the commercial use rate for glyphosate. Dose–response experiments determined that an estimated 3,890 g ae ha−1 glyphosate was required to obtain 50% biomass reduction of Des03; this was 23 times that of the susceptible standard. Neither growth stage nor glyphosate rate evaluated affected the level of resistance observed in the Des03 population. This population was determined to be more than 70% resistant at the levels reported. In addition to glyphosate, Des03 was also resistant to diclofop, a commonly used herbicide in wheat in Arkansas and other areas. As a result, alternative management strategies for Italian ryegrass are currently being explored.

Agroecosystems are inherently complex, and practices aimed at managing one component of the system can have unintended consequences for other components of the system. Management decisions, therefore, can be improved by assessing and understanding the multivariate nature of agricultural systems and the multifunctional character of particular agricultural management practices. The act of simultaneously assessing and evaluating multiple characteristics or functions in agriculture also can be a valuable education and extension activity, because it draws on active and experiential methods of learning and because the process effectively reveals important functions and tradeoffs associated with agroecosystems and their management. Here we introduce a tool (the spider plot) and present a case-study exercise in which we used this tool to evaluate the multiple characteristics and functions of different cover crops within a field day workshop format. We also provide examples of how this approach could be used to assess other management practices or properties of agroecosystems and communicate multivariate concepts within a weed science classroom or extension environment.

Seashore paspalum has high salinity tolerance, suggesting sodium chloride might have potential as a selective grassy weed herbicide. The objective of this research was to investigate sodium chloride rate and application timing for smooth crabgrass control and seashore paspalum and common bermudagrass injury. Five rates of sodium chloride (244, 488, 976, 1,952, or 3,904 kg ha−1) were compared with quinclorac at 0.84 kg ai ha−1 for controlling multileaf or multitiller smooth crabgrass. Sodium chloride at ≥ 976 kg ha−1 provided excellent control (90 to 100%) of multitiller smooth crabgrass from 7 to 28 d after treatment, but ≥ 1,952 kg ha−1 was required to achieve excellent control of multileaf populations. Furthermore, 976 kg ha−1 of sodium chloride applied to multitiller smooth crabgrass caused minimal seashore paspalum injury (0 to 6%), comparable to quinclorac, but was more injurious when applied earlier in the spring for multileaf smooth crabgrass control. Common bermudagrass injury increased with sodium chloride rate and was > 20% from sodium chloride at 488 and 976 kg ha−1 at both application timings. Overall, sodium chloride was most effective and safe on seashore paspalum when applied for smooth crabgrass control at the multitiller growth stage, whereas bermudagrass injury might be excessive at minimum rates required for control.

Common purslane is a widely distributed summer annual weed. It can reproduce vegetatively from stem cuttings by forming adventitious roots from the cut end of the stem. Apart from large stem cuttings, it is unclear whether purslane cuttings of various plant tissues differ in their ability to reproduce asexually. The objective of the study was to determine the survival and asexual reproductive capacity of purslane cuttings. A greenhouse study evaluated three cuttings from two stem locations and a leaf from one stem location for their survival and new leaf growth after 21 d. Cuttings included a stem node with either leaves attached or removed and a stem internode, all from proximal and distal stem locations relative to the root crown, and a leaf from a proximal stem node. Stem node cuttings had ≥ 70% survival, whereas internodes had 0% survival. Nodes with leaves attached further increased survival by > 20%. The location of the cutting on the main stem did not affect survival. Only noded cuttings produced new leaves, and cuttings with leaves attached produced the most new leaves. For purslane to vegetatively reproduce, nodes on stem cuttings are required, and the presence of leaves on the cutting improves the survival and new leaf growth of cuttings. Therefore, mechanical methods of weed control that chop and spread purslane leaves and stems might not be effective and could ultimately increase weed populations.