Nursery container preemergence herbicides must be applied multiple times, usually every 6 to 8 wk, in order to maintain acceptable weed control. Nursery growers have identified extended duration of container preemergence activity as a research priority for reduction of herbicide usage and costs. The objective of this study was to determine if the combination of slow-release (microencapsulated [ME]) formulations of alachlor and acetochlor with wood-based organic mulches could provide extended efficacy and reduced phytotoxicity vs. over-the-top (OTT) sprays or mulch alone. Efficacy and phytotoxicity studies were conducted over 3 yr with various plants. Both acetochlor formulation OTT sprays reduced spirea shoot dry weights at 45 and 110 days after treatment (DAT) compared with the controls, and emulsifiable concentrate (EC) acetochlor OTT spray also reduced shoot dry weights of rose. No herbicide-treated bark mulch (TBM) combination reduced rose or spirea shoot dry weights. EC acetochlor + hardwood (in 2003) was the only treatment to provide 100% weed control at 45 and 110 DAT. The addition of EC or ME acetochlor to mulch reduced phytotoxicity and extended efficacy in 2002 and 2003; alachlor EC or ME TBM did not. Regardless of bark type, 3-yr average EC and ME TBM were 80% more effective than untreated bark mulch (UBM) and 83% and 98% more effective at 45 and 110 DAT, respectively than their comparable OTT sprays. Of the eight treatments that received ratings above commercially acceptable, averaged over dates and years, the three providing the least phytotoxicity and greatest extent, consistency, and duration of efficacy were all TBM combinations: EC acetochlor + Douglas fir or hardwood bark, EC acetochlor + pine, and ME acetochlor + pine. TBM-reduced phytotoxicity compared with OTT sprays.

Brachypodium sylvaticum, a shade-tolerant, forest dwelling, and aggressive invasive grass native to Eurasia, is a noxious weed in California, Oregon, and Washington. This species could cause ecosystem collapse by altering forest fire regimes. To examine interactions with fire, we divided two Willamette National Forest sites into eight units and randomly selected half for treatment with prescribed fire in spring 2011. We assessed the effect of B. sylvaticum on fire (severity and intensity) as well as the effect of fire on B. sylvaticum (cover, seedling emergence, and dispersal). We found that B. sylvaticum cover decreased fire severity but had no effect on intensity. Furthermore, fire severity influenced B. sylvaticum cover; in areas receiving low-severity fire, the grass increased from 21 ± 15.05 to 34 ± 15.81%, but in areas of high-severity fire, cover remained consistently around 0% (0 ± 0% cover in yr 1 to 0.2 5± 0.25% in yr 3). In the field, prescribed fire decreased seedling emergence by 32% compared to controls, but not in an associated greenhouse experiment. However, in the greenhouse, severely burned plots had zero emergence, compared to 0.29 ± 0.14 seedlings low-severity m−2 plot. Fire severity also influenced dispersal in the field; we monitored plots with < 0.5% cover B. sylvaticum initially; when these plots experienced low severity fire, they had greater B. sylvaticum cover (increasing 1,200%), suggesting increased dispersal with less severe fires. High-severity dispersal plots did not experience increased cover. High severity fires have the potential to control the grass, but low-severity fires will likely increase its cover.

Seeds of Douglas fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco) were initially germinated at six constant temperatures (10–35°C), following 0–48 weeks incubation under moist conditions at 4°C, i.e. prechill or stratification. The best, single germination temperature was 15°C for determining the efficacy of subsequent dormancy breakage treatments. Seeds from the same seedlot were then adjusted to 10, 15, 20, 25, 30, 35 and 40% moisture contents (mcfw, fresh weight basis), prechilled for 0, 2, 4, 8, 16, 32, 64 and 128 weeks and transferred to 15°C. A smoothed bivariate spline was used to model the results and showed that virtually all combinations of moisture content and prechill duration significantly stimulated germination capacity, but that the optimal germination percentage (≥93%) was stimulated only by various combinations of between 30 and 35% mcfw and 25 and 48 weeks prechill. At optimal moisture contents (30 and 35%) , extending the prechill duration beyond 48 weeks led to a decrease in germination capacity. This was not due to dormancy reintroduction, but was caused largely by seed death. Regression models using a weighting function, to account for differences in standard deviations, demonstrated significant increases in the mean moisture content of individual seeds at higher moisture contents (≥25%) and longer prechill durations (≥64 weeks) that were concomitant with significant decreases in dry weight. The most likely explanation for this was seed respiration. The combined results suggest that dormancy breakage in Douglas fir seeds requires a hydration level sufficient for respiration to take place, and that, after maximal dormancy release, seeds at the highest mc (35–40%) exhaust their food reserves and begin to deteriorate.