In 1962, Silent Spring, written by Rachel Carson, was published highlighting the harm caused by the insecticide DDT to environmental and human health. Its publication led to widespread social concern regarding the unregulated use of herbicides, pesticides, and other chemicals for treating plants, crops, and pests. Thirty-four years later, the U.S. federal government passed the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), requiring all pesticides distributed and sold in the United States to be licensed by the EPA. As part of that licensing, it must be clear that the chemical “will not generally cause unreasonable adverse effects on the environment.” Those adverse effects include not just acute chemical effects, but lasting chronic effects from pesticide residuals. Since then, a number of other laws have passed pertaining to pesticide regulation and control, such as the Food Quality Protection Act.

All these activities point toward the current societal trend to question chemical use, and have concern over chemical effects. Indeed, such concern is warranted, for improper chemical use can lead to a myriad of environmental and human health concerns. Issues such as water pollution, soil leaching, groundwater contamination, and wildlife injury are consequences of improper pesticide use. These problems can persist for years past the initial chemical treatment. 

However, pesticides (which is a catch-all term for all types of chemicals from herbicides (plant-targeting) to insecticides (insect-targeting)) are an important tool for land management, vegetation removal, and habitat restoration. In fact, herbicides are one of the most effective tools we utilize for habitat management and land restoration. They can be useful in many parts of the restoration process, from site preparation to invasive species removal to native plant establishment and seedling release. The effectiveness of a restoration activity is often increased, while the cost is decreased, by using herbicide. 

So how do we handle this double-edged sword of pesticide use as both restoration ecologists and environmental stewards? Does the benefit of using herbicides in habitat restoration outweigh the possible adverse environmental effects? 

This is a complicated question, but one we encounter and must deal with every day. It’s also a question that any land or habitat manager must contend with when considering their management techniques. Therefore, this blog will focus on the ways NRP approaches pesticides, and how we incorporate safe herbicide use into our Light on the Land approach to land management and restoration. 

Choosing Your Herbicide

Safe herbicide use for the environment begins before you even get to the site to start treatment—it begins with choosing the correct herbicide formulation. This step is one of the most important ways of implementing safe herbicide use. To do this, we have two main considerations: what are we treating, and where are we treating it. Most herbicides are selective, meaning they only target certain plant types. If we are treating buckthorn, we will select an herbicide that specifically targets woody vegetation. This allows us to minimize kill to non-target species that don’t share the same characteristics as our target species. 

Secondly, we must consider where on the landscape we are applying the herbicide. If the area is near water, or if there is standing water on the site, we will select an herbicide specifically intended for aquatic use. Not only is this the law, but it helps protect water resources by using herbicide mixes that are specifically designed to break down in water without harming aquatic plants and animals. 

Finally, as part of this step, we consider alternatives to herbicide use. Depending on the project, there may be multiple alternatives to using herbicides, such as forestry mowing, prescribed burning, or mechanical removal. Utilizing any of these methods may eliminate the need for herbicides altogether. Additionally, we occasionally use an organic or non-synthetic chemical-based herbicide, though caution must be used with these herbicides, as some can still have adverse environmental effects.  

Application Methods

How you apply herbicide, and how much you apply is the second step to our safe herbicide practice. The greatest risk to the environment comes when you are out in the field, mixing and applying the herbicide directly. Therefore, there are a number of methods we utilize during our application to minimize risk to our crews and the environment. 

First, the majority of our herbicide mixes are low-concentration mixes. This means that only a small percentage of the total mix is the actual active chemical. For instance, in a standard mix, we typically only have 5% or less active ingredient. That’s a relatively low concentration, and some of our concentrations are even lower. We take care to ensure we are using the minimum concentration necessary to achieve the project goals. 

Secondly, we have a wide range of application techniques we utilize to decrease the amount of herbicide we apply:

• Stump Treatment: This technique uses a finite amount of herbicide that is applied around the outer rings of a recently cut stump. It uses a wick applicator which is one of the best types of applicators for preventing herbicide spread to non-target species. With this method, the only plant affected is the stump that is treated, and there is almost no risk of herbicide leaching into the water or soil.

• Spot Spray: This technique involves the application of herbicide to the leaves of specific plants. This is one of the most common methods we use. Instead of spraying an entire area with a large boom sprayer or high-pressure gun, we use backpack sprayers to hand spray individuals of the target species. There is a small chance of herbicide drift, but the risk is much lower due to the selective nature of picking out specific plant individuals.

• Basal Bark: This technique requires painting the herbicide onto the outer layers of bark of the target species. Similar to stump treating, basal barking uses a wick applicator and only targets individual plants with little risk to non-target plants. It is more time intensive, and requires a higher herbicide concentration, but is good for minimizing risk to neighboring plants, soil, and water resources.

Best Practices

To round out this discussion, there are a few best practices that we follow to further ensure our herbicide use follows our Light on the Land ethic. If you are considering herbicide use for your land project, we encourage you to consider some of these best practices as well. 

• Adjuvants: These are mixtures added to an herbicide mix. While they have no active ingredient affect, they can influence an herbicide’s effectiveness. We typically use adjuvants that help the herbicide stick to the leaf or wood surface better. The longer the herbicide sticks to the target plant, the more likely the herbicide will be absorbed into the plant instead of washing off into the environment.

• Weather: The weather conditions the day of application are arguable the most influential factor on if that herbicide gets into the environment. Herbicide drift refers to the movement of herbicide away from the intended target. This often occurs as a result of wind or rain. Sprayed herbicide can be blown by the wind away from the target area, and rain water can wash herbicide off target species into the ground. Therefore, we monitor wind speeds and adjust equipment calibration and application timing if necessary to limit drift, and we avoid spraying during super windy days. Additionally, we try to predict precipitation events, and avoid herbicide application in the few hours before and after a rain event. 

• Bee Mindful: Pollinator populations in Minnesota are declining. Herbicides can have multiple detrimental affects on pollinators, so understanding how to avoid impacting pollinators is an important part of safe herbicide use. Avoid spraying in areas designated as pollinator habitat, and avoid spraying in the middle of the day when pollinators are most active. Also, we are mindful of only treating target species, leaving the quality native flowers for the pollinators. 

• Low Hazard Herbicides: Pesticides are separated into four categories of signal words. These signal words indicate the relative toxicity of the pesticide to human and environmental health. The highest level of signal word—Danger, Poison—indicates the highest relative toxicity. Following, in order of most toxic to least, are the signal words, Danger, Warning, and Caution. The majority of the herbicides we use are only at the Caution level, the lowest toxicity level. Sticking to pesticides marked at the lower levels of this scale is a good step in keeping highly toxic herbicides out of the environment.

• Alternatives to Herbicide: We mentioned this one already, but it is an important one! We are always willing to discuss ways of completing projects without herbicide use. Good ecological restoration involves finding the balance between effective restoration activities and non-intensive restoration activities. If we can find that balance without involving herbicides, we will.