Neonicotinoids have become a hot button issue over the last few years, and many growers are confused about these chemicals.
There are two basic classes for greenhouse and nursery use. The biggest class is the nitroguanidines, which include active ingredients imidacloprid, thiamethoxam, clothianidin and dinotefuran. The “Big Four” have seen usage restrictions, risk assessments from the EPA, and have been the target of consumer protests that triggered bans at several large garden centers due to their potential damage to pollinators. While organizations made up of professional horticulturists, like AmericanHort, Society of American Florists, the Horticultural Research Institute and the American Floral Endowment have continued to cite studies showing that neonicotinoid pesticides, when used as directed, are not the primary cause of bee health issues, growers are left looking for alternatives.
The second class of neonicotinoid pesticides is cyanoguanadines. This class includes acetamiprid, or TriStar. Jill Calabro, research and science programs director for AmericanHort, says acetamiprid is not a nitroguanidine, and that the distinction is quite important.
“It’s very unfortunate when people say that all neonicotinoids are equal in terms of their impact on bees, when they’re not,” she says.
When used at its labeled rates, acetamiprid is much less toxic to bees than other neonicotinoids. It also has been EPA classified as a reduced risk insecticide, is compatible with many fungicides and miticides, and can be used as an effective resistance management tool.
As a class of chemistry all neonics share some common factors. They have a broad spectrum of control, which is very desirable to growers. They have low toxicity to humans, which is also desirable, and they are all systemic. Just how systemic they are can vary greatly from product to product and plant to plant, which can impact the insect spectrum of control and residue.
One thing that has made neonicotinoid insecticides popular in pest control is their water solubility, which allows them to be applied to soil and be taken up by plants. Soil insecticide applications reduce the risks for insecticide drift from the target site, and for at least some beneficial insects on plants. Both cyanoguanadines and nitroguanadines kill insects through the same pathway.
Both classes of neonics use the same mode of action, designated 4A by the Insecticide Resistance Action Committee. So it’s quite important to avoid using them successively. Switching to another insecticide with a different mode of action will minimize resistance problems.
It's important to note how insecticides move, as well. Contact insecticides cover the plant's surface and require the pest to touch the active ingredient. Systemic insecticides move within the entire plant, from the soil up to the new shoots and require the pest to ingest the active ingredient. All neonics offer translaminar activity, which means that the product can move short distances from the upper leaf surface to the lower leaf surface. Acetamiprid has both contact and systemic activity and works well as a foliar spray, which differentiates it from the other neonic insecticides that are primarily drenched.
One major difference between neonicotinoids, even within the class of nitroguanadines, is the speed of uptake. The different products vary greatly in this area. For instance, dinoteferan is much more systemic and water soluble than other active ingredients. As such, it moves much more quickly through the plant. It has a lower ability to bind to organic matter, so it moves into the upper canopy very quickly. Whereas imidacloprid and clothianidin by contrast move more slowly.
“If you think about longevity of control, products that are more water soluble and faster-absorbed, like dinotefuran, tend to have a shorter residual than products that are less water soluble and have slower uptake, like imidacloprid and clothianidin," Calabro says. “Products with slow uptake are present longer in the plant.”
However, there are instances in which growers would prefer prefer a fast moving insecticide. For instance, if there is already an infestation in place, or an introduced pest, or if they have missed their application window with the slower-moving imidacloprid. In these situations, a foliar spray like acetamiprid or a fast-moving drench like dinotefuran may be a good option.