New emerging weeds and their management Rob Gulden, Dept. of Plant Science, University of Manitoba, Winipeg, MB R3T 2N2 E-mail: gulden@cc.umanitoba.ca Abstract The relative importance of individual weed species changes over time. Many factors contribute to this including introductions of new crops, changes in management, changes in climate, and the introduction of new weeds to an area. In Manitoba, a number of relatively wet years in succession and reduced tillage has contributed to an apparent increase in the abundance of foxtail barley. Longer growing seasons and genetic improvements have contributed to an increase in the frequency in crops such as corn and soybean which are more common to eastern Canada. These crops are associated with a different suite of weeds and as a result, species such as biennial wormwood, ragweed species, and annual nightshades are more noticeable than in the past. This paper briefly discusses the biology and management of these species. Introduction The relative importance of weed species changes over time and this is caused by many factors. For example, the introduction of 2,4-D contributed to the rapid decline in the prominence of wild mustard (Sinapis arvensis) in western Canada. Other factors that affect weed populations include the life cycle of a crop, crop rotations, tillage practices, and fertility. In addition, changes in climate, in specific wet/dry cycles or a change in the length of seasons or winter harshness will affect the abundance of weed species or whether newly introduced species are able to persist or go extinct. Due to reduced tillage, the introduction of new crops, longer growing seasons, and a wet cycle in recent years, weed species including foxtail barley, biennial wormwood, the ragweed species complex and the nightshades are increasing in abundance in Manitoba. None of these species are new introductions to Manitoba and have been present for many decades, but rather are expanding into cropping systems as niches within these systems allow. For each of these species, a brief description of its biology is provided and this is followed by brief description of how to manage them. Foxtail barley (Hordeum jubatum) Biology and concerns Foxtail barley is a short-lived simple perennial grass that is native to North America. Being a simple perennial, this species reproduces by seed only with no vegetative reproduction. Foxtail barley is considered a facultative halophyte with medium tolerance to salt. The species prefers non-saline conditions, but becomes relatively more competitive as salt levels increase. More importantly, foxtail barley is associated with high water tables and foxtail barley tends to dominate the community in these areas (Best et al. 1978). Seeds tend to germinate in fall and the following year. Seedbank persistence is relatively short with maximum persistence for up to 7 years and high mortality rates during the first year (Best et al. 1978). Foxtail barley seeds can emerge from a depth up to 7.5 cm. Foxtail barley is a prolific seed producer and individual plants produce many spikes throughout the growing season leading to seed dispersion from July until freeze up. On individual spikes, seeds mature from the distal to the proximal end and mature seeds detach easily from the spike and are readily dispersed by wind, water, and by clinging to animals (Best et al. 1978). Foxtail barley is palatable to livestock at the vegetative stage, but becomes unpalatable after heading. The numerous long awns on each seed are irritable to livestock (Best et al. 1978).

