The biology of Canadian weeds. 65. Salsola tragus L. (updated)

This account updates that published by Crompton and Bassett in 1985 (classified then as Salsola pestifer A. Nels.). The taxonomy of this species has been controversial and confusing. Salsola tragus is an annual broadleaf weed species native to Eurasia and inadvertently introduced to the Americas in crop seed in 1873. This naturalized species is a common and economically important weed in crop production systems and non-cropped disturbed areas in semiarid to arid regions of western North America; in eastern North America, S. tragus commonly occurs along roadsides, railways, and other dry, stony, and sandy areas. Pollen-mediated gene flow and efficient seed dispersal aids both short- and long-distance spread. As a C4 species, S. tragus is highly competitive in semiarid and arid small-grain cropping systems because of its ability to emerge early, efficiently extract soil available water by its extensive root system, and tolerate heat, drought, and salinity. Moreover, the evolution of acetolactate synthase-inhibitor resistance has impacted herbicidal control of the species. The weed has been used as an emergency forage during drought, and is palatable when immature and non-toxic to livestock. Key words: Salsola tragus, Salsola pestifer, Salsola iberica, Salsola kali, Russian thistle, weed biology

Ecology and Control of Russian Thistle (Salsola iberica) After Spring Wheat Harvest

Russian thistle is the most problematic broadleaf weed for spring-sown crops in the low-precipitation (< 340 mm yr−1) region of the inland Pacific Northwest of the United States. A 6-yr field experiment was conducted at Lind, WA, to evaluate three postharvest control strategies for Russian thistle in continuous annual spring wheat. Postharvest treatments were (1) tillage with low-disturbance overlapping undercutter V-blade sweeps; (2) paraquat + diuron at the labeled rate, which is widely used by farmers; and (3) an untreated check (letting Russian thistle grow unhindered). The undercutter V-sweep consistently killed all Russian thistle with essentially no residue burial, and no seed was produced. In contrast, the paraquat + diuron treatment halted Russian thistle dry biomass production, but plants continued to extract soil water and produce an average of 310 seeds m−2on the lower branches. In the check, Russian thistle produced an average of 700 kg ha−1postharvest dry biomass and 5,670 seeds m−2. The undercutter V-sweep treatment had significantly more water in the 180-cm soil profile at time of wheat harvest, after a killing frost in October, and in mid March as well as greater spring wheat grain yield compared with the herbicide and check treatments. Results show that postharvest tillage with an undercutter V-sweep consistently achieved 100% control, retained ample wheat residue on the surface to control erosion, and was by far the most effective treatment in this experiment.

Seed germination in the Great Basin halophyte Salsola iberica

Salsola iberica Sennen & Pau, a halophytic forb in the family Chenopodiaceae, is widely distributed in inland salt deserts of Utah and widespread in North America. Experiments were conducted to determine the effects of NaCl and temperature on seed germination and their recovery of germination from saline conditions after being transferred to distilled water. Seeds of S. iberica were germinated at various temperatures and at various salinities in a 12 h light : 12 h dark photoperiod to determine their germinability under these conditions. Increases in NaCl concentration progressively inhibited seed germination. Few seeds germinated at 1000 mM NaCl. Cooler temperatures significantly inhibited germination, while high night (25°C) and high day (35°C) temperature regimes showed higher germination. Rate of germination decreased with an increase in salinity. Germination rate was higher at 25–35°C and lower at 5–15°C temperatures. Seeds were transferred from salt solutions to distilled water after 20 days, and those from low salinities recovered quickly at cooler temperature regimes. Recovery germination percentages substantially decreased with an increase in salinity and temperature.Key words: halophyte, recovery of seed germination, Salsola iberica, salt desert, thermoperiod, Utah.

Growth ofKochia scoparia, Salsola iberica, andTriticum aestivumvaries with temperature

Information on the influence of temperature on growth of springTriticum aestivumL. (wheat) relative toKochia scoparia(L.) Schrad. (kochia) andSalsola ibericaSennen and Pau (Russian thistle) could lead to more efficient weed management practices. An experiment was conducted to determine the growth of springT. aestivum, K. scoparia, andS. ibericaat 15, 23, and 30 C in growth chambers. Fresh weight at 15 C was greater for springT. aestivumthan forK. scopariaandS. iberica.Conversely, fresh weights at 23 or 30 C were greater forK. scopariaandS. ibericathan for springT. aestivum.Growth response to temperature is consistent with the physiological characteristics for photosynthesis of springT. aestivum, a C3plant, andK. scopariaandS. iberica, which are C4plants. The results indicate that cool temperatures that usually occur for early-seeded springT. aestivumwould give springT. aestivumthe competitive advantage overK. scopariaorS. iberica.Additionally, growing degree day (GDD) equations for height development ofK. scopariaandS. ibericawere determined and could be used to determine the optimum time for postemergence herbicide application.

Plant Movement and Seed Dispersal of Russian Thistle (Salsola iberica)

Russian thistle plant movement and seed dispersal were studied in 1991 and 1992 by placing Russian thistle plants in the center of wheat fields in eastern Washington. Three adjacent site treatments, with 24 plants on each site, were used each year; wheat stubble, summerfallow planted to winter wheat, and a “stationary” site. Plants in the “stationary” site were anchored to the ground to prevent tumbling. Plants in the stubble and summerfallow sites were allowed to tumble naturally. Individual plant movement was monitored and recorded weekly by satellite global positioning systems technology. Average estimated seed number per plant at the beginning of the experiment was 57,400 in 1991 and 66,000 in 1992. The direction plants moved correlated highly with wind direction. Some plants moved a maximum distance of 4069 m in 6 wks, while other plants moved only 60 m because of variable winds and being compressed by snow or frozen into wheat stubble. Average percentage seed loss in 1991 and 1992 for stationary plants was 15 and 26%, and for tumbling plants was 48 and 66%, respectively.

Sulfonylurea-Resistant Russian Thistle (Salsola iberica) Survey in Washington State

The repeated use of sulfonylurea (SU) herbicides to control broadleaf weeds in wheat fields and right-of-ways has selected for herbicide-resistant Russian thistle populations. A survey was conducted in 1991 and 1992 to ascertain the relative occurrence of SU-resistant Russian thistle in eastern Washington state. The 55 574 km2survey area was divided into 149 equal sample areas. All sample areas were surveyed for Russian thistle and seed was collected from plants in 86 sample areas. No Russian thistle was found in the center of the remaining 63 sample areas. Seeds were collected, by plant, from 30 plants at each site. Site samples were tested in the greenhouse for resistance or susceptibility to chlorsulfuron. Populations that were either homogeneous or heterogeneous for chlorsulfuron-resistance were found in 70% of the sample areas and all of the plants were susceptible in 30% of the sample areas.