Common Name: Japanese stiltgrass, Nepalese Browntop, Chinese packing grass, Annual stilt grass, Bamboo grass, Eulalia, Mary’s grass, Ashi-boso (Japanese for ‘slim foot’) – The East Asian provenance of this invasive plant was arbitrarily attributed to Japan early in the 19th Century. Stilt refers to the long stalk to which the leaf petiole is attached.
Scientific Name: Microstegium vimineum – The generic name is from the Greek micro meaning small and stege meaning roof. The species name is from the Latin vimineus which is a combination word for ‘pliant twig; the English word vimineous is derived from it to mean ‘producing slender twigs’. It was originally described in 1832 and is still sometimes referred to as Andropogon vimineus. Eulalia viminea is a third form occasionally referenced.
Potpourri: Just as Kudzu earned the epithet “the vine that ate the south,” Japanese stiltgrass is establishing a reputation as “the grass that covered the earth.” It paints the ground with a dense, contiguous leafy green carpet, a biological metaphor for the Sherwin Williams logo. In the absence of any predators, as is the case with all invasive species, it takes insidious advantage, blocking out the sun and consuming the nutrients at the expense of almost anything indigenous. It is a case study in globalism, population dynamics, and phenology.
Unlike kudzu, which was intentionally planted in the 1930’s as the ideal plant for remediation of the farmed out southern bottomlands according to the dictum of the USDA Soil Conservation Service, Japanese stiltgrass was a botanical Trojan horse. Its port of entry to North America was Knoxville, Tennessee, where it was first collected and analyzed in 1919; this is corroborated by more recent population growth analyses. The common name Chinese packing grass is an indication of its insurgency, which was innocuous. In the era that preceded Styrofoam, dried annual grasses were sometimes used as packing materials for the shipment of anything fragile, particularly porcelain. Originally the purview of the Dutch East India Company in the mid seventeenth century, Chinese porcelain has ever since been an aesthetic global icon in Western culture to the extent that it is commonly referred to simply as “china.” It is therefore hypothesized that it all started with a shipment of dishware, the discarded packing material carrying the seeds of despond. The toponym Japanese in lieu of Chinese for the resultant stiltgrass is a matter of etymological preferences of the time for anything of Asian provenance.
It has taken nearly a century for Japanese stiltgrass to transition from a few miniscule grass seeds in a Tennessee trash bin to malevolent, globe-trotting scourge. Its slow but inexorable progress is an interesting dichotomy between the frenetic passage of human time and the plodding certitude of nature time. Within ten years of its introduction it had spread to Virginia (1931), Alabama (1934), and Pennsylvania (1938) and by the turn of the century, it had reached New England. The language employed to describe its concentration in the Flora of the Southern and Mid-Atlantic States over time is equally provocative, from ‘local’ in 1950 to ‘sporadically naturalized’ in 1979 to ‘a rapidly spreading pernicious invader on moist ground’ in 1989. It is currently listed on the USDA Plants Database as a Class C noxious weed in Alabama, as banned in Connecticut and Massachusetts and it is listed on the noxious weed lists in 43 other states. Due to its appearance in the southern Caucasus and Anatolia regions, it was added to the alert list by the European and Mediterranean Plant Protection Organization (EPPO) in 2008. Apocalypse now, but hope for the best.
The success of Japanese stiltgrass is a matter of botanical ecology; a combination of a plant that rapidly adapts to a new environment before that environment can adapt to it, nominally through balancing predation by either an herbivore or a pathogen. The introduced species phenomenon, which has historically occurred intermittently and only at sailing ship speed has been a matter of some note since 1492; the New World and the Old World exchanged everything from apples (from Eurasia) to turkeys (from the Americas), most of the time slowly and intentionally. The mass movement of goods and services across vast oceans and formerly insurmountable mountains with the advent of container ship freight and air transport since the middle of the last century has wreaked havoc on local ecologies on a global scale. The International Union for the Conservation of Nature (IUNC) maintains a list of the 100 worst invasive species that are mostly animals such as rats, rabbits, and mosquitoes. While Japanese stiltgrass is not included, it is noted by the IUNC that “absence from the list does not imply that a species poses a lesser threat.” The Centre for Agriculture and Biosciences International (CABI), an organization dedicated to global environmental issues considers Japanese stiltgrass “a very serious invasive species and considered one of the most destructive introduced plants in the United States.”
