Barbara D. Booth

Weed ecology in natural and agricultural systems

Population ecology species interactions community ecology applied weed ecology. (Part contents).

Assembly theory applied to weed communities

Abstract Community assembly is a branch of ecology that looks at how communities are assembled as they follow trajectories through time. A trajectory is controlled by biotic and abiotic constraints (filters) that act at multiple scales. From a total species pool, environmental and dispersal constraints control which species enter an ecological species pool. Within this pool, internal dynamics determine which of these species becomes part of the extant community. Environmental filters act by removing species that lack specific traits. Thus, traits are filtered, and with them, species. In this paper, we present the basic ecological theory of community assembly and address how it can be used in conjunction with a trait-based approach to understand and possibly predict how weed community structure changes in response to imposed filters such as tillage or crop rotation. Weed ecologists have struggled with the need to place our practical knowledge of agriculture and weeds into a broader theory, and there have been many calls to integrate ecology with agronomy and weed science. Community assembly might be one way to do so.

Evaluation of alternative weed management systems in a modified no-tillage corn–soybean–winter wheat rotation: weed densities, crop yield, and economics

Abstract A 9-yr (1990–1998) study was conducted at Woodstock, ON, Canada, to evaluate weed densities, crop yields, and gross returns in a modified no-tillage (no primary tillage) corn–soybean–winter wheat rotation under three weed management treatments: (1) minimum, preplant application of glyphosate followed by mechanical control; (2) integrated weed management (IWM), preplant application of glyphosate followed by band application of preemergence herbicides plus mechanical control; and (3) conventional, preplant application of glyphosate followed by broadcast application of preemergence herbicides in corn and soybean. In wheat the minimum and IWM treatments had no additional weed control measures other than the preplant application of glyphosate, whereas the conventional treatment had a broadcast application of a postemergence herbicide. Weed densities were assessed each year, (except in 1990) once during the growing season in corn and soybean and immediately after crop harvest in wheat. Adjusted gross return was calculated as the gross revenue minus the unique costs for weed control for each of the treatments. Weed densities were greater in the minimum treatment compared with the IWM or conventional treatment in all crops. Weed densities in the IWM and conventional treatments did not differ. There was no apparent “buildup” of weed density with time in the rotation resulting from weed escapes. Hence, these data challenge current thinking that weed densities increase with time if weed escapes are allowed to go to seed. Corn and soybean yields in the IWM and conventional treatments did not differ. However, the minimum treatment had the lowest corn and soybean yields. Winter wheat yield was not affected by the treatments. All weed management treatments provided similar gross returns for each crop and for the rotation. Thus, the minimum treatment consisting of glyphosate applied preplant followed by shallow interrow tillage appeared to be a viable option, especially if practiced in a farming system capable of ensuring adequate timing of cultivation operations. Nomenclature: Glyphosate; imazethapyr; linuron; metolachlor; MCPB and MCPA; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; winter wheat, Triticum aestivum L.

Management in a modified no-tillage corn–soybean–wheat rotation influences weed population and community dynamics

Abstract Conservation tillage systems, such as no-tillage, are ecologically advantageous because they reduce soil erosion; however, they rely heavily on herbicide use. Our goal was to determine how weed communities of no-tillage systems are affected when the system is modified to reduce herbicide use through a combination of banded herbicides and interrow cultivation. To this end, we conducted a 9-yr study in a no-tillage corn–soybean–winter wheat rotation. All management systems had a preplant application of glyphosate, followed by either broadcast PRE herbicides (conventional no-tillage), interrow cultivation with banded PRE herbicides, or interrow cultivation alone. Aboveground weed densities were assessed each year and data were grouped into early (1991 to 1993) and late (1996 to 1998) time periods. Over time, weed communities became more distinct, showing a strong response to management and crop. In the early years, weed communities separated more in response to management than crop. In the late years, this was reversed. Weed communities in systems with interrow cultivation were more diverse than those in conventional no-tillage. The response to weed management system and crop was species specific. For example, the abundance of yellow foxtail was higher when interrow cultivation was employed, but abundance was equal in all crops. Dandelion was more abundant in conventional no-tillage of corn and soybean; however, it was equally abundant in all management systems in wheat. Seed bank species richness increased over time and was highest in systems with interrow cultivation. Herbicide use can be reduced in a modified no-tillage corn–soybean–wheat rotation by incorporating interrow cultivation, with or without banded herbicides, into the management plan. The weed community trajectory changes, and the weed community becomes more diverse. A more diverse weed community will not necessarily alter how we manage weeds. Nomenclature: Glyphosate; yellow foxtail, Setaria glauca (L.) Beauv.; dandelion, Taraxacum officinale Weber; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.

