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Weed Risk Assessment for

United States bicolor (L.) Moench nothosubsp. Department of drummondii (Steud.) de Wet ex

Animal and Davidse () – Shattercane Health Inspection Service

August 12, 2015

Version 1

Main: Shattercane in a Midwestern field in the . Inset: Shattercane enclosed by dark glumes (source: Pamela B. Trewatha, Missouri State University; Trewatha, 2015).

Agency Contact:

Plant Epidemiology and Risk Analysis Laboratory Center for Plant Health Science and Technology

Plant Protection and Quarantine Animal and Plant Health Inspection Service United States Department of Agriculture 1730 Varsity Drive, Suite 300 Raleigh, NC 27606 Weed Risk Assessment for nothosubsp. drummondii

Introduction Plant Protection and Quarantine (PPQ) regulates noxious weeds under the authority of the Plant Protection Act (7 U.S.C. § 7701-7786, 2000) and the Federal Act (7 U.S.C. § 1581-1610, 1939). A noxious weed is defined as “any plant or plant product that can directly or indirectly injure or cause damage to (including nursery stock or plant products), , , or other interests of agriculture, irrigation, navigation, the natural resources of the United States, the public health, or the environment” (7 U.S.C. § 7701-7786, 2000). We use the PPQ weed risk assessment (WRA) process (PPQ, 2015) to evaluate the risk potential of , including those newly detected in the United States, those proposed for import, and those emerging as weeds elsewhere in the world.

The PPQ WRA process includes three analytical components that together describe the risk profile of a plant (risk potential, uncertainty, and geographic potential; PPQ, 2015). At the core of the process is the predictive risk model that evaluates the baseline invasive/weed potential of a plant species using information related to its ability to establish, spread, and cause harm in natural, anthropogenic, and production systems (Koop et al., 2012). Because the predictive model is geographically and climatically neutral, it can be used to evaluate the risk of any plant species for the entire United States or for any area within it. We then use a stochastic simulation to evaluate how much the uncertainty associated with the risk analysis affects the outcomes from the predictive model. The simulation essentially evaluates what other risk scores might result if any answers in the predictive model might change. Finally, we use Geographic Information System (GIS) overlays to evaluate those areas of the United States that may be suitable for the establishment of the species. For a detailed description of the PPQ WRA process, please refer to the PPQ Weed Risk Assessment Guidelines (PPQ, 2015), which is available upon request.

We emphasize that our WRA process is designed to estimate the baseline—or unmitigated—risk associated with a plant species. We use evidence from anywhere in the world and in any type of system (production, anthropogenic, or natural) for the assessment, which makes our process a very broad evaluation. This is appropriate for the types of actions considered by our agency (e.g., Federal regulation). Furthermore, risk assessment and risk management are distinctly different phases of risk analysis (e.g., IPPC, 2015). Although we may use evidence about existing or proposed control programs in the assessment, the ease or difficulty of control has no bearing on the risk potential for a species. That information could be considered during the risk management (decision making) process, which is not addressed in this document.

Sorghum bicolor (L.) Moench nothosubsp. drummondii (Steud.) de Wet ex Davidse – Shattercane Species Family: Poaceae Information Synonyms: The classification of domesticated sorghum, Sorghum spp., and its wild and weedy relatives is very complex due to extensive variability in the group (Wiersema and Dahlberg, 2007). In the latest taxonomic treatment (Wiersema and Dahlberg, 2007), the taxa were consolidated into three subspecies: S. bicolor subsp. bicolor describes domesticated types, S. bicolor subsp. verticilliflorum contains wild relatives of domesticated biotypes, and S. bicolor subsp.

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drummondii contains weedy derivatives, which include shattercane. That last subspecies is also referred to as S. bicolor nothosubsp. drummondii because it is composed of the complex hybrids that have resulted from crossing between domesticated and wild types (NGRP, 2015). The prefix “notho” indicates that the taxon originated through hybridization. The following are some synonyms of S. bicolor nothosubsp. drummondii: drummondii Steud. (basionym), A. sorghum var. drummondii (Steud.) Hack, A. sorghum subsp. sudanensis Piper, sorghum var. sudanensis (Piper) Hitchc., Sorghum bicolor var. drummondii (Steud.) Mohlenbr., Sorghum × drummondii (Steud.) Nees ex Millsp. & Chase, S. sudanense (Piper) Stapf, S. vulgare var. drummondii (Steud.) Hitchc., and S. vulgare var. sudanense (Piper) Hitchc. (NGRP, 2015). Common names: Shattercane (NGRP, 2015), chicken corn (Horak and Moshier, 1994; NGRP, 2015), black amber (Stubbendieck et al., 2003), wild corn wild (Defelice, 2006), early amber (Horak and Moshier, 1994). Botanical description: Shattercane is a warm season annual that grows from one to four meters in height (Defelice, 2006). are lanceolate, 8 to 100 mm wide, and up to 100 cm long (Anonymous, 2014; Defelice, 2006). Shattercane resembles corn or johnsongrass seedlings and is indistinguishable from until the flowering stage (Anonymous, 2014). Shattercane has been called the “black sheep” of the due to the distinctive dark purple to black coloration of most of its panicles (Defelice, 2006). Shattercane does not produce any (Anonymous, 2014). It is diploid 2n=20 (Sahoo et al., 2010; Schmidt et al., 2013). Initiation: On February 22, 2013, the company CERES Inc. wrote to APHIS (Hamilton, 2013) seeking confirmation that their TRSBG101B Sorghum bicolor ssp. bicolor () plant, which they genetically engineered without any plant pest sequences using a biolistic (i.e., gene gun) method, was not a regulated article under APHIS’s biotechnology regulations (7 CFR § 340, 2015). The transformed sorghum produces greater and more fermentable than the untransformed parent (Hamilton, 2013). Although transgenic sorghum is not regulated by APHIS, the agency is concerned about the weed risk potential of TRSBG101B (APHIS-BRS, 2014) and its ability to hybridize with and transfer genes to two other sorghums that are common agricultural weeds: S. halepense (johnsongrass) and S. bicolor nothosubsp. drummondii (shattercane). In this document, we characterized the weed risk potential of shattercane, which is one member of the S. bicolor nothosubsp. drummondii complex. This subspecies also includes a biotype known as grass that is cultivated for (Essah et al., 2012; Schmidt et al., 2013). We restricted our analysis to the biotype shattercane because it acts as an agricultural weed. Foreign distribution: The exact native range of shattercane is not well known, but S. bicolor is believed to have originated in (Defelice, 2006). As domesticated sorghum was introduced to other regions, shattercane followed (Defelice, 2006). “Shattercane is now distributed throughout the world wherever sorghum is grown” (Defelice, 2006). U.S. distribution and status: It is not clear exactly when shattercane was introduced into the United States, but it was present at least by the mid-1800s (Defelice, 2006; Horak and Moshier, 1994). It was likely introduced several times, but it

