Biology and Management of Johnsongrass (Sorghum Halepense) Introduction

ANR Publication 8569 | February 2017 http://anrcatalog.ucanr.edu Biology and Management of Johnsongrass (Sorghum halepense) INTRODUCTION ohnsongrass (Sorghum halepense) is a summer Jperennial grass native to the Mediterranean region. It was introduced to the Southern United States in the early ALEX CESESKI, Department 1800s as a perennial forage crop and is still in use for cattle of Plant Sciences, University grazing in many states. After introduction, it escaped of California, Davis; KASSIM AL-KHATIB, Professor, Department cultivation and is now present or naturalized in nearly of Plant Sciences, University of every state in the continental United States. It is recognized California, Davis; and JEFFREY A. as invasive or as a noxious weed throughout the south, DAHLBERG, University of California southwest, and west and is one of the ten most troublesome Kearney Agricultural Research and weeds in the world. In California johnsongrass is classified Extension Center as a “C” list noxious weed (Fig. 1). Johnsongrass reaches 6 to 8 feet in height, with wide open, purple- brown panicles 4 to 20 inches long (Fig. 2). Stems and leaves are bright to deep green; leaves have a prominent white midvein and may reach 1 inch or more in width and 24 or more inches in length. Johnsongrass can reproduce via seed through self- or cross-fertilization and will reproduce vegetatively via a robust rhizome network. Figure 1. Mature johnsongrass stand. Photo: J. M. DiTomaso. ANR Publication 8569 | Biology and Management of Johnsongrass (Sorghum halepense) | February 2017 | 2 A B Figure 2. Johnsongrass panicles. A: Early-season panicle. Note emerging panicle in background. B: Mature panicle. Photos: A. Ceseski (A), J. M. DiTomaso (B). Since johnsongrass builds a substantial rhizome system in its first year, it can be very difficult to control once it is well established. Rhizome sprouts typically emerge early in the season and quickly reach full height, and they can easily outgrow and overtop desired plants. In addition, the extensive rhizome network can allow a single plant to be very competitive for water and nutrients over a substantial area. Significant crop yield reductions can be expected with acute johnsongrass infestation. For example, cotton can see a 20% yield reduction with as few as two tillers per square foot within rows (Keely and Thullen 1981). Corn without adequate control of johnsongrass can see yields reduced by up to 2 to 3 tons (70 to Johnsongrass establishes well in disturbed areas, rangelands, 100 bushels) per acre (Nagabhushana et al. 1995). Additionally, pastures, abandoned fields, and canals, as well as in virtually any disturbed portions of noncrop areas can quickly become dominated cropping system. It thrives in moist environments, but due to its by thick stands of johnsongrass if management is not practiced. extensive rhizome system it can persist in drier topsoils if they are above high water tables. Johnsongrass may not be a significant LIFE CYCLE AND PHYSICAL CHARACTERISTICS threat to recovered areas with sufficient established vegetation, so Johnsongrass can grow from seed or from overwintering rhizomes. avoiding disturbance in these areas is critical to preventing new Seed can germinate within a year and can remain viable for up to 6 or repeat infestations. Infestations usually begin in the margins of years in the soil. Seedlings may form new rhizomes as early as the affected areas, but livestock and machinery may inadvertently spread 5- to 6-leaf stage, about a month after emergence; buds of the new seed to the interiors of fields, orchards, pastures, and other areas. rhizomes may sprout the following year. Rhizome sprouting typically Johnsongrass is an alternate host to Maize Dwarf Mosaic Virus occurs in the early spring when daytime temperatures average above (MDMV), which affects corn (Zea mays), oats (Avena sativa), millets 60°F, but seed will germinate later, when daytime temperatures are such as pearl millet (Pennisetum glaucum) and foxtail millet (Setaria about 70° to 75°F. Date ranges for rhizome and seedling emergence italica), and sorghum (Sorghum bicolor). The presence of the virus vary by region, but early to late March for warmer areas and late in crops is often attributable to a nearby johnsongrass infestation. It March to mid April for cooler areas are good approximations. also readily hybridizes with grain, forage, or sudangrass sorghums, Sprouts from new rhizomes grow more rapidly than from seed, but which can reduce harvest quality due to contaminated seed. both grow quickly, and their development is essentially identical ANR Publication 8569 | Biology and Management of Johnsongrass (Sorghum halepense) | February 2017 | 3 A B Figure 4. Johnsongrass rachis: flowering spikelets; awns are visible on sterile spikelets. Photo: A. Ceseski. Figure 3. A: Johnsongrass seedlings. B: Johnsongrass rhizome sprout. Note that both the seedlings and the sprout are nearly indistinguishable. Photos: J. M. DiTomaso (A), A. Ceseski (B). Figure 5. Cluster of johnsongrass rhizomes. Note the (Fig. 3). Tillers usually appear at the 6-leaf stage, about a scaly texture and month after emergence. Flowering usually occurs 2 months cream to red color. from emergence and in California typically lasts from May Photo: A. Ceseski. to October, with each panicle producing up to 400 seed (Fig. 4). The rhizome network later expands during seed ripening; individual plants can produce 200 to 300 feet of new rhizome growth per year (Fig. 5). Aboveground structures and older rhizomes die off over winter, but new rhizome growth persists and forms new sprouts the following spring. Because it can propagate via self-crossing and rhizomes, a single plant, if left undisturbed, can cause a significant infestation of up to 180 square feet in 2 years (Fig. 6). Figure 6. A Johnsongrass seedlings can resemble young corn large roadside seedlings, but because their seed remain attached, johnsongrass johnsongrass is easily discernable if plucked. The first leaf infestation. is usually parallel to the ground; early leaves have a smooth Photo: A. Ceseski. surface with no discernable midrib and smooth edges. A white midvein may begin to show at the leaf base of seedlings. Seedling collars are usually pale green to whitish, and sheaths may begin to take on a red-purple tinge as the plant matures. ANR Publication 8569 | Biology and Management of Johnsongrass (Sorghum halepense) | February 2017 | 4 In California, johnsongrass can panicle or shatter into pairs or trios that consist of a lower fertile be as much as 8 feet tall at maturity spikelet and one or two sterile upper spikelets. Fertile spikelets are (Fig. 7). Stems grow from the crown, 0.15 to 0.25 inch long, and the smaller sterile spikelets may have are erect and unjointed at the nodes, bent and twisted awns up to 0.6 inch long (see Fig. 4)). Rhizomes and may have a red-purple base or are branching, scaly, and fibrous, 0.5 inch or more in diameter, and tinted internode. Nodes may have some reach up to 6 feet long. Rhizomes are usually cream or tan, may fine hairs, but internodes are usually have reddish brown streaks, and form a dense sod by the end of the smooth. Prop roots may form near the season (Fig. 11). base of stems (Fig. 8). The leaves are rolled in the bud, generally emerge A B C flat, and have a prominent midrib, especially at the base (Fig. 9). Mature leaves are hairless to nearly hairless and may have slightly rough edges, with a prominent fringed ligule up to 0.2 inch long or more (Fig. 10). Sparse hairs may be present on the leaf or sheath near the collar. Inflorescences form as large, open panicles that are pyramidal Figure 7. Johnsongrass Figure 8. Johnsongrass or conical in shape. Spikelets can range can reach 8 feet in height. prop-roots and aerial roots. from pale green or gray to golden to Photo: A. Ceseski. Photo: A. Ceseski. purple-brown. They may remain on the Figure 10. Johnsongrass ligules are variable. A: A prominent membranous ligule. B: An almost totally hidden ligule, which is composed entirely of fringe. C: A partially A B hidden fringed membrane ligule. Photos: J. M. DiTomaso (A); A. Ceseski (B and C). Figure 11. A sod of johnsongrass rhizomes. Photo: A. Ceseski. Figure 9. A: White midvein and an emerging leaf rolled in the bud. Note the purple tinge beginning to show on the internode. B: Prominent midrib on leaf underside. Photos: A. Ceseski. ANR Publication 8569 | Biology and Management of Johnsongrass (Sorghum halepense) | February 2017 | 5 MANAGEMENT Mowing Effective management of established infestations can be extremely Johnsongrass is known to be unable to tolerate repeated mowing. difficult. Johnsongrass readily colonizes disturbed areas, so field Mowing depletes the energy stores in the rhizomes and can reduce margins, canals, ditches, rights-of-way, and roadsides must be new rhizome growth. Mowing should begin when the plants are monitored closely if an infestation is suspected. Care must be taken about 8 to 12 inches tall, before panicle initiation–boot stage, and in pasture sown with johnsongrass as forage to prevent its escape. continue at intervals of 2 to 4 weeks. Mowing can kill seedlings but Livestock that may have eaten johnsongrass seed should not be may not kill all rhizomes, so when used alone it will only suppress taken to a johnsongrass-free pasture for at least a week, to prevent established infestations, not control them. the spread of seed through feces. Cleaning of equipment, especially Tillage shared or rented equipment, prior to relocation is an essential Tillage can aid carbohydrate depletion, but it must be used preventative measure against its spread into new areas. judiciously and only as a part of an integrated management program. A sound, integrated strategy must be employed to achieve Tillage is most effective when the soil is dry, as dried rhizomes are suitable management, whether the infestation is in crop land or less likely to sprout, and any sprouts will be less vigorous.

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