Do I Weed & Feed or Plant Seed First?. You can sow grass seeds now and kill weeds later with a post-emergent herbicide or kill weeds now with a pre-emergent herbicide and plant the seeds later. Weed-and-feed fertilizers are specially formulated combinations of turf fertilizer and herbicides that you apply either … Landscaping Neo-Liberalism: The Weed and Seed Strategy Abstract Weed and Seed, a federal initiative that started in the 1990s, seeks to improve economic and social conditions for residents in Weed communities in agronomic fields are dominated by annual species. Summer annuals initiate growth each spring from seeds found in the upper soil profile (Figure 1). In most fields, a small percentage of the emerging plants survive and contribute new seeds to the soil seedbank. Historically, most research of the annual weed life cycle has focused on seed dormancy and emergence (A), effect of control tactics on weed survival (B), and weed seed production (C). The fate of seeds between the time of maturation on the plant and entering the seedbank (D) has largely been ignored.
Do I Weed & Feed or Plant Seed First?
You can sow grass seeds now and kill weeds later with a post-emergent herbicide or kill weeds now with a pre-emergent herbicide and plant the seeds later. Weed-and-feed fertilizers are specially formulated combinations of turf fertilizer and herbicides that you apply either before you plant grass seeds or on established lawns.
You apply pre-emergent herbicides before weed seeds germinate, typically in the spring. Pre-emergent herbicides do not prevent weed seeds from germinating; they suppress the development of weed roots as they germinate. They’re usually effective for two weeks to three months, depending on the formulation, and you have to water the lawn after applying for the herbicide for it to be effective. There are pre-emergent herbicides to kill both broadleaf weeds and weedy grasses. You can apply them before you sow your grass seed. If you apply a pre-emergent herbicide that kills weedy grasses, you have to delay sowing your lawn seed.
Post emergent herbicides kill weeds after they appear. Some post-emergent, systemic herbicides that you can apply directly on lawns only kill weedy grasses, while others only kill weeds with broadleaf weeds. Contact herbicide such as those including the active ingredient glyphosate kills on contact. To use one of those on a lawn without killing the grass you have to daub it on individual weeds.
Pre-Emergent Weed-and-Feed Fertilizer
Fertilizers containing pre-emergent herbicides selectively prevent certain kinds of weeds from finishing their germination cycle. There is no point applying this type of weed-and-feed mix after weeds are growing on your lawn. You have to apply it early in the growing season before weeds appear. Make sure the pre-emergent herbicide in the fertilizer kills the kind of weeds that have plagued your lawn in the past. You might apply a starter fertilizer containing a pre-emergent herbicide before you sow your lawn seeds.
Post-Emergent Weed-and-Feed Fertilizer
Post-emergent weed-and-feed formulations kill selective weeds that are already growing in your lawn. Make sure that the herbicide in the formulation you buy kills the type of weeds that are growing in your lawn. Most weeds make their appearance in the spring, the best time to apply weed-and-feed fertilizer.
Landscaping Neo-Liberalism: The Weed and Seed Strategy
Weed and Seed, a federal initiative that started in the 1990s, seeks to improve economic and social conditions for residents in poor urban neighborhoods by removing criminals (weeding), and implementing programs designed and administered by conglomerates of state, local, and community level actors (seeding). This paper, however, seeks to outline the necessary questions about the program’s as yet unmeasured socio-economic outcomes. It argues first that the potential impact on targeted neighborhoods goes largely unaddressed in the strategy’s design, and ultimately threatens to undermine substantive neighborhood improvement. It further argues that while the project’s flaws may be cast as the perpetual imperfection of social policy and implementation design, they are instead products of the political-economic context in which they are embedded. In other words, it argues that Weed and Seed is a product of the neo-liberal state and reflects policy decisions that privilege capitalist development, re-enforce small-scale social spending, and the mass incarceration of the US prison system.