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also appears to have formed naturally through crossing between wild types of sudan grass and grain sorghum (Defelice, 2006; Horak and Moshier, 1994). Shattercane is listed as a state noxious weed in Indiana, Iowa, Maryland, Nevada, Ohio, and Pennsylvania (NRCS, 2015). Although it is not known to occur in every state, nor most counties, today it is widely scattered across the conterminous United States (Kartesz, 2015; NRCS, 2015). Shattercane may be underreported because it is difficult to distinguish from sorghum and corn. WRA area1: Entire United States, including territories.

1. Sorghum bicolor nothosubsp. drummondii analysis Establishment/Spread Given its spread in global agriculture (Defelice, 2006), shattercane has already Potential demonstrated a strong ability to establish and spread. This taxon has many life history traits that have promoted its spread. As a primarily self-fertilizing, wind- pollinated species (Furrer and Burnside, 1962; Sahoo et al., 2010; Schmidt et al., 2013), individual plants can readily spread to and colonize new sites. Dispersal by multiple vectors, such as water, animals, and people (see Appendix A) , further enhances that ability. Finally, prolific reproduction (Defelice, 2006; Vesecky et al., 1973) coupled with seeds that can survive in the soil for multiple years (Burnside et al., 1996) allows populations to build up rapidly and survive adverse years. We had low uncertainty for this risk element. Risk score = 21 Uncertainty index = 0.09

Impact Potential Shattercane is primarily an agricultural weed (Bridges, 1992; Defelice, 2006; Fawcett, 1981; Horak and Moshier, 1994). We found no evidence that it is problematic in natural or anthropogenic systems. In agricultural systems, it reduces yield by competing with crops for , water, and most importantly sunlight (Defelice, 2006). Heavy infestations can reduce corn, , and sorghum yields by 40 to 60 percent (Furrer and Burnside, 1962; Horak and Moshier, 1994; Vesecky et al., 1973). Because shattercane readily infests and hybridizes with grain sorghum, it lowers the quality and value of sorghum harvested for seed (Anonymous, 2014; Furrer and Burnside, 1962). Like some other species in the genus Sorghum, shattercane is also toxic to livestock under certain conditions (Burrows and Tyrl, 2013; Furrer and Burnside, 1962). Shattercane is a significant weed and is controlled in row crops such as sorghum, , and corn (Fawcett, 1981; Horak and Moshier, 1994). Although it has been present in the United States for at least 150 years (Defelice, 2006; Horak and Moshier, 1994), researchers continue to search for new methods of controlling it (Hilgenfeld et al., 2004; Hoffman et al., 2002; Mitchell et al., 2008). That is particularly true for populations that have become resistant to some herbicides (King and Hagood Jr, 2006; King et al., 2007; Lee et al., 1999). We had very low uncertainty for this risk element. Risk score = 2.6 Uncertainty index = 0.04

Geographic Potential Based on three climatic variables, we estimate that about 75 percent of the United States is suitable for the establishment of shattercane (Fig. 1). This predicted distribution is based on the species’ known distribution elsewhere in the world and

1 “WRA area” is the area in relation to which the weed risk assessment is conducted (definition modified from that for “PRA area”) (IPPC, 2012).

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includes point-referenced localities and areas of occurrence. The map for shattercane represents the joint distribution of Plant Hardiness Zones 5-13, areas with 0-100+ inches of annual precipitation, and the following Köppen-Geiger climate classes: tropical rainforest, tropical savanna, steppe, desert, Mediterranean, humid subtropical, marine west coast, humid continental warm summers, and humid continental cool summers. We had higher uncertainty in the potential distribution of shattercane because of the limited number of point-referenced localities available in the Global Information Facility (GBIF, 2015) and the limited number of county-level occurrences reported for the United States (Kartesz, 2015). This paucity of information was surprising given reports that it is closely associated with cultivated sorghum both abroad and in the United States (Defelice, 2006; Horak and Moshier, 1994; Klier, 1988). Perhaps it is underreported because it is very similar in appearance to cultivated sorghum. Regardless, because shattercane is derived from crosses between cultivated and wild sorghum (NGRP, 2015) and readily hybridizes with cultivated sorghum (Sahoo et al., 2010; Schmidt et al., 2013)., and because of its close association with sorghum, we supplemented distribution information from cultivated sorghum to estimate the geographic potential of shattercane (see Appendix A).