Management As foxtail barley is closely linked to high water tables, reducing the water table through drainage or growing crops that use water is a long-term strategy for managing this species. Being a simple perennial without vegetative reproduction suggests tillage as a viable control strategy provided that rootstocks including the crown are pulled to the surface to desiccate. Also effective is preventing seed production. This can be achieved by mowing plants no later than 10 days after heading (Best et al. 1978). Foxtail barley seed mature very quickly. Tillage followed by the establishment of a dense, competitive annual crop followed by tillage and an alfalfa crop is an effective management strategy. In pastures, early spring grazing results in significant setback of foxtail barley (Best et al. 1978). There are several herbicides that can be used to manage foxtail barley, although achieving complete control can be challenging. Top growth control can be achieved readily, however, this provides only temporary relief as effective control of the root system is necessary for complete control. For this, herbicides must be translocated to the roots which occurs primarily in fall and thus, timing is crucial. Herbicide options to manage foxtail barley are listed under special weed problems in the Manitoba Guide to Crop Protection (Anonymous 2008a). In the spring, a combination of a pre-seed application of glyphosate, followed by in-crop application of Assure II has been shown to be most effective in research conducted in Saskatchewan (Sapsford, pers. comm.). There are no known herbicide-resistant populations of foxtail barley. Biennial wormwood (Artemisia biennis) Biology Over the past decade, biennial wormwood has been an increasingly important weed species in the northern US states and on some farms in Manitoba. This species can be particularly problematic in soybean, field bean and sunflower fields. Biennial wormwood is native to North America, in particular the northwestern US and western Canada and has been spreading towards the east (Kegode et al. 2007). Despite its name, an annual biotype of this weed exists and it is this version that has become particularly problematic in annual crops. Biennial wormwood is a late emerging species. Research in North Dakota has indicated that soil type affects the initiation of emergence with increasingly delayed initiation of emergence as soil texture becomes more fine (Fronning & Kegode 2004a). Multiple flushes can emerge throughout the remainder of the growing season. This species can be identified by its deeply lobed true leaves (see below and Fig .1) and distinct fragrance emitted when leaves are crushed. In the vegetative stage, this species is often mistaken for common ragweed (Fig. 1). This species is a prolific seed producer, producing large numbers of small seeds per individual. Small seeds suggest seedling emergence occurs primarily from shallow depth, although this weed survives well in most tillage systems (Kegode et al. 2007). Management Biennial wormwood is difficult to manage with herbicides. Late. emergence results in this species often escaping pre-seed and in-crop herbicide applications. In addition, biennial wormwood is naturally tolerant to many herbicide modes of action including ALS inhibitors (Group 2), dinitroanalines (Group 3), PPO inhibitors (Group 14), Acetamides (Group 15), and HPPD inhibitors (Group 27/28)) and specific herbicides within a herbicide Group [i.e., bromoxynil (Group 6) and fuoroxypyr (Group 4)] (Kegode et al. 2007). Due to the prolonged emergence periodicity of this species, pre-emergence applied soil residual herbicides used in combination with post-emergence herbicides tend to provide the most effective control (Fronning and Kegode 2004b). Post-emergence herbicides are most effective

when applied to seedlings that are less than 8cm in height (Fronning & Kegode 2004b). At this time, however, there are few registered herbicides that provide adequate control of biennial wormwood available to Manitoba crop producers. There are a couple of herbicide options for managing this weed in pastures and other non-cropped areas listed under special weeds and elsewhere in the Manitoba Guide to Crop Protection (Anonymous 2008a). To date, no herbicide-resistant populations have been reported. Ragweed complex (Ambrosia spp.) Biology The ragweed complex can be divided into three species, common ragweed (Ambrosia artemiisifolia), giant ragweed (A. trifida) and perennial ragweed (A. psilstachya). In Manitoba, the common name of Iva xanthifolia is false ragweed whereas in other places this weed is typically referred to as Marshelder. False ragweed belongs to a different genus, has distinctly different flowers than other ragweeds and will not be discussed further here. Common ragweed and perennial ragweed look very similar. For perennial ragweed, distinguishing features include smaller individual plant size and creeping roots. As the species name of common ragweed (A. artemiisifolia) indicates, its leaves and those of perennial ragweed look very similar to those of biennial wormwood. Leaves of both species are highly lobed although in biennial wormwood, lobes are deeper and leave tips end in a point whereas in ragweed leaves lobes tend to be a bit wider and leaf tips are more rounded (Fig. 1). Giant ragweed have leaves that are entire at the younger part of the plant and develop characteristic leaves with three distinct lobes in the older parts of the plant. Giant ragweed plants, however, may have only unlobed leaves, in which case the vegetative phase of these plants is often mistaken for cocklebur (Xanthium spp.), sunflower (Helianthus spp.), or false ragweed.

Fig. 1. Individual leaves of perennial ragweed (left) and biennial wormwood (right) growing in Manitoba.

