This won't work. Your approach is too localized. You said 3 inch demarcation, you must have a hell of a colony or multiple colonies.
The only way to solve your issue:
Method 1
In a 1 litre three-necked flask, equipped with a thermometer, glycerine-sealed mechanical stirrer (compare Fig. II, 7, 10) and calcium chloride (or cotton wool) guard tube, introduce successively 700 g. (380 ml.) of concentrated sulphuric acid, 100 g. (53 ml.) of oleum (20 per cent. S03), 90 g. (81-5 ml.) of chlorobenzene and 68 g. of chloral hydrate. Stir the mixture rapidly enough to keep the materials well mixed for 1 hour: during this period the temperature rises to about 50° and some granular D.D.T. separates. Stir the mixture for a further 1 hour in order to complete the reaction. Pour the reaction mixture with stirring into 3 litres of a 2 : 1 mixture of ice and water. Filter the precipitated somewhat sticky solid at the pump and wash it well with cold water. Remove the occluded acid by transferring the crude product to a beaker containing 1 litre of boiling water and stirring well: this causes the D.D.T. to melt. Decant the aqueous layer, and repeat the washing with two further 1-litre portions of water. To the third washing add a little sodium bicarbonate and stir until the mixture is neutral to litmus. Filter at the pump, and dry upon filter paper in the air or in an air oven at 50-60°. The yield of crude product, m.p. ca. 90°, is 90 g.; the low m.p. is due to the presence of isomers of the para compound. The pure substance, m.p. 108°, may be obtained with 50-60 per cent, recovery by recrystallization from n-propyl alcohol (5 ml. per gram).
Method 2
Place 17 g. of chloral hydrate crystals and 25.5 g. (23 ml.) of chlorobenzene in a 500 ml. Pyrex glass-stoppered reagent bottle and warm on a water bath, with occasional shaking, until all the crystals have dissolved. Cool to room temperature and slowly add 180 ml. of concentrated sulphuric acid. Secure the glass stopper (rubber tubing over stopper held tightly by copper wire round neck of bottle) and shake mechanically for 1 to 1 -5 hours, and then allow to stand for 15 minutes. Pour the contents of the reagent bottle slowly and with constant stirring into 700 ml. of water contained in a litre beaker. When cold, filter the crude D.D.T. through a sintered glass funnel and wash several times with water. (A further 1 -5 g. of impure D.D.T. may be obtained by diluting the filtrate considerably.) Transfer the solid to a beaker and stir it for 5-10 minutes with 50 ml. of 2 per cent, sodium carbonate solution or 4 per cent, sodium bicarbonate solution. Filter and wash with distilled water until the filtrate is neutral to litmus; suck the solid as dry as possible. Transfer the residue to a small mortar, add 100 ml. of ethyl alcohol and triturate with a pestle for 5-10 minutes. Filter through a dry Buchner funnel, wash twice with 25 ml. portions of ethanol, and continue the suction until most of the solvent has been removed. Dry the residue at 70° in a steam oven (or on a water bath). The yield of D.D.T., m.p. 107°, is 15 g. The perfectly pure compound, m.p. 108°, may be obtained by recrystallization from n-propyl alcohol (5 ml. per gram).
We can make it very mild, it'll be extremely effective. Against everything. Including Mosquitoes.