Abstract
Weed escapes are often present in large production fields prior to harvest, contributing to seed rain and species persistence. Late-season surveys were conducted in cotton (Gossypium hirsutum L.) fields in Texas in 2016 and 2017 to identify common weed species present as escapes and estimate seed rain potential of Palmer amaranth (Amaranthus palmeri S. Watson) and waterhemp [A. tuberculatus (Moq.) J.D. Sauer], two troublesome species with high fecundity. A total of 400 cotton fields across four major cotton-producing regions in Texas [High Plains (HP), Gulf Coast (GC), Central Texas, and Blacklands] were surveyed. Amaranthus palmeri, Texas millet [Urochloa texana (Buckley) R. Webster], A. tuberculatus, ragweed parthenium (Parthenium hysterophorus L.), and barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] were reported as the top five weed escapes in cotton fields. Amaranthus palmeri was the most prevalent weed in the HP and Lower GC regions, whereas A. tuberculatus escapes were predominantly observed in the Upper GC and Blacklands regions. On average, 9.4% of an individual field was infested with A. palmeri escapes in the Lower GC region; however, 5.1 to 8.1% of a field was infested in the HP region. Average A. palmeri density ranged from 405 (Central Texas) to 3,543 plants ha–1 (Lower GC). The greatest seed rain potential by A. palmeri escapes was observed in the upper HP region (13.9 million seeds ha–1), whereas the seed rain potential of A. tuberculatus escapes was the greatest in the Blacklands (12.9 million seeds ha–1) and the upper GC regions (9.8 million seeds ha–1). Seed rain from late-season A. palmeri and A. tuberculatus escapes is significant in Texas cotton, and effective management of these escapes is imperative for minimizing seedbank inputs and impacting weed species persistence.
Highlights
Widespread adoption of herbicide-resistant crops, primarily glyphosate-resistant (GR) crops, has allowed growers to apply broad-spectrum postemergence (POST) herbicides for effective management of weeds
Sauer], a species closely related to A. palmeri, exhibits a prolonged emergence window in the Midwestern and Southern United States [5,6]
Field surveys were conducted in the fall of 2016 and 2017 across four major cotton-producing regions of Texas: High Plains (HP), Gulf Coast (GC), Central Texas, and Blacklands (Fig 1)
Summary
Widespread adoption of herbicide-resistant crops, primarily glyphosate-resistant (GR) crops, has allowed growers to apply broad-spectrum postemergence (POST) herbicides for effective management of weeds. Weeds may survive management interventions that are typically carried out during the early season (i.e. early-season survivors) or avoid these management practices by emerging later in the season (i.e. late-emerging cohorts), and be present at crop harvest as “escapes” [1]. The ability of certain weed species, such as Amaranthus spp., to emerge for an extended period during the growing season allows the late-emerging cohorts to avoid management practices. A study conducted in Pendleton, South Carolina reported that Palmer amaranth Waterhemp [A. tuberculatus (Moq.) J.D. Sauer], a species closely related to A. palmeri, exhibits a prolonged emergence window in the Midwestern and Southern United States [5,6]
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