Once a new organism is introduced, there are three factors that contribute to its spread: The rate of reproduction, the physiological adaptability, and the extent of predation. Japanese Stiltgrass is an annual plant that dies at the end of every season, relying on its seeds for future progeny. Most grasses produce copious seeds as an evolutionary feature of their competitive survival. Japanese stiltgrass flowers are both cleistogamous (self-pollinating) and chasmogamous (cross pollinating) to take full advantage of the wind for pollen transport for fertilization. The result is up to 1,000 seeds per plant with fecundity exasperated by longevity; the seeds are viable for up to 5 years and can survive a 2 month water immersion. The resultant seed bank repository that builds up under and adjacent to the parent plants is gargantuan; as many as 4 million seeds per square meter. If only 0.01 percent (or one out of every 10,000) of the seeds germinate, that would yield 400 plants, which is about what a really dense stand looks like it might have. Once an infestation starts, the seeds are spread mechanically by hikers and vehicles; the wide bands of Japanese stiltgrass that border trails and country roads are the result.
The physiological adaptability of Japanese stiltgrass has been the subject of extensive research over the last decade as it has become a more virulent intruder. Its relatively recent rise to prominence after decades of sub-rosa subversion is potentially a case study of the evolution of the increased competitive ability (EICA) theory that was first proposed in 1995. EICA posits that an introduced plant is able to apply more of its resources to adaptation in the absence of predation and that the time for the adaptation(s) to become manifest results in a lag between introduction and cancerous spread. Japanese stiltgrass is both cleistogamous to take advantage of the seed production of the former and chasmogamous to take advantage of the random mutations of evolution that result from sexual reconfigurations. Among adaptations, the most pernicious are those favoring Japanese stiltgrass over native perennial grasses under low light (< 5%) conditions such as those encountered in forests and parks under the tree canopy. It has been experimentally verified that it has a higher relative growth rate, a higher reproductive rate and consequently a greater epigeal biomass than its native competitors. One need only take a short hike through an inflicted forest to observe this directly. It apparently is also adapted to the sunfleck dappled light in the understory to the extent that it rapidly reaches full photosynthesis rates under these conditions. Conversely, it can also tolerate low nutrient soils in areas with full sunlight, demonstrating that it has what is called “extreme plasticity” in physiology; it is a very good weed.
The extent of predation of Japanese stiltgrass outside its Asian homeland is essentially nil as there are no native predators, a condition that is generally true for all invasive plants and animals. The complex ecological web of things eating and things being eaten takes centuries to evolve in any one locality. Insertion of a non-native species subverts the natural course. Cattle won’t eat Japanese stiltgrass and even goats reportedly avoid it. Ironically, our ubiquitous native herbivore white-tailed deer are daintily selective, consuming everything except the invasive species only to advance its onslaught; there is some evidence of forest regeneration failure under the synergetic effects of deer browse and stiltgrass spread. Arthropod predation of Japanese stiltgrass is measurably miniscule ranging from 0.4 to 10 percent of leaf removal. Insect populations actually declined by 39 percent and insect diversity declined by 19 percent in scientific field studies of stiltgrass infested areas compared to controls. More disturbingly, carnivores were reduced by 61 percent compared to 31 percent for herbivores; keystone species that maintain ecological balance are mostly in the former category. One study found that the natural regeneration of native species was reduced by 75 percent relative to control areas and those seedlings grew only half as high over a comparable growing season. All things considered, things do not bode well for a Japanese stiltgrass dominated environment.
