No abstract

Giant reed is an invasive plant of riparian habitats throughout California and the United States. Glyphosate is approved for controlling giant reed in California. Sources indicate that 1.5% to 5% glyphosate solutions are effective at controlling giant reed. There is little published data on the relative efficacy of different concentrations of glyphosate which can be used to select an appropriate application regime for California habitats. We conducted two field experiments to test the hypothesis that glyphosate concentrations of 1.5%, 3%, and 5% applied as foliar sprays were equally effective at killing giant reed plants. Leaf chlorophyll content and the proportion of living stems declined significantly following treatment with 1.5% or greater solutions of glyphosate. New stems were observed the spring following treatment for plants treated with 1.5% glyphosate. No new stems were observed for plants treated with either 3% or 5% glyphosate. A treatment that included ''bending and breaking'' stems prior to treatment with 5% glyphosate provided control similar to 5% glyphosate alone. There was no there evidence that plants sprayed with only a mixture of the surfactant (Agridex), water, and a marking dye were affected beyond the short-term. These results indicate that 3% or 5% foliar applications with glyphosate were the most effective and consistent treatments for killing giant reed with a single late-season application. This result is especially important if the goal of the treatment program is to minimize the number of treatments, thus reducing labor costs and minimizing impacts on sensitive habitats by reducing the number of site visits. Nomenclature: Giant reed, Arundo donax L. ABKDO.

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Cyanobacteria and algae are problematic in California rice fields that are typically shallow and have high nutrient levels, providing ideal growing conditions. Nostoc spongiaeforme is a problem because extensive floating mats dislodge rice seedlings or smother them when the mats accumulate in windward areas. There is little published information on growth requirements for N. spongiaeforme. We grew N. spongiaeforme in BG-11 medium at 24 combinations of light (22, 87, 162, and 400 mM m À2 s À1 ) and temperatures (10 C, 15 C, 20 C, 25 C, 30 C, and 35 C). Results were summarized as a quadratic equation relating light and temperature to growth and indicate that optimal growth occurred at 26 C and 227 mM m À2 s À1 of light. Thus, N. spongiaeforme grows well at water temperatures and light levels similar to those measured in rice fields during the critical 30 days following initial flooding of the field.

No abstract