Insecticide in pollinator garden - Ask Extension
Onslaught Fastcap was sprayed on my butterfly garden, do I need to cut down host plants? Will flowers that had not emerged before spraying still be po...
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Insecticide in pollinator garden #874884
Asked June 26, 2024, 9:18 PM EDT
Onslaught Fastcap was sprayed on my butterfly garden, do I need to cut down host plants? Will flowers that had not emerged before spraying still be pollinator safe? And is there anything I can do to help eliminate the insecticide from the plant?
Carroll County Maryland
Expert Response
There is unfortunately no way to flush-out a pesticide application made to the wrong plant, at least if it was applied to foliage and absorbed. Residues might dilute enough if rinsed off, but it really depends on the pesticide formulation; some are more "rain-fast" than others. The label we looked up for this product (which might differ from the one used, so you can ask the pesticide applicator for a copy for comparison) says it uses several active ingredients: esfenvalerate, prallethrin, and piperonyl butoxide.
Esfenvalerate belongs to a chemical class called pyrethroids, and they are broad-spectrum in action, meaning that they can affect a wide variety of insect types, unlike more selective ingredients. All pyrethroids would pose a risk to beneficial insects, as their residues are designed to last longer than their natural counterparts (pyrethrins) in order to maintain control of a pest for longer periods. Therefore, if residues are suspected of coating pollinator or host plants, it might be best to try to exclude pollinators from visiting them until a treatment wears off.
You may need to ask the manufacturer how long that period may be in the kind of weather Maryland experiences this time of year. One reference that we found, though from California, suggests that the half-life of the resides (how long it takes for half of the substance to break down) when exposed to direct sunlight may be just over 2 weeks. Other information in the same publication suggests that certain residues (possibly a breakdown byproduct) might remain on or in treated foliage for around two months, but this might be highly dependent on dosage applied and type of plant. (The example given in the publication was bean plant foliage.) With very low water solubility, it is not readily absorbed by plant roots if it winds-up contaminating soil.
Prallethrin is also a pyrethroid, and while we cannot find a reference providing similar information to esfenvalerate, we think it can be presumed to be of similar risk.
Piperonyl butoxide (PBO) is a synergist chemical, which isn't an insecticide by itself, but a substance that helps the other active ingredients function, in this case by helping the other chemicals resist degradation in insect digestive systems, giving them time to work more effectively. It is often combined with pyrethroids. By itself, it probably doesn't impact pollinators much, but as the synergist, it could increase the risk of exposure and harm to insects visiting surfaces treated with the pyrethroids.
Since there is very little (if any) systemic activity for the ingredients above, flowers forming later are probably going to be safe for pollinator visits. The same is true for host plant foliage that emerges after the spray, since it was not directly coated in insecticide. Existing host plant foliage, though, might remain contaminated for some time, though we can't say for certain exactly how long. The benefits and risks of pruning off sprayed foliage will depend partly on the overall health and age of the plant, as well as the species of plant.
Well-established herbaceous perennials could probably handle a cut-back reasonably well, though if they are late-blooming species, they might not flower as abundantly (or on time) this coming summer/fall since they'll have a lot of regrowth to generate. Younger plants might not recover as quickly from a drastic pruning. If practical, you might be able to net the plants instead, letting them keep photosynthesizing and growing, storing energy, while denying pollinators and egg-laying butterflies/moths access for the time being. Insect mesh netting still lets in most of the sunlight and permits decent airflow.
If a professional pesticide applicator made this application by mistake (the wrong product or the wrong property), you could report the incident to the Maryland Department of Agriculture's Pesticide Regulation section, the agency that regulates certified pesticide applicators.
Miri
Esfenvalerate belongs to a chemical class called pyrethroids, and they are broad-spectrum in action, meaning that they can affect a wide variety of insect types, unlike more selective ingredients. All pyrethroids would pose a risk to beneficial insects, as their residues are designed to last longer than their natural counterparts (pyrethrins) in order to maintain control of a pest for longer periods. Therefore, if residues are suspected of coating pollinator or host plants, it might be best to try to exclude pollinators from visiting them until a treatment wears off.
You may need to ask the manufacturer how long that period may be in the kind of weather Maryland experiences this time of year. One reference that we found, though from California, suggests that the half-life of the resides (how long it takes for half of the substance to break down) when exposed to direct sunlight may be just over 2 weeks. Other information in the same publication suggests that certain residues (possibly a breakdown byproduct) might remain on or in treated foliage for around two months, but this might be highly dependent on dosage applied and type of plant. (The example given in the publication was bean plant foliage.) With very low water solubility, it is not readily absorbed by plant roots if it winds-up contaminating soil.
Prallethrin is also a pyrethroid, and while we cannot find a reference providing similar information to esfenvalerate, we think it can be presumed to be of similar risk.
Piperonyl butoxide (PBO) is a synergist chemical, which isn't an insecticide by itself, but a substance that helps the other active ingredients function, in this case by helping the other chemicals resist degradation in insect digestive systems, giving them time to work more effectively. It is often combined with pyrethroids. By itself, it probably doesn't impact pollinators much, but as the synergist, it could increase the risk of exposure and harm to insects visiting surfaces treated with the pyrethroids.
Since there is very little (if any) systemic activity for the ingredients above, flowers forming later are probably going to be safe for pollinator visits. The same is true for host plant foliage that emerges after the spray, since it was not directly coated in insecticide. Existing host plant foliage, though, might remain contaminated for some time, though we can't say for certain exactly how long. The benefits and risks of pruning off sprayed foliage will depend partly on the overall health and age of the plant, as well as the species of plant.
Well-established herbaceous perennials could probably handle a cut-back reasonably well, though if they are late-blooming species, they might not flower as abundantly (or on time) this coming summer/fall since they'll have a lot of regrowth to generate. Younger plants might not recover as quickly from a drastic pruning. If practical, you might be able to net the plants instead, letting them keep photosynthesizing and growing, storing energy, while denying pollinators and egg-laying butterflies/moths access for the time being. Insect mesh netting still lets in most of the sunlight and permits decent airflow.
If a professional pesticide applicator made this application by mistake (the wrong product or the wrong property), you could report the incident to the Maryland Department of Agriculture's Pesticide Regulation section, the agency that regulates certified pesticide applicators.
Miri
