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Orville C. Baldos, Joseph DeFrank, and Glenn S. Sakamoto

Tanglehead (Heteropogon contortus) is a native Hawaiian grass that has been used in restoration and has potential for expanded re-vegetation use. Although interest and demand for tanglehead re-vegetation has increased, the supply of tanglehead seeds has remained limited as a result of a lack of seed production protocols addressing seed dormancy. Smoke water from burning vegetation may provide an economical and practical seed treatment because aerosol smoke has been reported to stimulate tanglehead seed germination. Dose rate and side-by-side comparison studies were conducted to evaluate the germination stimulation efficacy of food-grade liquid smoke, xylose smoke-infused water, tanglehead smoke-infused water, karrikinolide (KAR1), and cyanide (i.e., mandelonitrile and potassium cyanide). Optimum smoke water dilutions were 1% v/v for food-grade liquid smoke and undiluted for xylose smoke-infused water and tanglehead smoke-infused water. KAR1 was not stimulatory at concentrations between 0.0067 and 66.7 μm. Potassium cyanide stimulated tanglehead seed germination at concentrations between 50 to 500 μm. Germination was promoted to even greater levels with the cyanohydrin, mandelonitrile, indicating a role for benzaldehyde (a byproduct of mandelonitrile decomposition) in stimulating tanglehead seed germination. Benzaldehyde was confirmed to be stimulatory at concentrations between 50 to 100 μm. The presence of cyanide at stimulatory levels was confirmed in tanglehead smoke-infused water (i.e., ≈100 μm), but not in food-grade liquid smoke or xylose smoke-infused water. Germination with non-cyanide-containing smoke waters indicates the presence of other compounds in smoke that can stimulate tanglehead germination. In the side-by-side comparison study, food-grade liquid smoke (1% v/v) and undiluted tanglehead smoke-infused water provided consistent germination stimulation comparable to 500 μm potassium cyanide. Undiluted xylose smoke-infused water did not provide significant germination stimulation in the comparison studies. This may be the result of differences in seed batch sensitivity to the germination stimulant, seed storage duration as well as subtle differences in the preparation of xylose smoke-infused water.

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Orville C. Baldos, Joseph DeFrank, Matthew Kramer, and Glenn S. Sakamoto

Tanglehead (Heteropogon contortus) is a drought- and fire-tolerant native Hawaiian grass that possesses seed dormancy on shedding. Although a dry after-ripening period is known to break dormancy, specific storage conditions to optimize this are not known. This study examined the effects of storage temperature and equilibrium relative humidity (eRH) on tanglehead seed dormancy loss and viability. Fresh seeds harvested in Mar. and Oct. 2011 were stored for 30 days in three eRH levels (12%, 50%, and 75%) and then incubated for 0, 1, 3, 6, 9, and 12 months at three temperatures [10, 20 (ambient in laboratory), and 30 °C]. The eRHs were maintained during incubation by sealing seeds in airtight packages. Seed germination and tetrazolium tests were conducted after each incubation period to determine dormancy loss and seed viability. Analysis of germination and seed viability data indicated a significant interaction among eRH, storage temperature, incubation period, and seed harvest month. Storage at 12% eRH and 30 °C for 12 months optimized dormancy loss of tanglehead seeds. Seeds remained viable in all eRH and temperature combinations except those stored at either 75% eRH and 20 °C or 75% eRH and 30 °C. In these treatment combinations, significant seed deterioration and loss of viability were recorded. Harvest time (i.e., harvest month) within the year also affected the rate of dormancy loss of seeds. March-harvested seeds achieved maximum dormancy loss 3 months earlier than seeds harvested in October.

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Scott B. Lukas, Joseph DeFrank, Orville C. Baldos, and Glenn S. Sakamoto

In Hawaii, seashore dropseed (Sporobolus virginicus), a coastal native grass, has been identified as a useful species for roadside revegetation. Cuttings of seashore dropseed covered with a hydromulch cap, irrigated, and managed to control weeds have greater establishment success. In this study, the efficacy and phytotoxicity of the preemergence herbicide oxadiazon applied as a component of the hydromulch cap over seashore dropseed cut stems was evaluated. Oxadiazon in two formulations, granule and suspension concentrate (SC), was applied at two rates of 2.0 and 4.0 lb/acre, resulting in four chemical treatments. Seashore dropseed response was recorded as numerical counts of new shoots, aboveground biomass, and percent visual coverage. The highest new shoot counts of seashore dropseed, aboveground biomass, and visual canopy coverage were recorded in plots treated with the granular (G) formulation of oxadiazon applied at 2.0 lb/acre. All hydromulch cap treatments containing herbicides reduced weed pressure compared with the untreated control treatment. Granular oxadiazon at 2.0 lb/acre in the hydromulch cap provided commercially acceptable weed control while maintaining high levels of rooting and plant vigor during the establishment period.