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Cleaning Weed Seeds from a Combine – Video

Equipment that enters a field with mature herbicide-resistant weeds will easily become a vector for the spread of those weed seeds to other fields. Using proper precautions and thoroughly cleaning equipment after working in weed-infested fields can greatly reduce the spread of weed seeds to the next field.

Combines are a common cause of the introduction of herbicide resistant weeds to new fields. They’re a primary mode of weed seed spread across regions of the US including the Midwest, South, and mid-Atlantic. Things that make them a vector are: they process all plants within a field, including weeds, during a time of the year when remaining mature weeds are producing viable seed; there are many small spaces within a combine where weed seeds might hide; they are time-consuming to clean.

Other pieces such as tillage equipment and tractors have also been found to carry weed seed from field to field if they are used when plants have matured and produced seed.

Because many problematic resistant weed species can produce between 50,000-1 million seeds per plant, even the spread of a few seeds can cause a serious and costly infestation within a couple of seasons.

General Tips for Preventing Weed Seed Spread with Equipment Maintenance:

1) Harvest herbicide-resistant weed-infested fields last.

2) Know whether the combine entering the field has recently been in a field containing herbicide-resistant weeds such as waterhemp or Palmer Amaranth. If so, take the time needed to clean it or consider other available options.

3) When purchasing a used combine, take the necessary time to completely clean the combine before use.

4) Utilize an air compressor to remove the bulk of the weed seeds from the combine.

5) Check the rock trap, as weed seeds and debris may be caught here. Drop the rock trap and blow it out with the air compressor between fields.

6) Open trapdoors to clean the grain auger and tailings processor with an air compressor.

7) On a rainy day, consider a thorough 4-5 hour combine cleaning as a rainy day activity.

8) Since weed seeds can also travel on tillage equipment, clean this equipment after infested fields as well.

Interspecific variation in persistence of buried weed seeds follows trade‐offs among physiological, chemical, and physical seed defenses

The data analyzed in this publication are hosted at USDA AgData Commons as the following data resource: Davis, Adam (2016) Data from: Interspecific variation in persistence of buried weed seeds follows trade‐offs among physiological, chemical, and physical seed defenses. Ag Data Commons: http://dx.doi.org/10.15482/USDA.ADC/1288753.

Abstract

Soil seedbanks drive infestations of annual weeds, yet weed management focuses largely on seedling mortality. As weed seedbanks increasingly become reservoirs of herbicide resistance, species‐specific seedbank management approaches will be essential to weed control. However, the development of seedbank management strategies can only develop from an understanding of how seed traits affect persistence.

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We quantified interspecific trade‐offs among physiological, chemical, and physical traits of weed seeds and their persistence in the soil seedbank in a common garden study. Seeds of 11 annual weed species were buried in Savoy, IL , from 2007 through 2012. Seedling recruitment was measured weekly and seed viability measured annually. Seed physiological (dormancy), chemical (phenolic compound diversity and concentration; invertebrate toxicity), and physical traits (seed coat mass, thickness, and rupture resistance) were measured.

Seed half‐life in the soil (t 0.5) showed strong interspecific variation (F 10,30 = 15, < .0001), ranging from 0.25 years (Bassia scoparia) to 2.22 years (Abutilon theophrasti). Modeling covariances among seed traits and seedbank persistence quantified support for two putative defense syndromes (physiological–chemical and physical–chemical) and highlighted the central role of seed dormancy in controlling seed persistence.

A quantitative comparison between our results and other published work indicated that weed seed dormancy and seedbank persistence are linked across diverse environments and agroecosystems. Moreover, among seedbank‐forming early successional plant species, relative investment in chemical and physical seed defense varies with seedbank persistence.

Synthesis and applications. Strong covariance among weed seed traits and persistence in the soil seedbank indicates potential for seedbank management practices tailored to specific weed species. In particular, species with high t 0.5 values tend to invest less in chemical defenses. This makes them highly vulnerable to physical harvest weed seed control strategies, with small amounts of damage resulting in their full decay.

1. Introduction

A large body of theory has been developed to advance our understanding of how aboveground plant life stages are defended, but little theory exists for the defense of seeds in the soil seedbank (Dalling, Davis, Schutte, & Arnold, 2011). For annual arable weeds, this is a critical knowledge gap, as their elasticity of population growth rate to seed survival in the soil seedbank is unity (Davis, 2006). Given the relatively recent, rapid proliferation of herbicide‐resistant genotypes (Powles & Yu, 2010), whose preferential survival allows them to contribute disproportionately to the replenishment of weed seedbanks, it is especially important to improve our understanding of intrinsic, seed‐based regulation of weed seed survival so that we may develop better management strategies targeted at the ecology of individual weed species (Gibson et al., 2016; Long et al., 2015).

In Dalling et al. (2011), we introduced a nascent framework for a seed defense theory to guide future investigations of intrinsic seed defense traits related to seed persistence in the soil seedbank. At its core is the concept of “seed defense syndromes” related to variation in seed dormancy types. Seeds of species with physical dormancy should be protected primarily by physical seed traits and rely upon rapid germination to escape pathogens. Seeds with physiological dormancy should be protected by a mixture of physical and chemical seed traits. Those species whose seeds are quiescent (nondormant and remain permeable over time) should rely on a mixture of chemical seed traits and mutualisms with microbial endophytes.