Management of Weed Seedbanks in the Context of Populations and Communities

Abstract In agricultural systems, weed seedbanks provide insights into cropping and management history as well as potential weed problems. Seedbank management is an integral part of a long-term weed management system. In this article, we propose a framework for managing weed seedbanks by putting weed seedbanks into the context of populations and communities. Early in the plant invasion process, it is possible to eradicate or contain the weed species through intensive focused management. Weed populations that become established and pose unique or extreme problems should be managed using population-based strategies such as targeted removal or trap crops. Established weed populations that pose no specific problem should be managed as part of the weed community using a variety of strategies such as tillage, crop rotation, cover crops and mulches, soil solarization, and microorganisms.

The role of seed rain in determining the assembly of a cliff community

. Cliff-face communities of the Niagara Escarpment in Ontario, Canada, are dominated by long-lived Thuja occidentalis and a consistent assemblage of other plants. Our objective was to determine whether seed rain plays a role in determining why these species are dominant. Seed rain was collected from the cliff face and from the surrounding plateau-and talus communities at two sites over a 2-yr period in order to compare these three adjacent, but different communities. Multivariate Discriminant Analysis first separated the two sites: primarily due to the importance of Betula papyrifera at one site. The three community types were also separated, although there was still substantial overlap. There was a predictable array of species associated with each community although the seed rain on the cliff faces differed slightly. When characterized by univariate ANOVAs, seed rain in the cliff faces and plateaus had a lower species richness and lower total seed density than the talus sites. Seeds of two of the 11 species analysed individually showed an influence of habitat type on their number. Seed morphology did not influence patterns of seed rain. Finally, there was no correlation between the seed rain and above-ground vegetation in any of the communities. We conclude that the seed rain patterns that exist do not act to filter the plants that form the mature vegetation of cliffs.

Constraints on the assembly of cliff communities at the seed bank stage.

Abstract Seed banks on cliffs of the Niagara Escarpment, southern Ontario, Canada, were examined and compared to different, but immediately adjacent, communities on plateaus and talus slopes to evaluate the role of the seed bank in controlling the mature vegetation of cliff-face communities. Soil samples were collected five times at two sites over three years. Data were analyzed three ways: multiple discriminant analysis on community composition, univariate ANOVAs of seed density data, and analysis of seed characteristics. The emergence of constraints on final plant community structure was clearest for the discriminant analysis: year of collection separated the seed bank centroids the most, but a secondary effect we observed was the clear separation of the three community types and their association with species found in their specific mature communities. ANOVAs and the analyses of seed characteristics did not show statistically significant community-related sorting. Although the cliff-face community structure was discriminated at the seed bank stage, it was not directly correlated with the above-ground vegetation; therefore subsequent processes such as seed germination and seedling survivorship must also be responsible for final community composition.

Invasive Ecology of Weeds in Agricultural Systems

No community is truly safe from plant invaders. Nor should it be. Succession is the normal process of species invading and replacing other species (Huston, 1994; Johnstone, 1986; Rejmanek, 1989), although this connection between invasion and succession is often ignored (Davis et al., 2001). The problem is that some plant invasions have high ecological and economic costs associated with them (Parker et al., 1999; Pimentel et al., 2000, 2001). Some economic costs of invasion are easily quantifiable (e.g. the cost of weed control, yield loss) whereas other are not (e.g., damage to ecosystems, loss of recreational land, aesthetics). The cost of invasive plants to crop and pasture land in the United States is calculated as well over 34 billion dollars annually (Pimentel et al., 2000), while in India, the cost stands even higher at 38 billion per year (Pimentel et al., 2001). Any ability to predict what species could invade will therefore have economic and ecological benefits.