Alternative Approaches to Weed Management

Herbicide technology and use have been the focus of weed management research for the past several decades. Herbicides are an important component of weed management and will remain so for years to come. However, there is increasing pressure to improve the efficiency of herbicide use and develop alternative control methods. Herbicides are used on over 95% of the com and soybean in the Com Belt because of the presence of weeds and the need to minimize their adverse economic impacts. Large inputs of herbicides and tillage are needed to control weeds because of the lack of knowledge of weed biology and ecology, continuous production of summer annual row crops, and the absence of control alternatives. Currently, weed science has few, if any, alternatives to herbicides and tillage that are both economically and environmentally desirable

Tillage Systems and Weed Population Dynamics

Conservation tillage (CT) has had more impact on weed control in row crop production than any other recent change in management practices. In conventional tillage systems, moldboard plowing and secondary tillage just before planting help crop seedlings get an equal start with weed seedlings. In CT systems, herbicides are used to substitute for some or all of this tillage

Occurrence of common milkweed (Asclepias syriaca) in cropland and adjacent areas

Interest in the population dynamics and geographic distribution of common milkweed (Asclepias syriaca L.) has recently increased due to the importance of common milkweed in the life cycle of the monarch butterfly (Danaus plexippus). A survey of common milkweed occurrence in various habitats was conducted in Iowa in June and July of 1999. Common milkweed was found in 71% of the roadsides and approximately 50% of the corn (Zea mays L.) and soybean (Glycine max L. Merr.) fields. Corn and soybean fields had 85% fewer patches than roadsides. Conservation reserve program fields had the greatest average area infested. While common milkweed was frequently found in corn and soybean fields, average frequency and patch sizes were much greater in noncrop areas

Biologically intensive manipulation of foxtail seed banks for enhanced mortality

Studies were conducted at several Iowa locations to determine the fates and long-term carry-over of giant foxtail in agricultural soil weed seed banks, and the variability of these seed fates

Initial dates of weed emergence

Timing of weed emergence varies both from year to year and also across the state. The table provides information on the initial date of emergence of five early weed species at locations across Iowa. Giant ragweed, one of the earliest emerging summer annuals found in crop fields, initiated emergence in the last week of March or first week of April in both 1998 and 1999. At most locations giant foxtail began emergence about 4 weeks after giant ragweed, but at the SE (Crawfordsville) location there has been only a 2-week difference in initial emergence of these species

Effect of Separating Giant Foxtail (Setaria faberi) Seeds from Soil Using Potassium Carbonate and Centrifugation on Viability and Germination

Changes in weed seedbank composition are often monitored by removing seeds from soil samples. One extraction method accomplishes this by creating a slurry of soil and a concentrated inorganic salt solution. Centrifugation is then used to separate constituents of differing densities. We have found that centrifugation of giant foxtail seeds in 3.2 M potassium carbonate solution as conducted in a centrifugation/flotation extraction method can reduce viability as measured by germination and tetrazolium tests. In one experiment, centrifugation/flotation separation reduced germination of giant foxtail seeds from 94 to 52%. The likely cause of seed damage was the high pH of the potassium carbonate solution in conjunction with the increased hydrostatic pressure due to centrifugation. While centrifugation affected quantitative measures of seed viability, it did not alter qualitative viability estimates using a pressure test

Emergence Characteristics of Several Annual Weeds

No other event in the life cycle of weeds affects scouting and management timing as greatly as weed emergence. The timing and intensity of weed emergence affect everything from the effectiveness of burndown herbicides and preplant tillage, to timing of postplant tillage and herbicide application, to competitiveness of weeds that escape control, to seed production by surviving plants, to eventually population shifts. Given the importance of weed emergence to all forms of weed management, it seems logical that we should give greater attention to understanding and predicting weed emergence as affected by environmental factors, weed species, and management practices

Spring-seeded smother plants for weed control in corn and soybeans

Smother plants are specialized cover crops developed for their ability to suppress weeds and may provide an alternative, non-chemical method of weed control. The goal of this project was to define the characteristics and mechanics of establishing a successful spring-seeded smother plant system and to study and exploit the competitive interactions among weeds, smother plants, and the crop

Emergence Patterns of Annual Weeds of Corn and Soybean

A better understanding of weed biology is critical for the development of more efficient weed management systems. Improved information on weed biology will not allow us to eliminate the inputs currently used to manage weeds. However, it provides the foundation for the development of new strategies and more efficient techniques to use these tools, resulting in more reliable weed management systems that are cost-effective and pose less threat to the environment

Relative Emergence of Weeds of Corn and Soybean

The success of integrated weed management relies on matching control strategies to the specific weed problem in a field. This requires information not only on what weed species and how many of these weeds are present in a field, but also knowledge of the distribution of the weeds throughout the field and the stage of development of these weeds. Weed control recommendations typically provide information on appropriate tillage methods and herbicide selection. The information concerning weed infestations used to base these recommendations typically is not of sufficient detail to optimize the efficiency of these strategies