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Annual weed species represent a class of plants whose dependence upon adaptations for seed survival in the soil seedbank is extreme. All members of the population must pass through the seed stage at some point, yet mortality in any given year is likely to be high for both seeds and seedlings. Weed management tactics typically target seedlings, with mortality rates commonly ranging between 90 and 99% for herbicide applications; tactics aimed at seeds are possible (Walsh, Newman, & Powles, 2013) but rare. Weed seeds also face numerous environmental hazards. They are an important food source for many small vertebrates and invertebrates (Westerman, Borza, Andjelkovic, Liebman, & Danielson, 2008), with pre‐ and postdispersal granivory ranging from 30% to 90% of total annual seed production (Davis, Daedlow, Schutte, & Westerman, 2011). Tillage practices that move weed seeds below their maximum germination depth and stimulate germination at the wrong time of year and conditions favoring pathogenic fungi all increase seed mortality to fatal germination (Benvenuti, Macchia, & Miele, 2001; Davis & Renner, 2007). The importance of seed decay due to microbial attack varies by species, environment, and burial depth, with annual losses reaching 50% (Davis et al., 2005).

Exposed to such high levels of uncertainty and risk in their growing environment, annual weeds have evolved highly variable, complex forms of seed dormancy that include physical dormancy, innate dormancy, induced dormancy, conditional dormancy, deep and nondeep physiological dormancy, and subannual dormancy cycling, among others (Baskin & Baskin, 2001). Indeed, in annual cropping systems, seed dormancy appears to be a fundamental signature of weediness. For example, Bassia scoparia [L.] A. J. Scott (kochia) is a weed of the northern great plains of the USA that has historically been nondormant, or had very low levels of dormancy (Zorner, Zimdahl, & Schweizer, 1984). However, under increased intensity of weed management, dormancy levels in B. scoparia have risen steadily as has its weediness (Esser, 2014).

Weed communities tend to be species poor compared with early successional natural communities, often composed of one or two dominant species and 20 or less subdominant species. However, even the relatively short list of common weed species harbors considerable diversity in seed traits (Gardarin & Colbach, 2015), presumably because ongoing, stochastic change in agricultural management practices and climate maintains the adaptive value of divergent seed characteristics by creating an ever‐changing composition of niches in the soil seedbank. Seeds of annual weed species vary greatly in size, shape, mass, chemical composition, cohort size, seed dormancy type and level, dormancy‐breaking cues, maximum emergence depth, and recruitment cues, among numerous other dimensions (Gardarin & Colbach, 2015; Long et al., 2015). Thus, not only do weed seedbanks represent an important but underutilized management target, but also they are particularly well suited for investigating the relationship between seed persistence and seed traits.

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Our aim was to determine the level of empirical support for the existence of seed defense syndromes (Dalling et al., 2011) among annual weeds of arable lands. Experimental objectives were framed by the hypothesis that seedbank persistence covaries with seed traits of arable weeds, such that the balance of physiological, chemical, and physical seed defenses varies among weed species with different half‐lives in the soil seed bank. Our experimental objectives were to (1) quantify long‐term persistence of 11 seedbank annual weed species in a common environment, (2) characterize their physiological, chemical, and physical seed traits, and (3) relate findings of this study to previous work through a broad quantitative comparison.

We found that while physiological, chemical, and physical seed traits all contribute to seed persistence in the soil seedbank, physiology (seed dormancy) is a primary driver of seed persistence. Covariances among seed traits offered some support for the theory of seed defense syndromes comprised of suites of traits. Quantitative comparisons of our results to other published work indicated that weed seed dormancy underlies seed persistence across a broad range of weed species and growing environments and that early successional species’ relative investment in chemical and physical seed defenses depends strongly on their level of persistence in the soil seedbank.

2. Materials and Methods

2.1. Burial study

We performed a common garden weed seed burial study at the University of Illinois Crop Sciences Research and Education Center in Savoy, IL (40.048757 N, −88.237206 E), from October 2007 through October 2012. The experiment was arranged in a split‐plot design with four replications of the subplot variable species nested within main plot variable burial duration (1–5 years). Eleven annual weed species were included, spanning a broad range of seed sizes, dormancy types, and seedbank persistence (Table  1 , Table S1, Fig.  1 ): Abutilon theophrasti Medik (velvetleaf), Ambrosia trifida L. (giant ragweed), Amaranthus tuberculatus [Moq]. Sauer (common waterhemp), Bassia scoparia [L.] A. J. Scott (kochia), Chenopodium album L., Ipomoea hederacea Jacq. (ivyleaf morningglory), Panicum miliaceum L. (wild proso millet), Polygonum pensylvanicum L. (Pennsylvania smartweed), Setaria faberi Herrm. (giant foxtail), Setaria pumila [Poir] Roem. (yellow foxtail), and Thlaspi arvense L. (field pennycress).