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Ecologists have explored community assembly through the framework of ecological filters, which predicts that species must overcome a series of challenges (i.e. pass through "filters") to successfully establish in a given community. In the context of restoration, these filters (dispersal, abiotic, and biotic) can be manipulated to alter the resulting plant community by favoring native species or disadvantaging non‐native invasive species. We conducted two studies manipulating assembly filters at two California grassland sites previously dominated by non‐native species. At Site 1, we explored how variations in sequential seeding of native grasses and forbs (to overcome dispersal and biotic filters caused by priority effects) influenced the resulting community. At Site 2, we explored how thatch removal (to overcome the abiotic filter of light limitation) and herbicide‐based weed control (to overcome the biotic filter of competition from non‐native species) influenced the addition of native forbs into a partially restored grassland. Native forbs at Site 1 did not suffer from arriving after grasses, but native grasses benefited when given 1 year priority over forbs. At Site 2, dethatching increased native forb cover in a high rainfall year. Herbicide application reduced non‐native grass cover in dethatched plots without negatively affecting native cover. Native forb and grass cover were significant predictors of non‐native grass cover. However, they accounted for only 29% of the variation observed, suggesting there are other influential factors not considered in this study. Our results suggest that forbs can be incorporated into established native grasslands more successfully after dethatching. [ABSTRACT FROM AUTHOR]

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The invasive Oomycete pathogen Phytophthora ramorum has killed millions of susceptible oak and tanoak trees in California and southern Oregon forests and is responsible for losses in revenue to the nursery industry through mitigation activities. In addition, infestation of forests in the United Kingdom by this organism has resulted in the destruction of many hectares of larch plantations. Resprouting stumps can be a reservoir for the inoculum of P. ramorum persisting on a site. In areas where the application of herbicides is not permitted, a biocontrol treatment would be an indispensable alternative. Treatment of stumps with the sap-rotting fungus Chondrostereum purpureum (Pers.) Pouzar has been shown to be an effective tool for the suppression of resprouting on several species, most notably red alder. In this project, the ability of C. purpureum to suppress resprouting was evaluated on stumps of two host species, tanoak (Notholithocarpus densiflorus) and California bay laurel (Umbellularia californica). Laboratory testing of three California isolates of C. purpureum indicated that the fungus can colonize bay laurel stems. Field trials were established near Brookings, Oregon, on tanoak and on bay laurel near Soquel, California. Early results of field testing showed that C. purpureum was able to colonize the stumps of tanoak following treatment and was found to occur naturally on tanoak logs and stumps. Formulations of C. purpureum appear to have some effect on reducing sprout survival in tanoak, but the most effective and rapid treatment for this host is the hack and squirt method of applying the herbicide imazapyr. Sprayed herbicide prevents sprouting on bay laurel, and there was evidence that resprouting was inhibited on stumps treated with C. purpureum. Over time, applications of C. purpureum may be a more permanent solution as the stumps begin to decay. [ABSTRACT FROM AUTHOR]

Processing-tomato (Lycopersicon esculentum L.) cultivation in California has transitioned to the use of transplants, subsurface drip irrigation (SDI), and shallow tillage from direct-seeded, flood-irrigated, deep-tillage systems. Observation of stunted tomato plants in fields treated with preplant herbicides suggests that the herbicides may not be disintegrating as rapidly in the newer system. Greenhouse studies were conducted to assess plant response to trifluralin, S-metolachlor, and pendimethalin at soil-residue levels of 0, 0.03, 0.06, 0.12, 0.25, and 0.5 ppm (0, 0.03, 0.06, 0.12, 0.25, and 0.5 mg l-1, respectively; 1 ppm = 1 mg l-1). Plants grown for 45 days after transplanting showed that all three herbicides at levels as low as 0.03 ppm (0.03 mg l-1) reduced shoot and root growth. Therefore, appropriate methods need to be developed to reduce soil carryover effects of these herbicides in tomatoes grown with SDI system. All herbicides resulted in some reduction in shoot and root biomass of the tomato plants at the higher doses (>0.12 ppm) compared to the non-treated plants. Both S-metolachlor and trifluralin caused significant reductions in shoot and root biomass at 0.5 ppm and the potential of the plants to recover from herbicide injury is unknown. Pendimethalin had a lower potential to cause injury than the other two herbicides. Although the effect of shoot and root biomass reduction on fruit yield and quality was not recorded, this study suggests that preplanting soil tests and appropriate management to reduce soil carryover of these herbicides may be necessary in processing tomatoes grown with SDI. [ABSTRACT FROM AUTHOR]