The area of the United States shown to be climatically suitable (Fig. 1) is likely overestimated since our analysis considered only three climatic variables. Other environmental variables, such as soil and habitat type, may further limit the areas in which this taxon is likely to establish. Shattercane is primarily an agricultural weed, but it can also be found in other disturbed areas. It occurs in fields, fallow land, roadsides, ditches, bottomlands, fencerows, and canal margins (Defelice, 2006; Furrer and Burnside, 1962). It grows best in warm temperate to subtropical areas on well-drained, fertile soil where warm-season moisture exists, but can tolerate hot, dry conditions (Anonymous, 2014).

Entry Potential We did not assess the entry potential of shattercane because it is widely established in the United States (Kartesz, 2015; NRCS, 2015) and has been present at least since the mid-1800s (Defelice, 2006; Horak and Moshier, 1994).

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Figure 1. Predicted distribution of Sorghum bicolor nothosubsp. drummondii (shattercane) in the United States. Map insets for Alaska, Hawaii, and Puerto Rico are not to scale.

2. Results Model Probabilities: P(Major Invader) = 91.5% P(Minor Invader) = 8.2% P(Non-Invader) = 0.3% Risk Result = High Risk Secondary Screening = Not Applicable

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. Figure 2. Sorghum bicolor nothosubsp. drummondii (shattercane) risk score (black box) relative to the risk scores of species used to develop and validate the PPQ WRA model (other symbols). See Appendix A for the complete assessment.

. Figure 3. Model simulation results (N=5,000) for uncertainty around the risk score for Sorghum bicolor nothosubsp. drummondii (shattercane). The blue “+” symbol represents the medians of the simulated outcomes. The smallest box contains 50 percent of the outcomes, the second 95 percent, and the largest 99 percent.

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3. Discussion The result of the weed risk assessment for S. bicolor nothosubsp. drummondii (shattercane) is High Risk (Fig. 2). Based on the results of our uncertainty analysis (Fig. 3), we believe our results are robust. Because this taxon is relatively well known and characterized, our uncertainty was very low. Shattercane is primarily an agricultural weed that causes a variety of impacts in row crops, particularly grain sorghum, corn, and soybeans (Anonymous, 2014; Furrer and Burnside, 1962; Vesecky et al., 1973). It spread around the world in association with grain sorghum (Defelice, 2006; Horak and Moshier, 1994; Klier, 1988).

This WRA was initiated due to concerns that there may be gene flow to shattercane from a sweet sorghum (S. bicolor subsp. bicolor) biotype that has been genetically engineered for increased biomass. We did not intend in this risk assessment to evaluate the likelihood of that gene flow process occurring, but to establish the baseline risk potential of shattercane. However, we note that all races of cultivated sorghum can hybridize with shattercane (Defelice, 2006; Schmidt et al., 2013). In fact, it is generally believed that all subspecies and races within S. bicolor frequently hybridize and introgress with each other (Fawcett, 1981; Hoffman et al., 2002; Horak and Moshier, 1994). In one field study, researchers planted shattercane in arcs at varying distances from a field of cultivated sorghum and concluded that genes from cultivated sorghum will likely be introduced into shattercane populations within distances of at least 200 meters (Schmidt et al., 2013). Other researchers found that fitness components of F1 hybrids of shattercane and cultivated sorghum were similar to those of shattercane, suggesting that crop genes may pass on to successive generations of shattercane if the genes are not deleterious (Sahoo et al., 2010).

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sorghum competition in grain sorghum. Weed Science 21(1):28-32. Walker, R. 2014. Parasitic Plants Database. Rick Walker. http://www.omnisterra.com/bot/pp_home.cgi. (Archived at PERAL). Wiersema, J. H., and J. Dahlberg. 2007. The nomenclature of Sorghum bicolor (L.) Moench (Gramineae). Taxon 56(3):941-946. Yang, X., B. E. Scheffler, and L. A. Weston. 2004. SOR1, a gene associated with bioherbicide production in sorghum root hairs. Journal of Experimental Botany 55(406):2251-2259. Zelaya, I. A., and M. D. K. Owen. 2004. Evolved resistance to acetolactate synthase-inhibiting herbicides in common sunflower (), giant (Ambrosia trifida), and shattercane (Sorghum bicolor) in Iowa [Abstract]. Weed Science 52(4):538-548.

