Jun 4, 2011 – Hot Or Cold?
QUESTION:
What are the real pros and cons of Thermal fogs and Cold aerosols (ULV) in a mosquito management program in a home complex?
ANSWER:
Thermal foggers essentially dribble the liquid insecticide onto a hot plate that then vaporizes the material, creating very tiny droplets of the liquid that are capable of floating or staying aloft for much longer periods of time. This may be beneficial if you are trying to release the fog at one point but allow it to drift with the breeze for a greater distance from that point. The droplets are in the range of 1 to 5 microns, compared with ULV droplets that are in the range of 5 to 20 microns in diameter. The ULV size is still pretty darned small, but being larger it falls faster, so in that same light breeze the ULV fog is not going to be carried as far.
I found an interesting chart one time that listed the differences in drift potential for various droplet sizes, and while the exact numbers may not be 100% accurate it still gives an amazing comparison. To start with the spray droplets that may be created by power spraying, where a lot of these fine droplets are in the realm of 500 microns in diameter, a droplet released at 10 feet of height in a 3 mph breeze will take only 1.5 seconds to hit the ground and travel only 7 feet off site. The fine particles in that spray may be 100 microns in diameter, and in that same 3 mph breeze will fall that 10 feet in 10 seconds but potentially travel 410 feet off site. This would be plenty of time to thoroughly coat a neighbor's yard with pesticide they did not want there if you were not careful while spraying trees, shrubs or fences in a customer's yard.
If we get down to that 5 micron droplet of a thermal fogger or even many of the smaller particles from a ULV fogger, in a 3 mph wind from 10 feet high the droplet takes 66 minutes to reach the ground and can travel as far away as 3 miles!! Here is your possible concern with thermal fogging - that fog is going to go a long distance, and you have no control over where it ends up. This may be what you want in a wooded or rural setting, but perhaps not so desirable in a residential setting. Since mosquito "misting" devices produce ULV droplets this points out the concern some states have regarding a system of one person's property delivering pesticide onto the neighboring properties, and those neighbors may have strong concerns about pesticides and not want their properties sprayed in this manner.
I think you also have more options with ULV foggers, including some relatively low cost electrical models. Some of the older thermal foggers also were pretty noisy, so using them discreetly was not likely to happen. There even was an opinion I once read, but it may have been the opinion of someone who sells ULV foggers trying to convince us that thermal foggers were inferior. This opinion, though, was that the thermal fogger droplet size could be so small that it did not even attach to insects as well as ULV droplets do, but was more likely to just drift on by the mosquito and miss it. How realistic this is I really don't know, but I toss it out for your consideration.
View past Ask Mr. Pest Control questions.
What are the real pros and cons of Thermal fogs and Cold aerosols (ULV) in a mosquito management program in a home complex?
ANSWER:
Thermal foggers essentially dribble the liquid insecticide onto a hot plate that then vaporizes the material, creating very tiny droplets of the liquid that are capable of floating or staying aloft for much longer periods of time. This may be beneficial if you are trying to release the fog at one point but allow it to drift with the breeze for a greater distance from that point. The droplets are in the range of 1 to 5 microns, compared with ULV droplets that are in the range of 5 to 20 microns in diameter. The ULV size is still pretty darned small, but being larger it falls faster, so in that same light breeze the ULV fog is not going to be carried as far.
I found an interesting chart one time that listed the differences in drift potential for various droplet sizes, and while the exact numbers may not be 100% accurate it still gives an amazing comparison. To start with the spray droplets that may be created by power spraying, where a lot of these fine droplets are in the realm of 500 microns in diameter, a droplet released at 10 feet of height in a 3 mph breeze will take only 1.5 seconds to hit the ground and travel only 7 feet off site. The fine particles in that spray may be 100 microns in diameter, and in that same 3 mph breeze will fall that 10 feet in 10 seconds but potentially travel 410 feet off site. This would be plenty of time to thoroughly coat a neighbor's yard with pesticide they did not want there if you were not careful while spraying trees, shrubs or fences in a customer's yard.
If we get down to that 5 micron droplet of a thermal fogger or even many of the smaller particles from a ULV fogger, in a 3 mph wind from 10 feet high the droplet takes 66 minutes to reach the ground and can travel as far away as 3 miles!! Here is your possible concern with thermal fogging - that fog is going to go a long distance, and you have no control over where it ends up. This may be what you want in a wooded or rural setting, but perhaps not so desirable in a residential setting. Since mosquito "misting" devices produce ULV droplets this points out the concern some states have regarding a system of one person's property delivering pesticide onto the neighboring properties, and those neighbors may have strong concerns about pesticides and not want their properties sprayed in this manner.
I think you also have more options with ULV foggers, including some relatively low cost electrical models. Some of the older thermal foggers also were pretty noisy, so using them discreetly was not likely to happen. There even was an opinion I once read, but it may have been the opinion of someone who sells ULV foggers trying to convince us that thermal foggers were inferior. This opinion, though, was that the thermal fogger droplet size could be so small that it did not even attach to insects as well as ULV droplets do, but was more likely to just drift on by the mosquito and miss it. How realistic this is I really don't know, but I toss it out for your consideration.
View past Ask Mr. Pest Control questions.
