Hello Ann,

In order to determine how the chemicals work, we'd need to know exactly what products were used (the active ingredients at a minimum, or the entire product name). The applicator should be able to give anyone asking for it a copy of the pesticide label, which will include that information. Some ingredients break down very quickly in rain, sunlight, or microbial activity after a brief period of time. Others last longer.

Any applicator who misapplies a pesticide (either the wrong chemical, in an unsafe way, or on the wrong property) can be reported to the Maryland Department of Agriculture's Pesticide Regulation Section, as they certify and regulate pesticide applicator licenses. They should not be spraying a property they were not hired to spray, and the MDA takes violations seriously.

When you mention milkweed "pods," are you talking about seed pods, or flower buds? Seed pods are not likely to risk much insect impact if they were accidentally sprayed, since not much feeds on the seeds, but flower buds might if the residues persist until the flowers open. If you aren't certain, feel free to send us a photo of the stage of growth they are in right now.

Although we realize you might not be able to convince your neighbor to stop spraying regardless, we do not recommend yard sprays to combat mosquitoes. They are not as effective as eliminating (or treating with low-toxicity, targeted pesticides) breeding sites, and as you note, they residues risk harming other organisms, including pollinators or beneficial insects. Our Controlling Mosquitoes web page has more information.

Miri

Hello Ann,

Thank you for the photos and additional information. The milkweed pictured is Common Milkweed (botanical name Asclepias syriaca), and it is aptly named as a very common species among the several milkweed species that grow in Maryland. It is also the most aggressive, spreading eagerly from root runners and sometimes hard to contain in a garden bed. The daylily pictured is hard to ID (as many varieties of them can be orange), but it might be Hemerocallis fulva, the particular species that escapes cultivation and seeds into natural areas, acting as an invasive species. If it is that species, it would ideal to either remove and replace it, or at least dead-head it so no flowers that were pollinated develop seeds.

A safety data sheet (SDS) is not the same as the product label, but we can use the product name on it to look that up. (It might not be the exact label version as was on the product the sprayer used, but it's the closest we can come.) The active ingredients in it appear to be bifenthrin, novaluron, and pyriproxyfen.

Bifenthrin is a pyrethroid, which are synthetic versions of the organic insecticide pyrethrum/pyrethrin, derived from a certain plant extract. Pyrethroids were developed to have longer persistence (how long the residues remain effective) in order to provide a longer period of pest control or to withstand some weathering (rain, resisting degradation in sunlight, etc.). This trait makes them pose a potentially greater risk to other organisms since the application does not degrade as quickly as the organic version could. Pyrethroids are broad-spectrum pesticides, which means they have the potential to affect a wide range of insects that the residues come into contact with.

Novaluron is an insect growth regulator (IGR), which is a type of chemical that disrupts the normal growth and development of juvenile insects. In this case, it does this by inhibiting the formation of the key component in insect exoskeletons. In products containing only this ingredient, it is listed as a larvicide (kills mosquito larvae), and directed to be applied to sources of water where mosquito larvae are found. We do not see any indication that the chemical is at all mosquito- or fly-specific, though to be fair, very few insecticides would be.

Pyriproxyfen is also an IGR, though in this case, it interferes with insect growth hormones. As such, it too targets juvenile insects, not mature insects. Its effects are not limited to mosquitoes, and presumably might also impact bees, butterflies, and other pollinators.

If concern over the plight of pollinators and pesticides (and even just aesthetically-appealing insects like butterflies) isn't enough for the neighbor to try other mosquito control approaches, then we're not sure what other actions you can take other than reporting misuse by certified applicators (or any for-hire applications by uncertified individuals) and potentially also planting a buffer strip that might help to block drift from the yard next door. Granted, you might not have room in your current landscaping space for this.

Rinsing-off residues that might have settled onto your plant foliage or flowers after an application next door might help to reduce pesticide exposure to pollinators, but other than that, not much can be done once an application is made; its residues will degrade in time.

Miri