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Appendix A. Weed risk assessment for Sorghum bicolor (L.) Moench nothosubsp. drummondii (Steud.) de Wet ex Davidse (Poaceae). Below is all of the evidence and associated references used to evaluate the risk potential of this taxon. We also include the answer, uncertainty rating, and score for each question. The Excel file, where this assessment was conducted, is available upon request. Question ID Answer - Score Notes (and references) Uncertainty ESTABLISHMENT/SPREAD POTENTIAL ES-1 [What is the taxon’s f - negl 5 The exact native range of shattercane (Sorghum bicolor establishment and spread status nothosubsp. drummondii) is not well known, but S. outside its native range? (a) bicolor is believed to have originated in Africa (Defelice, Introduced elsewhere =>75 years ago 2006). As domesticated sorghum (S. bicolor subsp. but not escaped; (b) Introduced <75 bicolor) was introduced to other regions of the world, years ago but not escaped; (c) Never shattercane was introduced as well, likely as a seed moved beyond its native range; (d) contaminant (Defelice, 2006; Horak and Moshier, 1994; Escaped/Casual; (e) Naturalized; (f) Klier, 1988). Shattercane is widely distributed in , Invasive; (?) Unknown] , and Australia (Horak and Moshier, 1994), indicating it readily spread in the past. Although present in the United States since at least 1832, "[s]hattercane appeared as a serious and quickly spreading weed in the late 1950s and the 1960s with the popular introduction and quick adoption of hybrid grain sorghum in the Great Plains of the United States" (Defelice, 2006). In their detailed summary of the biology of shattercane, Horak and Moshier (1994) state that it rapidly spread in some U.S. states following the introduction and use of hybrid sorghum seed (Horak and Moshier, 1994). Alternate answers for the Monte Carlo simulation were both "e." ES-2 (Is the species highly n - negl 0 We found no evidence that S. bicolor nothosubsp. domesticated) drummondii is highly domesticated. Although people at one point cultivated forms of shattercane (e.g., chicken corn; Furrer and Burnside, 1962; Horak and Moshier, 1994) and have created sterile lines (Sattler et al., 2013), the taxon as a whole is not domesticated and is genetically diverse due to frequent crop/weed hybridization and introgression (Fawcett, 1981; Hoffman et al., 2002; Horak and Moshier, 1994). Other members of this subspecies include sudan grass that is cultivated for forage (Schmidt et al., 2013). ES-3 (Weedy congeners) y - negl 1 The genus Sorghum includes about 30 species (Mabberley, 2008). Sorghum halepense is one of the world's worst weeds (Holm et al., 1977; Maillet, 1991; Randall, 2012). It reduces yield (McWhorter, 1989), increases the costs of production (Keeley and Thullen, 1981), and is toxic to livestock under some circumstances (Burrows and Tyrl, 2013). Sorghum bicolor subsp. verticilliflorum is a principal and serious weed in five countries (listed as S. arundinaceum and S. verticilliflorum in Holm et al., 1979). ES-4 (Shade tolerant at some stage of n - mod 0 Shattercane occurs in crop fields, fallow land, roadsides, its life cycle) ditches, bottomlands, fencerows, and canal margins (Defelice, 2006; Furrer and Burnside, 1962), which are mostly open habitats. We found no direct evidence that this taxon is shade-adapted. Although some types of shattercane do not require light for germination (Defelice, 2006), this taxon is not reported to grow in

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Question ID Answer - Score Notes (and references) Uncertainty shady environments. Consequently, we answered no with moderate uncertainty. ES-5 (Climbing or smothering growth n - negl 0 Taxon is an erect grass that grows from 1 to 4 meters in form) height (Defelice, 2006; Horak and Moshier, 1994). It is not a vine or an herb with a basal rosette of leaves. ES-6 (Forms dense thickets) y - high 2 We only found one anecdotal comment relating to dense populations: "A dense shattercane stand in row crops can completely eliminate grain production" (Burnside, 1980). Because the author published several detailed works on shattercane and is considered an authority, we answered yes, but used high uncertainty. ES-7 (Aquatic) n - negl 0 This taxon is a terrestrial species that infests row crops (Defelice, 2006; Fawcett, 1981). It is not an aquatic. ES-8 (Grass) y - negl 1 This taxon is a grass (Defelice, 2006; NGRP, 2015). ES-9 (Nitrogen-fixing woody plant) n - negl 0 We found no evidence that shattercane fixes nitrogen. Shattercane is not a member of a plant family typically associated with nitrogen fixation (Martin and Dowd, 1990; Santi et al., 2013). Although the congener johnsongrass (S. halepense) is associated with endophytic bacteria that exhibit nitrogen fixation (Rout and Chrzanowski, 2009; Rout et al., 2013), neither taxon is woody. Consequently, we answered this question as no, but with negligible uncertainty. ES-10 (Does it produce viable seeds y - negl 1 Reproduces by seeds (Anonymous, 2014; Fawcett, 1981; or spores) Stubbendieck et al., 2003). ES-11 (Self-compatible or apomictic) y - negl 1 It is self-compatible (Sahoo et al., 2010) and sorghums (including shattercane) are self-pollinated crops (Fawcett, 1981). In one study, the authors selfed shattercane for six generations to obtain a line that was inbred for a particular trait (Schmidt et al., 2013). ES-12 (Requires special pollinators) n - negl 0 Shattercane is wind-pollinated, as demonstrated by a field study where wind was shown to be a significant factor in the production of hybrids between grain sorghum and shattercane (Furrer and Burnside, 1962; Schmidt et al., 2013). ES-13 [What is the taxon’s minimum b - negl 1 An annual (Defelice, 2006), with plants shattering their generation time? (a) less than a year seed pods within 98 days of crop planting (Horak and with multiple generations per year; (b) Moshier, 1994). Seeds of shattercane can germinate 1 year, usually annuals; (c) 2 or 3 within 3 days of maturity, suggesting that in some years; (d) more than 3 years; or (?) climates a second generation may be possible, but the unknown] viability of seed from later germinating plants is much lower (Horak and Moshier, 1994). Shattercane is a non- rhizomatous grass (Stubbendieck et al., 2003). Although it produces tillers (Horak and Moshier, 1994; Sahoo et al., 2010), those are part of the same plant because they emerge from the root crown (e.g., like multiple stems) and not from creeping rhizomes. Consequently, without , we answered “b” with both alternate answers as "a." ES-14 (Prolific reproduction) y - negl 1 We estimated that shattercane is a prolific seed producer using both plant-based and field-level methods. First, it produces from 500 to 2000 seeds per panicle (Anonymous, 2014; Defelice, 2006), or about 2321 to

