Consumers want plants with no signs of pest or insect damage. For environmental horticulture growers to meet this demand and produce high quantities of damage-free plants, they find pesticides to be useful and often indispensable tools. Growers use pesticides made from human-designed chemistry, extracts from plants and microbes, and live microbes.

Plant with a few flowers and the leaves barely damaged.
Marigold plant with little damage from thrips.
Plant with a few flowers and the leaves slightly damaged.
Marigold flower with some damage by thrips.

There is concern, however, because certain pesticides can have detrimental effects on bees. Neonicotinoids in particular are a common pesticide class known for having low toxicity to humans yet highly effective in managing insects. They have come under scrutiny because they are widely used and travel through plant tissue, eventually reaching a plant’s pollen and nectar—the plant products most used by bees.

Environmental horticulture growers are aware of the growing concern and want to ensure their practices minimize the risks for bees and the environment, but they face some key issues: scant data on pollen and nectar residue levels in environmental horticulture plants, the complex interactions between plants and pesticides, and little information on alternatives to neonicotinoids.

Little data on pesticide residue in pollen and nectar for environmental horticulture plants

The first issue is that few studies have examined pesticide residue levels in the pollen and nectar of environmental horticulture plants.

Although plenty of studies have examined pesticide residue levels in pollen and nectar, the vast majority of these studies have been conducted on agricultural plants. In addition, the studies that have been conducted on environmental horticulture plants did not measure residue levels in the plant’s pollen and nectar. Instead, they measured residues levels in the entire flower. Residue data from entire flowers are not appropriate for assessing the risks posed to pollinators, since residue can be present in flower petals yet not in pollen or nectar.

The lack of appropriate data for environmental horticulture plants makes it challenging for growers to determine whether their pesticide applications pose risks to pollinators.

Complex interactions between pesticides and plants

The second issue is that many types of chemically or biologically-derived pesticides exist, and each product has different properties affecting how it travels through a plant. This means that even when we understand how one pesticide interacts with a plant, we cannot generalize to how other pesticides interact with the same or other plants.

All pesticides—whether derived from human-designed chemistry, extracts from plants and microbes, or live microbes—are intended to manage pests, but like how different medicines target different types of molecules, each pesticide product has a unique molecular structure that underlies its interactions with a targeted plant or insect. Such differences mean that knowing the rate at which one pesticide travels to a plant’s nectar or pollen does not correlate to how another pesticide travels to the same or a different plant’s nectar or pollen.

To make informed decisions, data are needed for different classes of pesticide, interacting with different types of environmental horticulture plants.

Unclear effects of alternatives to neonicotinoids

The final issue is that if growers are confronted with pest problems and choose to avoid using neonicotinoids, it is difficult to pick from the alternatives types of pesticides available. When considering alternatives to neonicotinoids, a host of potential issues come up for growers: the possibility that alternatives will translate to higher production costs, higher toxicity for other animals or the environment, or that alternatives will be less effective for pest management, which may lead to more frequent applications.

To date, there has been no systematic comparison of the economic, toxicological side-effects, or treatment efficacy of the various available pesticides. In addition there are questions about the impacts to growers’ business models if they switch to non-neonicotinoids pesticides. With such a resource, growers could make more informed decisions on how to manage pests while protecting pollinators.


To address these key issues faced by growers, we developed four research questions revolving around different pesticides and their residues in the pollen and nectar of environmental horticulture plants, efficacy, environmental side-effects, and economic impact on growers.

Research Questions and Plans

Cluster of rhododendron flowers with a pipette tip touching the middle of one flower.
Using a pipette to extract nectar from rhododendron flowers after pesticide treatment.


How much do different classes of pesticides travel into the pollen and nectar of plants?

To understand how pesticides travel through plants with different traits, we are conducting field and greenhouse trials. We are testing how five different pesticides impact different types of plants. Three of these are from the neonicotinoid pesticide class while the other two represent two other classes.

Each plant species is being treated with various classes of pesticides that are applied as both drench (allowing the treatment to soak into the soil) and foliar sprays (spraying the treatment onto the plant). At regular intervals, we are sampling the nectar or pollen of each plant, and analyzing the amount of pesticide residue in all samples.

Researchers: Drs. James Bethke, JC Chong, Richard Cowles, Dave Smitley, Cristi Palmer, Daniel Potter, Nishanth Tharayil

States: CA, CT, KY, MI, NJ, SC


If growers want to use alternatives to neonicotinoids, how effective are alternative pesticides in managing pests?

We are compiling data from existing studies that test how effectively various pesticides manage pests. We are focusing on products that target aphids, fungus gnats, whiteflies, mites, mealybugs, and thrips.

Upon completion, these tables will be compiled into easy-to-use tables and made available on this site, so that environmental horticulture growers can select the appropriate product for their pest problem and situation.

Researchers: Drs. James Bethke, JC Chong, Dave Smitley,  Cristi Palmer, and Dan Gilrein

States: CA, MI, NJ, NY, SC


Which pesticide options have adverse effects on humans, other wildlife, or the environment?

We are compiling data from existing ecotoxicology reports on various pesticides, and incorporating this information into easy-to-use tables that will be made available on this website.

Researchers: Drs. James Bethke, JC Chong, Dave Smitley,  Cristi Palmer, and Dan Gilrein

States: CA, MI, NJ, NY, SC


If growers want to use alternatives to neonicotinoids, how would switching to alternative impact the economics of their business?

We are conducting surveys with environmental horticulture growers to obtain data on growers’ costs and revenue details. This data will be used to calculate differences in projected growers’ financial returns based on a switch to using an alternative pesticide.

We are also conducting online and mail surveys to understand growers’ perceptions of neonicotinoids, their current and projected use of neonicotinoids, and their views on barriers to using alternative pesticides.

Researchers: Dr. Hayk Khachatryan

States: FL

Additional Research Areas

Research Updates

Daylily, petunia, and pansy flowers, with a hosta plant.

As described in a previous post, growers were surveyed about their production costs, their current and projected uses of pesticides, and their perception on neonicotinoids. We have some preliminary results to report, with more forthcoming in future publications. When it comes to growers’ production costs, we found that production costs vary significantly among growers. Differences [...]

Inside a horticultural plant nursery, with various plants being grown on both sides of the aisle.

Concerns over the effects of neonicotinoids on pollinators have prompted suggestions that growers use alternative pest control products. For growers, neonicotinoids are considered very effective in controlling pest and are safe for humans. As a result, neonicotinoids are widely used across the environmental horticulture industry.  It is unclear whether growers think switching to alternative pest [...]

Flowers crowding beds in a greenhouse.

The residue work continues, as our teams are in midst of collecting pollen and/or nectar from snapdragons and rhododendrons. Research teams in California, Connecticut, Kentucky, Michigan, New Jersey, and South Carolina are participating in this residue work, and our analytical lab has been busy processing the pollen and nectar samples for residue levels. Our research [...]

Screenshot of starting page for Ecotox Knowledgebase's website.

When growers experience pest outbreaks and need to decide on a pesticide product that will help, an important consideration is the product’s ecotoxicological profile. Ecotoxicology combines the fields of ecology and toxicology, and is the study of how chemicals affect groups of species and the environment. Before approving a pesticide, the EPA requires data on [...]