Field experiments were conducted to assess the tolerance of seashore dropseed (Sporobolus virginicus) to pre- and postemergence herbicides labeled for roadside right-of-way use. Dithiopyr (0.25 and 0.50 lb/acre a.i.), trifluralin + isoxaben (2.0 + 0.5 and 4.0 + 1.0 lb/acre a.i.), oxyfluorfen (0.25 and 0.50 lb/acre a.i.), oxadiazon (2.0 and 4.0 lb/acre a.i.), and granular table salt (99% sodium chloride, 1% sodium silicoaluminate; 83% of particles 0.5–0.25 mm in diameter, 400 lb/acre a.i.) were applied at 2 and 84 days after transplanting (DAT). Pre-emergence weed control with crop response measures as visual foliar injury ratings and aboveground biomass accumulation were recorded 38 days after the second application of herbicides (DAH2). Crop response to postemergence herbicides aminopyralid (1.10 lb/acre a.i.), triclopyr (3.0 lb/acre a.i.), a prepackaged mix of carfentrazone + (4-chloro-2-methylphenoxy)acetic acid + mecoprop + dicamba (0.02 + 1.11 + 0.22 + 0.11 lb/acre a.i.), and sulfosulfuron (0.06 lb/acre a.i.) applied at 70 and 98 DAT included visual foliar injury ratings and aboveground biomass accumulation at 28 DAH2. Although all pre-emergence herbicides (except table salt) exhibited acceptable weed control ratings, only oxadiazon and oxyfluorfen showed exceptional weed control and safety. The postemergence herbicide sulfosulfuron was the least injurious to seashore dropseed. The mixture of carfentrazone + (4-chloro-2-methylphenoxy)acetic acid + mecoprop + dicamba and triclopyr were the most injurious to seashore dropseed and should only be used as a directed spray treatment. An unintended overapplication of aminopyralid was phytotoxic, but it did not lead to complete plant death at 28 DAH2. These data identified oxadiazon, oxyfluorfen, and sulfosulfuron as safe and effective for establishing transplanted seashore dropseed plugs.
Orville C. Baldos, Joseph DeFrank and Glenn Sakamoto
Orville C. Baldos, Joseph DeFrank and Glenn Sakamoto
Tropical fimbry (Fimbristylis cymosa) is a salt, wind, and drought tolerant sedge under consideration as a native roadside revegetation species in Hawaii. Multiple rate studies were conducted on transplanted tropical fimbry plugs to identify pre- and postemergence herbicides that are safe for selective weed control during plant establishment. The response of newly transplanted tropical fimbry plugs to applications [1 and 44 days after transplanting (DAT)] of oxadiazon (2.0 and 4.0 lb/acre), oryzalin (2.0 and 4.0 lb/acre), and oxadiazon + oryzalin (2.0 + 2.0 and 4.0 + 4.0 lb/acre) were evaluated at 212 DAT through visual vigor ratings and seedhead counts. Response of established transplants to the postemergence broadleaf herbicides, aminopyralid (0.06 and 0.11 lb/acre) sulfosulfuron (0.06 lb/acre), prepackaged mixes of carfentrazone-ethyl + (4-chloro-2-methylphenoxy)acetic acid (MCPA) + mecoprop + dicamba (0.02 + 1.11 + 0.22 + 0.11 lb/acre), and carfentrazone-ethyl + 2,4-D + mecoprop + dicamba (0.02 + 0.77 + 0.24 + 0.07 lb/acre) were evaluated through visual vigor ratings 35 days after spraying (DAS). Results of the preemergence study indicate that low rates of oxadiazon and oryzalin provided an acceptable level of growth suppression to the sedge (>60% visual vigor). Postemergence applications of the prepackaged formulations of carfentrazone-ethyl resulted in moderate to high foliar injury (46% to 74%) and plant mortality (17% to 23%). Plants treated with sulfosulfuron showed signs of stunting (visual vigor of 36%), but exhibited the least foliar injury (16%) and no mortality. Plants treated with high and low recommended rates of aminopyralid exhibited very low injury ratings (1% to 2%) at 35 DAS. Results obtained from these preliminary studies identified oxadiazon, oryzalin, and aminopyralid as potentially safe for controlling weed species in transplanted tropical fimbry.
Scott B. Lukas, Joseph DeFrank and Orville C. Baldos
In Hawaii, Waltheria indica (uhaloa) has been identified for expanded usage as a roadside groundcover in lowland dry ecosystems. Seed dormancy through lack of germination of viable seeds was identified in uhaloa. The presence of physical dormancy in uhaloa seeds was determined and dormancy relief methods were evaluated including hand scarification, dry heat temperature exposure, hot water exposure, and mechanical abrasion in an electric drum scarifier. As a compliment to dormancy relief, long-term storage parameters were evaluated for scarified and nonscarified seeds. The elucidation of physical dormancy was determined through hand scarification, resulting in 96% germination compared with 8% of nonscarified seeds, but is not practical on a large-scale basis. The greatest practical dormancy relief was achieved with a mechanical electric drum scarifier lined with 80-grit sandpaper for a duration of 15 or 30 seconds producing 95% and 99% germination, respectively. Seeds immersed in boiling water for 3 and 5 seconds resulted in 58.6% and 57.7% germination, respectively. Dormancy relief through dry heat exposure was inferior to other relief methods, producing 39% germination at 75 °C for 60 minutes. Nonscarified seeds exhibited minimal loss of viability during 10 months of storage at 5 °C at 12% and 50% relative humidity (RH), but a significant decline in viability of scarified seeds was detected.
Scott B. Lukas, Joseph DeFrank, Orville C. Baldos and Ruijun Qin
Seed dormancy is an evolutionary adaptation for increasing seedling survival by delaying germination and is found in many families of seed plants. Although dormancy is ecologically important, it becomes problematic during agronomic production and restoration. Torrid panicgrass (Panicum torridum) is a native Hawaiian annual grass that has been identified as a re-vegetation candidate for seasonally dry areas. Torrid panicgrass seed appears to possess a nondeep to intermediate physiological dormancy. This research aimed to characterize dormancy relief parameters by 1) evaluating exogenous hormonal, reactive oxygen intermediates, and simulated combustion product treatments; and 2) determining optimized storage conditions of relative humidity (RH) and temperature over a 10-month duration. Results indicate that all exogenous chemical treatments tested were not effective at relieving the dormancy present in torrid panicgrass. Optimal storage conditions to relieve dormancy were found with seeds equilibrated to 12% RH, stored at 30 °C for a period of 8 months resulting in 55% germination. Maintenance of viability for long-term storage up to 10 months was best achieved with seeds stored at 12% RH at 10, 20, or 30 °C.
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.
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.
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.