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Question ID Answer - Score Notes (and references) Uncertainty 2408 seeds per plant (means from two different tests; Sahoo et al., 2010). Shattercane plants produce many tillers that will flower throughout the growing season as each one develops in turn (Fawcett, 1981). Plants grown from seed on the surface produce 2 to 6 tillers and 2 to 4 flowering heads per plant (an average of 3), whereas plants emerging from seeds that are increasingly deeper in the soil produce fewer tillers and heads (Horak and Moshier, 1994). In agricultural fields, density may be 2 to 3 plants per square meter (estimated from data in Furrer and Burnside, 1962). Assuming, shattercane plants produce 2321 seeds per plant (Sahoo et al., 2010), then we would need approximately 2.15 plants per square meter to meet the threshold for a prolific reproducer. Given the field density estimated from Furrer and Burnside (1962) and the planting densities of shattercane in competition studies (Fellows and Roeth, 1992; Raey et al., 2005), an average of 2.15 plants per square meter is very likely. For the second method of estimation: One experimental study reported yields of 4.27 tons of shattercane seed per hectare at the highest planting density (Vesecky et al., 1973). Estimates of the number of seeds per gram range from 38.0 (AOSA, 2014) to 76.9 (Sahoo et al., 2010). Assuming the higher seed weight of 38 seeds per gram, then field-level estimates of seed production indicate about 14,719 seeds per square meter. Given that 88 percent to 92 percent of seeds emerged in a field experiment (Sahoo et al., 2010), both methods of estimating fecundity (minimum estimates) result in more than 5000 viable seeds per square meter. Additional evidence: "A single plant can lead to severe infestations in a few years if left uncontrolled" (Fawcett, 1981). Numbers of shattercane seeds in the top 4 inches of soil have been reported at 49 to 21,000 per square meter (Fawcett, 1981), but that includes production over multiple years. ES-15 (Propagules likely to be y - negl 1 Once established in an area, seeds can be spread from dispersed unintentionally by people) field to field by harvest and tillage equipment (Fawcett, 1981). To limit spread, field equipment should be cleaned after use in infested fields (Horak and Moshier, 1994). We used negligible uncertainty because in general agricultural weeds are readily spread by farm machinery (e.g., Andújar et al., 2013; Barroso et al., 2012; Heijting et al., 2009). ES-16 (Propagules likely to disperse y - negl 2 Infests grain sorghum seed for planting (Burnside et al., in trade as contaminants or 1977; Furrer and Burnside, 1962). "Shattercane seed hitchhikers) cannot be separated from cultivated sorghum seed with standard separation techniques because they are similar in size and shape" (Horak and Moshier, 1994). The suggestion to "when growing sorghum, select high quality seed from a reputable dealer" (Fawcett, 1981) suggests that shattercane seeds readily contaminate agricultural seed. Shattercane also spreads in manure (Fawcett, 1981), which itself can be a .

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Question ID Answer - Score Notes (and references) Uncertainty ES-17 (Number of natural dispersal 2 0 and seed description for ES-17a through ES-17e: vectors) Shattercane seeds are football to egg-shaped, dark reddish-brown to black, and about 2.5-4 mm wide by 2-6 mm long (Anonymous, 2014; Defelice, 2006). An abscission layer forms at the base of each spikelet in most plants at the time that seeds reach maturity and usually before crops are harvested; these seeds just drop onto the soil (Defelice, 2006). ES-17a (Wind dispersal) n - low We found no direct evidence that seeds are wind- dispersed. Given that seeds are somewhat large and lack any special adaptations for wind dispersal (Anonymous, 2014; Defelice, 2006), this taxon seems unlikely to be wind-dispersed. Because it is a relatively well- characterized taxon, we answered no with low uncertainty. ES-17b (Water dispersal) y - negl Seeds float and are dispersed via irrigation and water runoff (Fawcett, 1981; Furrer and Burnside, 1962). Best management practices include filtering contaminated irrigation water (Horak and Moshier, 1994). ES-17c (Bird dispersal) n - mod We found no direct evidence that this taxon is dispersed by birds; however, one source reports that its seeds are eaten by birds (Stubbendieck et al., 2003). Consequently, we answered no with moderate uncertainty. ES-17d (Animal external dispersal) n - low We found no direct evidence that seeds are dispersed by animals externally. We also found no evidence of specialized structures that facilitate attachment to fur or feathers. Given it is a relatively well-characterized taxon, we answered no with low uncertainty. ES-17e (Animal internal dispersal) y - negl Seeds are eaten by mammals (Stubbendieck et al., 2003). Approximately 16 percent of shattercane seed ingested by pass within 4 days in a viable state (Fawcett, 1981). Best management practices include limiting the movement of cattle having ingested seed (Horak and Moshier, 1994). ES-18 (Evidence that a persistent y - negl 1 In a 17-year seed burial experiment, although most seeds (>1yr) propagule bank (seed bank) is of shattercane lost viability after 3 years, some formed) germinated after 17 years of burial (Burnside et al., 1996). Seeds can survive in the soil for up to 12 years, but most either germinate or lose viability before then (Burnside et al., 1977; Fawcett, 1981). Seed longevity is correlated with the presence of glumes enclosing the seeds; glumes that remain attached retard germination for many years (Horak and Moshier, 1994). ES-19 (Tolerates/benefits from ? - max 0 Unlike johnsongrass, shattercane does not produce mutilation, cultivation or fire) rhizomes (Stubbendieck et al., 2003); it does, however, produce tillers from the root crown (Anonymous, 2014). The entire plant, including the crown, must be removed to prevent stem regeneration and subsequent seed production prior to (Horak and Moshier, 1994). We answered unknown without specific evidence that it resprouts more aggressively than other grasses. ES-20 (Is resistant to some herbicides y - negl 1 Shattercane has developed resistance to ALS-inhibiting or has the potential to become herbicides in several locations in the United States

