Solanum elaeagnifolium, commonly known as Silverleaf Nightshade or White Horsenettle, is a resilient perennial plant belonging to the Solanaceae, or nightshade, family. It is known for its hardiness and ability to thrive in various environments. Plants typically grow to a height ranging from 10 centimeters to 1 meter.
Physical Characteristics and Identification
The leaves of Solanum elaeagnifolium are a striking silvery-green color, due to a dense covering of fine, star-shaped hairs (stellate trichomes) that lie flat against the surface. These lance-shaped to oblong leaves typically measure between 5 and 15 centimeters long and 0.5 to 2.5 centimeters wide, often displaying wavy or scalloped edges.
The plant’s stems are erect and branched, similarly covered with fine hairs, giving them a silver-white appearance. These stems, along with the main veins on the underside of the leaves, are frequently armed with slender, sharp, yellowish to reddish prickles, usually 2 to 5 millimeters long.
Flowers of Silverleaf Nightshade are star-shaped, with five fused petals, spanning 2.5 to 3.5 centimeters in diameter. They commonly appear in shades of purple or lavender, though white or blue variations exist, blooming from April through October. A prominent cluster of five bright yellow stamens stands out in the center of each flower.
Following flowering, the plant produces smooth, globular berries, typically 0.9 to 1.5 centimeters in diameter. These fruits initially appear green with dark striations, then mature to a glossy yellow or orange color, turning brown as they dry. The berries resemble small tomatoes and can persist on the plant throughout winter, with each plant producing up to 60 berries.
Habitat and Geographic Distribution
Silverleaf Nightshade is primarily native to the southwestern United States and northern Mexico. It is also indigenous to parts of South America, including Argentina, Uruguay, and Chile.
Beyond its native range, the plant has widely naturalized across many extra-tropical regions, establishing populations in Australia, parts of Africa like South Africa, Morocco, and Egypt, and countries within the Mediterranean Basin, including Greece, Italy, France, and Spain. It has also spread to India, the Pacific Islands like Hawaii and Cuba, and Taiwan.
The plant thrives in disturbed environments, commonly found along roadsides, in cultivated fields, and in overgrazed pastures, as well as waste areas. It shows strong adaptability to semi-arid regions that receive 300 to 500 millimeters of annual rainfall. The species tolerates various soil types, including dry, poor, coarse-textured, sandy, clay, and loam soils, and can even grow under irrigated or saline conditions.
Toxicity and Effects on Livestock
The plant’s poisonous nature stems from its content of steroidal glycoalkaloids, specifically solanine. These toxic compounds are present in all parts of the plant, with the highest concentrations typically found in the unripe green berries. The toxic properties of Silverleaf Nightshade are notably retained even after the plant material has dried.
Upon ingestion, these glycoalkaloids irritate the gastrointestinal tract and can be metabolized into alkaloids or alkamines. These act as nerve toxins by interfering with acetylcholinesterase, an enzyme involved in nerve function. This can severely affect grazing animals, particularly cattle, horses, and sheep, though goats show greater resistance to the toxins.
Livestock consuming Silverleaf Nightshade may display various symptoms. Cattle, for instance, can show moderate poisoning signs if they ingest 0.1% to 0.3% of their body weight in ripe berries. Symptoms include gastrointestinal distress (excessive salivation, colic, diarrhea, bloating) and neurological issues (depression, drowsiness, muscle tremors, incoordination, hind leg paralysis, rapid heart rate). In severe cases, consumption can lead to coma and death.
Management and Control Challenges
Managing Solanum elaeagnifolium is difficult to manage, primarily due to its extensive and deep perennial root system, penetrating 2 to 5 meters deep and spreading horizontally. This robust root network allows vigorous regeneration, even from root fragments as small as 0.5 to 1 centimeter, contributing to rapid vegetative spread. Its seeds are also highly viable, remaining dormant in the soil for at least a decade, ensuring long-term persistence.
Mechanical control methods, such as mowing or slashing, can temporarily suppress growth and reduce seed production. However, these methods often fail to eradicate the plant; it readily develops new rosettes below mower blades and quickly recovers. Tillage, rather than providing effective control, can worsen infestations by breaking roots into fragments and dispersing them to uninfested areas, promoting further spread.
Chemical control often relies on systemic herbicides, designed to translocate throughout the plant, including its deep root system. Herbicides like glyphosate, glufosinate, and picloram are effective, particularly when applied during early vegetative or flowering stages, or in autumn to target root reserves. Multiple applications are often necessary for sustained control and to deplete underground reserves.
Cultural control strategies complement other management efforts by fostering a competitive environment. Promoting healthy, dense pasture grasses (e.g., lucerne, Smuts finger grass, or blue buffalo grass) can suppress Silverleaf Nightshade by competing for moisture and nutrients. Preventing seed spread is also important. This involves avoiding grazing sheep in infested areas when fruits mature and quarantining livestock from infested zones for about 14 days to allow ingested seeds to pass through their digestive systems. Thoroughly cleaning agricultural machinery after use in infested fields also helps prevent dispersal of viable root fragments and seeds to new locations.