Herbicides have recently been designated as one of the most frequently detected chemical types in aquatic systems. We evaluated the effect of the herbicide formulations Clearcast® (active ingredient imazamox) and Galleon® SC (active ingredient penoxsulam), in conjunction with the adjuvant Agri‐dex®, on the diatom Thalassiosira pseudonana and the copepod Eurytemora affinis and whether their application in invasive aquatic weed control has acutely negative effects on important delta food web species. Herbicide–adjuvant mixtures were more toxic than herbicide formulations alone. For the diatom, 50% inhibition concentration (IC50) were 84.4 mg/L for Clearcast, >100 mg/L for Galleon SC, and 38.5 mg/L for Agri‐dex. In the herbicide mixture diatom tests, IC50s decreased to 2.8 mg/L for Clearcast + 64 mg/L Agri‐dex and to 6.6 mg/L for Galleon SC + 41 mg/L Agri‐dex. In the copepod tests, 50% effect concentrations (EC50s) were 45.4 mg/L for Agri‐dex, 31.2 mg/L for Galleon SC, and >100 mg/L for Clearcast. When tested together, EC50s were reduced to 24.1 for Galleon SC and 67.6 mg/L for Clearcast in the presence of 50 mg/L Agri‐dex. Environmentally relevant herbicide–adjuvant mixture ratios were at the no‐observed‐effect level. Mixture interactions between herbicides and adjuvants indicate the potential for increased toxicity in herbicide formulations and tank mixes, especially in consideration of the unlisted, proprietary ingredients which are included in herbicide formulations, making predicting nontarget effects challenging. Environ Toxicol Chem 2020;39:1375–1381. © 2020 SETAC [ABSTRACT FROM AUTHOR]

Chemical control of unwanted trees can be a cost-efficient tool for forest management and restoration. In California, United States, the response of merchantable conifers to hardwood control is poorly understood. We studied the tree growth of coast redwood (Sequoia sempervirens (Lamb. ex D. Don) Endl.) following herbicide frill treatment of competing tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, C.H. Cannon, & S. Oh), coinciding with a partial harvest of conifers. The radial growth of 420 redwoods in 45 plots was measured using increment cores. With or without partial harvesting, herbicide treatment of tanoak enhanced growth of most redwoods: 23% of redwoods in herbicide-only plots and 34% of redwoods in herbicide + harvest plots had ≥100% higher posttreatment basal area increment (BAI). In untreated plots, 67% of redwoods displayed declining BAI. The response of redwoods (the ratio of 8-year postharvest BAI to 8-year preharvest BAI) was 59% higher in herbicide-only plots and 108% higher in herbicide + harvest plots compared with untreated control plots over the same period. Redwoods with long crowns maintained rapid growth with or without treatment. Trees growing slowly before treatment exhibited the greatest response, provided that they had relatively long crowns and were not left in suppressed crown positions. Forest managers implementing partial harvesting and (or) chemical control of hardwoods can expect to maintain or promote rapid growth of most residual redwoods. [ABSTRACT FROM AUTHOR]

Every batch of cannabis sold legally in California must be tested for more than 100 contaminants. These contaminants include 66 pesticides, for 21 of which the state's tolerance is zero. For many other substances, tolerance levels are much lower than those allowed for food products in California. This article reviews the state's testing regulations in context, including maximum allowable tolerance levels -- and uses primary data collected from California's major cannabis testing laboratories and several cannabis testing equipment manufacturers, as well as a variety of expert opinions, to estimate the cost per pound of testing under the state's framework. We also estimate the cost of collecting samples, which depends on the distance between cannabis distributors and laboratories. We find that, if a batch fails mandatory tests, the value of cannabis that must be destroyed accounts for a large share of total testing costs -- more than the cost of the tests that laboratories perform. Findings from this article will help readers understand the effects of California's testing regime on the price of legal cannabis in the state -- and understand how testing may add value to products that have passed a series of tests that aim to validate their safety. [ABSTRACT FROM AUTHOR]

The article presents a study on the residues of herbicides specifically glyphosate, triclopyr, and hexazinone in thirteen plant species in the areas of Eldorado, Lassen, Stanislus, and Sierra National Forests in California. The study was conducted to monitor plants that have potential exposures to herbicides in order to avoid Native Americans from collecting the said plant materials. The method of the study was carried out through collective sample of plant species and parts for discussion with Native Americans and site observation, and analytical method of the herbicides. The study reveals that 45 of 92 samples collected from inside treatment contained detectable residues of herbicides while 4 of 119 samples collected outside the treatment areas.