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Question ID Answer - Score Notes (and references) Uncertainty resistant) (Heap, 2015; Zelaya and Owen, 2004). ES-21 (Number of cold hardiness 9 0 zones suitable for its survival) ES-22 (Number of climate types 9 2 suitable for its survival) ES-23 (Number of precipitation bands 11 1 suitable for its survival) IMPACT POTENTIAL General Impacts Imp-G1 (Allelopathic) y - low 0.1 Sorghum bicolor exude sorgoleone (Czarnota et al., 2003), which is a bioactive compound that is phytotoxic to broadleaf and grass weeds in concentrations similar to some herbicides (reviewed in Yang et al., 2004). Sorgoleone inhibits photosynthetic and mitochondrial electron transport (Yang et al., 2004). A field study with a of sudan grass (S. bicolor subsp. drummondii) showed that when sudan grass was planted as a cover crop and later shredded, plant biomass under several different treatments significantly retarded the growth of weeds relative to control plots (Stapleton et al., 2010). In another field study, when tomato, broccoli, and lettuce seedlings were planted into a recently killed sudan grass cover crop, within 3 to 5 days, all three taxa showed symptoms of phytotoxicity and ultimately resulted in 50 to 75 percent mortality (Summers et al., 2009). Other studies have come to the same conclusion that sudan grass when used as a cover crop can suppress weeds in cultivated crops (Mennan et al., 2009; Urbano et al., 2006). The evidence suggests that S. bicolor is allelopathic. However, because none of this evidence was specific to shattercane, we used low uncertainty rather than negligible. Imp-G2 (Parasitic) n - negl 0 We found no evidence that it is parasitic. Furthermore, it is not a member of a plant family known to contain parasitic plants (Heide-Jorgensen, 2008; Nickrent, 2009; Walker, 2014). Impacts to Natural Systems Imp-N1 (Change ecosystem processes n - low 0 We found no direct evidence that shattercane is an and parameters that affect other environmental weed or that it has impacts in natural species) areas. "Shattercane is a serious agronomic weed but is rarely problematic in landscapes" (Bradley and Fishel, 2010). Because this taxon is relatively well characterized, we answered no with low uncertainty for all questions in this sub-element. Imp-N2 (Change community n - low 0 We found no evidence. structure) Imp-N3 (Change community n - low 0 We found no evidence. composition) Imp-N4 (Is it likely to affect federal n - low 0 We found no evidence. Threatened and Endangered species) Imp-N5 (Is it likely to affect any n - low 0 We found no evidence. globally outstanding ecoregions) Imp-N6 [What is the taxon’s weed a - low 0 We found no evidence that shattercane is considered to

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Question ID Answer - Score Notes (and references) Uncertainty status in natural systems? (a) Taxon be a weed of natural systems. Alternate answers for the not a weed; (b) taxon a weed but no Monte Carlo simulation were both "b." evidence of control; (c) taxon a weed and evidence of control efforts] Impact to Anthropogenic Systems (cities, suburbs, roadways) Imp-A1 (Impacts human property, n - low 0 We found no evidence. Because this is primarily an processes, civilization, or safety) agricultural weed that is relatively well characterized, we used low uncertainty for most questions in this subelement. Imp-A2 (Changes or limits n - low 0 We found no evidence. recreational use of an area) Imp-A3 (Outcompetes, replaces, or n - low 0 We found no evidence. otherwise affects desirable plants and vegetation) Imp-A4 [What is the taxon’s weed a - mod 0 In addition to agricultural areas, shattercane is found in status in anthropogenic systems? (a) disturbed sites and roadsides (Anonymous, 2014). Taxon not a weed; (b) Taxon a weed However, we didn't find any evidence that it is but no evidence of control; (c) Taxon considered a weed of these types of environments. a weed and evidence of control Consequently, we answered no with moderate efforts] uncertainty. Alternate answers for the Monte Carlo simulation were both "b." Impact to Production Systems (agriculture, nurseries, forest plantations, orchards, etc.) Imp-P1 (Reduces crop/product yield) y - negl 0.4 Shattercane competes aggressively with crops for nutrients and water, but most importantly light, and significantly reduces crop yield, including that of corn, soybeans, and grain sorghum (Anonymous, 2014; Defelice, 2006). Heavy infestations in Nebraska and Kansas corn fields reduce yield from 15 to 49 percent (Furrer and Burnside, 1962; Horak and Moshier, 1994). One study showed that with one shattercane plant every 90 cm in rows of grain sorghum, grain yield decreased by 63 percent (Vesecky et al., 1973). In soybeans, yield losses exceeded 50 percent with weed densities of 6.6 per meter crop row (cited in Horak and Moshier, 1994). Based on information from 1992, it was estimated that shattercane was resulting in an economic loss of more than $15 million per year in Nebraska soybeans (Fellows and Roeth, 1992). Imp-P2 (Lowers commodity value) y - negl 0.2 "Fungi, bacteria, and can infect weedy sorghums and then cause agricultural problems. Weedy sorghum serves as an alternate host to pests such as sorghum midge, , and viruses causing mosaic, maize chlorotic dwarf, and corn stunt" (Anonymous, 2014). Shattercane infestations result in a loss of seed quality due to seed contamination (Schmidt et al., 2013). Elimination (from sorghum grain) is difficult by cleaning (Furrer and Burnside, 1962). Hybrid seed producers of sorghum must be very vigilant to eliminate shattercane within half a mile of their fields to prevent fertilizing sorghum plants with pollen from shattercane, otherwise their seed may be rejected (Furrer and Burnside, 1962). Infestations of shattercane result in

