Mosquitoes can't hide in Chatham County

by Bill Lavender

SAVANNAH, GA --I thought I just heard a clearance for "Air Tractor", as I made the approach into SAV. In my aircraft I had Georgia's Republican nomination for the next governor in this year's November election. Interestingly enough, the controller had just cleared me to land number two behind "Air Tractor". I commented to my political passenger (a pilot and friend of agriculture), "Wonder who that is?" Sure enough, I found myself in line on the taxi way behind an Air Tractor AT-401 with big broad, black lettering across the top and bottom side of its wings, "Mosquito Control"; the mystery was solved.

After dropping off my passengers at the FBO, I trotted over to where the Air Tractor was parked, off to the side of the main ramp by a row of T-hangars. The pilot was cleaning the windshield. I asked how things were going. "Oh, just fine. Doing a little mosquito control".

I introduced myself to the Chatham County Mosquito Control Commission's (CCMC) fixed-wing pilot, Robbie Gardner, once a seven-year veteran ag-pilot. We only had a few minutes to talk about the virtues of mosquito control, therefore Robbie invited me for a return visit where I could meet the fine folks of this organization. I recanted I had written an article about Chatham County's mosquito control project many years ago when Oscar Fultz was its director. Now CCMC's director/entomologist is Henry Lewandowski, Ph.D..

Since my last visit, the CCMC has updated its aircraft fleet to an Air Tractor AT-401, C-model Aztec and MD 500E helicopter. This is quite an improvement from the days of my earlier interview when the CCMC used two Hughes 269s, the Aztec and an Ag-Cat. I promised Robbie I'd be back in about a week for the story.

Most aerial applicators avoid drift like the plague, measure their application runs in swath width, and fly relatively low to the target area. These proven techniques for most agricultural crops do not apply for effective mosquito control. There are two basic methods of mosquito control; adulticiding and larviciding. For the most part, larviciding is conducted by applying a liquid or dry product into standing water, while adulticiding is accomplished by applying selected chemicals over large target areas that usually include populated sites.

Robbie Gardner flies the Aztec about 75 hours and the Air Tractor about 200 hours during a season. The season's applications begin when the ambient air temperature exceeds 65¡F. This typically begins in March through November, although applications take place any month of the year under the right conditions.

CCMC's Air Tractor only applies dry larvicide material. A liquid product, Altosid Liquid Larvicide concentrate (ALL), is mixed at a rate of 54 ounces per 700 pounds of medium grade blasting sand, enough for 70 acres. Multiple loads are mixed, and then a conveyor belt delivers about 1400 pounds of finished material into the hopper of the Air Tractor. A more efficient and larger mixing system is being installed at the new facility nearing completion. As one can imagine, sand is extremely hard on the spreader. Robbie uses a Breckenridge spreader whose stainless steel vanes are protected with a special Teflon strip. Before the introduction of the Teflon strip, two sets of vanes were replaced during an average season (about 100,000 pounds of sand). This year, after applying more than 265,000 pounds of sand, the vanes have not been replaced. Before the end of this season, more than 40,000 acres will be treated with ALL by the Air Tractor and the MD 500E.

The application pattern of the spreader is routinely tested and adjusted by the CCMC. Rows of buckets are placed across the Air Tractor's flight path while dispersing sand. The sand captured in the bucket is poured into vials and weighed to evaluate the evenness of the application; the Air Tractor has an 80-foot swath.

Robbie also flies the 1966 C-model Aztec. The CCMC-designed stainless steel booms support two AU4000 Micronair units that rotate at 10,000 rpm. This allows for a droplet spectrum with a medium diameter of 22-25 microns. CCMC droplet tests reveal this set up produces zero droplets over 70 microns. Research indicates that a 50-micron droplet marginally provides adulticide control, thus the need for the smaller droplets. With 25-micron droplets there are no deposition concerns and no non-target kills. The 25-micron droplet is too small to be visible on surfaces (like cars and windows) and not toxic enough to kill larger insects, while still being effective on the mosquito. Inside the Aztec, the rear seats have been removed and replaced with a 50-gallon poly tank for the product and another 12-gallon in-flight rinse tank. The pump is driven by a 12V DC 1/2 horsepower motor. A rheostat controls the motor's rpm to deliver a flow rate of 2.3 gallons per minute.

The Aztec's adulticide applications are made with 350-foot lanes at 150 feet AGL, traveling at 130 knots. All of the Aztec's applications, are made with an observer on board. When the Aztec is used in highly congested areas, where there are numerous towers, this observer is essential for the safety of the flight. The primary adulticide used is malathion at 2.6-3.0 ounces per acre. In cooler weather, pyrethroids are used at rates up to one ounce per acre. Typically, pyrethroids are used at the beginning of each season. All of the CCMC's adulticiding aircraft use a smoker. The pilots are able to determine exactly where the liquid adulticide will travel. This is critical when gauging how high and close to fly to the ground or tree line, as well as where to fly during an inversion.

The third aircraft in the CCMC fleet is a 1988 MD 500E, flown by Scott Yackel, who holds an A&P Certificate with Inspection Authorization. Scott has removed 250 pounds of excess weight from the aircraft, but has replaced that with 177 pounds of spray equipment. The Isolair-built side-mounted broadcast spreader has a 20 cubic foot capacity. The side tanks have been mounted lower than normal for ease of loading the aircraft. The MD 500E's adulticide spray system is unique with its two horsepower 24-volt high-pressure pump. When malathion is applied it is released through 24 internal impeller nozzles with a .005 diameter orifice delivered at a working pressure of 1500 psi. This produces an average droplet size of 25 micron. Pyrethroids are applied using a .020 orifice size at a boom pressure of 800 psi.

Dry applications with the MD 500E are also made using an Isolair bucket. Scott added vanes to the bucket to increase the swath width to 100 feet at 80 mph and 200 feet AGL to spread sand mixed with ALL. For safety reasons, the Isolair bucket is only used in remote areas. Side unit broadcasters are used in congested areas. The helicopter's dry work is supported by a truck and trailer unit, also designed by the CCMC. This combination unit utilizes pre-loaded bags of 700 pounds of mixed sand. The trailer, with a capacity of 10 bags, is driven to the target site, where the MD 500E is loaded.

Of the 450 hours Scott flies the MD 500E, it is used not only for aerial applications of both larvicides and adulticides, but is also the primary mode of transportation for Entomology Technicians to survey aerial target sites. From the site inspections, CCMC learns in advance where the next brood of mosquitoes will emerge and thus begins larvicide applications to prevent adult mosquitoes from reaching surrounding communities. In the spring, mosquito adulticide applications take place the first two and last two hours of the day. In summer, these applications take place only during the first two hours of the day. Applications are not made over open marshes or water. Adult mosquitoes are treated only over dry land areas, while larvae are treated in standing water sites.

Larviciding by ground and air is CCMC's first line of defense against the mosquito. Adulticiding by either ground or air is used to compliment the larvicide program. The nuisance level that adult mosquito populations are placing on citizens determines how and when adult mosquito control operations are conducted. Flooding of mosquito breeding sites from spring rains or late summer tropical storms typically sets off a mosquito egg hatch. The ALL larvicide must be applied by early fourth instar (growth stage) of the mosquito larvae for mosquito control to be effective. It takes CCMC's two pilots about four days to inspect and larvicide a typical 8,000 acre "event", the name given for a mosquito egg hatch.