Mexican sprangletop (Leptochloa uninervia or Leptochloa fusca ssp. uninervia) is a common grass species. This annual or sometimes short-lived perennial plant is widespread, making its characteristics and management important for land managers and gardeners.
Identifying Mexican Sprangletop
Mexican sprangletop typically grows as an annual, though it can sometimes persist as a short-lived perennial, forming upright to spreading clumps. Its height can range from 2 to 3 feet, occasionally reaching up to 4 feet tall. The stems are branched and can be round or slightly flattened in cross-section.
The leaves are light to medium green, featuring a rough texture and a hairless surface. They are flat or loosely rolled, 4 to 20 inches long, and display a distinct whitish midrib. A key identifying feature is its seedhead, which consists of branched, upright to arching panicles. These spikelike clusters transition in color from gray-green when young to a straw-colored hue at maturity. Flowering occurs from May through November.
Habitat and Growth Cycle
Mexican sprangletop thrives in disturbed soils with ample moisture. It is found in agricultural fields, along roadsides, and in ditches. This grass is native to California and other parts of North America, and its distribution extends into Central and South America, as well as the West Indies.
The plant reproduces primarily by seed. Growth commences around April, and under favorable conditions, it can produce two distinct seed crops: one in the spring and another in the fall.
Impact and Significance
Mexican sprangletop is a problematic weed, particularly in agricultural settings. It increases rapidly in areas such as orchards, field edges, and ditchbanks, especially in locations where control programs heavily rely on glyphosate or specific pre-emergent herbicides. This grass competes with cultivated crops for resources such as light, water, and nutrients.
Competition from Mexican sprangletop reduces crop yield. In rice production, its uncontrolled presence can reduce grain yield by up to 36%, with severe cases reporting losses of 65% to 75% in paddy fields. Large infestations also interfere with harvesting operations. The grass can serve as a host for pests, such as lygus bugs.
Effective Management Strategies
Managing Mexican sprangletop involves a combination of approaches. Cultural control methods focus on creating an unfavorable environment for the weed while promoting crop health. This includes crop rotation, which helps disrupt the weed’s life cycle and can reduce the weed seed bank in the soil.
Maintaining healthy, competitive crops through optimized irrigation and appropriate fertilization also helps crops outcompete the weed. In specific agricultural systems, such as rice fields, managing water levels, like maintaining deep water, can help suppress sprangletop. General sanitation practices, including removing plant debris, can also reduce habitats for the weed.
Mechanical control involves physically removing or disrupting the weed. Hand-weeding is effective for smaller infestations or individual plants when the soil is moist. Tillage, especially repeated cultivation during dry summer months, can help control existing populations. Mowing is another mechanical option that can suppress growth and prevent seed production, though its effectiveness varies depending on the weed’s growth stage and density. Specialized lightweight equipment is used in areas like irrigation channels.
Chemical control involves applying herbicides. Post-emergent herbicides like glyphosate are effective when Mexican sprangletop plants are small, though repeat applications may be needed. Pre-emergent herbicides such as oryzalin, pendimethalin, and pronamide provide control before the weed emerges.
Other effective herbicides include clethodim, fluazifop-p-butyl, and sethoxydim. For rice cultivation, fenoxaprop-p-ethyl and cyhalofop butyl control sprangletop. Resistance to herbicides, including glyphosate, has been observed in sprangletop populations, necessitating careful selection and rotation of chemical treatments.
Integrated Pest Management (IPM) combines these strategies for weed control. IPM aims to minimize weed populations rather than eradication, focusing on long-term management. This involves diversifying crops and cultural practices to disrupt the weed’s ecological niche, reducing the risk of resistant weed populations developing. By blending cultural, mechanical, and chemical methods, IPM manages Mexican sprangletop.