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Question ID Answer - Score Notes (and references) Uncertainty indirect losses when farmers have to switch to lower yield crops in order to control shattercane (Furrer and Burnside, 1962). Imp-P3 (Is it likely to impact trade) y - low 0.2 Shattercane is a contaminant of sorghum grain and seed (see evidence under ES-16) and is thus able to follow trade pathways. Although we found no evidence it is regulated by other countries (APHIS, 2015), it is regulated as a state noxious weed in Indiana, Iowa, Maryland, Nevada, Ohio, and Pennsylvania (NRCS, 2015). Consequently, seed contaminants entering these states may be rejected or subjected to other mitigations. Imp-P4 (Reduces the quality or n - mod 0 We found no evidence. availability of irrigation, or strongly competes with plants for water) Imp-P5 (Toxic to animals, including y - negl 0.1 Like all sorghums, shattercane is potentially toxic under livestock/range animals and poultry) some circumstances (Furrer and Burnside, 1962). "[O]nce exposed to frost, drought, trampling, or herbicides" leaves of shattercane can produce levels of hydrocyanic acid that are toxic to cattle if grazed (Anonymous, 2014). It is "well accepted that Sorghum is toxic in certain environmental conditions. In many instances, the risk of seems to be greater in times of drought, but this has not been a consistent finding. The genus produces four disease syndromes - ataxia, cystitis, and teratogenesis; photosensitization; nitrate accumulation; and cyanogenis" (Burrows and Tyrl, 2013). Imp-P6 [What is the taxon’s weed c - negl 0.6 Very serious weed of in (Defelice, 2006) status in production systems? (a) and soybeans in (Raey et al., 2005). Troublesome Taxon not a weed; (b) Taxon a weed weed of corn, grain sorghum, and soybeans in the United but no evidence of control; (c) Taxon States (Bridges, 1992). Various chemical, mechanical, a weed and evidence of control and cultural control strategies for row crops such as efforts] sorghum, soybeans, and corn are available (Fawcett, 1981; Horak and Moshier, 1994). Infestations also occur in beets and castor bean (Furrer and Burnside, 1962). Controlling shattercane in sorghum is very difficult since they are essentially the same plant, but the greater height of shattercane can be exploited with rope wick applicators (Fawcett, 1981). Researchers continue to search for new methods of controlling shattercane (Hilgenfeld et al., 2004; Hoffman et al., 2002; Mitchell et al., 2008), particularly for populations that have become resistant to some herbicides (King and Hagood Jr, 2006; King et al., 2007; Lee et al., 1999). Alternate answers for the Monte Carlo simulation were both "b." GEOGRAPHIC POTENTIAL Unless otherwise indicated, the following evidence represents geographically referenced points obtained from the Global Biodiversity Information Facility (GBIF, 2015). Overall there was limited geo-referenced information for shattercane. Because shattercane and cultivated sorghum readily hybridize (Defelice, 2006; Schmidt et al., 2013), and because shattercane is closely associated with sorghum cultivation (Defelice, 2006), we considered climatic evidence for cultivated sorghum here

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Question ID Answer - Score Notes (and references) Uncertainty as well. Plant hardiness zones Geo-Z1 (Zone 1) n - negl N/A We found no evidence that shattercane or sorghum occur in this hardiness zone. Geo-Z2 (Zone 2) n - negl N/A We found no evidence that shattercane or sorghum occur in this hardiness zone. Geo-Z3 (Zone 3) n - high N/A We found no evidence that shattercane or sorghum occur in this hardiness zone. Geo-Z4 (Zone 4) n - high N/A Shattercane occurs in one U.S. county (Kartesz, 2015). Cultivated sorghum occurs in one point on the edge of this zone in the United States (GBIF, 2015). Geo-Z5 (Zone 5) y - low N/A Shattercane: some U.S. counties (Kartesz, 2015). Geo-Z6 (Zone 6) y - negl N/A Shattercane: many U.S. counties (Kartesz, 2015). Geo-Z7 (Zone 7) y - negl N/A Shattercane: some U.S. counties (Kartesz, 2015). Geo-Z8 (Zone 8) y - negl N/A Shattercane: two points in Australia (GBIF, 2015), and some U.S. counties (Kartesz, 2015). Geo-Z9 (Zone 9) y - negl N/A Shattercane: Australia (GBIF, 2015). Some U.S. counties (Kartesz, 2015). Geo-Z10 (Zone 10) y - negl N/A Shattercane: Australia (GBIF, 2015). Some U.S. counties (Kartesz, 2015). Geo-Z11 (Zone 11) y - negl N/A Shattercane: Australia (GBIF, 2015). Some U.S. counties (Kartesz, 2015). Geo-Z12 (Zone 12) y - high N/A We found no evidence that shattercane occurs in this hardiness zone. Cultivated sorghum: , , , and (GBIF, 2015). Geo-Z13 (Zone 13) y - high N/A We found no evidence that shattercane occurs in this hardiness zone. Cultivated sorghum: India, Nigeria, , and Sudan (GBIF, 2015). Köppen -Geiger climate classes Geo-C1 (Tropical rainforest) y - high N/A We found no evidence that shattercane occurs in this climate class. Cultivated sorghum: India, Kenya, , , and (GBIF, 2015). Geo-C2 (Tropical savanna) y - high N/A We found no evidence that shattercane occurs in this climate class. Cultivated sorghum: Ghana, Nigeria, and Uganda (GBIF, 2015). Geo-C3 (Steppe) y - negl N/A Shattercane: some points in Australia (GBIF, 2015) and some U.S. counties (Kartesz, 2015). Geo-C4 (Desert) y - mod N/A Shattercane: one point in Australia (GBIF, 2015) and a few U.S. counties (Kartesz, 2015). Geo-C5 (Mediterranean) y - negl N/A Shattercane: a few points in Australia (GBIF, 2015) and some U.S. counties (Kartesz, 2015). Geo-C6 (Humid subtropical) y - negl N/A Shattercane: some points in Australia (GBIF, 2015) and some U.S. counties (Kartesz, 2015). Geo-C7 (Marine west coast) y - low N/A Shattercane: some points in Australia, and one point in each of Angola and (GBIF, 2015). Geo-C8 (Humid cont. warm sum.) y - negl N/A Shattercane: some U.S. counties (Kartesz, 2015). Geo-C9 (Humid cont. cool sum.) y - mod N/A Shattercane: a few U.S. counties (Kartesz, 2015). Geo-C10 (Subarctic) n - low N/A We found no evidence that shattercane occurs in this climate class. Cultivated sorghum: two points in Germany, but because they occur in the Alps where rapid changes in elevation can have a large impact on map accuracy, we did not consider these points as convincing