Based on the introduction of North American invasive plants to Great Britain in the 16th Century without any attempts at any countermanding controls, it is estimated that 500 years are necessary for a new set of predators to adapt and evolve to fill the emergent non-native nutrition niche. In the end that may be the only recourse to the current global problem, but alternative controls have been successful with other invasives and should be field tested and utilized according to result. There are four methods that merit consideration: biological control with exotics, biological control with endemics, extermination with herbicides, and extermination by mechanical means. Biological controls are the obvious preference as they offer a nature-like solution with human intervention for selection and scientific experimentation. Like the CRISPR (Clustered Regularly Interspersed Short Palindromic Repeats) gene-editing to produce clones and GMO’s in lieu of the blind trial and error cross breeding of animals and plants, science can offer a more precise technological solution.
Exotic biological controls offer the most promising leads, as the invasive species in question had to have come from somewhere as a non-invasive hemmed in by locavores. Introducing alien species is, however, fraught with dangers that are implicit in the very act; the mongooses introduced to Hawaii in the 19th century to control sugar cane eating rats decimated the bird population. An enhanced measure of uncertainty is inherent in the case of Japanese stiltgrass; the grass family includes some of the most important agricultural crops – wheat, rice, corn, cereal grains and bamboo among others. Extirpating stiltgrass at the expense of bread would be a Faustian bargain of epic proportion. In spite of the toponym, Japanese stiltgrass likely originated in China; it is found in 15 provinces and there are 15 coeval species in the genus Microstegium in addition to vimineum. The limited research that has been done to date revealed that there are 7 members of the Lepidoptera order of butterflies and moths whose larvae feed on the genus but there has been no comprehensive survey. Biological controls are also feasible that include fungal or bacterial pathogens. However, due to the critical importance of grasses, this has never been studied and it is unlikely that a pathogen would gain approval.
Endemic biological controls are less threatening since they are not alien per se; however, Japanese stiltgrass has been successful due to a dearth of native predation. Observations of test plots have revealed that there are a number of orthopterans (grasshoppers and such) and hemipterans (the true bugs) that have evidently adapted to eat it; however it took 15 years of continuous exposure, an observation that supports the 500 year theory for control of invasives with natural evolutionary pressures. Invoking a plague of locusts to control stiltgrass is not a very appealing proposition and one that would not likely gain approval. In 2009, leaf blight disease caused by a fungus from the genus Bipolaris was discovered that caused lesions, wilting and in some cases death of stiltgrass. A subsequent laboratory test of the fungus resulted in infection of the host plant in 72 hours with lesions after 10 days. The diseased plants produced 40 percent less seeds than the control. There may be some hope The USDA Technical Advisory Group (TAG) for the Biological Control Agents for Weeds approved project 16-03 to initiate a host test plant list to evaluate biological controls as of April 2017. This would be needed to prevent an unintended consequence; Bipolaris sacchari, for example, is a plant pathogen that causes root and stem rot in wheat.
Lastly, there are the age-old control methods of kill it, cut it or remove it. Herbicides are chemicals engineered for their toxicity, their beneficence a measure of the degree to which they are narrowly targeted to the offending plant and the degree and speed with which they decompose to harmless chemicals. Glyphosate, an organophosphate compound that is the active ingredient in herbicides like Roundup™, is at one end of the spectrum in that it kills almost everything green but breaks down into harmless constituents within about 50 days after application with only a modest reduction in soil phosphates as a result. Herbicides that are grass specific, such as Fusilade™ used in Shenandoah National Park, have the advantage of minimal collateral damage to trees and wildflowers. However, residual chemicals in these treatments buildup in the soil; some even contain arsenic. Mechanical methods are a last resort; there is an element of Sisyphean Labor in mowing or pulling stiltgrass out by the roots only to watch it grow back from its seed bank the following year. Ultimately it is a matter of a combination of methods that can only keep Japanese stiltgrass in check to prevent it from becoming “the grass that covered the earth” until something can be found to kill it or eat it. These pictures of the same trail before and after treatment demonstrate that success is achievable.