All three ragweed species are native to North America. All three species have been recorded in the botanical record of Manitoba with more known populations of perennial ragweed than common ragweed (Basset & Crompton 1975, Basset & Crompton 1982). Common ragweed is the most abundant ragweed in the eastern regions of North America. Giant ragweed, also an annual like common ragweed, is the most competitive of the ragweeds. Seeds of this species germinate early in the season, and plants have high growth rates and can attain a height of up to 2.8 m. Therefore, giant ragweed tends to dominate weed communities in which it occurs and is highly competitive with all field crops (Abul-Fatih 1977). Naturally occurring hybrids between common ragweed and giant ragweed and common ragweed and perennial ragweed have been found. Ragweed species are wind-pollinated and the many bell-shaped male flowers located at the distal end of branches produce large amounts of pollen. Ragweed pollen contains allergens that are a significant cause of hay fever in humans. Plant oils on ragweed leaves can cause skin irritation (Basset & Crompton 1975). On the other hand, giant ragweed is reported to make a high quality forage. Ragweed species tend to prefer rich soils and occur on agricultural and non-agricultural lands. Common ragweed and giant ragweed are well adapted to disturbed areas and produce seed of variable size which possess a seed coat dormancy and require scarification (physical disruption of the seed coat) before they germinate (Basset & Crompton 1975, 1982). Ragweed seedling can establish from seeds buried from 2 cm to 16 cm. Management Annual ragweed species tend to be more problematic in crop production fields than perennial ragweed. The small stature of perennial ragweed precludes this species from being very competitive. Giant ragweed is very competitive due to its germination ecology and rapid growth rates. If herbicides are not an option, early flushes can be managed well with tillage and later flushed of giant ragweed can be clipped above the canopy to reduce competition and seed production. Ragweed species are sensitive to a number of herbicide modes of action and these can be found in the Guide to Crop Protection (Anonymous 2008a). Ragweed species are sensitive to Group 4 herbicides, Group 5, Group 6, Group 7, Group 9, Group 10, Group, and Group 14. The degree of sensitivity of the ragweed species to each Group or product vary among the species. Parts of the Ontario Guide to Weed Control [Pub. 75] (Anonymous 2008b) may serve as an additional resource for information on managing these species. A number of herbicide resistant populations of common ragweed have been identified in the US and Canada. There is one Canadian population resistant to herbicides belonging to Group 5 and one population resistant to herbicides in Group 7. Globally, several Group 5 resistant populations, numerous populations resistant to Group 2 herbicides, one multiple resistant population to Groups 2 and 14, and three populations resistant to glyphosate (Group 9) exist (Heap 2009). Herbicide resistant populations of Giant ragweed also have been documented. To date, six populations resistant to Group 2 herbicides have been identified. Since 2004, three populations resistant to glyphosate (Group 9) have also been identified (Heap 2009).

Annual Nightshades (Solanum spp.) Biology The annual nightshades are also not newly introduced species to Manitoba, but have been present for many decades in non-agricultural lands. The nightshades are in the same family as potato (Solanum tuberosum) and tomato (Lycopersicon esculentum) and therefore look very similar. The increase in potato corn and soybean acres, however, appears to be providing niches for these species to expand their range from garden and non-cropped areas to cropped lands. There are two main concerns with these species. The fruit are dark in colour and retain water into fall. Thus, a small quantity of these fruit can discolour pulse or other crops during harvest to make these unmarketable. Nightshades also can be poisonous to a variety of livestock and humans. They contain solanin (a poisonous alkaloid) and high levels of nitrate. The factors that contribute to poisoning are not well understood (Basset & Munroe 1985). There are a number of annual nightshade species that occur in North America including hairy nightshade (Solanum sarrachoides), black nightshade (S. nigrum), eastern black nightshade (S. ptycanthum) and American nightshade (S. americanum). They have similar leaf structure and are therefore may be difficult to differentiate at the vegetative stages. The vegetative stage of hairy nightshade, however, can be identified readily by its distinct pubescence. The undersides of the true leaves of eastern black nightshade may be purple in some plants, however, this is not a universal characteristic of this species. In contrast to the other nightshade species, the mature berries of black nightshade have a matte black sheen, while the mature berries of the other nightshade species are glossy black in appearance (Basset & Munroe 1985). Eastern black nightshade and American nightshade are differentiated by subtle differences in the berries. Eastern black nightshade has unequal calyx lobes that are triangular at the tip, more sclerotic granules (hard granules that are not seed) in the fruit (usually 6 or more), and fruit tend to detach with the pedicel (stem) attached. American nightshade has equal calyx lobes that have rounded tips, have four or fewer sclerids per fruit, and tend to detach at the receptacle without a short stem attached to the fruit (Basset & Munroe 1985). There are other characteristics that distinguish these species and a guide may assist for clear identification. Nightshades have a long-emergence period that ranges from spring through summer and produce mature fruit four to five weeks after flowering (Basset & Munroe 1985). Seeds are dispersed in fruit by animals, water, and humans and can survive in soil for a number of decades, although in most cases, the majority of seeds loose viability after 5 years (Munroe & Basset 1985). Germination tends to be greater in disturbed soils than undisturbed conditions indicating that annual nightshades are well adapted to the disturbed conditions of agricultural fields. These nightshade species can hybridize naturally. This is important and suggests that herbicide resistance can be transferred among these species via inter-specific hybridization. Management There a number of effective techniques for managing these species. As these are annual species, techniques that reduce seed production will assist in managing these species. Nightshades do not compete well in forage crops and other competitive crops. Therefore, establishment of a crop that is competitive early in the season will assist in reducing future populations. Nightshades respond well to a number of different herbicides modes of action (i.e., Groups 2, 6, 9, 10, 14, 15 and 22) and are suppressed by Group 3 and Group 8 herbicides. However, clear identification is important as the species respond differentially to a number of the

