Article Citation: Hancock, J., Bischof, M., Coffey, T. and M. Drennan. 2019. The effectiveness of riparian hedgerows at intercepting drift from aerial pesticide application. Journal of Environmental Quality, 48: 1481-1488. doi:10.2134/jeq2018.12.0447
Sometimes actions can have unintended consequences. You go into a situation looking to solve one problem, only to create another new problem with your solution. Unfortunately, this is a common story that plays out when humans try to solve environmental issues.
One example of this story is the use of pesticides. Pests plague several foods as farmers try to grow them. Pesticides can help kill off these pesky organisms; however, they can also harm other plants and wildlife nearby.
In northwest Washington State, blueberries are now facing a new foe – Spotted wing Drosophila. This insect is an invasive species that arrived in the U.S. from Asia in 2011. If left unchecked, it can wreak havoc on crops and destroy up to 80% of a crop yield. One solution to fighting this pest is to spray applications of a pesticide called malathion from the air. However, malathion has been shown to produce toxic effects in some fish as well as other aquatic organisms.
Does Vegetation Help?
Researchers wanted to understand if having woody vegetation (large shrubs and trees) as a buffer between agricultural fields and streams could reduce malathion entering the streams where it could have a negative effect on aquatic life.
Researchers studied five different blueberry farms – three of which had woody vegetation between the field and nearby stream, and two of which did not – all in the same County of Washington State. At each of these sites, the scientists measured several characteristics about the streams, vegetation and weather throughout the study period. Sample collectors were also set up at the edge of the agricultural fields, each side of the vegetation, and in the middle of the stream themselves to measure the concentration of malathion in each spot. They took samples at all five farms after eight different applications of malathion.
With the information collected on the different stream and vegetation metrics, researchers used mathematical modeling to determine which of these had the greatest influence on malathion concentrations at the sample points.
Vegetation Helps…To a Point
At the sites that had woody vegetation, researchers found 96% less malathion on average in the stream itself than at sites that had no woody vegetation at all – highlighting that something about woody vegetation can help reduce this pesticide in streams.
Based on their mathematical modeling, researchers found six different variables that influenced the concentration of malathion in the stream itself. Of those six variables, they noted two were the most feasible for farmers to modify: 1) bank canopy cover (the area along the stream covered by woody vegetation) and 2) the distance between the field and the middle of the stream. Farmers may be able to reduce negative effects of pesticides if they plant more woody vegetation along streams, and move the edge of their field farther away from the stream itself.
But, spraying malathion is not completely in the clear. The study also found that even though sites with woody vegetation reduced the amount of malathion in streams, it is estimated that the average concentrations found at some of the sites could still harm some fish and aquatic organisms such as insects and snails.
Vegetation Can Be a Multitool
Woody vegetation on banks can have multiple positive impacts for a stream ecosystem. For example, it can help prevent erosion and improve habitat. Now, researchers have highlighted that it may also help reduce pesticide runoff. The next steps are to find out whether or not we can optimize this tool to reduce environmental harm while still fighting invasive species that destroy our crops. Increasing woody vegetation on the edges of farm fields seems like an action with no unforeseen consequences, but more research and time will tell if this story will have a different ending.