In 1993, the United States Department of Justice initiated Operation Weed and Seed, a community-based crime prevention program that has spread to over 250 communities across theUnited States(OJP 2009). Weed and Seed is a federal initiative that aims to improve social and economic conditions in poor urban neighborhoods through the combination of aggressive law-enforcement practices and collaborative community programming. The Weed and Seed approach pursues better economic and social conditions in targeted neighborhoods by removing criminals (weeding), and implementing initiatives designed and administered by conglomerates of state, local, and community level actors (seeding).
At the federal level, the Weed and Seed strategy is intentionally vague, thereby delegating most design, implementation, and funding mechanisms for initiatives to local and community leaders (OJP 2009). The logic of the Weed and Seed model largely frames criminals and uncoordinated service provision as the primary obstacles for socio-economic growth in blighted urban neighborhoods. In other words, “weeding” criminals out of neighborhoods, and “seeding” in local service programs marks a departure from the Keynesian model of welfare that proliferated in the 1960’s and 70’s, a model that framed federally funded cash and in-kind public assistance programs as America’s preferred anti-poverty edifice. This divergence is most pronounced in the Weed and Seed strategy’s reliance on theU.S.prison system as an institution instrumental to keeping criminals out of targeted neighborhoods. Further, politicians aligned the strategy to neo-liberal ideals that position capitalist development as a viable strategy for improving conditions in poor neighborhoods, providing legitimacy for small-scale social spending and mass incarceration.
This paper argues that Weed and Seed, shaped by a post-Keynesian penology, is a strategy that satisfies a contemporary neo-liberal agenda that effectively reproduces class stratification. It begins by describing, in more detail, the Weed and Seed strategy, then illustrates the concept of a post-Keynesian penology, and lastly explores the strategy as it relates to the neo-liberal agenda. To provide a richer understanding of the relationship between the post-Keynesian state and the US prison system, the paper draws on Ruth Wilson Gilmore’s (1999) theory of the post-Keynesian militarism, as well as the work David Harvey (2005) and William Sites (2003) to provide a historical framework of neo-liberalism, and to provide critical points of analyses through which to demonstrate that Weed and Seed is a product of the neo-liberal state.
Weed and Seed: A Brief Overview
Weed and Seed is a strategy, not a program. “[It] is a means to mobilize resources in coordinated efforts, not simply a mechanism to fund local activities that share no collective aim” (Dunworth et. al. 1999, 15; italics added). Whereas a program might generate the expectation of uniform implementation at every site, the Weed and Seed strategy requires a significant amount of planning at the local level for its implementation. Because socio-economic landscapes (crime patterns, police presence, organizations, businesses and community groups) vary, the format and implementation of a Weed and Seed mission can look quite different from neighborhood to neighborhood.
However, every Weed and Seed site has three core components: weeding, seeding, and community policing. The first element, weeding, aims to remove criminals from the neighborhood through targeted operations and elevated police presence. Commonly utilized tactics include identifying and securing locations of high-crime activity, aggressive use of search and arrest warrants, undercover “buy busts,” and extended police coverage with an emphasis on field interrogations (Miller 2001). The second component, seeding, uses new resources from the program to leverage pre-existing community resources and actors in the planning and implementation of self-selected initiatives. While seeding initiatives vary based on locally defined priorities, all sites are required to have a “safe haven,” a multi-service center or space that hosts a variety of different programs and activities. Popular seeding efforts include youth prevention and intervention programs, adult employment programs, family support services, community building and neighborhood beautification initiatives (Dunworth et. al. 1999). The third component is community policing, in which the police and community proactively collaborate to address and respond to pressing problems.
Each Weed and Seed site has a designated a Grantee Organization, which is responsible for program coordination and implementation. Steering committees are charged with designing the program and, often chaired by officials such as an attorney general or mayor, consist of a mix of public sector representatives and community members (Dunworth et. al. 1999). For example, the Crawford-Roberts Weed and Seed site inPittsburghhad a task force that consisted of members from the local police department, the Federal Bureau of Investigation (FBI), the Drug Enforcement Administration (DEA), and the Immigration and Naturalization Services (INS) (Bynum et. al. 1999).