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Question ID Answer - Score Notes (and references) Uncertainty evidence (GBIF, 2015). Geo-C11 (Tundra) n - negl N/A We found no evidence that shattercane occurs in this climate class. Cultivated sorghum: five points in Germany and Austria, but because they occur in the Alps where rapid changes in elevation can have a large impact on map accuracy, we did not consider these points as convincing evidence (GBIF, 2015). Geo-C12 (Icecap) n - negl N/A We found no evidence that shattercane occurs in this climate class. 10-inch precipitation bands Geo-R1 (0-10 inches; 0-25 cm) y - high N/A Shattercane: one point in Australia (GBIF, 2015) and a few U.S. counties (Kartesz, 2015). Cultivated sorghum: some points in the United States (GBIF, 2015). Shattercane is reported to tolerate hot, dry conditions (Anonymous, 2014). We expect it may be able to survive in either more favorable microsites of this precipitation band or perhaps during wetter seasons. Geo-R2 (10-20 inches; 25-51 cm) y - negl N/A Shattercane: a few points in Australia (GBIF, 2015) and a few U.S. points counties (GBIF, 2015; Kartesz, 2015). Geo-R3 (20-30 inches; 51-76 cm) y - negl N/A Shattercane: some points in Australia and the United States (GBIF, 2015). Geo-R4 (30-40 inches; 76-102 cm) y - negl N/A Shattercane: a few points in Australia, one point in Angola, and one point in Argentina (GBIF, 2015). Geo-R5 (40-50 inches; 102-127 cm) y - negl N/A Shattercane: one point in Australia and some in the United States (GBIF, 2015). Geo-R6 (50-60 inches; 127-152 cm) y - negl N/A Shattercane: one point in Australia and some in the United States (GBIF, 2015). Geo-R7 (60-70 inches; 152-178 cm) y - low N/A Shattercane: some points in the United States (GBIF, 2015). Geo-R8 (70-80 inches; 178-203 cm) y - high N/A We found no evidence that shattercane occurs in this precipitation band. Cultivated sorghum: India and Nigeria (GBIF, 2015). Geo-R9 (80-90 inches; 203-229 cm) y - high N/A We found no evidence that shattercane occurs in this precipitation band. Cultivated sorghum: a few points in India, Nigeria, and Sierra Leone (GBIF, 2015). Geo-R10 (90-100 inches; 229-254 cm) y - high N/A We found no evidence that shattercane occurs in this precipitation band. Cultivated sorghum: a few points in India, Nigeria, and Sierra Leone (GBIF, 2015). Geo-R11 (100+ inches; 254+ cm) y - high N/A We found no evidence that shattercane occurs in this precipitation band. Cultivated sorghum: a few points in India, Nigeria, and Sierra Leone (GBIF, 2015). ENTRY POTENTIAL Ent-1 (Plant already here) y - negl 1 Shattercane is widely established in the United States (Kartesz, 2015; NRCS, 2015) and has been present since the mid-1800s (Defelice, 2006; Horak and Moshier, 1994). Ent-2 (Plant proposed for entry, or - N/A entry is imminent ) Ent-3 (Human value & - N/A cultivation/trade status) Ent-4 (Entry as a contaminant) Ent-4a (Plant present in , - N/A

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Question ID Answer - Score Notes (and references) Uncertainty Mexico, , the Caribbean or ) Ent-4b (Contaminant of plant - N/A propagative material (except seeds)) Ent-4c (Contaminant of seeds for - N/A planting) Ent-4d (Contaminant of ballast - N/A water) Ent-4e (Contaminant of aquarium - N/A plants or other aquarium products) Ent-4f (Contaminant of landscape - N/A products) Ent-4g (Contaminant of containers, - N/A packing materials, trade goods, equipment or conveyances) Ent-4h (Contaminants of fruit, - N/A , or other products for consumption or processing) Ent-4i (Contaminant of some other - N/A pathway) Ent-5 (Likely to enter through natural - N/A dispersal)

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