effective herbicides (Anonymous 2008a, 2008b). Nightshades are not very sensitive to Group 4 herbicides when applied alone. Globally a number of different herbicide resistant populations exist. Currently, eastern black nightshade is resistant to herbicides belonging to Groups 2 and 5, black nightshade is resistant to herbicides in Groups 2 and 22, and American nightshade is resistant to Group 22 herbicides (Heap 2009). In Ontario, a number of eastern black nightshade populations resistant to Group 2 herbicides exist (Tradif; pers. comm.). To date, herbicide resistance has not been reported in hairy nightshade. Summary The internet is an excellent resource for learning more about weeds that are new to an area. A number of identification sites can be found on the internet which often include pictures that allow for clear identification of a species. To assist with identification, contact your local agronomists, weed supervisor or University. For weeds that are traditionally more prominent in eastern Canada and are major species in that region (e.g., ragweeds and nightshades), Ontario’s guide to weed control may be an important resource to consult. This publication also is available online. For more information on biennial wormwood, search the web pages of the North Dakota State University weed scientists who have studied this species in recent years. Literature cited Anonymous. 2008a. Guide to Crop Protection. Manitoba Agriculture, Food, and Rural Initiatives – MAFRI, Carman, MB.

Anonymous. 2008b. Guide to weed control 2004 publication 75. Ministry of Agriculture, Food and Rural Affairs, Ontario, Canada. Toronto, ON, Canada: Queen’s Printer for Ontario.

Best K. F., J. D. Banting & G. G. Bowes. 1978. The biology of Canadian weeds. 31. Hordeum jubatum L. Can. J. Plant Sci. 58:699-708.

Basset I. J. & C. W. Crompton. 1975. The biology of Canadian weeds. 11. Ambrosia artemisiifolia L. and A. psilostachya DC. Can. J. Plant Sci. 55:463-476.

Basset I. J. & C. W. Crompton. 1982. The biology of Canadian weeds. 55. Ambrosia trifida L. Can. J. Plant Sci. 62:1003-1010.

Basset I. J. & D. B. Munroe. 1985. The biology of Canadian weeds. 67. Solanum ptycanthum Dun., S. nigrum L. and S. sarrachoides Sendt. Can. J. Plant Sci. 65:401-414.

Fronning , B. E. & G. O. Kegode. 2004a. Biennial wormwood (Artemisia biennis) early-season control with herbicides. Weed Technol. 18:611-618.

Fronning , B. E. & G. O. Kegode. 2004b. Biennial wormwood (Artemisia biennis) postemergence control in soybean. Weed Technol. 18:380-387.

Heap, I. 2009. International survey of herbicide resistant weeds. [Online] http://www.weedscience.org [Accessed Nov 8 2009]

Kegode G., R. Zollinger & M. Ciernia. 2007. Biology and management of biennial wormwood. NDSU Extension Service, North Dakota State University, Fargo, ND, USA. 12 pgs.