While the above components and organizational elements define the general outline of the strategy, such governing committees are not uniformly implemented, and rely on varying funding sources. Depending on the site, community members and organizations can use more or less discretion in relation to selecting which seeding initiatives to fund. This exercise of community power, however, can only be activated once seed funding is made available. For example, funding for seeding initiatives in the Crawford-Roberts Weed and Seed site was largely unavailable until two full years after weeding began (Bynum et. al. 1999).
Nevertheless, the Crawford-Roberts neighborhood experienced decreases in crime within four years of strategy implementation, and residents perceived improvements neighborhood safety and quality of life (Bynum et. al. 1999). A cross-site analysis (Dunworth et al. 1999) showed similar findings in four other neighborhoods. This crime reduction trend is also evident in a more recent study of homicide rates, which found that, 55% of the two hundred and twenty Weed and Seed site respondents reported a decline in homicide rates from the time period between 1996 and 2001 (O’Connell, Perkins and Zepp 2003).
While many of the Weed and Seed sites are selected on the basis of high crime rates and high density of indicators of poverty (unemployment and income status) (Miller 2001), outcomes measuring the latter are not widely publicized in available program materials. The evaluation of the Crawford-Roberts reports little to no improvement in unemployment (Bynum et. al. 1999), and the cross-site analysis (Dunworth et. al1999) omits these outcomes all together. In sum, while reduced crime rates and improved community perception indicate some success, the absence of data regarding the economic wellbeing of communities suggest that such success is perhaps too narrowly defined.
Post- Keynesian Penology
In addition to decentralized control of resources, there is the propagation of criminal incarceration without rehabilitation. While weeding focuses largely on identifying and arresting criminals, incarceration is an integral element of the strategy as a whole. Miller (2001) describes the Weed and Seed strategy as an expression of a penology that largely positions crime as an unpreventable phenomena whose elements are to be managed, and negative impacts to be mitigated.
These attributes reflect the greater political economic climate of the 1990s. Starting in the 1970s the Keynesian model of economic governance, which proscribes the deployment of state controlled public money to mitigate free-market failures (e.g., unemployment and poverty), lost much of its popularity (Harvey 2005). TheUSfederal government had fewer resources (and less political incentive) to launch significant public assistance campaigns. In other words, the Weed and Seed focus on crime reduction and neighborhood development are hallmarks of a distinctly post-Keynesian response to poverty. Instead of treating poverty as a primary producer of criminal behavior, the logic of the Weed and Seed largely inverts this causal story by localizing criminality onto individuals.
Such an orientation to crime, as Miller (2001) describes it, provides little in the way of programming to meet broader social goals, and decentralizes state responsibility for the contexts in which crime is embedded. In short, this penology justifies purging social programs in favor of reactive measures that aim to separate criminals from law-abiding citizens, and often diffuse remedial responsibilities to local contingents. The abandonment of rehabilitative services for criminals, the intensified commitment to removing criminals from neighborhoods, and the (minimal) support provided to citizens in the community correspond to the model she describes. Lastly, the delegation of crime control responsibility to local organizations is a primary characteristic of both this penology and the Weed and Seed approach as state and elected officials are insulated from assuming accountability for crime rates.
Ruth Wilson Gilmore’s (1999) work onUSprison growth further places this penology in a post-Keynesian state. As Gilmore frames it, the corporate tax-rebellion and social militancy of the 1960s left the state with fewer resources to spend on social programs, and a white electorate that was no longer in favor of funding the war on poverty. The accumulation ushered in by lower tax barriers and a growth in the popularity of finance capital created an environment in which pools of money were amassed with few outlets for investment. While suburban development channeled some land (and financial) surplus, capital had still withdrawn from rural areas as a result of agribusinesses forced out by debt (driven by international commodity markets and natural disasters). Such restructuring of agricultural and industrial markets also lead to a surplus in labor, land, and unemployment, and the restructuring of taxes meant that social programs would not be implemented to put labor surpluses back to work. Gilmore argues that prisons became the post-Keynesian state’s outlet for surpluses in capital, land, and labor.
