Determination of Soil Contamination at the Wildland-Urban Interface after the 2021 Marshall Fire in Colorado, USA.

Wildfires at the wildland-urban interface (WUI) are increasingly common. The impacts of such events are likely distinct from those that occur strictly in wildland areas, as we would expect an elevated likelihood of soil contamination due to the combustion of anthropogenic materials. We evaluated the impacts of a wildfire at the WUI on soil contamination, sampling soils from residential and nonresidential areas located inside and outside the perimeter of the 2021 Marshall Fire in Colorado, USA. We found that fire-affected residential properties had elevated concentrations of some heavy metals (including Zn, Cu, Cr, and Pb), but the concentrations were still below levels of likely concern, and we observed no corresponding increases in concentrations of polycyclic aromatic hydrocarbons (PAHs). The postfire increases in metal concentrations were not generally observed in the nonresidential soils, highlighting the importance of combustion of anthropogenic materials for potential soil contamination from wildfires at the WUI. While soil contamination from the 2021 Marshall Fire was lower than expected, and likely below the threshold of concern for human health, our study highlights some of the challenges that need to be considered when assessing soil contamination after such fires.

Quantification of insecticide spatial distribution within individual citrus trees and efficacy through Asian citrus psyllid reductions under different application methods.

BACKGROUND: Citrus greening disease (Huanglongbing, HLB) has infected >90% of Florida's oranges and thus growers are desperate to improve pest management strategies. In this field study, insecticide application efficacy was investigated with liquid chromatography mass spectrometry to determine if insecticide concentration and distribution were effective at killing the target pest Asian citrus psyllids (ACP). Sample discs attached to leaves were sprayed with imidacloprid and malathion at a field site in Florida. Application method, canopy height and depth, cardinal side of tree, and leaf side were considered to assess the spatial distribution of insecticides throughout citrus trees. Furthermore, ACP were inspected before and after insecticide applications to quantify psyllid population response. RESULTS: Our findings show that although insecticide concentrations were high enough to kill ACP, the spatial distribution of insecticides throughout individual trees was highly variable and live ACP were detected after insecticide application. The top side of leaves received significantly more insecticide than the underside of leaves. Additionally, inadequate distribution to different areas of the tree canopy was observed for all application methods tested (aerial, ground speed-sprayer, and ground side-sprayer). Inspections of ACP populations before and after insecticide applications resulted in reductions of 85% (malathion) and 48-80% (imidacloprid). CONCLUSIONS: The variability in insecticide spatial distribution due to application method allows remaining ACP to continue spreading citrus greening disease to unprotected trees. Further research is needed to improve insecticide application methods and technology for citrus trees in order to implement effective pest management strategies and fully target ACP to eliminate HLB. © 2020 Society of Chemical Industry.