In other words, the mass incarceration and harsh sentencing that Miller (2001) refers to may well be the result of the recent dramatic increase in the state’s criminal storage capacity. Gilmore argues that the demand needed to both justify and meet the rise in supply of “cages,” was achieved by a politically and economically crafted “crime” crisis. Fueled by the militant civil rights movement that threatened race and class hierarchies, Nixon’s “law and order” campaign recast radical activism as crime that needed to be controlled (Gilmore 1999). After a decade of moral panic, the harsher sentencing and massive prison construction that started in California in 1982 seemed justified to the American public, regardless of the fact that crime rates had been steadily declining since 1980 (Gilmore 1999).
When President Bush introduced the Weed and Seed Act of 1992, Congress was not receptive to the bill. It wasn’t until later in the year, after the Los Angeles riots had gained significant media attention, that funding was appropriated for Weed and Seed under the Tax Fairness and Economic Growth Act of 1992 (Ruben 1994). This provides support for the notion that crises energize reform efforts, and as Gilmore argues, particularly those that reinforce standing social orders. The result was a combination of mass incarceration, harsh sentencing, and a limit on rehabilitative programs and services.
The Weed and Seed strategy is a prime example of the way in which the post-Keynesian penology is able to reproduce the crisis of crime, and thereby create a steady supply of prisoners. Weeding in targeted neighborhoods results in more arrests, and consequently in more incarcerated community members. During incarceration, these community members are unable to participate in the labor market, maintain personal and professional connections, or contribute to the economic and social wellbeing of family members (Solomon, Fischer, Le Vigne and Osborn 2006). Upon release, the majority of reentering prisoners stay with their families, returning many to the neighborhood in which they lived prior to incarceration with relatively little to offer (Visher and Farrell, 2005). Meager job prospects, untreated mental and physical health conditions, few public benefits, and sometimes major debt accumulations (one study found that a quarter of prisoner respondents owed an average of $25,000.00 in child support) make reentering prisoners difficult community members to re-integrate successfully (Solomon, Fischer, Le Vine and Osborn and 2006). In effect, the weeding component ends up concentrating disadvantage by maintaining the socio-economic conditions correlated with crime.
Planting a Neo-liberal Agenda
The Weed and Seed approach served goals other than crime reduction and local social programming as politicians embedded the strategy in legislation that positioned Enterprise Zones as a legitimate means to improve poor neighborhoods. Originally introduced inEnglandin response to neighborhood “blight” produced by urban deindustrialization, Enterprise Zone initiatives provide tax-breaks and other financial incentives to encourage entrepreneurial development in poor neighborhoods. Following up on campaign promises to implement Enterprise Zones in the United States, George Bush introduced the Weed and Seed Implementation Act of 1992. The Bush model marked an innovation of traditional constructions of Enterprise Zones, which according to Rubin (1994), were unsuccessful in spurring economic growth due to an over-reliance on the free-market and failure to address social obstacles.
The origins of Operation Weed and Seed suggest that it emerged as a solution to the problems of developing surplus urban space. Target neighborhoods for Weed and Seed implementation were selected based on indicators of underdevelopment and economic promise (Miller 2001). For example, the Crawford-Roberts neighborhood occupied a central location in the Hill District in Pittsburghthat had once been a populous African American urban center for commerce and cultural activity. As a result of fleeting industrial production from the city, the Hill District had seen a 70% drop in population by the 1990s and was home to neighborhoods with the highest violent and drug crime-rates in the city (Bynum et al.1999). The combination of tax incentives, aggressive law enforcement, and growing community involvement through small-scale neighborhood investments were to stimulate economic development and improve conditions in neighborhoods like Crawford-Roberts.
According to David Harvey (2005), such disarming impediments to free market growth is at the top of neo-liberal agenda. Harvey(2005, 19) argues that neo-liberalization of the state is a “political project to re-establish the conditions for capital accumulation and to restore the power of economic elites.” Harveyfurther outlines the dramatic increase in income inequality that followed drastic shifts in monetary policy of the 1970s to assert that political pursuit of a free-er market system produces hyper-concentrations of capital for a very small economic elite. This new model of governance, one that prioritizes corporate welfare over human welfare, was not strictly created by legislation. As an example, he cites theNew York City fiscal crisis of the 1970s is an example of the way that neo-liberal practices took hold of city government, and became a compelling model for social and economic policy during the Reagan era. The crisis came to a head in 1975 when a coalition ofNew York investment bankers refused to roll over the City’s debt, which pushed the city into virtual bankruptcy in the midst of a national recession. What followed,Harvey shows, was a series of concessions that required the city to render tax revenues to bondholders, and the large scale re-orientation of city government priorities from pubic employment and services to entrepreneurial development. New York’s fiscal recovery, engineered by the “cadre” of investment bankers, brought both new practices and justifying ideologies. City government resources were increasingly utilized to attract investment capital by building infrastructure and providing tax incentives and subsidies for new enterprise (Harvey 2005).
As Sites (2003) asserts, out of the crisis and “recovery” emerged a narrative that laid blame for the city’s fiscal failure on the “excessive demands of poor people, municipal workers, racial minorities, and community groups – and . . . the liberal politicians who supported them” (39). This definition of the crisis, Sites shows, justified major cuts to public services that the poor and working-class residents relied on, and set a precedent for distributing public money and political attention to business entrepreneurs and corporate leaders. WhileHarveyis careful to point out that this mass reallocation of public resources wasn’t necessarily an overt effort to restore class power to economic elites, Sites (2003) demonstrates that the neo-liberal approach, as “philosophy for public action,” functions to fix the needs of free-market enterprise at the top of the political agenda. Because the expansion of enterprise relies on growing private pools of capital, politicians must then protect capital concentrations against redistributive policies and practices. The neo-liberal model rationalizes expanding and protecting investment opportunities for the economic elite (Harvey 2005), and initiatives to eliminate obstacles to free-market proliferation (Sites, 2003).
Urban revitalization initiatives, of which Empowerment Zones are an example, are a product of theNew Yorkfiscal crisis recovery that were subsequently reproduced throughout theUnited States. As an appendage to urban revitalization efforts, the Weed and Seed works to facilitate urban economic development by reducing crime and increasing community engagement, all while constricting – by increasing arrests and incarceration – the already limited opportunities for capital accumulation for residents of those targeted neighborhoods. Gilmore (1999) argues that high rates of incarceration create a pool of low-cost labor. Since living wages for low-skilled work are an obstacle for competition in the global economy, prison labor functions as a mechanism to reduce the cost of production and post-incarceration, ex-prisoners feed the increasingly “flexible” workforce that characterizes the neo-liberal labor market.
Western and Beckett (1999) identify a key paradox in the short and long-term labor market effects of theUSprison system. Prisoners are excluded from unemployment figures in theUnited States, deflating the unemployment rate and creating the illusion of a stronger economy in the short-run. But because incarceration reduces job prospects for ex-offenders, they argue that consequences of a rapidly expanding penal system are sustained long-term unemployment and deepening social inequality: “Incarceration . . . deepens inequality because its effects are increasingly detrimental for young black and unskilled men, whose incarceration rates are highest and whose market power is weak” (1031). This unemployment contradiction marks the potential long-term negative impact on recidivism in targeted neighborhoods.
Dunworth and others (1999) and Miller (2001) document local level resistance to Weed and Seed implementation. Miller’s documentation of a Seattle Weed and Seed site illustrates the ways in which strategy implementation and design activated effective community opposition and control. Not only was this neighborhood successful in initially staving off program implementation, but when they eventually “accepted” the initiative – they were able to lead campaigns that increased seed funding and granted more community control over funding streams.
While the activation of opposition cannot be held up as an accomplishment of the strategy as a whole, community investment in seeding initiatives can be a positive outcome of its decentralized design. However, this shows how both success and failure are projected on the neighborhood level, while program elements are highly dependent on a host of state and local institutions. Community groups in the Crawford-Roberts neighborhood were similarly included as seeding strategists, but they were not granted access to seed funding until two years into implementation. Both by history and design, Operation Weed and Seed is thus a hallmark of a neo-liberalism in theory and in practice, which, as Harvey (2005) emphasizes, delegates state responsibility, projecting accountability on a more local and individual level.
While economic outcomes for residents and local businesses have yet to be measured or made accessible, the initiative’s alignment with the principles of free-market growth gave Weed and Seed political legitimacy. This neo-liberal strategy, characterized by decentralized responsibility, tight social spending, and the prioritization of short-term tactics over long-term social gains, functions to cut off vast numbers of individuals and families from the accumulation of both physical and social capital.
Despite federal-level warnings about accelerated recidivism, and community mistrust of its aggressive law enforcement techniques, the Weed and Seed strategy was ratified by law and enacted in neighborhoods throughout the country. While some communities have implemented seeding programs for reentering prisoners (Solomon, Palmer, Atkinson, Davidson and Harvey 2006), such programs compete for a portion of limited seed funding that could otherwise be spent on a host of other prevention programming. Because rehabilitative services are not a fixed and securely funded part of the strategy, communities incur the cost of socio-economic losses accumulated during incarceration.
Particularly at the municipal level, the Weed and Seed approach enables local governments to brand spaces of social disorder, and strategically infiltrate these spaces to eradicate free-market obstacles. The Weed and Seed strategy embodies a post-Keynesian penology that justifies the acceleration of concentrated disadvantage, and further expands economic opportunity for the capital class through tax incentives and cheap labor. This strategy threatens to create, if even indirectly, a recurring criminal crisis that both justify and shore up demand for a growing supply of “cages,” and reproduces a landscape in which minorities inhabit socio-economic spaces devoid of power and opportunity.
Certainly, improving the conditions of poor urban neighborhoods and increasing community involvement through crime reduction and social programming are practical goals at the state and local level. In some cases, crime reduction, improvements in the way that residents felt about their neighborhood, and institutional collaboration are positive outcomes of the Weed and Seed strategy. What remains is a question of whether these positive outcomes create substantive gains for the communities in which the strategy is implemented. While further research is needed to answer this question, the studies included in this paper suggest that prisoner re-entry presents significant challenges for ex-offenders, their families, and the communities. These findings stimulate further questions about the net social value of a policy that seeks to improve poor neighborhoods by removing residents without providing any support for their inevitable return. In looking forward, it’s important to understand Weed and Seed as a product, not an artifact, of social policy-making in a neo-liberal environment, one that continues to be reproduced in urban communities throughout theUnited States. For this reason, it is imperative that the socio-economic impact on targeted neighborhoods is carefully studied moving forward so that the design of the Weed and Seed strategy can be enhanced to ensure maximum benefit for urban communities.
Bynum, Timothy, Gregory Mills and Kristen Jacoby. 1999. National evaluation of weed and seed: Pittsburgh case study. Washington,D.C.:U.S. Department of Justice, National InstituteofJustice.
Dunworth, Terrance and Gregory Mills, Gary Cordner and Jack Greene. 1999. National evaluation of weed and seed: cross-site analysis. Washington,D.C.:U.S. Department of Justice, National Institute of Justice.
Gilmore, Ruth Wilson.1999. Globalisation and US prison growth: From military Keynesianism to post-Keynesian militarism. Race and Class 40: 171-188.
Harvey, David. 2005. A brief history of neoliberalism.Oxford:OxfordUniversity Press.
Miller, Lisa. 2001. Looking for the postmodernism in all the wrong places; Implementing a new penology. The British Journal of Criminology 41: 168-184.
O’Connell, Jack, Matthew Perkins and Jim Zepp. 2003. A Comparison of homicide trends in local weed and seed sites relative to their host jurisdictions, 1996 to 2001 . Justice Research and Statistics Association. http://www.weedandseed.info/docs/ studies_other /jrsa-comparison-homicide.pdf.
Rubin, Marilyn M. 1994. Can re-orchestrations of historical themes reinvent government? A case study of empowerment zones and enterprise communities act of 1993. Public Administration Review 54:2: 161-169.
Sites, William. 2003. Remaking New York: Primitive globalization and the politics of urban community .Minneapolis:University ofMinnesota Press.
Solomon, Amy L., Christy Visher, Nancy G. La Vigne and Jenny Osborne. 2006. Understanding the challenges of prisoner reentry.Washington,D.C.: The Urban Institute.
Solomon, Amy, Tobi Palmer, Alvin Atkinson, Joanne Davidson and Lynn Harvey. 2006. Prisoner reentry: Addressing the challenges in weed and seed communities. Washington, D.C.: The Urban Institute.
Visher, Christy and Jill Farrell. 2005.Chicagocommunities and prisoner reentry. WashingtonD.C.: The Urban Institute.
Western, Bruce and Katherine Beckett. 1999. How unregulated is theU.S.labor market? The penal system as labor market institution. American Journal of Sociology 104(4): 1030- 1060.
Weed seed predation in agricultural fields
Weed communities in agronomic fields are dominated by annual species. Summer annuals initiate growth each spring from seeds found in the upper soil profile (Figure 1). In most fields, a small percentage of the emerging plants survive and contribute new seeds to the soil seedbank. Historically, most research of the annual weed life cycle has focused on seed dormancy and emergence (A), effect of control tactics on weed survival (B), and weed seed production (C). The fate of seeds between the time of maturation on the plant and entering the seedbank (D) has largely been ignored. However, current research at Iowa State University and other organizations has shown that significant seed losses routinely occur in agronomic fields, and these losses may influence the effectiveness of weed management programs. This article will provide a brief summary of some of the current research in this area and the potential importance of seed predation to weed management.
Prairie deer mouse – a common seed predator.
Plant seeds are storage organs for high energy compounds that supply plant embryos the resources needed to germinate and develop into seedlings. These energy reserves are an excellent food source for a variety of animals that live in or near agricultural fields, including ground beetles (carabid beetles), crickets, mice and others. Estimates of cumulative seed losses due to seed predators have ranged from 20% for barnyardgrass and lambsquarter in a chisel plow system (Cromar et al. 1999) to 88% for giant ragweed in no-tillage (Harrison et al. 2003).
A common method of measuring seed predation involves lightly attaching seeds to sandpaper or a similar material and placing the seed cards in the field. After a few days the card is retrieved and the percentage of seeds removed is determined (Westerman et al. 2005). Averaged over 12 sampling periods from May through November, seed losses ranged from 7 to 22% per day depending on the crop present in the field in a study conducted near Boone, IA (Figure 2). The higher predation rates in small grain and alfalfa compared to corn and soybean may be due to differences in crop canopy development. The rate of seed predation typically increases as a crop canopy develops within a field. Corn and soybean canopies provide little protection for predators early in the growing season compared to small grain or alfalfa, and thus predators may seek other habitats when little canopy is present. Later in the season, predator activity is typically similar in corn and soybeans as in other field crops.
Insect predators (field crickets, ground beetles, etc.) are active during the growing season when temperatures are favorable for cold-blooded species, whereas field mice are active year round. Seed predators have a remarkable ability to locate seeds on the soil surface; however, once seeds move into the soil profile the threat of predation is greatly reduced. The highest rates of seed predation likely occur in late summer and early fall when weed seeds are shed from plants onto the soil surface. Tillage buries the majority of seeds at depths where predation is minimal. Avoiding or delaying fall tillage following harvest should increase seed losses due to predation. Seeds can also enter the profile due to the impact of rain droplets, by falling into cracks, or due to freezing/thawing cycles during the winter. Ongoing research at ISU is evaluating the fate of seeds on the soil surface and how long they remain available to predators.
Field crickets on seed card.
The preference of predators for different species of weed seeds in the field is poorly understood. When given a choice, seed predators often will feed preferentially on one species over another (van der Laat et al. 2006; Figure 3). A common question is whether seed predators pose a threat to crop seed. Seed size and depth of planting minimize risks of corn and soybean seed losses to predators. Small-seeded legumes and grasses are at greater risk for predation losses, but proper planting where the majority of seed are placed under the soil surface should minimize losses.
Significant numbers of weed seeds are consumed by predators in agronomic fields, but the full impact of seed predation on weed densities and weed management is poorly documented. Clearly, destruction of a significant percentage of the weed seeds produced in a field will impact the following year’s weed density. The impact of giant foxtail seed rain and seed predation on giant foxtail densities was evaluated near Boone, IA (Figure 4). Giant foxtail seed (750 / sq ft) were spread on the soil surface in standing corn in late September 2004. The field was planted to no-till soybean in 2005 and foxtail emergence monitored throughout the season. The experimental area had a history of good weed control, thus foxtail densities were very low (
Modeling efforts at ISU have shown that seed predation can significantly affect long-term weed population dynamics within agricultural fields. For example, in a 4-year crop rotation (corn/soybean/small grain+alfalfa/alfalfa) the seed bank of giant foxtail rapidly increased from 2000 seed/m 2 to 4.3 million seed / sq m over an 18 year simulation period in the absence of predation (Figure 5). However, allowing for 25% seed predation resulted in a static seed bank, whereas any seed predation in access of 25% resulted in a decline in the seed bank density. The diverse rotation required 80% less herbicide than a conventionally managed corn-soybean rotation.
The value of intercepting weed seed before they enter the seed bank is somewhat of a forgotten control tactic. In the 1930’s and 40’s, combines were commonly equipped with a weed seed collector that separated and collected weed seed from chaff as the crop was harvested. When modern herbicides were introduced in the 1950’s, it was considered less expensive and more convenient to control weeds with chemicals, and these accessories quickly disappeared from combines. In Australia, seed collectors are again being used on combines due to widespread herbicide resistance and the loss of effective herbicides. Rigid ryegrass infestations have been reduced by as much as 70% through use of weed seed collectors during harvest (Gill, 1995). The effectiveness of weed seed collectors varies among weed species depending on timing of seed shed. Weed species that drop the majority of their seed prior to crop harvest would not be impacted significantly by use of weed seed collectors.
Weed seeds are an important food source for a variety of organisms that live within or adjacent to agricultural fields. It is clear that seed predation is an important form of biological control that influences weed communities within agricultural fields. Yet to be defined is how cropping systems can be manipulated to enhance the activity of seed predators and maximize their benefit, therefore allowing reductions in other more disruptive control tactics.
ISU research cited in this article was partially funded by:
The Leopold Center for Sustainable Agriculture
USDA National Research Initiative
Cromar, H.E, S.D. Murphyand C.J. Swanton. 1999. Influence of tillage and crop residue on postdispersal predation of weed seeds . Weed Sci. 47:184-194
Gill, G.S. 1005. Development of herbicide resistance in annual ryegrass in the cropping belt of Western Australia. Aust. J. Exp. Agric. 35:67-72.
Harrison , S.K., E.E. Regnier and J.T. Schmoll. 2003. Postdispersal predation of giant ragweed seed in no-tillage corn. Weed Sci. 51:955-964.
van der Laat, R., M. D.K. Owen and M. Liebman. 2006. Quantification of post-dispersal weed seed predation and invertebrate activity-density in three tillage regimes. J. Agric. Ecosys. Envir. Under review.
Westerman, P.R., M. Liebman, F.D. Menalled, A.H. Heggenstaller, R.G. Hartzler and P.M. Dixon. 2005. Are many little hammers effective? – Velvetleaf population dynamics in two- and four-year crop rotation systems. Weed Sci. 53:382-392.